Q Re; driver sensitivity?

[Jonathan Bright]

Most manufacturers quote driver sensitivity in the following form: db/watt/mtr.
E.g. 90/watt/m....at a specified impedance, say 8ohms.

KEF use a different form.

E.g. 96db at one Meter for 10volts (RMS)

Please could someone explain how to convert the second form into the first form......(if we assume pink noise and a similar impedance).

Thanks, Jonathan

[kelticwizard]

For an 8 ohm speaker, one watt normally equals 2.83 volts.

10 volts is about four times 2.83 volts, (actually it's 3.53 times but we can round up without going off too much).

So at 10 volts, for an 8 ohm speaker, you are receiving about four times the power that you would get at 2.83 volts.

Two times the power = +3 dB.
Four times the power = +6 dB.

So take the KEF speaker rating at 10 volts, subtract 6 dB, and you should have the reading for one watt, (2.83 volts). This applies only to an 8 ohm speaker.

[kelticwizard]

PS: Just remembered the formula now:

SPL = 10 Log V1/V2

=10 Log (2.83/10)

= 10 Log (.283)

= -5.48 dB

Subtract 5.48 dB from your KEF speaker rated at 10 volts to give the equivalent of one watt input into an 8 ohm speaker.

[Jonathan Bright]

Thanks. Eggsactly what I needed!! Jonathan.

[AllenB]

Not quite. Voltage would be 20x rather than 10x. This is because as voltage doubles, it causes current to double as well, so power quadruples.

20 x log(10/2.83) is 11dB.

That's if dB/2.83V/m is an acceptable base for your needs.

[kelticwizard]

My apologies. 20 Log V1/V2 is the correct formula for voltage. 11 dB is the correct answer.

[Jonathan Bright]

Thanks again guys. Nice to have a civilized and constructive interaction.