Speaker Asylum

RE: Correct- and it is measured 1 watt/1 meter nt

207.167.13.69

This Post Has Been Edited by the Author

In Reply to: RE: Correct- and it is measured 1 watt/1 meter nt posted by Ralph on May 09, 2017 at 09:14:47

Nope.
Sensitivity is, and always has been, expressed in 1W/1m.
"Efficiency" is often used to describe sensitivity while taking into account impedance. (Sensitivity compensates for impedance). This is not really what actual efficiency is... efficiency is really an expression of electrical power in compared to acoustic power out.
A tweeter that is 90db 1W/1m sensitive is 0.6% efficient
A prosound woofer that is 97db 1W/1m sensitive is 3% efficient.
The rest goes into heat (I^2*R coil losses and overcoming frictional forces of the mechanical system, which also results in heat).
I always refer to this calculator page for efficiency.
http://www.sengpielaudio.com/calculator-efficiency.htm
Although 32 and 16 ohm speakers were once very common, 8 ohms became a common "nominal" impedance for speakers for many decades. As such, the voltage used for efficiency is 2.83V, as this voltage when applied to an 8 ohm nominal load gives 1 Watt.
P = (V^2) / R
P = 2.83^2 / 8
P = 8 / 8
P = 1W
Interestingly, this means an 8 ohm speakers will have the same value for efficiency and sensitivity!
When you apply 2.83 volts to a 16 ohm speaker you get
P = (V^2) / R
P = 2.83^2 / 16
P = 8 / 16
P = 0.5W
When you apply 2.83 volts to a 4 ohm speaker you get
P = (V^2) / R
P = 2.83^2 / 4
P = 8 / 4
P = 2W
Efficiency takes into account the speakers impedance in so far as how it impacts power. Sensitivity compensates for this by adjusting the input voltage to keep input power constant.
Cheers,
Presto

Edits: 05/09/17 05/09/17

Follow Ups: