Class-D lack of sustained bass Myth - diyAudio
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Old 4th June 2009, 08:30 PM   #1
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Default Class-D lack of sustained bass Myth

I am having a discussion with a friend that is under the understanding that class-D amplifiers are not good for bass/subwoofer use because they cannot sustain there power long term at low frequencies.

I remember reading some info on the B&O ice power modules something to that effect and that the newer tope of the line model corrected that somehow.


I am looking for info either direction on the issue to back up the argument either way.

The application would be a powered subwoofer or LF cabinet for Live sound use that will be used for Dance music that has quite a bit of sustained LF information.
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Old 4th June 2009, 08:45 PM   #2
Nisbeth is offline Nisbeth  Denmark
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That's got nothing to do with class D as such, it is (mainly) a question of how the PSU is designed and sized. Many class D amps will have poor FTC-ratings because they don't have the same thermal inertia as a class AB amp and FTC is full power for 5 mins so the class D amp will overheat, but that is not the same as what your friend claims.

The ICEpower modules were in fact designed for PA active speaker applications and they are used in enough PA speakers from companies like DAS, EAW, Renkus-Heinz etc. that I believe they have proved they are up to the task.


/U.
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Old 4th June 2009, 11:13 PM   #3
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I'm All for using class-D for this application. he seems to think not. so that's why im looking for info
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Old 5th June 2009, 12:27 AM   #4
Eva is offline Eva  Spain
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This is just a myth.

In class D it's easier to sustain full power for longer because much less heat is being generated and less input power is being used.

Some designers try to take too much advantage of this fact, though.
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Old 5th June 2009, 12:39 AM   #5
bwaslo is offline bwaslo  United States
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I think your friend is thinking of the wrong end of the spectrum. The early ICEpower amps couldn't do sustained high power out at HIGH frequencies. That is because they had a zobel in the output circuit, (needed to keep stable apparently), and the zobel would generate heat at high frequency. The resistor wasn't rated for high power, so the ICEpowers couldn't do sustained high power high frequency tones without damage. (Tweeters don't handle that well, either, so no real loss).
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Old 5th June 2009, 02:58 AM   #6
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Quote:
Originally posted by bwaslo
I think your friend is thinking of the wrong end of the spectrum. The early ICEpower amps couldn't do sustained high power out at HIGH frequencies. That is because they had a zobel in the output circuit, (needed to keep stable apparently), and the zobel would generate heat at high frequency. The resistor wasn't rated for high power, so the ICEpowers couldn't do sustained high power high frequency tones without damage. (Tweeters don't handle that well, either, so no real loss).
Couple that with the fact some of them are only capable of a sustained 1/8th of their rated RMS output do to poor thermal design.
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Old 5th June 2009, 03:00 AM   #7
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cant the thermal design be...redesigned with added or revised heatsinks?? fan cooling etc?
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Old 5th June 2009, 05:34 AM   #8
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Many of big high powered high priced pro-sound subs are class-d these days.

http://www.jblpro.com/catalog/genera...?PId=214&MId=4

As are many home theater plate amps and car sub amps winning competitions.
Low heat, high efficiency, much smaller heat sinks are needed.
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Old 5th June 2009, 07:50 AM   #9
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There are a few different types of ICEpower amps:

The A and ASP series can sustain full power with the use of external cooling. I've tested the 1000ASP @ 1000W sinewave output for 30 minutes, no problem what so ever.

The ASC and ASX2 is a different story, as both the power supply and output stage is designed to deliver audio signals with no less than 9 dB (1/8) crest factor, which should be sufficient on full bandwidth audio signal.

The point is that most amps are designed for delivering music signals, not continous sinewave. There are many class AB amps that can't deliver sustained full power either because of insufficient cooling!

So - if you're into buying an ICEpower-based amp for live sound, look for one thats using the ASP modules.

And no - you cant buy ICEpower modules for DIY.
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Old 5th June 2009, 12:27 PM   #10
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Quote:
Originally posted by StigErik
The ASC and ASX2 is a different story, as both the power supply and output stage is designed to deliver audio signals with no less than 9 dB (1/8) crest factor, which should be sufficient on full bandwidth audio signal.
Quote:
Originally posted by Zero Cool
cant the thermal design be...redesigned with added or revised heatsinks?? fan cooling etc?
Not really. These particular ICEpower modules use surface mount FETs which make it difficult and inefficient to mount heatsinks. You could attach heatsinks to the plastic body of the FETs, but that isn't the most effective way to cool a device.
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