Can any one explane - 3DB?

Question

I have just started a job in the hi-fi industry and have got to learn the tecnical stuff about speakers , im slowly getting there but dont understand the - 3 db thing and struggeling to get me head round it, Can any one explane it to me simply ???

Answer 1

To understand -3dB you need to understand decibels.
This is a means of comparing values using a logarithmic scale.

Don't switch off yet.
To compare a value in Bels = log(value1/value2)
A decibel is 10th of a bel therefore = 10*log(value1/value2)
log(0.5) = -0.301 (try log 0.5 on a scientific calculator)
so if value2 = 2*value1
then in dB value1/value2 ~= -3dB

In audio terms -3dB is half the volume (or power) of a reference value.
As the scale is logarithmic -6dB is a quater of the volume and -9dB is an eigth.

Answer 2

dB is decibel. It is an exponential scale used to describe the level of a signal, whether it be electrical or sound.

An exponential scale is used because of the power aspects of sound - a sound that is is twice as loud or half as quiet is actually many times more in terms of actual amplitude.

The "3dB thing" has to do with level. A 6 dB change is a "quadrupling" of amplitude, a 3dB change is 50% on attenuation or a doubling on gain.

Another thing that is important in terms of "hi-fi" is signal to noise ratio - that is how "quiet" a system can actually get before you reach the level of the apparent "noise" that is in the system. A "good" system should exceed 90 dB signal to noise ratio (the noise is 10 to the 90th of the maximum producible amplitude of signal).

If you memorize "signposts" in terms of common dB ratings (like the example of the 6 dB ratio above), you are well on your way. Just remember that 3dB attenuation is 1/2, 6dB gain is "quadruple", etc. and you will get it.

Here's a link - http://www.eham.net/articles/7877

Answer 3

One dB (deciBel) is one tenth of 1 Bel. 1 Bel is a ratio in power of 1:10, so a sound at 20dB (2Bel) has 10 times the power of a sound at 10dB (1Bel) - not 19dB as stated elsewhere. It is a logarithmic scale, as correctly stated elsewhere. 3dB indicates a ratio of roughly 1:2, so the -3dB point is the point at which power is halved.

Answer 4

db is the unit of measurement for sound level. The louder the sound, the higher the db number. It is a logarithmic scale so that 20db is ten times louder than 19db.