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In loudspeaker data you never find the efficiency in percent,
but usually there is the sensitivity in dB/W/m instead.
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- but it is possible to convert efficiency to sensitivity and vice versa:
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| 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 | |
| 0.001 | 0.1 % | 82 dB | |
| The sensitivity of a loudspeaker is the sound pressure between 125 Hz (250 Hz) to 4 kHz (8 kHz) at a specific distance - when you have a constant voltage - 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. |
Efficiency
The efficiency of a system is defined as the ratio between the useful delivered
power output divided by the input power, denoted by the Greek letter small eta (η).
Acoustic efficiency η (Eta) of a loudspeaker is:  |
| 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 = 1 m. 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 car and disco freaks need for their huge loudspeakers:
The Big Power Formulas
Electrical and mechanical power calculation.
How many decibels (dB) is twice (double, half) or three times as loud?
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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".  If you need even more efficiency you have to think of a siren on emergency vehicles. But  dB drag racing (racer) is a competition rewarding the person who can produce the loudest sound inside a vehicle with a car's sound system. Current world record is over 177 dB-SPL. These audio gear does not play usual wideband pop music, like black metal or gangsta rap, but a single (!) tone. Only by this way an extremely high efficiency can be achieved; see emergency horn. |
| 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. |
Sometimes the efficiency is given in decibel instead of percent.
| Enter simply the value to the left or the right side, and use the TAB key or click the mouse to an empty space on the page to get to the solution. The calculator works in both directions of the ↔ sign. The damping value in dB must begin with a minus sign. |
Decibel to Percentage Converter
Decibel Table - Comparison Chart - dB Scale
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