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Watts or SPL, which is relevant?

So how do you compare the loudness of two speakers? A lot of people do this by the number of watts (or kilowatts (kW)) being used to power the speakers. The higher the number of watts, the greater the output of the speaker. But is this the case?

Lets take two speakers and see. The D&B Audiotechnik C4 Top and the Martin Blackline F12+. The peak power rating of the C4 Top is 800 watts, compared to the F12+'s 1200 watts. Based on this, you may think that the F12+ has a greater output, but you'd be wrong. In actual fact, the C4 can output 140dB SPL compared to the F12+'s 126dB SPL. As can be seen, the number of Watts that you can safely drive a speaker with is irrelevant on it's own, as ultimately, it's the sound pressure level that tells you which system is louder.

This is because every speaker has a different power requirement to produce a certain sound level. The specification that can tell you this is the sensitivity. This is usually written as the sound pressure level achieved at a distance of 1m, when the speaker is driven with a signal at a power of 1 watt. If speaker A has a sensitivity of 100dB SPL and speaker B a sensitivity of 97dB SPL, speaker A will require half the amount of amplifier power to achieve the same level of sound.

In summary, using watts to assess the output of a speaker is completely inaccurate unless the sensitivity of both speakers is the same. Because of this, it is always preferable to compare sound pressure levels of speakers using dB SPL.

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Damon Oldacre trading as RKDO Sound & Light