One question that has been bugging me for a while is: what is the difference between the controls on an amplifier such as Boost and Gain. I know some people think that they are synonymous with the volume control of the sub, but I have a feeling that this is not the case. So, is the control on the headunit the only real "volume" control for the subwoofer? And, are the other settings (Gain and Boost), used for SQ and tuning purposes only? Thank you.

 

The gain on your amp also dictates power to your sub(ie. volume) the boost gives a little additional power and generally will make the sub BOOM more instead of hitting tight. The HU does effect how the sub performs of course but not as much as the amp's gain control does. The bass boost is there to give you a little extra boom as I said and that is about it.

 

Actually, sorry, but no.

The amplifier is always capable of generating the same amount of power.

Gain. The input gain, input voltage, or input sensitivity setting determines how much signal IN is required to reach a given power level.

Since the amp is always as powerful, you are changing at what point on the main volume control you reach rated power. Above that point you will still have distortion. If you turn your gain way up even the background noise gets amplified and you have more audible hiss and perhaps other sounds as well. Not a good idea.

Boost. Boost is entirely different. If you think about the bass and treble controls on most stereos, they are two-band equalizers. They let you emphasize or decrease the volume of a certain portion of sound. Bass controls usually affect the area centered around 100 Hz - too high to affect the sound of many sub very well.

Many amps (this was popularized by Rockford in the 80's, and now is very common) have a bass control, Bass EQ, Bass Gain, or some other EQ setting that acts as a one-band equalizer at a given note - 40 Hz is pretty common.

But when you ask for 3dB more volume at any note, if the speakers stay the same, the amp has to generate 2X more power at that note. Not my idea, just how it is. 3dB isn't much audible difference - definitely noticable, but not huge. If you turn up the amp bass gain 6dB, you are asking for your amp to generate 4X more power at that note. It might start distorting when it tries.

Woofer amp volume knobs. Many of those volume controls for the amp simply decrease the signal down to 0. At full volume, you are not boosting anything, it's simply an ability to decrease from the setting you selected for the gain in the first place.

 

so is it safe to say, that the input sensitivity should be as low as possible?

The boost knob, when it says +3,+10, +15 is telling you how much more power the amp has to generate?

now does the volume on the headunit where it says "Sub" does that just boost the signal the HU is sending to the amplifier?

 

1. You want to set the gain as high as possible without causing distortion. I have a shop adjust mine because they use some electronic device to detect the best gain level.

2. Depends what frequency your boost is set at. For example, an increase of +3 db at 40 hz. Increasing bass.

3. Yes, you are right. You can adjust the signal to the sub amp.

 

1) Yes. The electronic device, if they really use one (FEW do) is a sine wave test disc and a voltmeter. Not very hi-tech.

2) It is NOT power, it's DB. But, as my dear old dad used to say, those numbers are printed with the ink left over from making comic books. Most of them go to +15dB or 18dB, but most of them are a good way to overdrive an amp. +15dB is 32x the wattage.

Good thing our ears hear bass distortion much less, especially from trunk speakers.

3) If the HU has a SUB RCA output and you are using it, it controls the volume to the sub amp relative to the main volume.

 

I always enjoy reading your posts eldude. As someone who makes their living working with live concert sound systems, I find your answers to be complete, accurate and well-worded. I'm sure it's been said repeatedly, but you're a huge asset to this community.