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Originally Posted by robert bartsch
Is it fair to say that speaker sensitivity ratings are a measure, in part, of the strenght of the electro-magnetic field within the voice coil gap?
Isn't this rating indicative of the mechanical efficency of the driver?
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The measure of strength you are describing is called BL.
Eminence has a very good definition.
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Originally Posted by robert bartsch
Some of the professional series speakers have some monster magnets, super high sensitivity ratings (+100 DB), and can make high sound pressure levels with moderate power. Therefore, isn't a high sensitivity rating beneficial; if not, why are these ratings provided?
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Magnet size is not an indication of high BL though. You have to know the size of the magnetic gap, the strength of the magnets, the type of steel used in the motor and the size, windings, layers of wire in the voice coil. All of that combines to determine the BL. Normal cermic magnets are cheap and pretty powerful. Neodymium magnets are MUCH stronger size for size when compared to ceramic magnets. I have a 45 pound sub motor with ceramic magnets and a 20 pound sub motor with neo magnets and they are basically the same.
Moving mass of the cone or dome (mms specification) is a better indication of sensitivity. Also, the frequency range that the driver is designed to play over is a huge factor. A driver can't play a 20hz tone at 100db with 1 watt of power. The current technology isn't there.
Hoffman's Iron Law is also in effect here. It basically says that you trade sensitivity for lower frequency response. Like all of speaker design, everything is a tradeoff when you are trying to reach your goals.
-Robert