Speaker Asylum General speaker questions for audio and home theater.

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Re: sets and speakers

Posted by Duke (D) on February 17, 2007 at 11:08:51

In Reply to: sets and speakers posted by mayanitis on February 17, 2007 at 07:39:02:

The impedance and the efficiency both matter.

First, some nomenclature. Manufacturers often use the terms "efficiency" and "sensitivity" interchangeably, which creates confusion. "Sensitivity" refers to the output level with a 2.83 volt input, and "efficiency" refers to the output level with a 1 watt input. The two are the same for an 8 ohm load, but different for anything else.

A sensitivity of 92 dB/2.83 volts/1 meter is ambiguous without knowing the impedance. If this is an 8 ohm speaker, then the efficiency is 92 db/1 watt/1 meter. But if it's a 4 ohm speaker, then the efficiency is really only 89 dB/1 watt/1 meter, because 2.83 volts into a 4-ohm load is 2 watts, not 1 watt.

It gets worse.

Very seldom does a speaker have a smooth impedance curve. Usually the impedance curve has peaks and dips, and these tend to make the load more difficult. Dips especially so, peaks less so (generalizing here). And it's not uncommon for a speaker to have an impedance dip down to barely over half its rated value.

So...

If our 92 db/2.83 volt speaker is a 4 ohm speaker with an impedance dip to 2.5 ohms around 150 Hz (where there's lots of music energy), then it's going to be a very difficult load for an SET amp.

On the other hand, if we have a speaker that's 89 db/2.83 volts/1 meter sensitive and the impedance curve stays between 6 and 12 ohms, it will be a much easier load and our SET amp will not only sound better but also play louder before clipping.

Hope this helps.

Duke

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