Why use "dB"?

Isn't it a bit of a misnomer to claim control over the decibel level? The definition is a relative measurement, and requires an exponential increase in power to double the sound pressure. Going from 1db to 2db should theoretically double the sound pressure at the speakers.

Besides, the scale is way off - 1 db is well below audible range. ;-)

Just wondering how I can cause trouble.

As I understand dB, going from 1 to 2 db would only increase power output by approx. 25%. to double the loudness requires a 10dB increase and 10 times the power. Every three db requires twice the power. Using dB provide a standard with which to measure 'true' output, I suppose. Unlike a knob that is simple labeled from 1 to 10 or to 11 as in "Spinal Tap":)

You're partially right. It would be more accurate to label the volume control "Output Voltage" and give a range from 0.0v to 4.0v in-car or 0-1v on AC.

But no one would understand what it meant, and it would end up being just as arbitrary as "-3.5dB" is now...

You mean maximum output voltage. But then it would have to take into account EQ and other settings.

Calvin

The decibel level is a meaure of the "gain" of the pre-amplifier stage of the empeg audio circuit when compared to the units maximum potential output power.

Therefore, a gain of 0dB represents no reduction of output power (play a full volume track and get a full 4V output). A gain of -3dB would be half the theoretical maximum output, -6dB would be a quater etc.
-58dB is generally regarded as no output for most pre-amplifier circuits (almost completely silent) and of course a "minus infinity" dB gain is completely silent.

Going from 1db to 2db should theoretically double the sound pressure at the speakers.

Besides, the scale is way off - 1 db is well below audible range. ;-)

The empeg's volume control accurately describes the power of the signal offered to the amplifier. If your amplifier is non-linear, that's not our problem.

And although it is effectively an output voltage range control, bear in mind it's a log, not linear, adjustment of the voltage.

As you yourself pointed out, dB is a relative measurement, so "1dB is well below audible range" isn't very meaningful unless you tell me what 0dB point you're starting from. The empeg's 0dB point is where the output of the notional "preamp" stage is equal to its input. Think of the empeg as an audio component feeding line-level to a preamp (the volume control) which in turn feeds line-level to your power amp. 0dB is where the volume control is doing nothing to the signal; this corresponds to full slew (100% rated power) on your power amp.

Peter

I think that the problem is that most of us learned about decibels solely as an absolute scale, and not a relative scale, even though it can be used as both.

It can be used as both but that does not make it accurately used as both. Actually, "dB" does imply a relative scale. It is often confused with dBm which is an absolute power measurement (dB gain in relation to a fixed value of 1 milliwatt). A good summary of dBm is provided at: http://www.physlink.com/Education/AskExperts/ae350.cfm

This subject always seems to cause a little confusion...

-Cory