[wetired]

What is DB gain when associated with home theatre speaker volumes? Each speakers volume is set with DB gain starting at 0 with settings - and + from 0. I have no idea what it represents.

[DanielF]

The quick answer to your question is "It doesn't really matter!". It's just a number that represents a change in volume. But I'll give you the 'full' answer now, in case you're really interested (skip to the last paragraph if you're not!)...

The decibel (dB) is a logarithmic expression of a ratio of two values. It is used in electronics and sound engineering to express the ratio between two voltages, or two currents, or two powers, or two sound pressure levels (SPL). Being logarithmic, small numbers can be used to express huge ratios.

The decibel value is calculated from a ratio of two voltages or currents as follows:
20 * log10(V2 / V1)
while for a ratio of two powers or SPLs, it is:
10 * log10(P2 / P1)

[The * means 'multiplied by', the / means 'divided by', log10 means 'logarithm to base 10' (of the value in brackets).]

By way of examples, here are a few dB values and the power ratios they represent:
dB••••••Ratio (n:1)
0••••••••••1.0
1••••••••••1.26
3••••••••••2.0
10••••••••10
20•••••••100
-1••••••••••0.79
-10•••••••••0.1
(Sorry about the ugly dots separating columns; I haven't learned how to do a table in HTML.)

So if you adjust a speaker level by +1dB, you have increased its power by a factor of 1.26 relative to the 'reference' level (whatever that is, and it doesn't matter in the case of a home theatre setup). If you adjust it by -1dB, the power is reduced to 0.79 of the reference level.

By way of guidelines, a 1dB (plus or minus, doesn't matter) change in power gives an only-just audible perceived volume difference. 3dB is a quite noticeable difference, and 10dB is approximately a doubling/halving of perceived volume. So just adjust each speaker's level in 1dB steps until all four/five sound the same volume, using the white noise test tone provided (with the 'master' volume control set to your 'normal' listening volume). Of course one speaker will be left at 0db (no change) while the others are adjusted up or down to match volume, if required.

Hope I haven't just confused you. Like I said at the beginning, you don't need to understand what dB means to make the volume (level) adjustments, it being obvious that a + adjustment is higher volume, and - is lower. The aim is to have all speakers sounding equally loud with the test tone, when sitting at the listening position (and there can be only one 'correct' listening position - the user guide will show you where that is in relation to the speakers).

Daniel

[KISS]

Here is a power point presentation on loudness. A little tough to muster. There should be a free powerpont reader on Microsoft Corporation.

Physics, Physiology and Psychology of Loudness

What I can tell you is that db is always based on a reference level and sound is logarithmic. The formula for power using db and two signal levels is different than if we were using two voltages.

This should explain things a little better.

dB: What is a decibel?

I THINK that a 3 db change results in twice as loud or a 10 fold increase in power.

The point is, the gain of an amp (some multiplier) say 2, does not mean it 2 times louder. The db levels should translate into a perceived loudness relative to the maximum output which has the reference level of 0 db.

-infinity is no sound. That's why the numbers go negative.

Loudness is a complex subject. There are weighting curves. Sometimes 0 db is the threshold of human hearing. Now you can describe the absolute sound level of a jackhammer or an airplane.

Signal to noise ratio is also expressed in dm.

ANtenna gain is also in db. Losses in transmission lines are in db. Using db cuts out a lot of multiplication or division.

[KISS]

Here is a power point presentation on loudness. A little tough to muster. There should be a free powerpont reader on Microsoft Corporation.

Physics, Physiology and Psychology of Loudness

What I can tell you is that db is always based on a reference level and sound is logarithmic. The formula for power using db and two signal levels is different than if we were using two voltages.

This should explain things a little better.

dB: What is a decibel?

I THINK that a 3 db change results in twice as loud or a 10 fold increase in power.

The point is, the gain of an amp (some multiplier) say 2, does not mean it 2 times louder. The db levels should translate into a perceived loudness relative to the maximum output which has the reference level of 0 db.

-infinity is no sound. That's why the numbers go negative.

Loudness is a complex subject. There are weighting curves. Sometimes 0 db is the threshold of human hearing. Now you can describe the absolute sound level of a jackhammer or an airplane.

Signal to noise ratio is also expressed in dm.

ANtenna gain is also in db. Losses in transmission lines are in db. Using db cuts out a lot of multiplication or division.

[nirupa]

it is a measure to calculate the output to input ratio of a signal in an electrical system.it is represented by
gain in dB=10*log(Vo/Vi)
where Vo=output voltage
Vi=input voltage