a Power vs Volume Question

If I understand correctly:
For acoustic SPL and electric voltage, 20dB is a tenfold rise. For (electric or acoustic) power, 20dB is a hundredfold rise; 10dB is tenfold.
So:
appx. 6dB SPL is a doubling of spl and a fourfold of power, and appx. 3dB is a doubling of power.
The human ear is quoted as having a 120dB range. This spans a millionfold spl (10E6 = 6 20dB steps) and a trillionfold (US convention, 10E12 is 12 10dB steps) power range.
You guys made me look it up. (grin)
cheers ww

Nope, Herman, tsk, tsk:)
I referred to dB spl: 20log(delta L). Remember, the relation W = V2/R. It's 20 log, so 6.
See elevick's chart above. Cheers.

Does the above volume/db chart hold for speakers that are 4 ohm, or would the value have to be doubled?

Greg, you are confused, do some research and you will see you are wrong on all counts except that 6dB is 4x power.

Elvick's chart clearly shows a doubling of power for every 3dB. Robert Harley's book on high end audio states “each increase in SPL of 3 dB requires a doubling of amplifier power output.”

Yes, 6dB is 4 times the power but that is because it is 3dB plus 3dB which is double times double (2x2=4) however another 3db for a total of 9dB would be 8 times the power (2x2x2=8)

Your formula is for voltage, not power.

dB power is 10 log p1/p2

dB voltage is 20 log v1/v2

Why is one 10 and the other 20? Since power is proportional to the square of the voltage this keeps the dBs in step. An increase in voltage of 6dB will result in a 6dB increase of power. A few examples:

If I double the voltage I get 4 times the power (2 squared = 4)

Voltage dB = 20 log 2 = 6 dB
Power dB = 10 log 4 = 6 dB

If I produce 5 times the voltage I get 25 times the power (5 squared = 25)

Voltage dB = 20 log 5 = 14 dB
Power dB = 10 log 25 = 14 dB

and it isn't delta. Delta means the "amount of change" so the delta from 200 to 300W is 100W. The formulas use the ratio so you would take the log of 300 divided by 200.

tsk,tsk:)

cheers

Mbacinello, yes it holds true, a watt is a watt.

The confusion is caused by manufactures who state sensitivity in terms of voltage instead of power. It takes 2.83V to produce 1W into 8 ohms. This same voltage produces 2W into a 4 ohm speaker.

This means a 90dB/1W/1m 4 ohm speaker will be a 93dB/2.83V/1m 4 ohm speaker since the voltage spec is actually 93dB/2W/1m. This can can be misleading but the manufacturer will say that since most amplifiers are voltage amps and can produce twice as much power into 4 ohms as they can into 8 ohms they are justified in inflating their sensitivity by 3dB.