Amplifier Frequency Response Question - AVS Forum
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post #1 of 10 Old 02-15-2012, 06:26 AM - Thread Starter
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Hey Guys, I'm new to the forum and to home theater audio. I'm trying to put together a music/home theater system and have been buying my various speakers/reciever/amps etc.

I was able to get Cerwin Vega RE38's for my mains, Cerwin Vega E312's for my surrounds, a Pioneer 1018 A/V Reciever, and I was really excited to get a Servodrive Contrabass subwoofer on craiglist. I still need to buy a center channel and also an amplifier to power the Servodrive. I have a Crown CTs4200 to hopefully power my mains and surrounds.

My question is, on the amp for my subwoofer, every amplifier I've come across has a listed frequency response of 20hz-20khz. The Servodrive can get down to 16hz at pretty much full power. Is an amplifier rated down to 20hz frequency response gonna cut it? Or do I need to find one that is rated to a lower frequency response? If so, any suggestions?

Thanks for the help!
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post #2 of 10 Old 02-15-2012, 07:15 AM
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Not all amps only do 20-20k. Broader bandwidth will open your sound stage usually.
Continuous power output:
http://parasound.com/halo/a51.php
250 watts RMS x 5, 20 Hz - 20 kHz, 8 Ω, all channels driven
400 watts RMS x 5, 20 Hz - 20 kHz, 4 Ω, all channels driven

Current capacity:
60 amperes peak per channel

Power bandwidth:
5 Hz - 100 kHz, +0/-3 dB at 1 watt

Now so many say a watt is a watt "all everything" sounds the same. I don't agree, watts are not the only thing that counts. Watts, amperage, current & bandwidth all come into play on the sound of an amp.

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post #3 of 10 Old 02-15-2012, 07:54 AM
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Quote:
Originally Posted by Dr_Mark View Post

Not all amps only do 20-20k. Broader bandwidth will open your sound stage usually.
Continuous power output:
bandwidth all come into play on the sound of an amp.

Amps and current are the same thing and when multiplied by the voltage you get watts.
Every double blind test comparing consumer amps has shown that there is no difference in sound quality as long as they are not clipped. There are amps that have a distinctive sound but they are Class A SET amps with very low output and mostly DIY.
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post #4 of 10 Old 02-15-2012, 08:09 AM
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OP, I'd ask this question in the DIY speakers and subs forum. The folks who hang out there are more likely to know actual sub 20Hz capabilities of a variety of amps. I suspect the Behringer stuff goes below 20 Hz, for example, because lots of people seem to use them. I'd title the thread to make clear I'm looking for sub 20 Hz performance.
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post #5 of 10 Old 02-15-2012, 08:14 AM
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Quote:
Originally Posted by Dr_Mark View Post

Not all amps only do 20-20k. Broader bandwidth will open your sound stage usually.
Continuous power output:
http://parasound.com/halo/a51.php
250 watts RMS x 5, 20 Hz - 20 kHz, 8 Ω, all channels driven
400 watts RMS x 5, 20 Hz - 20 kHz, 4 Ω, all channels driven

Current capacity:
60 amperes peak per channel

Power bandwidth:
5 Hz - 100 kHz, +0/-3 dB at 1 watt

Now so many say a watt is a watt "all everything" sounds the same. I don't agree, watts are not the only thing that counts. Watts, amperage, current & bandwidth all come into play on the sound of an amp.

I think most amps will do below 20hz. But some will be rolling off response around that frequency. I could be wrong, but providing the amp is not running out of power, the other restriction on power is a capacitor which blocks DC, so there's some practical lower limit. There's probably another factor I have forgotten.

Note that bandwidth is not absolute, it's typically the bandwidth in which the response is within +/- 3 dB. Competent solid state amps should have no problem meeting that over the audible range. I think tube amps are a bit different in that respect.

As Theresa said, technically power (watts) is equal to voltage multiplie by current (amps.) P = V*V/R (power is equal to voltage squared divided by resistance) or P = V*I (voltage times current.)

That being said, I believe you can optimize an amp for voltage output, so it looks better when driving 8 ohm speakers, or lower the power supply voltage for better performance into lower impedance speakers. That seems to be what Harmon Kardon has done historically. I know Yamaha ran the power supply on my receiver at a very high voltage, so perhaps that's another way to deal with the situation by starting high, to cope with the voltage drop under load (that's a total guess on my part.)

"But this one goes up to 11"
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post #6 of 10 Old 02-15-2012, 08:16 AM
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Careful..
There are 2 specs here...

The 1st is the power bandwidth, spec used in the power output rating typically is 20Hz-20kHz
The 2nd is frequency response usually taken @ 1 Watt..

Just my $0.02...
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post #7 of 10 Old 02-15-2012, 08:16 AM
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I was thinking current, not volts. Volts it is.

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post #8 of 10 Old 02-15-2012, 08:17 AM
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I believe amplifier manufacturers post the frequency response as the limits of "audible" distortion free signal production. It's not indicative of the frequency range, or how low a signal it can process.

With subsonic frequencies below 20hz, you can get away with up to 10% THD as far as being able to hear or notice it.
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post #9 of 10 Old 02-15-2012, 08:23 AM - Thread Starter
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Thanks for all the responses guys and gals! I'll also post this in the DIY speakers and subs forum as suggested.
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post #10 of 10 Old 02-15-2012, 11:46 AM
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Quote:
Originally Posted by eastonmaxx View Post

My question is, on the amp for my subwoofer, every amplifier I've come across has a listed frequency response of 20hz-20khz. The Servodrive can get down to 16hz at pretty much full power. Is an amplifier rated down to 20hz frequency response gonna cut it? Or do I need to find one that is rated to a lower frequency response? If so, any suggestions?

Thanks for the help!

I agree with the poster who recommended posting in the subwoofer forum. I'm sure they have some good options if you are only powering a sub.

Also, 20-20 is a bandwidth. To specify frequency response you need to post how close to 0dB, i.e. 20-20 +/-2dB. Bandwidth is typically much wider than frequency response because there is greater deviation from flat (0dB). I.e. a product may be rated 20-20kHz +/- .5 dB with a bandwidth of 5-100kHz. You'll want an amp with greater bandwidth, that is relatively flat down to whatever frequency is important to you.

As another mentioned you might have greater distortion, but not necessarily and most likely won't be an issue. If the load is constant (impedance) as some have also brought up you probably won't get great deviations.

B.
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