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#2

Mar 23, 2009, 11:09 PM

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What is DB gain?

Asked Mar 23, 2009, 08:24 PM — 4 AnswersWhat is DB gain when associated with home theatre speaker volumes? Each speakers volume is set with DB gainstarting at 0 with settings - and + from 0. I have no idea what it represents.

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4 Answers

DanielF Posts: 158, Reputation: 65

Junior Member

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:

DBRatio (n:1)

01.0

11.26

32.0

1010

20100

-10.79

-100.1

(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

What is DB gain? - Ask Me Help Desk http://www.askmehelpdesk.com/home-electronics/what-db-gain-333012...

1 of 4 17-Jan-13 10:51 PM

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#3

Mar 23, 2009, 11:18 PM

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#4

Mar 23, 2009, 11:18 PM

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

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KISS Posts: 12,593, Reputation: 4378

Uber Member

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.

Helpful

KISS Posts: 12,593, Reputation: 4378

Uber Member

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.


2 of 4 17-Jan-13 10:51 PM

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#5

Dec 21, 2011, 09:02 AM

Reply

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.

Helpful

nirupa Posts: 1, Reputation: 10

Junior Member

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

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