ProSoundWeb Community

Please login or register.

Login with username, password and session length
Advanced search  

Pages: [1] 2  All   Go Down

Author Topic: Get More Power Out of an Amp  (Read 1075 times)

Victor Estrada

  • Newbie
  • *
  • Offline Offline
  • Posts: 46
Get More Power Out of an Amp
« on: December 20, 2018, 12:21:18 pm »

Is it possible to get more power out of an amp by increasing the resistance (lower Ohms)?

For example:

Amp can do (per channel):
3850W RMS at 2 ohms
2400W RMS at 4 ohms
1330W RMS at 8 ohms

But the single speaker is rated at 2400W RMS 4800W Peak @ 8 Ohms

My goal is to push this sub to the max, but unfortunately, this amp does not support bridge mode
Logged

Tim McCulloch

  • SR Forums
  • Hero Member
  • *
  • Offline Offline
  • Posts: 19717
  • Wichita, Kansas USA
Re: Get More Power Out of an Amp
« Reply #1 on: December 20, 2018, 12:50:59 pm »

No.  The *total* amount of available current does not change, regardless of impedance.  Once it's at the end of the PSU capability there is nothing left.  Where do you think it would come from?  Garden fairies with unicorns delivering it?

Also, if you're thinking about adding a resistor in parallel to drop the impedance - where do you think that power will go?  HINT - you can warm your hands but not make more sound.
Logged
"Practicing an art, no matter how well or badly, is a way to make your soul grow, for heaven's sake. Sing in the shower. Dance to the radio. Tell stories. Write a poem to a friend, even a lousy poem. Do it as well as you possible can. You will get an enormous reward. You will have created something."  - Kurt Vonnegut

Keith Broughton

  • Hero Member
  • *****
  • Offline Offline
  • Posts: 3000
  • Toronto
Re: Get More Power Out of an Amp
« Reply #2 on: December 20, 2018, 04:09:27 pm »

First, one small correction...lowering Ohms is DECREASING resistance not increasing. That is why you see the power going up when the resistance goes down.
But, as Tim said, there is only a certain amount of power available based on the design of the amp and no Golden Fairies can help. ;-)

Given the power rating of the sub, it looks like your amp is a bit under powered to "take it to the limit"
There is a way to bridge the amp but it might not be something a novice should try.
Logged
I don't care enough to be apathetic

Luke Geis

  • Hero Member
  • *****
  • Offline Offline
  • Posts: 1660
    • Owner of Endever Music Production's
Re: Get More Power Out of an Amp
« Reply #3 on: December 20, 2018, 08:28:39 pm »

There is a way to extract a little more, BUT....... it isn't practical and only works if you set your system up a certain way. And even after you employ the trick, it's only good for about 10-15% more, which is negligible.
 
How it's done:

1. Place amp in bridge mono mode.

2. Connect the leads of one speaker to the channel 1 side like normal.

3. Connect the leads from the other speaker to channel 2 in reverse. Negative goes to positive and vise versa. 

Now keep in mind 10-15% of 1,000 watts is only 100 - 150 watts. This will do absolutely nothing for you at all. It will not increase headroom and it will not increase SPL potential.

How it works is simple. When you switch the amp into bridge mono mode, all it does is swap the polarity of one of the power amp channels. This swap reduces the load on the power supply by an itsy bitsy bit and allows the dissipation of we bit more power. Not all amps will respond to this trick though. Switching mode PS, Class D amps are less likely to see any change at all because the PS is already so efficient and class D amps are so efficient. Basically, you can't squeeze any more out of it because it has already been extracted.

The long and short answer is NO you can't get any more than what the amp is rated for. Trying to run loads on the amp that are lower than the minimum impedance of the amp will cause it to overheat and burn up if ran too hard. If you need more SPL, you need either a bigger amp or a more efficient speaker.

The downsides to amp power:

1. It takes 2X the power to acquire a 3db increase in SPL from the speaker.

2. 2X the power is often cost prohibitive, or beyond the rating of the speaker you are powering.

3. More amplifier power is often not the answer if nothing else changes. You typically need a more efficient speaker, or more speakers period.

Logged
I don't understand how you can't hear your self

David Allred

  • Hero Member
  • *****
  • Offline Offline
  • Posts: 1625
Re: Get More Power Out of an Amp
« Reply #4 on: December 21, 2018, 10:46:31 am »

Is it possible to get more power out of an amp by increasing the resistance (lower Ohms)?

For example:

Amp can do (per channel):
3850W RMS at 2 ohms
2400W RMS at 4 ohms
1330W RMS at 8 ohms

But the single speaker is rated at 2400W RMS 4800W Peak @ 8 Ohms



My goal is to push this sub to the max, but unfortunately, this amp does not support bridge mode

What is the output of the speaker at 1300w?

You could run the amp heavily clipped.  Higher continuous output, but no higher peaks.  I'd rather have a speaker cruise than stress.  As you have it, that speaker is is practically fool proof, and catastrophe proof.
Or
Buy another amp and bridge them.
Logged

Tim McCulloch

  • SR Forums
  • Hero Member
  • *
  • Offline Offline
  • Posts: 19717
  • Wichita, Kansas USA
Re: Get More Power Out of an Amp
« Reply #5 on: December 21, 2018, 12:58:13 pm »

There is a way to extract a little more, BUT....... it isn't practical and only works if you set your system up a certain way. And even after you employ the trick, it's only good for about 10-15% more, which is negligible.
 
How it's done:

1. Place amp in bridge mono mode.


Victor indicated the amplifier does not have a bridged mono mode.
Logged
"Practicing an art, no matter how well or badly, is a way to make your soul grow, for heaven's sake. Sing in the shower. Dance to the radio. Tell stories. Write a poem to a friend, even a lousy poem. Do it as well as you possible can. You will get an enormous reward. You will have created something."  - Kurt Vonnegut

Caleb Dueck

  • Hero Member
  • *****
  • Offline Offline
  • Posts: 845
Re: Get More Power Out of an Amp
« Reply #6 on: December 21, 2018, 08:55:21 pm »

Is it possible to get more power out of an amp by increasing the resistance (lower Ohms)?

For example:

Amp can do (per channel):
3850W RMS at 2 ohms
2400W RMS at 4 ohms
1330W RMS at 8 ohms

But the single speaker is rated at 2400W RMS 4800W Peak @ 8 Ohms

My goal is to push this sub to the max, but unfortunately, this amp does not support bridge mode

What model amp and sub?  If the amp was a QSC GX7 (for example), the output power rating is short enough duration to be near meaningless.  If it's a Powersoft K6 (for example) the numbers are more realistic.

Bridging into a 4 ohm load means the amp operates at 2 ohms per channel, and likely current limits well shy of outputting full rated power for any usable duration. 

Even if you buy a new, sold amp - the extra 2.5-ish dB won't be drastic.  It may take you from "seriously under-subbed" to "very under-subbed". 
Logged
Experience is something you get right after you need it.

Victor Estrada

  • Newbie
  • *
  • Offline Offline
  • Posts: 46
Re: Get More Power Out of an Amp
« Reply #7 on: December 26, 2018, 12:16:46 pm »

What model amp and sub?  If the amp was a QSC GX7 (for example), the output power rating is short enough duration to be near meaningless.  If it's a Powersoft K6 (for example) the numbers are more realistic.

Bridging into a 4 ohm load means the amp operates at 2 ohms per channel, and likely current limits well shy of outputting full rated power for any usable duration. 

Even if you buy a new, sold amp - the extra 2.5-ish dB won't be drastic.  It may take you from "seriously under-subbed" to "very under-subbed".

It's a Peavey IPR2 7500, was thinking of using it to power 2 of those subs, but at 8 ohms and no bridge mode, it won't be pushing them to the max, right? I pretty much need the speakers to be 4ohms to get the 2400 watts RMS out of the amp per channel, or bridge mode to power both of them at 4ohms and get the 4800w needed to power them, right?
Logged

Lee Buckalew

  • Classic LAB
  • Hero Member
  • *
  • Offline Offline
  • Posts: 1299
  • St. Louis, MO area
    • Pro Sound Advice, Inc.
Re: Get More Power Out of an Amp
« Reply #8 on: December 26, 2018, 12:48:26 pm »

It's a Peavey IPR2 7500, was thinking of using it to power 2 of those subs, but at 8 ohms and no bridge mode, it won't be pushing them to the max, right? I pretty much need the speakers to be 4ohms to get the 2400 watts RMS out of the amp per channel, or bridge mode to power both of them at 4ohms and get the 4800w needed to power them, right?

Victor,
You were also asked what make and model of speaker that you are referring to here.  It would help to be able to explain the real world needs of the speakers if you let us know what they are.

You have noted that the speakers have a 4800 watt at 8 ohm peak rating and a 2400 watt at 8 ohm RMS rating.  This would tend to indicate that the continuous capability of these speakers is approximately 1200 watts at 8 ohms (approximately the rating of the amplifier that you have).

You can't simply get extra power from the amplifiers by changing the impedance of the attached load. 
What is really moving the cones is voltage, not wattage. 
The available voltage is not changing due to a change in impedance.  1200 watts at 8 ohms = 2400 watts at 4 ohms in terms of voltage. 

When you parallel 2 speakers to a single amp channel each of the speakers will "see" the same voltage but the two speakers combined will require twice the current from the amplifier.  The ratings of the amp that you noted do not show that it can double its current output at 4 ohms compared to 8 ohms (if it could the wattage rating should double when going from 8 ohm to 4 ohm) so you will actually be getting less available voltage at 4 ohms than at 8 ohms.


Lee
« Last Edit: January 04, 2019, 10:45:12 pm by Lee Buckalew »
Logged
Lee Buckalew
Pro Sound Advice, Inc.

Luke Geis

  • Hero Member
  • *****
  • Offline Offline
  • Posts: 1660
    • Owner of Endever Music Production's
Re: Get More Power Out of an Amp
« Reply #9 on: December 26, 2018, 03:56:58 pm »

Victor,

     Watts are not really important. Also, you cannot power a speaker at its rated peak wattage. Going back to what I said in another post, even if you double the power, you will only see a 3db increase in output. 3db is a pretty small and relatively useless gain in the grand scheme of things. For example:

If your speakers were 2,400 watts peak @ 8 ohms. you would actually only be able to realistically power them with an amp capable of about 1,200 - 1,500 watts. You probably won't find an amp that you will afford that can actually produce 2,400 watts at 8 ohms. anyway.

If you parallel the speakers, their total peak wattage doubles and you would then have a 4 ohm. load. You would need an amp capable of about 2,400 - 3,000 watts at 4 ohms. to properly power them. Let's break this down more.

There are three wattage ratings for a speaker, an ohms. rating and a speaker sensitivity rating. The three wattage specs are its peak, program and continuous rating and tells you in a nutshell how powerful of an amp to buy. The other specs basically line out what the speaker can do and make it possible to calculate the potential performance. Let's see what your speaker likely has going on for it ( this is a hypothetical because we don't know what your speaker is ).

1. Your speaker has a peak rating of 2,400 watts @ 8 ohms.

2. Your speaker has a program rating of 1,200 watts @ 8 ohms.

3. Your speaker has an RMS/Continuous rating of 600 watts @ 8 ohms.

4. Your speaker has a likely sensitivity of 98db @ 1 watt - 1 meter. This is the sensitivity of the speaker.

All this info is simple to break down. You cannot exceed 2,400 watts of power, your ideal wattage to power the speaker with is 1,200 watts and for long-term safe usage, you should not exceed 600 watts of power. That's is all the wattage numbers mean. Now for output, the math is a little more complex but easy enough. If the speaker gives you a peak SPL number it is generally easier to come up with a theoretical SPL number. Since we don't know we can use simply use the sensitivity to come up with that. 1 watt will = 98db ( in theory ). If doubling power gives us a 3db boost then 2 watts would = 101db. We have to continue doubling the power to see that 3db boost, so 4 watts would = 104db, 8 watts = 107db, 16 watts = 110db, 32 watts = 113db, 64 watts = 116 and so on. You can see how you quickly get to a point of diminishing returns. The next doubling of power is 128 watts, then 256, then 512 and 1,024 etc. etc. By the time we get to 1,024 watts, we have only doubled the wattage 10 times for a total of 30db in gain. So 98db + 30db = 128db. So what about a 2,400-watt amplifier? Well, the answer is 131.8db, or a gain of 3.8db!!!!! So that last 1,376 watts is worth less than 4db of output!

So we can now see the point of diminishing returns comes quick. You can't power that speaker with an amp that actually provides 2,400 watts of power, you are looking for one that will provide roughly 1,200 watts which will provide you with an output of roughly 128.8db. 3db less than your theoretical peak. Which then means powering the speaker with an amp that only provides 600 watts will again only be 3db lower for 125.8db in output.

It doesn't matter if you place both speakers in parallel either. You have doubled the wattage potential of the speakers and the amp, so it washes out completely and you still end up with the same output potential. You can't cheat the math on it and even if you grossly overpower the speakers you won't really gain anything. If you actually tried to power a single speaker with the full 2,400 watts, it would burn up and die in just a few moments.

You may have heard the term ' There is no replacement for displacement " as it relates to cars engines? It is exactly the same with subs. For more output, you need a speaker that can move more air, or more subs to move more air ( displacement of air ). And like a big engine needs gas to power it, wattage is needed to power a speaker. A big powerful speaker needs lots of wattage to get it to its peak performance. A smaller less powerful speaker utilizes less wattage and hence has less performance.

Logged
I don't understand how you can't hear your self
Pages: [1] 2  All   Go Up
 


Page created in 0.068 seconds with 21 queries.