Was discussing a project with a client when they mentioned needing a “5-Watt” speaker for their product. I asked how they arrived at that number, and they said they’d used one previously and liked its loudness. I want to clarify a common mistake folks make. More Watts Doesn’t Always Mean More Volume. In fact, Watts might not even be the right way to choose a speaker. Let’s discuss this.
Speaker loudness is actually measured by Sound Pressure Level (SPL), expressed in decibels (dB), not watts. Watts only indicate how much electrical power a speaker can handle. SPL tells you how loud a speaker will get at a given distance and power input. Specifically, speaker sensitivity measures loudness in decibels at 1 meter away using just 1 watt of input. This is your real guide for loudness, and you will find this value in good speaker datasheets.
To get just a 3dB increase in volume, you must double the power. So, if one speaker has a sensitivity rating of 90dB and another is rated at 80dB, the first speaker is significantly louder at the same wattage. For instance, a 50-watt speaker with a 90dB rating will outperform a 100-watt speaker rated at 80 dB. Why? Because the higher sensitivity speaker converts electrical power into sound more efficiently.
SPL(dB) = Sensitivity(dB) + 10 log(Power)
For the 90dB speaker at 50W : 90 + 10 log(50) = 90 + 16.99 ≈ 107dB
For the 80dB speaker at 100W: 80 + 10 log(100) = 80 + 20 = 100dB
Remember, sound decreases by approximately 6dB each time the distance doubles, so you use this a tip to estimate levels at longer distance from the speaker. A speaker producing 90dB at 1m drops to about 84dB at 2m.
BTW fun fact, humans perceive a 10 dB increase as roughly twice as loud, but this actually requires about ten times more power.
So next time you’re selecting speakers, first check the sensitivity rating (dB/W/m) and not Watts alone.
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