a Power vs Volume Question

You think 172dB is double the volume of 85dB? You are kidding, right?

Maab, the ampunt of power delivered is determined by the input to the amp and the gain of the amp. The gain is basically how many times the amp multiplies the strength of the input signal. A 10W amp can have the same gain as a 1,000W amp, but the 10W amp will reach it's maximum limit and clip before the 1,000W one will.

If both amps have the same gain then they will produce the same volume with the same input. The differences are as Suarbrie pointed out and the headroom.

This is a simplified response:

Sound pressure levels are expressed in dB and the softest sound a normal person can hear is around 4dB. The threshold of pain is somewhere around 130dB, but this isn't 32.5 times the pressure level of 4dB. It is closer to 4,000,000,000,000 times the pressure level since the scale is logarithmic.

130db – 4dB = 126dB
126dB = 10 times log (pressure at 130dB divided by pressure at 4dB)
12.6 = log (pressure at 130dB divided by pressure at 4dB)
Inverse log 12.6 = about 4,000,000,000,000

This isn't exactly the same thing as loudness since it takes about 10 times the pressure level (10db) to be perceived as twice as loud and the ear's sensitivity changes with frequency and pressure level, but they are correlated.

check this out

loudness

..

Each doubling of power increases loudness by 6 db. The ear perceives a 10 db increase in sound level as a doubling of volume.

Actually a doubling of power is 3dB, a doubling of voltage is 6dB.

Loudness and volume are the same thing.

It should read "Each doubling of power increases sound pressure levels (SPL) by 3 db. The ear perceives a 10 db increase in SPL as a doubling of volume."

each doubling of SOUND PRESSURE level (i.e. spl), i.e. what we "listen to", is 6dB. You need four times the "power" to achieve double sound pressure -- in fact twice "as loud". Yr mic should record +6 dB when your power rises 4times.
In other words... on paper, going from 200W to 300W gives you an extra 1,4dB.

Greg, I believe you are a bit off in your analysis.

Incorrect: Doubling SPL is not 6dB, it is 3 dB,

Correct: Double it again for 4 times and that is 6dB as you stated.

Incorrect: Going from 200 to 300W is not 1.4dB, it is 1.76dB.
dB = 10 log (300/200)
dB = 10 log 1.5
dB = 1.76dB

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.

Aolmrd, I don't think it is a matter of louder but cleaner. Think in terms of energy.

The capacitor bank in the amp can only store a finite amount of energy. Bass notes take a lot more energy to reproduce than treble notes. If you free the amp from having to provide energy to the bass notes it can loaf when providing energy to the spectrum above and can therefore play more cleanly.