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[Robert Healey]

Ivan, where do we find pro power amps that provide "only" 150w at 8 ohms, or 300w into 4ohms?

I use a QSC CX302 for my high drivers (EV ND6s in Xi1122 boxes). They're 16 ohm drivers, which helps, but the CX302 is only 200W into 8 ohms anyway.

[Brian Jojade]

Ivan, where do we find pro power amps that provide "only" 150w at 8 ohms, or 300w into 4ohms?

http://qsc.com/products/Power_Amplifiers/Rmxa_Series/RMX_850a/

[Luke Geis]

The very first thing I found about " proper " amp power that made any sense to me was 20 years ago. Perhaps some will remember the formula. I believe it went like this? Take the peak power and subtract the the continuous power from it and then add 25% of the continuous rating and add it back. I.E. 500 watts peak usually has a 125 watt continuous rating. So 500 - 125= 375. 25% of 125= 31. 31+375=406. So in essence a 400 watt amp. There is more than 1 way to come to this same number. You could take peak and subtract 25% then add 1/16th power back, or roughly 6% of peak ( this would roughly be 25% of the initial 25% that you subtracted) making this equation equal 405 or still a 400 watt amp. Whether this was a well accepted model I do not know? What I do know is that the model had too much math and although it made sense there was an easier way that I found made sense and left you between the two extremes of too little and too much.

I usually suggest an amp that is simply 75% of peak power. In other words subtract the continuous rating from the peak and find the closest amp to that you can get. Using the same scenario as above you would take 500 X .75= 375. So you your looking for an amp that is 350-400 watts. From an application standpoint you can never expect to get a 500 watt speaker to last very long with an actual 500 watts going through it. Perhaps only a few moments? On the other hand running an amp that only runs at the program power rating of 250 watts leaves you with a 3db deficit in possible output power. Not being able to get that last 3db is not a big deal, but clipping at or below that point is also a waste of the speakers ability to convert power into acoustic output. Seeing as how we should never see a big, fat, red light on the amp at all and certainly not for any length of time, means that running an amp capable of cleanly producing at least the program power of a speaker is a good goal. An amp that is 75% of peak does this quite well. It will pass at least the program power cleanly and start to show red lights very soon after. This is your warning light. No red lights flickering means that your somewhere between continuous and just about program power. I have yet to ever lose a speaker following this formula. Time may change that constant?

Getting back to what Ivan says, he is basically saying get an amp that produces no more than " program " power and clipping is still not ok. To which I agree is at least a goal to acquire. If the client can't afford 75% of peak power I tell them to get the most powerful amp that they can afford as long as it's between continuous and program power. I give them the warning that red lights will result in ungood things that may mean the cost saved on the amps now only offsets the cost of repairs that will probably have to be made later if they buy an amp rated close to continuous power.

Perhaps Ivan could elaborate on what he means by HIGH POWER amp TO THE RAILS. An example of speaker and amp wattage perhaps. I'm ASSuming he means running an amp rated for the peak power of the element or higher than it's powering?

[Rob Spence]

I guess we've been lucky. We've been driving QRX212 horns with a plx3102 (550w @8ohms, 900 @4) for years and have yet to see a driver failure caused by that power. These are processed with a BSS omnidrive 366t with the limiter set to "fast" at 2x rms voltage.

Ivan, where do we find pro power amps that provide "only" 150w at 8 ohms, or 300w into 4ohms?

I use a PLX1602 with either one or two HF drivers per channel depending on if I have one or two cabs per side.

I use a 3402 channel for each cabinet LF.



Sent from my iPad using Tapatalk HD

[paul bell]

All this makes me remember the JBL recommended amplifiers for the VerTec line array when it first came out. MA5000 for every section including the compression drivers.

[duane massey]

I have always gone against the norm on this. I've always taken a very conservative approach to powering speakers, especially compression drivers. Dating back to the days of "RMS" we would always match the RMS rating of the amp to the speaker rating, or slightly less. I still use the same "less is safer" approach to this day, and I rarely have any blown driver/speaker issues UNLESS there is a serious malfunction in the food chain or a non-qualified person gets into the system and makes adjustments.
Many, many years ago I suffered the painful experience of having to re-diaphragm 6 TAD 2" drivers, and I have been very cautious since.

[Ivan Beaver]

The very first thing I found about " proper " amp power that made any sense to me was 20 years ago. Perhaps some will remember the formula. I believe it went like this? Take the peak power and subtract the the continuous power from it and then add 25% of the continuous rating and add it back. I.E. 500 watts peak usually has a 125 watt continuous rating. So 500 - 125= 375. 25% of 125= 31. 31+375=406. So in essence a 400 watt amp. There is more than 1 way to come to this same number. You could take peak and subtract 25% then add 1/16th power back, or roughly 6% of peak ( this would roughly be 25% of the initial 25% that you subtracted) making this equation equal 405 or still a 400 watt amp. Whether this was a well accepted model I do not know? What I do know is that the model had too much math and although it made sense there was an easier way that I found made sense and left you between the two extremes of too little and too much.

I usually suggest an amp that is simply 75% of peak power. In other words subtract the continuous rating from the peak and find the closest amp to that you can get. Using the same scenario as above you would take 500 X .75= 375. So you your looking for an amp that is 350-400 watts. From an application standpoint you can never expect to get a 500 watt speaker to last very long with an actual 500 watts going through it. Perhaps only a few moments? On the other hand running an amp that only runs at the program power rating of 250 watts leaves you with a 3db deficit in possible output power. Not being able to get that last 3db is not a big deal, but clipping at or below that point is also a waste of the speakers ability to convert power into acoustic output. Seeing as how we should never see a big, fat, red light on the amp at all and certainly not for any length of time, means that running an amp capable of cleanly producing at least the program power of a speaker is a good goal. An amp that is 75% of peak does this quite well. It will pass at least the program power cleanly and start to show red lights very soon after. This is your warning light. No red lights flickering means that your somewhere between continuous and just about program power. I have yet to ever lose a speaker following this formula. Time may change that constant?

Getting back to what Ivan says, he is basically saying get an amp that produces no more than " program " power and clipping is still not ok. To which I agree is at least a goal to acquire. If the client can't afford 75% of peak power I tell them to get the most powerful amp that they can afford as long as it's between continuous and program power. I give them the warning that red lights will result in ungood things that may mean the cost saved on the amps now only offsets the cost of repairs that will probably have to be made later if they buy an amp rated close to continuous power.

Perhaps Ivan could elaborate on what he means by HIGH POWER amp TO THE RAILS. An example of speaker and amp wattage perhaps. I'm ASSuming he means running an amp rated for the peak power of the element or higher than it's powering?

Back "in the 'ol days" it was very common to use the same amplifier model for all the passbands in a system.  This made it real easy to swap things around if needed.

But then again-"back in the day", we did not have the "super power" woofers that we do today and did not have the "super power" amps that are available today.

So some "ideas" need to change-hence my change in my suggestions.

By "going to the rails" means the voltage rails. ALL amplifiers have voltage "rails" that is the DC supply voltage that the amplifier works off of.  The higher the "wattage" capability-the higher the voltage rails HAVE to be-assuming the same load impedance. 

In the old days rails of 60-80V very very common.  Today they easily exceed 200V.  The HF capability of drivers today are not all that different than those decades ago-yet the amps have been able to go WAY up in terms of power.

These "super power" amps can deliver HUGE amounts of voltage for short periods of time-to cause the damage I am speaking of. That is what Lab Gruppen makes a big deal out of in their marketing-large voltage swings.

That is NOT a bad thing-in fact it is a good thing-for loudspeakers that can handle large voltage swings without damage.

 The tiny wires in the HF devices (needed to get higher performance) simply cannot take that kind of voltage-even for a short period of time.

Regarding SIZING of amplifiers.  That is very hard-as there are all kinds of different "formulas" out there.  Some don;t make any sense and simply "try to be complicated" just to make them sound more "legit".
I still stand by my comments of no more than twice the continuous (or 1/2 the peak rating).  It is easy to figure and remember

HOWEVER-the type of program material PLAY A LOT into the heating and damage of voice coils of HF drivers.

When I started on one of my "projects" (protection of HF diaphragms), I first set out find the most "abusive" type music.

I measured (with various meters) things like peak-average-response times and so forth and actually blowing up many diaphragms while watching the levels going to the them.  Then looking at the damage to get an idea of what went wrong/what type of failure etc.

I started with the "obvious" (or so I thought) "hard" types of music.  Things like compressed EDM-fast metal (Dragon Force) etc.

What I found was surprising (but makes sense).  Pop Big Band and harmonica based blues did more damage to HF diaphragms than other sources of material.

Think about those styles.  What is very prominent and people "like" about them.  It is the "screaming/continuously held" notes of things like trumpet-sax-harmonica.

That is the "excitement" of those styles.  NOT blistering fast guitar lines that don't produce heat to the HF voice coil or short sharp "cracks" of sound/noise (EDM).  Just  monitor a "screaming trumpet" and watch how fast and how long the voltage goes to a HF diaphragm :0

So the "pop" Big band type tracks are my "go to" for abuse and testing things like limiters/protection and so forth.

Hopefully that helps explain it a little.

[Keith Broughton]

[quotePop Big Band and harmonica based blues did more damage to HF diaphragms than other sources of material.][/quote]
i came to the same conclusion after blowing a couple of HF drivers in Meyer UPMs doing a harmonica playing singer for an auto show booth.
Wasn't really THAT loud but the sustained notes were killers.
I have struggeles with the idea of different amps per bandpass or all the same for convenience of trade outs.
Years back I was using a Meyer UPA/650 rig with a rack of BGW 750s. Sounded great (bitch to lift) but as Ivan said, they really were not the kind of power we have at our disposal today.
Just got a hold of 4 iNuke 12000 amps for a 3 way system.
Might have to re think the concept.

Will report on the iNukes later in anopther post.

[Ivan Beaver]

[quotePop Big Band and harmonica based blues did more damage to HF diaphragms than other sources of material.]

I have struggeles with the idea of different amps per bandpass or all the same for convenience of trade outs.
Years back I was using a Meyer UPA/650 rig with a rack of BGW 750s. Sounded great (bitch to lift) but as Ivan said, they really were not the kind of power we have at our disposal today.
Just got a hold of 4 iNuke 12000 amps for a 3 way system.
Might have to re think the concept.

Will report on the iNukes later in anopther post.

Yes it is a "delima".

What appears to be "the problem" is NOT so much the size of the amps-or how hard they are pushed (within normal reason), but RATHER-what is happening "on stage".

In my (current) opinion, as long as everything is working fine-having a large amp on the HF is just fine.

But when there are "accidents" (loose connections on cables for example)-that can cause a large fast spike that gets transferred to the HF diaphragm and it fails so fast you have no idea that it even happened.

In a system that does not have a lot of gain on the front end (DJ rig for example), there is less of a possibility that a large spike could be amplified and get through.

A lose connection on the output of a mixer will generate smaller spikes than a loose connection on a microphone.

So even with large amps, you could go a number of shows with no issues-and then do a show that is run at a lower level and take out the diaphragms-if some spikes come through.

I am not 100% sure, but based on my experience in looking at this -this is the best idea that I have for the particular "odd" failures of HF drivers-that were not obviously overheated or a period of time.

So until I am convinced otherwise, this is my theory.

I am just trying to "throw out some caution" to others so hopefully they do not have to deal with the issues and save some money.

[Keith Broughton]

I think your theory is ...well...sound.
It makes sense that a short term, high voltage spike can take out a driver coil without the usual burning or pitting that you see when drivers have been repeatedly clipped or over powered.
This can happen if a condenser mic is disconnected and re connected before you can mute the channel.

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