Efficiency and sensitivity conversion - loudspeaker percent and dB

calculator calculate conversion chart calculation comparison noise white and pink thermal noise Johnson Nyquist convert bandwidth and temperature noise voltage pollution formula faranheit farenhiet degree scales table tables temperature scale level formulae cold icy warm dB freezing boiling point body comparison compare absolute zero degrees bandwidth RMS point water degree Formla Formlas equation equations conversion American English deg Reaumur Réaumur NF noise figure factor Sengpiel Berlin sengpielaudio

Deutsche Version

• Conversion of sensitivity in dB per watt and meter •
• to energy efficiency in percent for passive loudspeakers •

The used browser does not support JavaScript.
You will see the program but the function will not work.

In loudspeaker data you never find the efficiency in percent, but usually there is the sensitivity in dB/W/m.

Efficiency is not the same as sensitivity, but it is possible to convert efficiency to sensitivity:

Sensitivity in dB = 112 + 10 log (efficiency)

Efficiency = 10^{(Sensitivity in dB – 112)/10}

Loudspeaker data
Efficiency	In percent	Sensitivity
0.1	10 %	102 dB
0.05	5 %	99 dB
0.02	2 %	95 dB
0.01	1 %	92 dB
0.005	0.5 %	89 dB
0.002	0.2 %	85 dB

The sensitivity of a loudspeaker is the sound pressure between 125 Hz (250 Hz) to 4 kHz
(8 kHz) when you have a constant voltage at a specific distance; measured in dB per watt and meter. Mostly it is the voltage of constant 2.83 volts, the distance is 1 meter, at 8 ohms nominal impedance For instance is the sensitivity of a good 8 ohms loudspeaker:
92 dB / 2.83 volts / 1 meter. Herewith is the power P = V ² / R = 2.83² / 8 = 1 watt. With a
4 ohms loudspeaker you generate 2 watts. To get the reference value of 1 watt, you have to subtract from the sensitivity 3 dB.
It is not the efficiency you get here, it is the sensitivity.
The very small value of the efficiency is never shown by a manufacturer. Usual values for HiFi speakers and studio monitors are between 0.2 % and maximum 2 % – that is an efficiency
of 0.002 to 0.02.
There is no connection between the efficiency and the sound quality.

Acoustic efficiency η (Eta) of a loudspeaker:

Where does the 112 dB come from? The 0 dB reference level for sound is 10^–12 watts.
1 acoustical watt means 120 dBSPL.
The standard measurement for loudspeakers is done with an infinite baffle sounding in a half room with a distance of r = 1m.
The resultant factor 2 π × r² (area of a half sphere) equals –8 dB. Therefore we get for an efficiency of 1 = 100 % a sensitivity of 120 – 8 = 112 dB.

This calculation works correct if the loudspeaker radiates in a half circle 2 π. Otherwise you must add the Q factor because of directionality.

Many disco freaks need for their loudspeakers:
The Big Power Formulas
Electrical and mechanical power calculation

Studio monitors have a small energy efficiency arround 1 %, but that gives a very high uncolored sound quality.

If you are looking for big party loudspeakers with high efficiency you have really to think of power matching and megaphones. They have always an efficiency of more than 10 %, but with the well known distortions and giving a strange colored sound. That comes really through and has "pressure" and you can hear the "power".
Megaphon - high efficiency

If you need even more efficiency you have to think of a siren on emergency vehicles. But the frequency bandwidth is very limited.

Extremes:
dB drag racing is a competition rewarding the personDreamweaver 8 who can produce the loudest sound inside a vehicle with a car's sound system.

Typical Question: Calculate the maximum sound pressure level of a loudspeaker in 1 m distance, when the sensivity level of 98 dB/1W/1m is given and the wattage is 300 W.
Answer: At 1 Watt you get 98 dBSPL in 1 m distance. At 300 W there is 10 × log 300/1 = 24.77 dB more level, that means 122,77 dBSPL.

back

next

home