Power – test review. Stereophile Magazine.

Power output of an Icon Audio MB150 valve amplifier reads 135W at a 1% distortion limit.



Power, measured in Watts, tells us how loud an amplifier can go. A 100 Watt amplifier goes louder than a 20 Watt amplifier for example. However, it does not go five times louder, much less in truth (+7dBW), and with a sensitive, modern floor standing loudspeaker 20 Watts will go very loud, loud enough for most homes. That’s because it gives +13dBW more power than 1 Watt and just 1 Watt gives 93dB at one metre from a stereo pair of 90dB sensitive floorstanders. That amounts to 106dB (93+13) sound pressure level at full output just 1m away which is extremely loud. In a room (i.e. reverberant field) this will decrease around -4dB for every doubling of distance, so expect 98dB at 4m (12ft) from the loudspeakers – and that is very loud. A 40 Watt amplifier adds 3dB to this and an 80 Watt amplifier 6dB, so suit less sensitive loudspeakers and bigger rooms

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