Does doubling audio power mean you double audio output?
Many people think that doubling the power (watts) into your speakers will make the audio that comes out of them sound “twice as loud”. In actual fact, doubling the power provides very subtle changes to SPL (Sound Pressure Levels). It takes a pretty big increase in power to sound "twice as loud". Let's check out what increases in power are needed to make changes in SPL.
The smallest change in sound pressure level that the human ear can pick up is one dB - and this is under very controlled conditions. A one dB change in level is actually very difficult to hear when listening to dynamic music.
What happens when you double the power into your audio system?
When you double the power of your audio system, you increase the dB by three.
A change of three dB is accepted as the smallest difference in level that is easily heard by most people listening to speech or music.
To put this into a scenario, if you're getting 102 dB SPL from 100 watts and you want 105 dB SPL, you will need 200 watts of power.
This also works in reverse. To produce a decrease of –3 dB you need half the power, so you would reduce power from 100 watts to 50 watts.
2 x the power = +3dB
1/2 the power = –3dB
What happens when you quadruple audio power?
A change of six dB is accepted as a significant difference in level for any listener listening to speech or music. It's quite a noticeable increase or decrease in loudness. To produce an increase of +6 dB you need to increase power (watts) by a factor of four.
So, if you're getting 102 dB SPL from 100 watts and you want 108 dB SPL, you will need 400 watts of power (it adds up fast, doesn’t it?). To produce a decrease of –6 dB you need to divide the reference power by 4, so you would reduce power from 100 watts to 25 watts.
This 6dB plateau also results in happy ratios that should be memorised:
4 x the power = +6dB
1/4 power = –6dB
So, how many dBs are needed to double output?
A change of 10 dB is accepted as the difference in level that is perceived by most listeners as “twice as loud” or “half as loud”.
If you want to increase the power output by +10 dB, you'll need to increase power (watts) by a factor of 10. So in essence, to make your speakers sound twice as loud you need ten times the power!!!
To put this into a scenario, if you're receiving 100 dB SPL from 100 watts and you want 110 dB SPL, you will need 1000 watts of power. If you want to decrease the sound pressure levels by –10 dB you need to divide the reference power by 10, so you would reduce power from 100 watts to 10 watts.