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Inside Loudspeaker Sensitivity: What’s A Watt Anyway?

Shedding some light on the sensitivity specification and how it may translate to the real world performance of a loudspeaker system...

Loudspeaker B should have slightly greater output when driven by this broadband pink noise signal. In fact, loudspeaker B measured 0.8 dB greater than loudspeaker A, 97.0 dB compared to 96.2 dB.

From these examples one should be able to see that the SPL generated by a loudspeaker is a function of both the loudspeaker’s transfer function and the spectrum of the signal being reproduced.

Several acoustical room modeling programs take this into account when calculating the SPL produced over an intended audience area. They may allow for the selection of pink noise, some sort of speech spectrum, or a user-defined spectrum.

This should aid the sound system designer, while still at the drawing board stage, to better understand the potential SPL capabilities of the sound system with the typical program material the system is likely to be reproducing.

The other item I mentioned at the beginning of this article was referencing sensitivity measurements to one watt being dissipated by the DUT. There are several reasons why I think that this is not beneficial with modern sound systems.

First, it is somewhat cumbersome to determine how much voltage is required across a particular DUT such that the input current drawn from the driving source yields 1 watt. This can be done using dual channel FFT measurement systems and an appropriate current monitor or probe. But would this give us useful information for the design and/or specification of loudspeakers or sound systems?

We can simplify this measurement procedure so that we don’t concern ourselves with the dissipation of a real watt by the DUT. Instead we apply a voltage across the DUT that would dissipate one watt in a pure resistance having the value of the rated impedance of the DUT.

This certainly is easier, but again, does this give us useful information for the design and/or specification of loudspeakers or sound systems? Perhaps. My thought is that more useful comparative information would be gained by applying the same voltage across the DUT regardless of its impedance.

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