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Title: Why do Class D amps seem to pull less power than they make?
Post by: Alex Berry on January 23, 2015, 08:44:20 pm
So first, if this is in the wrong place or has already been answered, I apologize. I've been reading some stuff on these forums recently but am a brand new member. Anyways, on with my question.

Exactly that which the title says. Why do Class D amps seem to pull less power than they make? For instance, a Powersoft K10 is rated to pull 1250 watts from the wall in order to make 1500 watts. Whereas a Class H amp, like a QSC PLX3402 takes around 1400 watts to make around 400 watts. I understand this is simply due to Class H not being nearly as efficient as Class D, but here's where I start to get even more confused.

I have used 5 QSC PLX3402 amps in a school before, all of them run off of just two 20A 120V circuits. Two were wired in 4 ohm stereo each, to feed a total of four JBL SR4719X subs and we're being run just beneath clip/limit. The other three were being used to bi-amp four JBL 4873 tops, two amps run to the 15" and mid frequency horns, and the last amp ran to the high frequency horns. As you can imagine, these amps we being stressed nowhere near as much as the sub amps. Now this whole system, as previously stated, ran off of two 20A circuits without any problems. How is this even remotely possible? In theory, just the sub amps alone should have overloaded both circuits? I'm wondering not just out of curiosity but also because in February I'm going to be running two Powersoft K10 amps off of these same two 20A circuits, powering eight Sound Bridge 7218SWX subs. Now I'll only be running the subs at about 500wrms per cabinet, but considering the ability to run the QSC amps off the same circuits, I should be more than fine to run these amps at this capacity, correct?

I'm hoping I can get an in depth answer on this as I love learning about this subject, and for a long time it has confused the crap out of me. Thanks in advance for any replies!

Alex
Title: Re: Why do Class D amps seem to pull less power than they make?
Post by: Ivan Beaver on January 23, 2015, 09:02:07 pm
So first, if this is in the wrong place or has already been answered, I apologize. I've been reading some stuff on these forums recently but am a brand new member. Anyways, on with my question.

Exactly that which the title says. Why do Class D amps seem to pull less power than they make? For instance, a Powersoft K10 is rated to pull 1250 watts from the wall in order to make 1500 watts. Whereas a Class H amp, like a QSC PLX3402 takes around 1400 watts to make around 400 watts. I understand this is simply due to Class H not being nearly as efficient as Class D, but here's where I start to get even more confused.

I have used 5 QSC PLX3402 amps in a school before, all of them run off of just two 20A 120V circuits. Two were wired in 4 ohm stereo each, to feed a total of four JBL SR4719X subs and we're being run just beneath clip/limit. The other three were being used to bi-amp four JBL 4873 tops, two amps run to the 15" and mid frequency horns, and the last amp ran to the high frequency horns. As you can imagine, these amps we being stressed nowhere near as much as the sub amps. Now this whole system, as previously stated, ran off of two 20A circuits without any problems. How is this even remotely possible? In theory, just the sub amps alone should have overloaded both circuits? I'm wondering not just out of curiosity but also because in February I'm going to be running two Powersoft K10 amps off of these same two 20A circuits, powering eight Sound Bridge 7218SWX subs. Now I'll only be running the subs at about 500wrms per cabinet, but considering the ability to run the QSC amps off the same circuits, I should be more than fine to run these amps at this capacity, correct?

I'm hoping I can get an in depth answer on this as I love learning about this subject, and for a long time it has confused the crap out of me. Thanks in advance for any replies!

Alex
THEY DON'T

They will ALWAYS pull more power than they can put out.

The reason is that they can't deliver full power for any length of time.

Typically you get full power for around 0.080seconds before dropping the power down-sometimes as much as 6dB or 1/4 of the peak or burst power.

Amps of years past could deliver their rated power for very long periods of time (an eternity in term of todays amps)

However music is of a burst nature anyway-so there is no need to deliver constant power.

Many years ago one of the "audio gods" said "What we need is an amp that can produce 100 watts continuous and reproduce 20dB peaks".

We are almost getting to that stage -20dB over 100 watts is 10,000 watts.

HOWEVER that can be an issue with some forms of music (EDM-rap-Dance etc) that have sustained tones that are MUCH longer than the normal 0.08 seconds burst tones.

Some manufacturers can only produce full power for 0.02 seconds (20ms)  That is ONE CYCLE at 20Hz.  Much music has tones that are longer than that.

If the amps could deliver more power than they pulled-then the power companies would be all over them :)
Title: Re: Why do Class D amps seem to pull less power than they make?
Post by: Alex Berry on January 23, 2015, 09:07:06 pm
THEY DON'T

They will ALWAYS pull more power than they can put out.

The reason is that they can't deliver full power for any length of time.

Typically you get full power for around 0.080seconds before dropping the power down-sometimes as much as 6dB or 1/4 of the peak or burst power.

Amps of years past could deliver their rated power for very long periods of time (an eternity in term of todays amps)

However music is of a burst nature anyway-so there is no need to deliver constant power.

Many years ago one of the "audio gods" said "What we need is an amp that can produce 100 watts continuous and reproduce 20dB peaks".

We are almost getting to that stage -20dB over 100 watts is 10,000 watts.

HOWEVER that can be an issue with some forms of music (EDM-rap-Dance etc) that have sustained tones that are MUCH longer than the normal 0.08 seconds burst tones.

Some manufacturers can only produce full power for 0.02 seconds (20ms)  That is ONE CYCLE at 20Hz.  Much music has tones that are longer than that.

If the amps could deliver more power than they pulled-then the power companies would be all over them :)

Thanks for the reply! I kind of figured, these sort of specs listed by the manufacturer just confused me. I should have specified what music was and will be played. 95% of it will be rap/EDM, the the big, long sustained bass notes. So I guess what I'm asking now is, does this fact change anything? And will I be safe running the Powersoft amps at a total of 4000wrms output combined? I ran those QSC amps harder than that and the Powersoft amps should be much more efficient.
Title: Re: Why do Class D amps seem to pull less power than they make?
Post by: Tim McCulloch on January 23, 2015, 09:11:34 pm
Thanks for the reply! I kind of figured, these sort of specs listed by the manufacturer just confused me. I should have specified what music was and will be played. 95% of it will be rap/EDM, the the big, long sustained bass notes. So I guess what I'm asking now is, does this fact change anything? And will I be safe running the Powersoft amps at a total of 4000wrms output combined? I ran those QSC amps harder than that and the Powersoft amps should be much more efficient.

Hook it up at the shop on a pair of 20's  and see what happens.
Title: Re: Why do Class D amps seem to pull less power than they make?
Post by: Alex Berry on January 23, 2015, 09:15:54 pm
Hook it up at the shop on a pair of 20's  and see what happens.

Unfortunately, this isn't an option as I'm renting the gear and do not own it. In theory though, I should be fine. At this point I'm basically just looking for someone with more experience than me to tell me whether I'm right or I'm wrong. Knowing how those QSC amps worked on two 20A's would be the cherry on top.
Title: Re: Why do Class D amps seem to pull less power than they make?
Post by: Ivan Beaver on January 23, 2015, 09:31:35 pm
Unfortunately, this isn't an option as I'm renting the gear and do not own it. In theory though, I should be fine. At this point I'm basically just looking for someone with more experience than me to tell me whether I'm right or I'm wrong. Knowing how those QSC amps worked on two 20A's would be the cherry on top.
Since music is DYNAMIC- it depends on how lour for how long with music of a certain dynamic range.

One style of music will run just fine without tripping a breaker-and a different style of music will trip them easily.

It is POWER OVER TIME-not just power or peak power.

It is a VERY COMPLICATED set of parameters and there is no way of knowing some exact answer.

It ALSO depends on the type of breakers (some can handle peaks for longer times than others), how many times the breaker has been tripped (the more they are tripped the less they can handle) and there is a normal tolerance for the current rating.

The only way to give an exact answer is to know WHAT SONG (you can't play a different song because of a different dynamic range) , how hot the speakers are (if they are into power compression there will be less power delivered by the amp-even though the voltage will be the same) and so forth and so on

The BEST thing is to try to oversize the breakers and the system and run it all "easy".  But that is A LOT easier said than done-believe me!
Title: Re: Why do Class D amps seem to pull less power than they make?
Post by: Alex Berry on January 23, 2015, 09:42:00 pm
Since music is DYNAMIC- it depends on how lour for how long with music of a certain dynamic range.

One style of music will run just fine without tripping a breaker-and a different style of music will trip them easily.

It is POWER OVER TIME-not just power or peak power.

It is a VERY COMPLICATED set of parameters and there is no way of knowing some exact answer.

It ALSO depends on the type of breakers (some can handle peaks for longer times than others), how many times the breaker has been tripped (the more they are tripped the less they can handle) and there is a normal tolerance for the current rating.

The only way to give an exact answer is to know WHAT SONG (you can't play a different song because of a different dynamic range) , how hot the speakers are (if they are into power compression there will be less power delivered by the amp-even though the voltage will be the same) and so forth and so on

The BEST thing is to try to oversize the breakers and the system and run it all "easy".  But that is A LOT easier said than done-believe me!

More than 90% of the music played on the QSC amps was highly compressed EDM and rap and there were 0 problems over 3 hours of continuous music. I don't think the subs were in power compression as they were being run slightly beneath their continuous rating. None of the circuits have ever been tripped while I was using them, and the circuits are located in a gymnasium that's only a couple years old.  Also, I actually am totally able to oversize the system and run it easy. All of the eight Sound Bridge subs I'm planning on running at 1/4 continuous power. Although this time the system is gonna be run for 12 hours of almost continuous music. Thanks again for all the info! Would you say I have a decent chance of being fine or should I be concerned?
Title: Re: Why do Class D amps seem to pull less power than they make?
Post by: Ivan Beaver on January 23, 2015, 09:46:45 pm
More than 90% of the music played on the QSC amps was highly compressed EDM and rap and there were 0 problems over 3 hours of continuous music. I don't think the subs were in power compression as they were being run slightly beneath their continuous rating. None of the circuits have ever been tripped while I was using them, and the circuits are located in a gymnasium that's only a couple years old.  Also, I actually am totally able to oversize the system and run it easy. All of the eight Sound Bridge subs I'm planning on running at 1/4 continuous power. Although this time the system is gonna be run for 12 hours of almost continuous music. Thanks again for all the info! Would you say I have a decent chance of being fine or should I be concerned?
There is no way of saying.

When you say " I'm planning on running at 1/4 continuous power." what does that exactly mean?  How are you "planning" on doing that?

If the breakers blow-then turn it down!
Title: Re: Why do Class D amps seem to pull less power than they make?
Post by: Alex Berry on January 23, 2015, 09:56:07 pm
There is no way of saying.

When you say " I'm planning on running at 1/4 continuous power." what does that exactly mean?  How are you "planning" on doing that?

If the breakers blow-then turn it down!

It means I'm planning on running each amp to only output 2000 watts. According to the Powersoft K10 documentation, the amps have a "User selectable maximum output power for each channel" feature and I plan on using it. The subs are rated for 2000wrms so sending around 500 to each box should be at a quarter of the potential continuous power. Sorry for not being clear enough about that.
Title: Re: Why do Class D amps seem to pull less power than they make?
Post by: Lee Buckalew on January 23, 2015, 09:58:28 pm
It means I'm planning on running each amp to only output 2000 watts. According to the Powersoft K10 documentation, the amps have a "User selectable maximum output power for each channel" feature and I plan on using it. The subs are rated for 2000wrms so sending around 500 to each box should be at a quarter of the potential continuous power. Sorry for not being clear enough about that.

The K series amps can also be set to draw no more than a given line current if you wanted to do that.

Lee
Title: Re: Why do Class D amps seem to pull less power than they make?
Post by: Alex Berry on January 23, 2015, 10:00:29 pm
The K series amps can also be set to draw no more than a given line current if you wanted to do that.

Lee

I saw that as well and plan on using that too. Such awesome features. My current inventory consists of EV ZLX and ETX gear with the only outboard amp I own being a Crown XLS1000. The kind of features the Powersoft amps have are the kind of things dreams are made of.
Title: Re: Why do Class D amps seem to pull less power than they make?
Post by: Jelmer de Jong on January 24, 2015, 06:07:10 am

I have used 5 QSC PLX3402 amps in a school before, all of them run off of just two 20A 120V circuits. Two were wired in 4 ohm stereo each, to feed a total of four JBL SR4719X subs and we're being run just beneath clip/limit. The other three were being used to bi-amp four JBL 4873 tops, two amps run to the 15" and mid frequency horns, and the last amp ran to the high frequency horns. As you can imagine, these amps we being stressed nowhere near as much as the sub amps. Now this whole system, as previously stated, ran off of two 20A circuits without any problems. How is this even remotely possible? In theory, just the sub amps alone should have overloaded both circuits? I'm wondering not just out of curiosity but also because in February I'm going to be running two Powersoft K10 amps off of these same two 20A circuits, powering eight Sound Bridge 7218SWX subs. Now I'll only be running the subs at about 500wrms per cabinet, but considering the ability to run the QSC amps off the same circuits, I should be more than fine to run these amps at this capacity, correct?

120V/20A is about 2400W. Two sockets makes 4800W. The PLX amp delivers 2200W total in 4ohm clip. If your music is a pure sine wave a clipping amp will actually use half the power you thing because a sine's peak is 3dB higher than its avarage power. So your 4 ohm dual channel amp will not draw 2200W from the wall but 1100. But music is not a pure sine wave(mostly), so your actual power usage will be even less if the clipping occours at peaks that are 10-15dB above the avarage power, that's 10-30 times less continuous power than you will think.
Title: Re: Why do Class D amps seem to pull less power than they make?
Post by: Steve M Smith on January 24, 2015, 07:46:22 am
Why do Class D amps seem to pull less power than they make?


It's an old salesman's trick known as lying!


Steve.
Title: Re: Why do Class D amps seem to pull less power than they make?
Post by: Alex Berry on January 24, 2015, 08:17:20 am
120V/20A is about 2400W. Two sockets makes 4800W. The PLX amp delivers 2200W total in 4ohm clip. If your music is a pure sine wave a clipping amp will actually use half the power you thing because a sine's peak is 3dB higher than its avarage power. So your 4 ohm dual channel amp will not draw 2200W from the wall but 1100. But music is not a pure sine wave(mostly), so your actual power usage will be even less if the clipping occours at peaks that are 10-15dB above the avarage power, that's 10-30 times less continuous power than you will think.

This is only true assuming that the QSC amps are 100% efficient. They're actually more like 30% efficient. So with that in mind, it would take, for example, around 1000 watts just to make roughly 300 watts. Considering this, and the fact most of the music played through the amps was highly compressed EDM and rap with copious amounts of long bass tones and almost no transients, we're looking at some serious power draws. I'm really starting to understand the fact that because I was able to run such an inefficient system off the pair of circuits, I'll be easily able to run a much more efficient system that is less powerful off of the same pair of circuits. But thanks for the input!


It's an old salesman's trick known as lying!


Steve.

Then how can Powersoft put in the specifications that the K10 is specifically rated to pull 1250 watts from the wall to output 1500 watts? I don't understand how this form of blatant lying could be tolerable.
Title: Re: Why do Class D amps seem to pull less power than they make?
Post by: Steve M Smith on January 24, 2015, 08:34:47 am
It's the way the measurements are made.  If you look at various manufacturers' specifications, you will see that power can be measured in RMS (Root Mean Square), PMPO (Peak Music Power Output) and various other Instantaneous peak measurements where the output can only be sustained for a small amount of time.

An even better demonstration of this would be the flash for a camera.  It might take ten seconds to charge up then the flash of light lasts only for about 1/10,000 of a second.

The energy put into the flash tube is huge but it doesn't last long. The current taken from the batteries is relatively low but over a fairly long time.

In my opinion, the only honest measurement is RMS.  However, when salesmen realised that a peak power measurement would allow them to advertise something as twice as much power, that is exactly what they did.  I first noticed this being done in the 1980s with lower end hi-fi equipment.


Steve.
Title: Re: Why do Class D amps seem to pull less power than they make?
Post by: Alex Berry on January 24, 2015, 08:45:27 am
It's the way the measurements are made.  If you look at various manufacturers' specifications, you will see that power can be measured in RMS (Root Mean Square), PMPO (Peak Music Power Output) and various other Instantaneous peak measurements where the output can only be sustained for a small amount of time.

An even better demonstration of this would be the flash for a camera.  It might take ten seconds to charge up then the flash of light lasts only for about 1/10,000 of a second.

The energy put into the flash tube is huge but it doesn't last long. The current taken from the batteries is relatively low but over a fairly long time.

In my opinion, the only honest measurement is RMS.  However, when salesmen realised that a peak power measurement would allow them to advertise something as twice as much power, that is exactly what they did.  I first noticed this being done in the 1980s with lower end hi-fi equipment.


Steve.

I'm actually already pretty familiar with all of the information you have mentioned. Imagine if all the manufacturers would just be honest and rate their equipment according to real world values, and not something never attainable in practical use. Imagine how cool it would be if we could take specs at face value and not with a grain of salt. But anyways, thanks for your response.

Although, if you can be specific, how is Powersoft able to make this claim? Are they saying something along the lines of "it takes X amount of RMS current to make Y amount of peak current" without specifying? Otherwise I just cant understand how they're able to say that their amps are 120% efficient, when it's an obvious lie. It takes power to make power, simple as that.
Title: Re: Why do Class D amps seem to pull less power than they make?
Post by: Ivan Beaver on January 24, 2015, 08:51:15 am
120V/20A is about 2400W. Two sockets makes 4800W. The PLX amp delivers 2200W total in 4ohm clip. If your music is a pure sine wave a clipping amp will actually use half the power you thing because a sine's peak is 3dB higher than its avarage power. So your 4 ohm dual channel amp will not draw 2200W from the wall but 1100. But music is not a pure sine wave(mostly), so your actual power usage will be even less if the clipping occours at peaks that are 10-15dB above the avarage power, that's 10-30 times less continuous power than you will think.
You can't change "scales" in the middle of talking about things that are compared.

The wall power is measured in RMS voltage-like the output power.

You can't talk about the "peak" of one waveform and the RMS of another when trying to make a point.

The voltage is the measurement of a particular point on a waveform-the most common being: Average=63.6% of the peak, RMS=70.7% of the peak and of course the peak voltage which is 100%

The power is the area "under the curve".

Of course you can "change scales"-but it does not make sense and only serves to confuse others.

Which is the idea of course with a lot of audio specs--------------
Title: Re: Why do Class D amps seem to pull less power than they make?
Post by: Ivan Beaver on January 24, 2015, 08:57:10 am

Although, if you can be specific, how is Powersoft able to make this claim? Are they saying something along the lines of "it takes X amount of RMS current to make Y amount of peak current" without specifying? Otherwise I just cant understand how they're able to say that their amps are 120% efficient, when it's an obvious lie. It takes power to make power, simple as that.
Modern amps can provide the power as speced FOR ( as I stated earlier) FOR VERY BRIEF periods of time.

THere is no "lying" going on-they are not talking about continuous power-but rather peaks.

And if you think this is bad-take any loudspeaker and look at the "output SPL" specs and see if you can actually measure that SPL with a normal SPL meter with music.

You will not be anywhere near close to that.  But it is how the "average SPL meter" is reading (time wise) vs what the speaker can produce on peaks.

When you "change scales" all sorts of things don't "make sense".
Title: Re: Why do Class D amps seem to pull less power than they make?
Post by: Alex Berry on January 24, 2015, 09:08:56 am
Modern amps can provide the power as speced FOR ( as I stated earlier) FOR VERY BRIEF periods of time.

THere is no "lying" going on-they are not talking about continuous power-but rather peaks.

And if you think this is bad-take any loudspeaker and look at the "output SPL" specs and see if you can actually measure that SPL with a normal SPL meter with music.

You will not be anywhere near close to that.  But it is how the "average SPL meter" is reading (time wise) vs what the speaker can produce on peaks.

When you "change scales" all sorts of things don't "make sense".

I completely agree about the loudspeaker analogy. I've actually done this before. EV claims to have measured the ETX-18SP to output 135db peak with broadband pink noise, whereas I measured around a 130db peak at 50hz.

Anyways, I didn't mean to sound like I had anything against Powersoft or their products, I'm just still confused how they can make a claim that their amps make more power than they consume. If they are indeed referring to peaks in the rating, it still doesn't make any sense that the amp could pull a very very brief peak of 1250 watts, and then somehow turn that brief peak of 1250 watts into a brief peak of 1500 watts and send it to the speaker. I am basing this all off of their specs, which dictate that at 1/8 max output power at 4 ohms (max output power at that resistance being 12000 watts, 1/8 being 1500 watts) the amp is only pulling 1250 watts. At 1/4 max output power at 4 ohms its rated to pull 2500 watts, with 1/4 max output power at that resistance being 3000 watts. Hopefully you can point out my error in this and I can learn from it and stop asking these stupid questions, lol!
Title: Re: Why do Class D amps seem to pull less power than they make?
Post by: Jelmer de Jong on January 24, 2015, 10:19:33 am
You can't change "scales" in the middle of talking about things that are compared.
You're right. My physics teacher will slap me if he sees this.  :-[
Quote
Of course you can "change scales"-but it does not make sense and only serves to confuse others.

Which is the idea of course with a lot of audio specs--------------
This sucks big time. Two amps with built in processing are limited to 1200W@8ohm, both have a RMS and separate peak limiter. The first amp needs 98V entered in the peak limiter to deliver 1200W, the second needs 138V according to manufacturer software. With these settings both amps deliver the same power. None of the manufacturers talk about Vpk or VRMS, just V. Maybe thats where my thoughts went south... :(
Title: Re: Why do Class D amps seem to pull less power than they make?
Post by: Ivan Beaver on January 24, 2015, 10:22:54 am
I completely agree about the loudspeaker analogy. I've actually done this before. EV claims to have measured the ETX-18SP to output 135db peak with broadband pink noise, whereas I measured around a 130db peak at 50hz.

Anyways, I didn't mean to sound like I had anything against Powersoft or their products, I'm just still confused how they can make a claim that their amps make more power than they consume. If they are indeed referring to peaks in the rating, it still doesn't make any sense that the amp could pull a very very brief peak of 1250 watts, and then somehow turn that brief peak of 1250 watts into a brief peak of 1500 watts and send it to the speaker. I am basing this all off of their specs, which dictate that at 1/8 max output power at 4 ohms (max output power at that resistance being 12000 watts, 1/8 being 1500 watts) the amp is only pulling 1250 watts. At 1/4 max output power at 4 ohms its rated to pull 2500 watts, with 1/4 max output power at that resistance being 3000 watts. Hopefully you can point out my error in this and I can learn from it and stop asking these stupid questions, lol!
The problem with SPL and power measurements is the integration time (response time) used for the measurement.

I bet if you had a SPL meter that could measure the instantaneous peak SPL, it would be higher.  That could be up to 10dB higher than the "fast" response time of the meter.

Regarding amps-I will say ONCE AGAIN, it is for a VERY BRIEF period of time-NOT continuously.

The power supply has a "voltage supply" that is constantly being charged up by the wall power.  When a short peak comes along-it can "dump" a bunch of that supply into the load (loudspeaker), but it cannot dump it for very long or it "runs out" and the power output drops (as much as 6dB or more)

An analogy is drag racing.  There are those people that "believe" those cars can go over 200MPH.  BULLSHIT!!!!!!!!!!!

Have you ever seen a drag race in which the cars even drove for a MINUTE-MUCH LESS and HOUR!!!!!!!!!!!!!!  The race is 1/4mile long-NOT for an hour.

No-the cars can't do that-but people "say they can".  Heck they can't even hold that much fuel------------.

Yes they can do that speed for a very short period of time-but not for very long.

So I dare you to go to a drag strip and try to bring up how they are lying about how fast the cars go-----------------

Music is the same way.  Just look at any musical waveform. The "average" level is FAR below what the peaks are.  And the peaks are what the large power is for.

It can be as much as 20dB (which is a factor of100 times) greater.

I don't know of any other way to explain it.

NOW-for what it is worth-times have changed.  I have an entire wall of my office that is full of old amplifiers that were designed to produce SINE WAVE outputs for long periods and that is how they were rated.

But music is not continuous sine waves.  So while the old methods were fine at the time-modern amps are more "realistic" in terms of power.

HOWEVER they are not rated the same.  This "peak power" that they can deliver varies quite a bit from model to model.  The real answer when it comes down to comparing amps is as follows: "How long can it produce that peak AND what level does it drop down to after that-if driven with a sine wave".

This matters more on some types of music than others.

It is also the "we don't want to talk about that" point that most amp manufacturers try to avoid.

HEY-LET'S JUST TALK ABOUT THE "POWER SPEC" and hope people believe what we are saying.

As I say all the time-you can't answer a complicated question with a simple answer.  But people try to all the time
Title: Re: Why do Class D amps seem to pull less power than they make?
Post by: Keith Broughton on January 24, 2015, 10:26:25 am
An analogy is drag racing.  There are those people that "believe" those cars can go over 200MPH.  BULLSHIT!!!!!!!!!!!
Your responses are quite entertaining Ivan :)
Title: Re: Why do Class D amps seem to pull less power than they make?
Post by: Ivan Beaver on January 24, 2015, 10:31:34 am
. The first amp needs 98V entered in the peak limiter to deliver 1200W, the second needs 138V according to manufacturer software. With these settings both amps deliver the same power. None of the manufacturers talk about Vpk or VRMS, just V. Maybe thats where my thoughts went south... :(
AGREED-this can be a very  deceiving point of argument.

It depends on what you call "peak".

From a purely engineering standpoint, the 138V is correct-but it is not what you would read on a standard voltmeter.

It IS IMPORTANT to understand exactly what the numbers mean-what the manufacturer was intending.

Sometimes being "technically correct" gets in the way of "general usage/knowledge".

Just like the original TEF audio measurement system.

It used BNC connectors for all put the mic inputs of the system.

The reason was that it was a piece of "test equipment" and "test equipment" of the day all used BNC connectors.  This meant you had to make your own cables-because nobody made a BNC to XLR cable.

THe new version is all XLR, but sometimes "engineering types" get in the way of practicality.

HENCE the reason FOR THE USER to understand what is really going on and not just rely on the "simple numbers" presented to them.

HOWEVER I could also argue that if you were to set the peak limiter to the RMS voltage (NOT POWER!!!!!! as some people here might think) fo the peak of the waveform, it would actually provide greater control and lower the possibility of damage-because it would be limiting early.

If it was the other way around-damage to the loudspeaker could happen easier.

Title: Re: Why do Class D amps seem to pull less power than they make?
Post by: Alex Berry on January 24, 2015, 10:32:30 am
The problem with SPL and power measurements is the integration time (response time) used for the measurement.

I bet if you had a SPL meter that could measure the instantaneous peak SPL, it would be higher.  That could be up to 10dB higher than the "fast" response time of the meter.

Regarding amps-I will say ONCE AGAIN, it is for a VERY BRIEF period of time-NOT continuously.

The power supply has a "voltage supply" that is constantly being charged up by the wall power.  When a short peak comes along-it can "dump" a bunch of that supply into the load (loudspeaker), but it cannot dump it for very long or it "runs out" and the power output drops (as much as 6dB or more)

An analogy is drag racing.  There are those people that "believe" those cars can go over 200MPH.  BULLSHIT!!!!!!!!!!!

Have you ever seen a drag race in which the cars even drove for a MINUTE-MUCH LESS and HOUR!!!!!!!!!!!!!!  The race is 1/4mile long-NOT for an hour.

No-the cars can't do that-but people "say they can".  Heck they can't even hold that much fuel------------.

Yes they can do that speed for a very short period of time-but not for very long.

So I dare you to go to a drag strip and try to bring up how they are lying about how fast the cars go-----------------

Music is the same way.  Just look at any musical waveform. The "average" level is FAR below what the peaks are.  And the peaks are what the large power is for.

It can be as much as 20dB (which is a factor of100 times) greater.

I don't know of any other way to explain it.

NOW-for what it is worth-times have changed.  I have an entire wall of my office that is full of old amplifiers that were designed to produce SINE WAVE outputs for long periods and that is how they were rated.

But music is not continuous sine waves.  So while the old methods were fine at the time-modern amps are more "realistic" in terms of power.

HOWEVER they are not rated the same.  This "peak power" that they can deliver varies quite a bit from model to model.  The real answer when it comes down to comparing amps is as follows: "How long can it produce that peak AND what level does it drop down to after that-if driven with a sine wave".

This matters more on some types of music than others.

It is also the "we don't want to talk about that" point that most amp manufacturers try to avoid.

HEY-LET'S JUST TALK ABOUT THE "POWER SPEC" and hope people believe what we are saying.

As I say all the time-you can't answer a complicated question with a simple answer.  But people try to all the time

Perfect! This is exactly the answer I was looking for! I completely forgot about the entire aspect of capacitors, which totally explains the ability to dump more than it pulls, but only for tiny amounts of time, equating like you said to peaks in music. Unfortunately for me, the type of music I play is extremely compressed and there aren't really any noticeable peaks. An unfortunate effect of the loudness war.

Many thanks for your help! Sometimes I get so caught up in something like "this amp claims to be 120% efficient" that I completely forget about electronic basics like the capacitor. And I agree with Keith, your responses are quite entertaining. :D
Title: Re: Why do Class D amps seem to pull less power than they make?
Post by: Ivan Beaver on January 24, 2015, 10:33:24 am
Your responses are quite entertaining Ivan :)
I just try to put things in term people can relate to.

OK- OK SOME people-----------------------

Others don't get my responses at all ;(
Title: Re: Why do Class D amps seem to pull less power than they make?
Post by: Ivan Beaver on January 24, 2015, 10:37:23 am
Perfect! This is exactly the answer I was looking for! I completely forgot about the entire aspect of capacitors, which totally explains the ability to dump more than it pulls, but only for tiny amounts of time, equating like you said to peaks in music. Unfortunately for me, the type of music I play is extremely compressed and there aren't really any noticeable peaks. An unfortunate effect of the loudness war.

Many thanks for your help! Sometimes I get so caught up in something like "this amp claims to be 120% efficient" that I completely forget about electronic basics like the capacitor. And I agree with Keith, your responses are quite entertaining. :D
And that is EXACTLY WHY you need to be looking at the DURATION TIMES that were used to come up with the output power numbers.

The longer the duration time-the better chance the amp has to deliver more power longer

Again-these vary WILDLY.  I have seen them as short as 0.02 seconds and up to 4 seconds.  0.08 seems to be some sort of a "standard"-but you need to look to be sure.
Title: Re: Why do Class D amps seem to pull less power than they make?
Post by: Keith Broughton on January 24, 2015, 10:46:12 am

Again-these vary WILDLY.  I have seen them as short as 0.02 seconds
And that's how Behringer makes a 6000 watt amp for $300!

I bought a couple iNuke 3000DSPs to do low level front fill for corporate. Works fine.
Then the boss said why not get some more for the main rig?
(sigh)
I just can't connect a Behringer amp to a Danley sub....I just cant! ;D
Title: Re: Why do Class D amps seem to pull less power than they make?
Post by: Alex Berry on January 24, 2015, 10:48:18 am
And that is EXACTLY WHY you need to be looking at the DURATION TIMES that were used to come up with the output power numbers.

The longer the duration time-the better chance the amp has to deliver more power longer

Again-these vary WILDLY.  I have seen them as short as 0.02 seconds and up to 4 seconds.  0.08 seems to be some sort of a "standard"-but you need to look to be sure.

As far as I can tell, the K10 doesn't specify the duration times. Like you said, probably not something Powersoft wants to publicly disclose.

Regardless, many thanks for all the help! Will definitely keep this in mind in the future.
Title: Re: Why do Class D amps seem to pull less power than they make?
Post by: John Roberts {JR} on January 24, 2015, 11:05:28 am
This is a very old topic so a search "should" reveal previous discussion threads.

As Ivan said this is a complex topic but consumers like to make purchase decisions based on simple data comparisons so it is not unheard of for power claims from overly enthusiastic marketers that defy physics.

I can't educate you all about how to make simple comparisons. That is why posts from forum member with experience using the subject amps with similar speaker loads and similar musical genres is so valuable. If you think you can understand this subject better than the equipment designers have at it. The marketplace is a reality check for new designs where amps that do not deliver adequate power get identified and shunned by customers.

Also why I continue to be a fan of powered speakers, let some design engineer with a pocket protector worry about these questions. 8)

JR

PS: @Ivan, only a fraction of the size and weight in your wall of old legacy power amps was to support 24x7 duty cycles. For example when the old school 24x7 CS800 was revised to allow higher short term output, the power changed from 800W to 1,200W. Significant but this alone does not explain the so much smaller size and weight of modern amp technology. Improved efficiency reduces the waste energy allowing for smaller heat sinks. An even larger reduction is due to power supply technology. Replacing the huge 50-60Hz power transformer with a small HF switching supply transformer scales down the transformer size proportionately with the increased power transfer frequency. This is a win-win situation only limited by cost of high frequency power devices and magnetics.     

Title: Re: Why do Class D amps seem to pull less power than they make?
Post by: Brian Oppegaard on January 24, 2015, 11:11:09 am

I wish the term "peak power" would go away. It is misleading and wrong. Power must be calculated with RMS voltage over at least one complete cycle to have any relevance to audio. For 20Hz, that's 50 ms. I prefer "tone burst power" Tone means audio, at least one complete cycle. Burst means time, how many cycles at what frequency. Power is the area under the curve which relates to the heating effect of the waveform.

Amplifier power can't be expressed with just one number these days. They are designed to have a short term power to get thru a Thump and a long term power to get thru EDM. A curve of power versus time will show both values and if the amp can transition smoothly between them without overshoot or oscillation.

In my bench testing I measured the K10 to do 3600W at 2 ohms for 1.5 seconds, then smoothly dropping to 1260W long term. Test conditions were 50Hz, both channels driven, 230VAC mains. Behavior was good but unfortunately Powersoft consistently overstates their power. I am sure their marketing people say "but everybody does it", and quite a few do, but I don't in my amps. http://www.speakerpower.net/comparative-performance.html

Title: Re: Why do Class D amps seem to pull less power than they make?
Post by: John Roberts {JR} on January 24, 2015, 12:02:29 pm
I wish the term "peak power" would go away. It is misleading and wrong. Power must be calculated with RMS voltage over at least one complete cycle to have any relevance to audio. For 20Hz, that's 50 ms. I prefer "tone burst power" Tone means audio, at least one complete cycle. Burst means time, how many cycles at what frequency. Power is the area under the curve which relates to the heating effect of the waveform.

Amplifier power can't be expressed with just one number these days. They are designed to have a short term power to get thru a Thump and a long term power to get thru EDM. A curve of power versus time will show both values and if the amp can transition smoothly between them without overshoot or oscillation.

In my bench testing I measured the K10 to do 3600W at 2 ohms for 1.5 seconds, then smoothly dropping to 1260W long term. Test conditions were 50Hz, both channels driven, 230VAC mains. Behavior was good but unfortunately Powersoft consistently overstates their power. I am sure their marketing people say "but everybody does it", and quite a few do, but I don't in my amps. http://www.speakerpower.net/comparative-performance.html

I have given this topic a great deal of thought over decades and the reality is music is the proverbial square peg that does not fit neatly into simple (round) power measurements, while consumers demand and get those simple numbers.

While few make this connection amp power output capability needs to mimic loudspeaker power handling capability, and to some extent, over time modern amps have evolved to meet market needs.  Unfortunately there is not one universal musical genre so there will always be a continuum or range of product capability.

I probably sound like a broken record but smart powered speakers offer the capability to protect transducers from amplifiers capable of breaking them if abused.

JR

PS: I am always reluctant to ASSume any brand intentionally and habitually over-states product specs. Market feedback should correct any egregious outliers.
Title: Re: Why do Class D amps seem to pull less power than they make?
Post by: Brian Jojade on January 24, 2015, 04:53:53 pm
Anyways, I didn't mean to sound like I had anything against Powersoft or their products, I'm just still confused how they can make a claim that their amps make more power than they consume.

The reason they can make that claim is that the power flowing out is not at the same rate as the power flowing in.  There are capacitors that store power.  What you need to look at is how many joules are going in and coming out of the amp.  Watts over a period of time will get you how many joules of energy you have.

If the amp has huge storage capacitors, you could have a very low continuous current pull from the wall, yet have huge reserves available for short burst which is what audio is.  e.g., if your amp draws 100 watts for 10 seconds and you could output 1000 watts for 1 second, then wait for it to charge back up. Rinse and repeat. (of course assuming 100% efficiency, but that's another topic)

Better amps will have larger reserve capacity and therefore will seem to have lower power demands from the wall. It's still getting the same amount of power, but the demand can be spread over time.  Cheaper amps with less reserve will pull from the wall when needed.  This isn't about efficiency, it's about storage reserve.

Class D amplifiers are very efficient can theoretically approach 100% efficiency.  Current amplifiers can be in the high 90's for efficiency.  Class AB amplifiers run in the 50-75% efficiency range. Therefore, using a class D amplifier will allow you to get more power to your speaker from the same circuit instead of just converting the power to heat within the amplifier.
Title: Re: Why do Class D amps seem to pull less power than they make?
Post by: Ivan Beaver on January 24, 2015, 05:08:31 pm

PS: I am always reluctant to ASSume any brand intentionally and habitually over-states product specs. Market feedback should correct any egregious outliers.
SHOULD is the key word.  But certainly not ALWAYS

Just sayin'-----------------
Title: Re: Why do Class D amps seem to pull less power than they make?
Post by: John Roberts {JR} on January 24, 2015, 08:23:32 pm
SHOULD is the key word.  But certainly not ALWAYS

Just sayin'-----------------

I thought ASSume was the key word... As I've always said lets name names... perhaps Powersoft will enlighten us to their scientific basis for peaks power specs. I am not aware of an industry peak duration standard (back in that day I used 20 mSec of 1 Khz tone burst, so seconds of burst power is a lifetime compared to that.)

  JR
Title: Re: Why do Class D amps seem to pull less power than they make?
Post by: Ivan Beaver on January 24, 2015, 08:31:30 pm
I thought ASSume was the key word... As I've always said lets name names... perhaps Powersoft will enlighten us to their scientific basis for peaks power specs. I am not aware of an industry peak duration standard (back in that day I used 20 mSec of 1 Khz tone burst, so seconds of burst power is a lifetime compared to that.)

  JR
I am not allowed to name names-but let's just say that some of the biggest names in the industry are "pulling these types of misconceptions".

I am citing specific examples (without using names but using screen captures of their data) in the paper I am working on (JR you were correct-I did not finish it over the Christmas break).

I don't think there is a standard for the length of the burst-but around 80ms seems to pop up a lot-which is very short
Title: Re: Why do Class D amps seem to pull less power than they make?
Post by: John Roberts {JR} on January 24, 2015, 10:40:08 pm
I am not allowed to name names-but let's just say that some of the biggest names in the industry are "pulling these types of misconceptions".
By all means scope photos are good, but before you call something a misconception show me the specification that it doesn't meet.
Quote
I am citing specific examples (without using names but using screen captures of their data) in the paper I am working on (JR you were correct-I did not finish it over the Christmas break).
keep plugging away...
Quote
I don't think there is a standard for the length of the burst-but around 80ms seems to pop up a lot-which is very short

I didn't want to go down this rabbit hole again but I designed a trick amp back in the '80s that used cap doublers in the amp PS rails so I could momentarily deliver 2x voltage which in theory "should" be 4x power... and perhaps it was 4x for a microsecond, but in the real world power rails start sagging as soon as you draw power.

Back then (like now) there was no industry spec for burst power so I had to use my own judgement. I gravitated to an even older hifi (IHF?) spec for burst power that consisted of 1 kHz tone burst that was on for 20 mSec and off for 480 mSec so repeated 2x a second..  My cute little 35W amp could put out close to the theoretical 140W momentarily, but as the mill-Seconds ticked off the un-clipped tone burst got smaller and smaller.  :'( It turns out for me to conservatively specify a clean tone burst for 20 mSec I had to de-rate the burst power to only 100W. Not bad for a 35W amp but marketing would prefer to call it a tens of watts more (I didn't ask their opinion). ****

Of course my 100W for 20 mSec wasn't the full story, for longer than 20 mSec it could put out 60W for something like 15 sec before a thermal breaker would open and the power collapsed to the base 35W 24x7. In my experience my little trick amp could hold it's own against 120W conventional amps on dynamic music. Of course driving a woofer in a multi-way system would be a different story, and that is the rub... Different duty cycle is required for different tasks...

At the risk of repeating myself in the same thread...  8) 8) I really like powered speakers because the design engineer who knows what he needs, and where, can apply power properly. This trying to understand a not clearly specified parameter really seems like to much mental gymnastics for civilians.

JR


PS: I have a new anecdote about the sheeple clinging to single number specs to buy products with. My old favorite was about vacuum cleaners ranked by line cord current draw (more must be better right?)... I recently had to replace my dishwasher when the old one started making end-of-service-life noises. The new metric to rank dishwashers by is Decibels.  8) 8) 8) I just bought a "55-Decibel" Whirlpool.  ;D (less must be better... it's more expensive.)
   

**** If you think about what musical transients look like, they do not look like 20 cycles of 1kHz but more like one or two really loud that quickly decay... but that is only one kind of transient. Burst power to reproduce a heavily compressed bass line may have much less crest factor and be harder. If it was easy to come up with a universal spec somebody would have by now. 
Title: Re: Why do Class D amps seem to pull less power than they make?
Post by: Steve Bradbury on January 25, 2015, 07:57:41 am
Quote
What you need to look at is how many joules are going in and coming out of the amp.  Watts over a period of time will get you how many joules of energy you have.

If you are measuring joules, that is a measure of work. A small amp at a long gig is likely to pass more joules in total than a larger amp at a short gig and thus do more work.

Power is the rate of doing work. It is equivalent to an amount of energy consumed per unit time. The unit of power (MKS) is the joule per second (J/s); more commonly known as the Watt.

The question that seems to be in dispute is what time frame you use to measure the number of joules coming in and out of the amplifier to define the power rating.

Is publishing the specifications showing the instantaneous power over a millisecond lying or not? It all depends on whose version of the truth you believe.
Title: Re: Why do Class D amps seem to pull less power than they make?
Post by: John Roberts {JR} on January 25, 2015, 11:05:47 am


The question that seems to be in dispute is what time frame you use to measure the number of joules coming in and out of the amplifier to define the power rating.

Is publishing the specifications showing the instantaneous power over a millisecond lying or not? It all depends on whose version of the truth you believe.
Exactly...  Back a few decades ago our seminar guy was promoting his theory that amp headroom was defined by PS rail voltage. I don't think I ever convinced him to discard that notion but it's more complicated than that and rail voltage at best only defines the very first instant of peak power.

The crest factor of different musical genres varies widely for full range, not to mention compressed band-passed applications that can be several times more demanding.

This is why there are different amps sold since light duty customers don't want to pay for heavier duty products they don't actually need. The market generally sorts out which products work for which applications and which don't. That is exactly why we abandoned 24x7 power decades ago.

If the industry put numbers to this, amp designers would game the numbers and marketers would hype them (in a more is better chase), probably like damping factor and slew rate. While more is always better, paying for more than we actually need is not, so after a learning process the marketplace would re-stabilize, but not without even more confusion than now. 

YMMV

JR   
Title: Re: Why do Class D amps seem to pull less power than they make?
Post by: John Schalk on January 28, 2015, 10:10:18 am
In my bench testing I measured the K10 to do 3600W at 2 ohms for 1.5 seconds, then smoothly dropping to 1260W long term. Test conditions were 50Hz, both channels driven, 230VAC mains. Behavior was good but unfortunately Powersoft consistently overstates their power. I am sure their marketing people say "but everybody does it", and quite a few do, but I don't in my amps. http://www.speakerpower.net/comparative-performance.html

Like the OP, I too have often wondered about the tremendous output that some amps claim to produce from a power cord with a 15 amp edison connector on the business end.  I have purchased 3 Powersoft amps (2 K2s, 1 M50q) with DSP in the past year, so after reading this thread, I did some research on Powersoft's website. I learned that the power output ratings they use are based on the EIAJ specification.  I've always understood that to be "1k @ 1% THD", but assumed that it was a steady state or continuous spec, like the FTC rating.  Despite my best efforts, the exact wording of the EIAJ spec has alluded me.  I did find the following information in a PDF that explains how to replicate the results for DIAGM amps:

1. Power RMS x Channel (1kHz, 0.5%THD):
Maximum continuous output power delivered to the load for at least 5 seconds, then internal limiting processor reduces output voltage swing to _ maximum output.
2. Power RMS x Channel in stereo working:
Maximum EIAJ standard test output power: average of RMS output voltage squared divided by load impedance.
Test signal 1kHz tone burst 8 cycles 0dB, 24 cycles no signal, THD 1%.

I can't quite understand what these two tests are telling me.  Is point 1 saying that a K2 will output 1000 watts into 8 ohms for 5 seconds, but measuring only a single channel? I don't get point 2 at all. Can someone enlighten me please?  And is this the EAIJ specification?

I did find a published test result for a K8 by ABELtronics which shows the K8 exceeding its 3000 watt rating at 1k and 10k, but missing by 84 watts at 40 Hz.  They defined continuous as 5 seconds for their testing.  Here is the link:

http://www.abeltronics.co.uk/amptesting/amp-meet-three.php (http://www.abeltronics.co.uk/amptesting/amp-meet-three.php)

Final comment; I am happy with my Powersoft amps.  I racked up a K2 and the M50q in a 2 space SKB style case and configured the DSP so that I have a biamped stereo system (K2 for lows, 2 channels of M50q for tops) and 2 monitor sends.  Now, when I walk into a breifcase gig, if the band's power looks dodgy, why I just bring in my amp "rack" in one hand!  I can't wait to ditch the copper snake.
Title: Re: Why do Class D amps seem to pull less power than they make?
Post by: John Roberts {JR} on January 28, 2015, 11:59:00 am

Final comment; I am happy with my Powersoft amps.  I racked up a K2 and the M50q in a 2 space SKB style case and configured the DSP so that I have a biamped stereo system (K2 for lows, 2 channels of M50q for tops) and 2 monitor sends.  Now, when I walk into a breifcase gig, if the band's power looks dodgy, why I just bring in my amp "rack" in one hand!  I can't wait to ditch the copper snake.
The computer ate my first answer so I'll keep this brief.

AFAIK the 5 sec duration for power testing is arbitrary so not an industry standard.

How the amps work for you in your application is the real test.

Don't just take my word for it, but have some trust in the market to identify and punish any serial liar who over-promises and under-delivers on amp power. Back in the '70s it was so bad that the government got involved. Any simple government imposed answer to a complex issue like amp duty cycle will cause unintended consequences (like the old FTC specs did).

Research actual end user reports about specific products on forums like this. Trying to understand dynamic power specifications is complicated (please trust me about that at least). 

JR
Title: Re: Why do Class D amps seem to pull less power than they make?
Post by: Brian Jojade on January 28, 2015, 12:17:06 pm
If you are measuring joules, that is a measure of work. A small amp at a long gig is likely to pass more joules in total than a larger amp at a short gig and thus do more work.

Power is the rate of doing work. It is equivalent to an amount of energy consumed per unit time. The unit of power (MKS) is the joule per second (J/s); more commonly known as the Watt.

The question that seems to be in dispute is what time frame you use to measure the number of joules coming in and out of the amplifier to define the power rating.

Is publishing the specifications showing the instantaneous power over a millisecond lying or not? It all depends on whose version of the truth you believe.


This is the measurement that answers the OP's question. 'Why do Class D amps seem to pull less power than they make?'  Stating rated maximum watts with a variable duty cycle makes it seem that the amp is making more power than it is drawing. But when you measure true total power going into the amp and total power coming out of the amp, you'll find that it's not making power at all.
Title: Re: Why do Class D amps seem to pull less power than they make?
Post by: Ivan Beaver on January 28, 2015, 12:24:40 pm

 But when you measure true total power going into the amp and total power coming out of the amp, you'll find that it's not making power at all.
EXACTLY the reason they should be called VOLTAGE AMPLIFIERS and not Power amplifiers.

They do amplify the VOLTAGE of the input, but not the POWER of the input (signal and AC power combined)

Just being picky-but truthful :)
Title: Re: Why do Class D amps seem to pull less power than they make?
Post by: Don Boomer on January 28, 2015, 07:29:14 pm

 But when you measure true total power going into the amp and total power coming out of the amp, you'll find that it's not making power at all.

Exactly ... amps just redirect the power they take in ... well except the perpetual motion variety  ;D

I just wanted to add that the current draw you see listed on the chassis usually reflects operation at 1/8 of the rated continuous output for agency compliance.
Title: Re: Why do Class D amps seem to pull less power than they make?
Post by: Peter Morris on January 28, 2015, 08:43:12 pm
The computer ate my first answer so I'll keep this brief.

AFAIK the 5 sec duration for power testing is arbitrary so not an industry standard.

How the amps work for you in your application is the real test.

Don't just take my word for it, but have some trust in the market to identify and punish any serial liar who over-promises and under-delivers on amp power. Back in the '70s it was so bad that the government got involved. Any simple government imposed answer to a complex issue like amp duty cycle will cause unintended consequences (like the old FTC specs did).

Research actual end user reports about specific products on forums like this. Trying to understand dynamic power specifications is complicated (please trust me about that at least). 

JR

Hi JR,

As I understand with Powersoft amplifiers there is peak power mostly determined by the PSUs maximum rail voltage, and a short continuous power rating determined by the amounts the rail voltage sags under continuous load.

There is also a thermal limit; I assume determined by the thermal capacity of the heat sinks and switch-mode HF transformer. After a short time the amp turns itself down.  The gain is reduced and there is no distortion form what I can remember.

In practice you can occasionally notice the amp turning itself down. When this has happened to me I have been grateful; all my speakers survived despite the efforts of some stupid operator who was determined to destroy something.
Title: Re: Why do Class D amps seem to pull less power than they make?
Post by: Steve Bradbury on January 29, 2015, 06:09:32 am
Quote
EXACTLY the reason they should be called VOLTAGE AMPLIFIERS and not Power amplifiers.

They do amplify the VOLTAGE of the input, but not the POWER of the input (signal and AC power combined)

Just being picky-but truthful :)

Whilst most power amplifiers are voltage followers, in that the output voltage is supposed to be a fixed multiple of the input voltage irrespective of the load impedance, for them not to be power amplifiers the output current capacity would have to go down such that the input and output Volts x Amps product remained constant.

As both the output voltage and current are increased when compared to the input signal then I think that it is not too untruthful to call them power amplifiers.

Quote
Exactly ... amps just redirect the power they take in ... well except the perpetual motion variety  ;D

I just wanted to add that the current draw you see listed on the chassis usually reflects operation at 1/8 of the rated continuous output for agency compliance.

The problem is that the terms power and energy are frequently confused. Whilst the amount of energy coming out cannot exceed that going in it is possible for the energy to be transferred to the load at a greater rate than it is coming in, albeit for limited periods.

For example say you have a battery powered amplifier. The charger may be limited to 10W output, but once the battery is charged the amplifier may be capable of producing 100W. The trade-off is that the battery takes 10 times as long to charge than it does to go flat.
Title: Re: Why do Class D amps seem to pull less power than they make?
Post by: John Roberts {JR} on January 29, 2015, 11:49:40 am
Hi JR,

As I understand with Powersoft amplifiers there is peak power mostly determined by the PSUs maximum rail voltage, and a short continuous power rating determined by the amounts the rail voltage sags under continuous load.

There is also a thermal limit; I assume determined by the thermal capacity of the heat sinks and switch-mode HF transformer. After a short time the amp turns itself down.  The gain is reduced and there is no distortion form what I can remember.

In practice you can occasionally notice the amp turning itself down. When this has happened to me I have been grateful; all my speakers survived despite the efforts of some stupid operator who was determined to destroy something.
Thanx.. yes that chart reveals the difficulty in coming up with an arbitrary peak power test time duration. Back in the 24x7 day that would be a 1000W amp, but I guarantee that those short term peaks play a lot louder than a 1000W amp in real world music use.

Powersoft designed their amp in response to their own bench work, hardware trade-offs, and years of customer feedback.  An arbitrary industry peak power test can make winners and losers depending on where they land wrt that metric. 5 seconds for 2 ohms would clearly understate the actual short term peak power available. In real music there are lots of transients that are shorter than 5 seconds, and very few that aren't (which is what their apparent 10 second threshold supports) .

THIS IS COMPLICATED but not rocket science. IMO an industry standard could create winners and losers not necessarily a bad thing but it could be for the losers.

Power vs time plots like this are good and I think a few of the big dog amps have published such plots.   

JR

PS: It must be a slow week... lots of pedantry about what words mean... I thought that was only me making such petulant complaints.  8)
Title: Re: Why do Class D amps seem to pull less power than they make?
Post by: John Schalk on January 29, 2015, 04:14:54 pm
Powersoft designed their amp in response to their own bench work, hardware trade-offs, and years of customer feedback.  An arbitrary industry peak power test can make winners and losers depending on where they land wrt that metric. 5 seconds for 2 ohms would clearly understate the actual short term peak power available. In real music there are lots of transients that are shorter than 5 seconds, and very few that aren't (which is what their apparent 10 second threshold supports) .

Here is a link to a PDF that contains the graph posted above for the K10. The 23 page file compares an fP-6400, an i-T8000 and both a K6 and K10.  The commentary that explains each test is pro-Powersoft, but that doesn't take away from the interesting results.  It's worth noting that the K10's rated output into 2 ohms stereo is 6,000 watts, so the fact that it can make 7,500 watts for a tenth of a second is pretty cool, I think.

http://www.diy.poweraudio.ro/albums/userpics/10001/BENCH_COMPARISON_TEST.pdf (http://www.diy.poweraudio.ro/albums/userpics/10001/BENCH_COMPARISON_TEST.pdf)

Here is a link to a very technical review of a K3, K10, and M50q, also with plenty of graphs, written by Langston Holland.  Some of it is a bit over my head, but interesting none the less.

https://soundforums.net/threads/3723-Powersoft-K3-K20-M50Q-(Part-II) (https://soundforums.net/threads/3723-Powersoft-K3-K20-M50Q-(Part-II))

My take away from this discussion is that I will continue to run my amps at 8 or 4 ohms and avoid setting up systems that require 2 ohm stereo or 4 ohm bridged operation.  As to how long is long enough, I have not had any issues with my current system so 10 seconds would seem to be the answer for me. 
Title: Re: Why do Class D amps seem to pull less power than they make?
Post by: John Roberts {JR} on January 29, 2015, 06:30:26 pm
Here is a link to a PDF that contains the graph posted above for the K10. The 23 page file compares an fP-6400, an i-T8000 and both a K6 and K10.  The commentary that explains each test is pro-Powersoft, but that doesn't take away from the interesting results.  It's worth noting that the K10's rated output into 2 ohms stereo is 6,000 watts, so the fact that it can make 7,500 watts for a tenth of a second is pretty cool, I think.
7500W/6000W is maybe 1 dBW no big deal and a reasonable spec headroom margin.
Quote
http://www.diy.poweraudio.ro/albums/userpics/10001/BENCH_COMPARISON_TEST.pdf (http://www.diy.poweraudio.ro/albums/userpics/10001/BENCH_COMPARISON_TEST.pdf)

Here is a link to a very technical review of a K3, K10, and M50q, also with plenty of graphs, written by Langston Holland.  Some of it is a bit over my head, but interesting none the less.
yup Langston is (was) a regular here and a solid citizen.
Quote
https://soundforums.net/threads/3723-Powersoft-K3-K20-M50Q-(Part-II) (https://soundforums.net/threads/3723-Powersoft-K3-K20-M50Q-(Part-II))

My take away from this discussion is that I will continue to run my amps at 8 or 4 ohms and avoid setting up systems that require 2 ohm stereo or 4 ohm bridged operation.  As to how long is long enough, I have not had any issues with my current system so 10 seconds would seem to be the answer for me.
+1 conservative system operators do not use 2 ohm operation for normal use. Handy for emergencies if you lose an amp channel or two and need to doble up a couple boxes.

Another aspect of system operation is that 8 ohm nominal loudspeakers can have regions of less than 8 ohm impedance, so some drive headroom is always a good thing. Amps also last longer if you don't flog them hard every moment.

JR
Title: Re: Why do Class D amps seem to pull less power than they make?
Post by: Peter Morris on January 29, 2015, 10:30:49 pm

Another aspect of system operation is that 8 ohm nominal loudspeakers can have regions of less than 8 ohm impedance, so some drive headroom is always a good thing. Amps also last longer if you don't flog them hard every moment.

JR

Absolutely, and in general mids are the worst where the speaker is operating in the frequency range where the impedance is the lowest. Subs however, especially reflex enclosures often have relatively high average impedances.  My Powersoft K10 tells me that my 4 ohm double 18s have an average impedance of 7 ohms, so I dont find any issues driving 2 x double 18s on one channel of a K10.

Its probably also worth mentioning that the maximum output current from a K10 is huge 125 amps peak.  In pratical performs terms the K10 is a very interetsing design / set of compromises. 
Title: Re: Why do Class D amps seem to pull less power than they make?
Post by: Ivan Beaver on January 30, 2015, 08:09:23 am
Absolutely, and in general mids are the worst where the speaker is operating in the frequency range where the impedance is the lowest. Subs however, especially reflex enclosures often have relatively high average impedances. 
I would not agree with that.

All loudspeakers (passive or multiamped) have peaks and dips in the impedance-depending on the freq you are talking aboutt.

HOWEVER-just to make it a bit more "interesting", the ohmage of the impedance is just ONE of the factors that makes it difficult for an amp to drive.

Something that is never talked about is the PHASE of the impedance.

This can put a VERY DIFFICULT load on amplifiers, causing them to get VERY hot and shut down, it it is to far "out of bounds".  Generaly +/- 45 is considered OK, beyond that it can start to be hard on an amp

Some examples:  THe old Servodrive speakers were HELL on an amp.  This was due to the almost purely inductive load.  Back when I was running them I had to pressurize my racks with every amp I tried or else they would easily shut down at no where near full output.

Piezo tweeters are another example on the opposite end.  They are almost purely capacitive-which some amps can't drive.

SO ONCE AGAIN- a simple number cannot possibly describe a complex situation.
Title: Re: Why do Class D amps seem to pull less power than they make?
Post by: John Roberts {JR} on January 30, 2015, 09:46:21 am
I would not agree with that.

All loudspeakers (passive or multiamped) have peaks and dips in the impedance-depending on the freq you are talking aboutt.

HOWEVER-just to make it a bit more "interesting", the ohmage of the impedance is just ONE of the factors that makes it difficult for an amp to drive.

Something that is never talked about is the PHASE of the impedance.

This can put a VERY DIFFICULT load on amplifiers, causing them to get VERY hot and shut down, it it is to far "out of bounds".  Generaly +/- 45 is considered OK, beyond that it can start to be hard on an amp

Some examples:  THe old Servodrive speakers were HELL on an amp.  This was due to the almost purely inductive load.  Back when I was running them I had to pressurize my racks with every amp I tried or else they would easily shut down at no where near full output.

Piezo tweeters are another example on the opposite end.  They are almost purely capacitive-which some amps can't drive.

SO ONCE AGAIN- a simple number cannot possibly describe a complex situation.
Load phase angle mattered most for old school class AB amps. Modern class D amps do not experience the same dissipation or secondary breakdown behavior in power devices from high current with high voltage at the same time. In class D the power devices are either off or switched hard on so no voltage and current at the same time.

JR
Title: Re: Why do Class D amps seem to pull less power than they make?
Post by: Ivan Beaver on January 30, 2015, 09:53:55 am
Load phase angle mattered most for old school class AB amps. Modern class D amps do not experience the same dissipation or secondary breakdown behavior in power devices from high current with high voltage at the same time. In class D the power devices are either off or switched hard on so no voltage and current at the same time.

JR
See-you learn something every day.  :)

My experiences with the "hard loads" was back in the "AB" days.

I can't say I have experienced those sorts of problems with the class D amps-but then again I am not driving them with those types of loads either.
Title: Re: Why do Class D amps seem to pull less power than they make?
Post by: John Roberts {JR} on January 30, 2015, 10:44:08 am
See-you learn something every day.  :)

My experiences with the "hard loads" was back in the "AB" days.

I can't say I have experienced those sorts of problems with the class D amps-but then again I am not driving them with those types of loads either.

I have heard musings by someone smarter than me that a reactive load (like a capacitive electrostatic loudspeaker) might be more efficient to operate since you don't have all that resistance wasting power as heat. The reactive load would just charge and discharge not really consuming as much power.

This is hypothetical and I am not aware of any practical examples.

JR
Title: Re: Why do Class D amps seem to pull less power than they make?
Post by: Art Welter on January 30, 2015, 11:31:08 am

As I understand with Powersoft amplifiers there is peak power mostly determined by the PSUs maximum rail voltage, and a short continuous power rating determined by the amounts the rail voltage sags under continuous load.

There is also a thermal limit; I assume determined by the thermal capacity of the heat sinks and switch-mode HF transformer. After a short time the amp turns itself down.  The gain is reduced and there is no distortion form what I can remember.

In practice you can occasionally notice the amp turning itself down. When this has happened to me I have been grateful; all my speakers survived despite the efforts of some stupid operator who was determined to destroy something.
Just before the holidays I conducted a battery of tests on some old amplifiers and a new Behringer NU4-6000 four channel amplifier. To my surprise, the  performed as well on low frequencies as on mid/high frequencies, and is capable of full power sine wave output with all four channels driven to rated output at two ohms, or two bridged mono pairs driving four ohm loads each. The  $350 NU4-6000 is within 3 dB of the K10 on sustained (more than 1 second) output.

The NU4-6000 with  two bridged mono pairs driving four ohm loads just below the illumination of the clip/limit light each put out 85.5 volts at 60 Hz (1828 watts), 84.6 volts at 30 Hz (1789 watts), dropping the mains voltage on a 100' 10AWG 120v line from 118.1 volts down to 107.2 volts, drawing 31 amperes.

Using just one bridged mono pair, the amp ran for 40+ seconds before I terminated the test, as the amp was drawing 19.8 amperes, and the "tired" 20 amp mains breaker had popped several times in various tests already. The amp would have put out more power given a full 120 volts, but the test represents "real world" situation, we don't generally plug our amplifiers in to an outlet two feet from the mains transformer.

I also tested my old "heavy iron"  bass favorite, a Crest CA9, bridged into a 4 ohm load it dropped the mains to 99.6 volts, drew 37.8 amps but only put out 80 volts (1600 watts). The NU4-6000 put out more power, and drew only 50% of the power from the mains compared to the CA9 !

My back (and bank account) are very pleased with the NU4-6000.

Art
Title: Re: Why do Class D amps seem to pull less power than they make?
Post by: John Roberts {JR} on January 30, 2015, 11:53:57 am
Yup, in case I haven't said this lately the modern cheap class D power amps are pretty remarkable. Peavey has been messing with class D variants for decades, but back when I was involved we just didn't have the high frequency, high voltage switching devices to make serious power. Back then it was a stretch to make 1kW. Nowadays I'm sure these guys are using a dedicated chip set for the front end and nice off the shelf power devices (speculation I've been out of the trenches for over a decade).

Regarding mains power, to accurately test a big dog amp you need a serious power drop. I recall having to re-wire dedicated mains power feeds for the amp designer's test bench. I always wince when consumers "test" power amps, because as often as not, they are are seeing the limitations of their power source. Of course that is real world, but can lead to some ugly conclusions if not factored in. More good news is that the modern designs are more power friendly too.

The budget amps are probably not taken very seriously, but that sounds like pretty serious power. i remember when UL would make us put camper plugs on smaller amps than that... Times have changed for the better.

JR
Title: Re: Why do Class D amps seem to pull less power than they make?
Post by: Richard Turner on January 30, 2015, 03:46:16 pm
Just before the holidays I conducted a battery of tests on some old amplifiers and a new Behringer NU4-6000 four channel amplifier. To my surprise, the  performed as well on low frequencies as on mid/high frequencies, and is capable of full power sine wave output with all four channels driven to rated output at two ohms, or two bridged mono pairs driving four ohm loads each. The  $350 NU4-6000 is within 3 dB of the K10 on sustained (more than 1 second) output.

The NU4-6000 with  two bridged mono pairs driving four ohm loads just below the illumination of the clip/limit light each put out 85.5 volts at 60 Hz (1828 watts), 84.6 volts at 30 Hz (1789 watts), dropping the mains voltage on a 100' 10AWG 120v line from 118.1 volts down to 107.2 volts, drawing 31 amperes.

Using just one bridged mono pair, the amp ran for 40+ seconds before I terminated the test, as the amp was drawing 19.8 amperes, and the "tired" 20 amp mains breaker had popped several times in various tests already. The amp would have put out more power given a full 120 volts, but the test represents "real world" situation, we don't generally plug our amplifiers in to an outlet two feet from the mains transformer.

I also tested my old "heavy iron"  bass favorite, a Crest CA9, bridged into a 4 ohm load it dropped the mains to 99.6 volts, drew 37.8 amps but only put out 80 volts (1600 watts). The NU4-6000 put out more power, and drew only 50% of the power from the mains compared to the CA9 !

My back (and bank account) are very pleased with the NU4-6000.

Art

I've been eyeballing that exact amp, Does it sound as musical as compared to old crest iron?  putting 3 units in a rack box and coming out under 50 lbs and having up to 12 channels in a flexible package for under $1200, Would it be too good to be true?

Is it still working as advertised after initial break in? No funny smells no melted bits after running fill tilt for 50 hours? Definelty attractive for a monitor rack and utility amp rack.

Heck 3 year warranty, if they don't take 90 days to effect repairs that's a solid selling point right there. Or is it in some fine print that actually using it commercially cripples the warranty term?
Title: Re: Why do Class D amps seem to pull less power than they make?
Post by: Keith Broughton on January 31, 2015, 09:32:23 am
Just before the holidays I conducted a battery of tests on some old amplifiers and a new Behringer NU4-6000 four channel amplifier. To my surprise, the  performed as well on low frequencies as on mid/high frequencies, and is capable of full power sine wave output with all four channels driven to rated output at two ohms, or two bridged mono pairs driving four ohm loads each. The  $350 NU4-6000 is within 3 dB of the K10 on sustained (more than 1 second) output.


Interesting results.
i have been toying with the idea of racking up 3 or 4  iNuke  6000DSP amps and putting them into real world use.
AT $385 CDN(dealer) you cant' beat the price!
Title: Re: Why do Class D amps seem to pull less power than they make?
Post by: John Schalk on January 31, 2015, 10:18:56 am
The NU4-6000 with  two bridged mono pairs driving four ohm loads just below the illumination of the clip/limit light each put out 85.5 volts at 60 Hz (1828 watts), 84.6 volts at 30 Hz (1789 watts), dropping the mains voltage on a 100' 10AWG 120v line from 118.1 volts down to 107.2 volts, drawing 31 amperes.

I looked up the specs on the NU4-6000 and Behringer states that the amp will produce 2 x 3,000 watts into 4 ohms.  They do not give any parameters for how those ratings were achieved.  Art measured ~1,800 watts which is well short of their advertised output, although still impressive for a 12lb, $350 piece of audio gear.

Trying to understand the gap even though JR has warned me about such foolishness, I found a bench test of the NU-6000 which states that, in the owner's manual, Behringer lists RMS figures of 1.1kW @ 8 ohms and 2.2kW @ 4 ohms for the 2 channel iNuke 6k.  Interestingly, the writer of this review reaches the same conclusion as Art did for the amp; stating that it should be good for 1.8kW long term into 4 ohms.  The reviewer also points out that the Behringer amp lacks Power Factor Correction and so may present a more challenging load on the mains circuit at your local pub. 

http://forum.speakerplans.com/behringer-inuke-nu6000-vs-kam-kxd7200-bench-tested_topic69202.html (http://forum.speakerplans.com/behringer-inuke-nu6000-vs-kam-kxd7200-bench-tested_topic69202.html)
Title: Re: Why do Class D amps seem to pull less power than they make?
Post by: Keith Broughton on January 31, 2015, 11:46:25 am
I looked up the specs on the NU4-6000 and Behringer states that the amp will produce 2 x 3,000 watts into 4 ohms.  They do not give any parameters for how those ratings were achieved.  Art measured ~1,800 watts which is well short of their advertised output, although still impressive for a 12lb, $350 piece of audio gear.

Trying to understand the gap even though JR has warned me about such foolishness, I found a bench test of the NU-6000 which states that, in the owner's manual, Behringer lists RMS figures of 1.1kW @ 8 ohms and 2.2kW @ 4 ohms for the 2 channel iNuke 6k.  Interestingly, the writer of this review reaches the same conclusion as Art did for the amp; stating that it should be good for 1.8kW long term into 4 ohms.  The reviewer also points out that the Behringer amp lacks Power Factor Correction and so may present a more challenging load on the mains circuit at your local pub. 

http://forum.speakerplans.com/behringer-inuke-nu6000-vs-kam-kxd7200-bench-tested_topic69202.html (http://forum.speakerplans.com/behringer-inuke-nu6000-vs-kam-kxd7200-bench-tested_topic69202.html)
I too would be interested to see how they arrive at
"Delivers 2 x 3100 Watts into 4 Ohms, 2 x 1600 Watts into 8 Ohms "
as stated on their product page when the amp actually does 2200/4.
The "real" numbers are good to know and ,yes, it is still quite good for the price.
Title: Re: Why do Class D amps seem to pull less power than they make?
Post by: John Roberts {JR} on January 31, 2015, 11:57:59 am
The crux of the biscuit is how do you come up with a single number for what is at least a two dimensional (power vs. time) envelope of power output capability. Any single power number is only describing one instant of that total power envelope. Further there is a short term and longer term power envelope limited by different parameters.

Note: Loudspeakers share a similar multi-dimensional power handling envelope.

Buy a powered speaker and let the engineers worry about this.

JR   
Title: Re: Why do Class D amps seem to pull less power than they make?
Post by: Ivan Beaver on January 31, 2015, 01:54:00 pm
The crux of the biscuit is how do you come up with a single number for what is at least a two dimensional (power vs. time) envelope of power output capability. Any single power number is only describing one instant of that total power envelope. Further there is a short term and longer term power envelope limited by different parameters.

Note: Loudspeakers share a similar multi-dimensional power handling envelope.


JR

EXACTLY.  And also why it gets hard to give a "nice simple" limiter number.

Different limiter parameter protect against different signal "times/amplitudes".

When you start to dig it can get deep REAL quick.
Title: Re: Why do Class D amps seem to pull less power than they make?
Post by: Art Welter on February 02, 2015, 10:22:09 am
1)I've been eyeballing that exact amp, Does it sound as musical as compared to old crest iron?  putting 3 units in a rack box and coming out under 50 lbs and having up to 12 channels in a flexible package for under $1200, Would it be too good to be true?

2)Is it still working as advertised after initial break in? No funny smells no melted bits after running fill tilt for 50 hours? Definelty attractive for a monitor rack and utility amp rack.

3)Heck 3 year warranty, if they don't take 90 days to effect repairs that's a solid selling point right there. Or is it in some fine print that actually using it commercially cripples the warranty term?
Richard,

1) The NU4-6000 sounds like what goes in, and the limiting circuit is musical, it does not sound bad when run to limit. It has by far the best $$ per watt ratio of any amp I have ever purchased, and in bridged mono mode it has more output in to 4 ohms than the Speakerpower SP 4000 I had been using.
2) Yes, still running fine, but I don't have many hours on it. I have used it twice with a modified square wave inverter and it is completely noise free. The efficiency is pretty amazing, even running 60 or 30 Hz sine waves the output of the fans was barely above ambient. Low heat generally means longer life for components.
3) No fine print as far as I can see, I bought three, from what I read Behringer warranty repair or replacement is good. With so many channels available one of the three amplifiers could go out and with a quick re-patch the show would go on, just with -3dB less LF output.

I expect there will soon be a Midas badged version of the amp,  with a circuit that slows down the fans at low output (the only drawback I found with the amp) dB markings on the volume pots, and digital connectivity,  and a cost 2-3 times the price of the NU4-6000.

Art