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Relate sensitivity/impedance to speaker efficiency

Can you help me relate speaker sensitivity and impedance to how efficient speakers are relative to one another?

What I mean is, given 2 speakers with the same or similar sensitivity (say 89 or 90), if one has a nominal impedance of 4 and another has a nominal impedance of 6, would the higher impedance speaker be easier to drive? Would the higher impedance speaker perhaps offer more flexibility in amplification (perhaps allowing the use of tubes?

What matters more for ease of amplification - a speaker with higher sensitivity or a speaker with a higher nominal impedance? (i.e. given similar nominal impedance, going from a speaker with a sensitivity of 87/88 to one with a sensitivity of 90/91; or given a similar sensitivity, going from a speaker with a nominal impedance of 4 to one with a nominal impedance of 6 or 8?)

I realize the answer to these questions is probably more complex, but are there some general rules to use as guidelines before actually trying the speakers out?
nnck

Showing 1 response by meiwan

meiwan
399 posts
 
The simple answer is the sensitivity is the sound pressure level with 1 watt of amplification at a specific frequency. Given 3db is a perceived doubling of loudness, going from 87 to 90 means the latter will sound twice as loud with the same power input.

Impedance is the resistance load put on the amplifier. A lower impedence puts more load on the amp. So a nominal 4 ohm load puts twice the load on the amp vs. an 8 ohm load. Hence you will see specs saying an amp will put out 50 watts into 8 ohms or 100 watts into 4 ohms - same loudness.

Generally, pretty much any amp will drive an 8 ohm load - sensitivity variances will affect perceived loudness only. A more robust power supply is needed to drive a lower load so that's where you need to be more selective in matching.

Hope this helps.
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