amplifier with flat FR to 10Hz or below for sub - diyAudio
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Old 27th February 2010, 12:07 AM   #1
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Default amplifier with flat FR to 10Hz or below for sub

I am a DIY speaker enthusiast, and I have parts and plans to build a sub that has frequency response extending down to the low teens. I need a single channel of amplification that is rated for about 300W-500W in to a 4 ohm nominal (min 3.2 ohms) load with low distortion. I can build my own crossovers, power supplies, etc. I am not looking for a plate amp with built in crossover, etc. but rather am looking for an amp board that I can use to power the driver cleanly. I would prefer using one of the designs that are more efficient than a Class AB output stage: class D, T or whatever.

There are certainly many, many choices for this power level, however one spec that is not always clear is the frequency response of the amplifier. I do not want to build a subwoofer that is flat to 12 Hz and then power it with an amp that rolls off at 20Hz. With that in mind, it seems that I should be looking for suggestions that would meet the above criteria and that are DC coupled or have a very low cut off frequency, e.g. well below 10Hz.

If you know of a good amp kit that would work for this application, please post in this thread.

Thanks for the help!

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Old 27th February 2010, 03:20 AM   #2
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Location: NorCal

Class D Audio has some kits in the power range you're looking for. They don't have bandwidth specs on the website, but you might want to drop them a note and ask. They were very quick to respond to a couple of questions I asked a while back.

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Old 27th February 2010, 05:12 AM   #3
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Default some possibilities

I checked out the ColdAmp BP4078. This seems to be perfect and it is spec's at -1dB@17Hz and -3dB at 7Hz. 400W in to 4 ohms with some room to breathe.

I have also looked at some lateral mosfet amps over at and the 600W amp at classDaudio but am less impressed with them.

Also, the Hypex UcD400 might be another possibility.

Any experiences with the ColdAmp product? I recall they are pretty reliable.


Last edited by CharlieLaub; 27th February 2010 at 05:19 AM.
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Old 27th February 2010, 09:34 AM   #4
godfrey is offline godfrey  South Africa
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Originally Posted by CharlieLaub View Post
... or have a very low cut off frequency, e.g. well below 10Hz.
That shouldn't be much of a restriction. With a circuit diagram or the amp in hand, it's pretty easy to figure out where the roll-off is, and how to change it to what you want.

Normally it will just involve changing the input coupling capacitor. Only problem is the warranty if you're using a new off-the-shelf amp.
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Old 27th February 2010, 10:06 AM   #5
AndrewT is offline AndrewT  Scotland
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After a lot of experimentation over a few decades I slowly came to realise that for a speaker with a nominal roll off at 60Hz and very little output at 20Hz still give better bass with an amp that has F-3dB <2Hz rather than 10Hz.

If this is applied to your 10Hz sub case, then expect to feel/hear improvement as you reduce the amplifier F-3dB from 10Hz to 0.5Hz.
regards Andrew T.
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Old 27th February 2010, 02:06 PM   #6
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Default DC coupled

Eagle 400 amplifier is DC responding so is flat down to DC as in no roll off at all. Maybe that would work for you if you can find one.

Last edited by sumaudioguy; 27th February 2010 at 02:06 PM. Reason: type
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