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Dave (and Pete),
in a simple English the Q-factor for a speaker is the relation of the braking forces to the inertia forces of the moving mass (the cone, the coil, partially the suspension and leads). The braking forces can be of mechanical type (like damping features of the suspension) or of electrical type (the output impedance of the amplifier's output stage).
A perfect example of moving-mass system with huge Q-factor: a bell. The better the bell, the more Q-factor it has: boom-m-m-m-m-m-m-m-m-m-m-mmm....
A perfect example of moving-mass system with very small Q-factor: a ball made of plasticine (you drop it... and nothing happens, it doesn't bounce back)
A speaker can rely - and does rely - on both type of braking forces. But designers of good speakers do their best to get rid of the mechanical brake (which eats and worsens speaker's impulse response) and go on with the electrical one only.
The following factors increase the Q-factor:
- heavier moving mass (affects both mechanical Qms and electrical Qes; but this lowers the resonant frequency), bigger the gap in the drive between the coil and magnetic core (affects Qes only; but this increases the handling power), the smaller the magnet (affects Qes only; this makes the speaker cheaper), the weaker the coil (affects Qes only; also makes the speaker cheaper), the stronger the suspension (affects both Qms and Qes; this lowers the Vas equivalent volume which makes possible to go with smaller speaker cabinet)
Putting impulse performance aside, it can be shown that a speaker with very high Q-factor does nothing, but mumbles on the resonant frequency. If we put it into extremes, then here's what happens with a series resistor between the amplifier and the speaker: all the speaker-induced (counter-) voltage will drop off on this resistor and the amplifier's output impedance will not be able to drive the speaker as it tries to. That's why they put all those thick copper wires with lots of 9999999s after the decimal point - to lower the resistance between amplifier and the speaker.
Dave,
I tried to show it as clear in simple English as possible. Please let me know if I better switch to the geek version.
Zig
posted by 188.134.4...
, Mon, 22 Oct 2012 13:49:13, Mon, 22 Oct 2012 21:13:28
1, Wed, 24 Oct 2012 10:05:20
, Wed, 24 Oct 2012 06:12:20, Wed, 24 Oct 2012 07:15:50
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