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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 elevick

elevick
2,636 posts
 
Meiwan, see if this helps:
at 8 ohms on 87db speakers, at 1 meter in front of them
1 watt = 87db
2 watts = 90db
4 watts = 93db
8 watts = 96db
16 watts = 99db
32 watts = 102db
64 watts = 105db
128 watts = 108db
It takes double the wattage to gain 3db.
You have to gain 10db to hear a "perceived" doubling of volume. No one is going to be able to tell the difference between an 87db speaker and a 90db speaker unless your amp is only 3 watts(2A3 tube amp).
However, impedance is another issue. Most solid state amps will double power output with halving of impedance. Some only give a 50% or so gain. Most tube amps will not give any increase in output.

For Nnck-are we talking stereo or theater. Almost any 2 channel amp will handle 4 ohms. Many theater receivers have issues driving five 4 ohm speakers. Be careful there. Do the math when looking but most theaters require 110db to 112db continuous output for THX or Ultra THX.
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