I've read several definitions, but I can't make heads or tails of them.
Qts, Qem, Qes ... all deeply mysterious to me.
Qts, Qem, Qes ... all deeply mysterious to me.
Q, in general for a resonant system, is the inverse of damping. In the case of a low frequency driver, there are several contributions to the total Q (or total damping); you've mentioned a few.
For a readable and in-depth discussion of the definition and what to do with the numbers once you have them, Dickason's "Loudspeaker Design Cookbook" can't be beat.
For a readable and in-depth discussion of the definition and what to do with the numbers once you have them, Dickason's "Loudspeaker Design Cookbook" can't be beat.
SY said:
I guess I'm just dense. I've got that book, but after several readings I still can't figure out what Qts means. I don't have it with me, but it says something like, Q is the ratio of reactance to resistance. Okay, so far so good. Then it says something like, Qts is the Q of the loudspeaker, taking all resistances into acount. I can't quite make that leap. Qem is even more mysterious to me. Don't these things have clear operational definitions?
Qts is the total Q of the unmounted driver, taking into account both mechanical (Qms) and electrical (Qes) damping.
1/Qts =1/Qes + 1/Qms
Really, all you need for basic design is the Qts.
1/Qts =1/Qes + 1/Qms
Really, all you need for basic design is the Qts.
SY put it pretty well. Q is the inverse of damping. A speaker has mechanical damping due to the surround, spider, etc. It also has electrical damping due to the motor.
Total damping (1/Qts) = electrical damping (1/Qes) + mechanical damping (1/Qms)
Total damping (1/Qts) = electrical damping (1/Qes) + mechanical damping (1/Qms)
Maybe this will help:
You can look it it like this. The moving parts of a speaker have a defined mass. When you apply a force to a mass it starts to move in the direction the force was applied in. So if you put a sine-wave into the coil of a speaker the magnetical forces will make the mass of the cone, coil,... move outward while the the amplitude is increasing. (and increasing velocity) At the top of the sine-wave these parts have to stop and start moving in the inverse direction. Well without spider or surround the cone will keep moving forward due to the energie still in it. So it will overshoot and over-excurt. (massa-traagheids-wet in Dutch, sorry forgot the English for it 😱 )
So this movement needs damping. It needs to be a smooth motion outward, decresing in speed towards the top of the sinewave. Stopping at the top and reversing direction. That's why the spider(s) and surround are there. These are the mechanical resitances. Out of these the Qms number is formed.
The electrical damping comes from the inductance of the coil and the way the magnetical field coming from the signal applied works with the statical magnetical field of the magnets. The resistance of the coil is not a constance. It varies with frequency, temperature etc. taking these electrical effects into acount you can find Qes. The effects dampen the motion too in a way.
Now if you take the mechanical and electrical damping together you have the total damping. Qts.
Q = Quality factor
e = electrical
m = mechanical
s = speaker/system
Hope this helps.
If I'm wrong in any way, please correct me. I'm not perfect either.
You can look it it like this. The moving parts of a speaker have a defined mass. When you apply a force to a mass it starts to move in the direction the force was applied in. So if you put a sine-wave into the coil of a speaker the magnetical forces will make the mass of the cone, coil,... move outward while the the amplitude is increasing. (and increasing velocity) At the top of the sine-wave these parts have to stop and start moving in the inverse direction. Well without spider or surround the cone will keep moving forward due to the energie still in it. So it will overshoot and over-excurt. (massa-traagheids-wet in Dutch, sorry forgot the English for it 😱 )
So this movement needs damping. It needs to be a smooth motion outward, decresing in speed towards the top of the sinewave. Stopping at the top and reversing direction. That's why the spider(s) and surround are there. These are the mechanical resitances. Out of these the Qms number is formed.
The electrical damping comes from the inductance of the coil and the way the magnetical field coming from the signal applied works with the statical magnetical field of the magnets. The resistance of the coil is not a constance. It varies with frequency, temperature etc. taking these electrical effects into acount you can find Qes. The effects dampen the motion too in a way.
Now if you take the mechanical and electrical damping together you have the total damping. Qts.
Q = Quality factor
e = electrical
m = mechanical
s = speaker/system
Hope this helps.
If I'm wrong in any way, please correct me. I'm not perfect either.
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