Digital Sound & Music: Concepts, Applications, & Science, Chapter 4, last updated 6/25/2013
Applying this formula, what if you start with a 300 W amplifier and want to get one that is 15 dB
You can see that it takes quite an increase in wattage to increase the power by 15 dB.
Instead of trying to get more watts, a better strategy would be to choose different
loudspeakers that have a higher sensitivity. The sensitivity of a loudspeaker is defined as the
sound pressure level that is produced by the loudspeaker with 1 watt of power when measured 1
meter away. Also, because the voltage gain in a power amplifier is fixed, before you go buy a
bunch of new loudspeakers, you may also want to make sure that you're feeding the highest
possible voltage signal into the power amplifier. It's quite possible that the 15 dB increase you're
looking for is hiding somewhere in the signal chain of your sound system due to inefficient gain
structure between devices. If you can get 15 dB more voltage into the amplifier by optimizing
your gain structure, the power amplifier quite happily amplifies that higher voltage signal
assuming you haven’t exceeded the maximum input voltage for the power amplifier. Chapter 8
includes a Max demo on gain structure that may help you with this concept.
18.104.22.168 Converting from One Type of Decibels to Another
A similar problem arises when you have two pieces of sound equipment whose nominal output
levels are measured in decibels of different types. For example, you may want to connect two
devices where the nominal voltage output of one is given in dBV and the nominal voltage output
of the other is given in dBu. You first want to know if the two voltage levels are the same. If
they are not, you want to know how much you have to boost the one of lower voltage to match
the higher one.
The way to do this is to convert both dBV and dBu back to voltage. You can then
compare the two voltage levels in dB. From this you know how much the lower voltage
hardware needs to be boosted. Consider an example where one device has an output level of
−10 dBv and the other operates at 4 dBu.
Convert −10 dBV to voltage:
Thus, −10 dBV converts to 0.316 V.
By a similar computation, we get the voltage corresponding to 4 dBu, this time using
0.775 V as the reference value in the denominator.
Convert 4 dBu to voltage: