Loudspeaker

A loudspeaker, or simply speaker, is an electromechanical device which converts an electrical signal into sound. The term is used to refer to both the transducer, or driver itself, and a complete system consisting of one or more transducers in an enclosure. The loudspeaker is the most variable element in an audio system. The audible differences between speaker systems are considerable.

Efficiency

The sound pressure level that a loudspeaker produces is measured in decibels or DBSPL. The efficiency is measured as dB/W/m - decibels output for an input of one nominal watt measured at one metre from the loudspeaker usually on the axis of the speaker. This is called the "sensitivity" rating. Loudspeakers are very inefficient transducers. Only about 1% of the electrical energy put into the speaker is converted to acoustic energy. The remainder is converted to heat. The main reason for this low efficiency is the difficulty of achieving proper matching between the acoustic impedance of the drive unit and that of the air. This is especially difficult at lower frequencies. The better the matching, the higher the efficiency. Large horn loudpeakers that used to be used in cinemas, were very efficient by todays hi-fi speaker standards. From a technical standpoint "sensitivity" is not the absolute reference of efficiency. As an example, a simple cheerleader's horn makes more sound output than the cheerleader does by herself, but technically the horn did not "improve" or increase the cheerleader's "efficiency". True or absolute efficiency is the ratio of "desired" output power divided by total input power .

Related Topics:
Decibel - DBSPL - Nominal - Watt - Matching - Impedance - Horn

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Normal loudspeakers have a sensitivity of 85 to 95 db/watt/meter.

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Nightclub speakers have a sensitivity of 95 to 102 db/watt/meter.

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Rock concert, stadium speakers have a sensitivity of 103 to 110 db/watt/meter.

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Current state-of-the-art loudspeakers can approach efficiencies of 70% or higher. This is partly due to a very high magnetic field and partly to a high amplitude displacement (speaker cone pumping in and out). The ratio of the sound output to the mass of the cone/coil combination grows significantly at high sound pressure levels i.e. above 140 decibels. In closed or small environments (such as cars or bedrooms) it is far more important to have a speaker with a high X max.(pumping amplitude) as opposed to high (db/watt/meter) rating. A few top of the line woofers have a very low "sensitivity" rating i.e. 80 to 86 db/watt/meter(sensitivity efficiency of 0.01% ). However at full power may achieve 160+ decibels at 20% to 40% "true" efficiency.

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• video of 158 db woofer at 80 millimeter amplitude 450kb mpeg

As shown in this example, sometimes the speaker with the lower sensitivity rating outputs a far higher amount of acoustic watt output.

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In general a higher quality speaker will have a higher sensitivity rating, larger and or heavier magnet, and a higher X max.

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