Um. Pay attention to this part right here:

Let's delve further into how an amplifier works... Gain control adjusts just how much power the audio signal "gains" as it works it's way through the amplifier circuitry (easy explanation).

While this paragraph starts out "contrary to popular belief," it then goes on to define exactly why the popular belief is correct - gain control DOES affect the amplifier's power output.

*Most of these numbers are theoretical to make the explanation easier to understand*


Lets say that my HU (an Eclipse CD7100) puts down it's 8V signal to the amplifier. Now, it doesn't always put down 8V, really it's dependent on volume level - but we'll say that it's linear and since there's 80 #'s on the volume control, each 10 numbers = 1V. Lets say we're using a 60Wx2 amplifier.

When I set the volume to 3/4 of it's max (where I adjust amplifier gains), we're putting down 6V to the amplifier input stage of an amplifier designed for a maximum input of 6V.

On the amplifier gain knob we see 6V on one end and 0.2V on the other. It appears to be backwards, but the way it works is that if we put in a 4V signal to the amp, it needs less gain to produce the same sound level (power) as a 6V amp - so the .2V setting is a higher gain (10x) and the 6V setting is a lower gain (1x).

With the gain all the way up (0.2V setting)ss, the amplifier takes that 6V, does it's magic, and puts out 60W on Chan A (10x gain).

Now, lets say that we turn down the gain on the amplifier to 1/2 it's max position (approx 3V input), the power output on the amplifier will be halved (if it's a linear power curve) because the gain is halved (5x at 6V) - 30W.

If I put an 8V signal in, the amplifier will continue to put out 60W until I have adjusted the gain to below a threshold, i.e. 10x gain at 8V = 80W, but the amp is maxed at 60W. 8x gain at 8V = 64W - again, the amp is maxed, but the gain is adjusted down approx 1/5. Both examples will result in what is known as clipping - the top and bottom 1/4 of the audio signal will be "clipped" because the amplifier output transistors are limited to 60W amplitude.



To put it simply, Power = Volume. And what the article is describing as tuning speaker volume is adjusting the gain on your amps so that all the speakers have the appropriate amount of power to have equivalent volume output (this is where speaker efficiency ratings take effect). To do so, you MUST be adjusting the power being put out. Gain, in any amplifier, is exactly that - how much power the amplifier gains.


The irony is that the article actually goes on to explain all this without acknowledging that the reason the output volume is so low is because the amount of power the amplifier is putting out has been lowered by turning down the "sensitivity" of the gain control.

edit again:

playing with the calculator at the bottom even proves that the gain control does indeed affect how much power the amplifier puts out. Just keep in mind that an amplifier does have a max power (sometimes slightly higher than rated power) that it will not exceed no matter where you have your gain setting (example is the 8V at 10x gain above)

 

+1 on above

too much power not a problem as long as the signal is not clipping.
and you have to remember the watt ratings on equiptment are not all rated on the same scale (problem the car audio industry has had forever, home equiptment is regulated) but i would rather put 500watts of good power to speaker over 100 watts of clipping power.
And watt ratings are max power output, do you listen to your stereo at 100% volume all the time, no, and music is changing frequency + intensity so the power output is dependant on the signals input.
I never buy or setup a system soley based on power ratings.

 

thanks for chiming in Sputniks, you think the "low power" mentioned in this scenario (50w compared to 100 or 200w) would cause clipping?

 

it doesn't matter whether your amp's maximum power is too high or too
low compared to the speaker's rating - what matters is that you don't
drive any component beyond its rating. If your speaker is designed for
100 watts RMS maximum, you shouldn't put more than that into it, but
the speaker doesn't care if the 100 watts comes from a 100 watt amp
pushed to its limit, or a 200watt amp only cranked to 1/2 its max power.
Alternately, if you have a 75watt amp that you try to drive to 100watts,
the output will be clipped (distorted) and the waveform that the speaker
is trying to reproduce is not a shape it's designed for, so even though
you have not exceeded that speaker's maximum, you could still damage
the speaker.
In either case, the average listener is not going to trash their speakers
because most of the time they'll be waaaay below the maximum output
of their amps. But some people like their music REALLY LOUD, and
they're the ones who need to be careful.

 

Outstanding.

Thank you all so much for posting such clear and well-constructed posts.
I truly appreciate the lesson.

 

Only if the amp itself clips at that level.

Clipping is caused by the amp, distortion is caused by the speaker reaching (or getting close to) it's mechanical limits.

Both are bad for the speaker, and can be bad for the amp.

 

oh i see

 

Clipping is usually when the input signal is driven so hard that you hit the top of the amps volume range and the top of the waveform gets "clipped" off.



The waveform is the sound input. The red lines are the highest and lowest that the amp can drive itself. Once the wave crosses those lines they get clipped



This is a bad situation because you are holding the coil at max power with essentially a DC signal instead of the usual AC signal. Those milliseconds between vibrations do a lot to cool everything.

Sorry about the MS Paint. Feel free to dice up my explanation NS. I know I got something wrong.

 

[QUOTE=SgtB,May 5 2009, 02:26 PM] Clipping is usually when the input signal is driven so hard that you hit the top of the amps volume range and the top of the waveform gets "clipped" off.



The waveform is the sound input. The red lines are the highest and lowest that the amp can drive itself. Once the wave crosses those lines they get clipped



This is a bad situation because you are holding the coil at max power with essentially a DC signal instead of the usual AC signal. Those milliseconds between vibrations do a lot to cool everything.

Sorry about the MS Paint. Feel free to dice up my explanation NS.

 

Good read. Thanks.