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Old 1st November 2004, 04:39 AM   #1
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Default Woofer with high Qms

I have a woofer with a Qms of 11.6. This seems very high. Is this a bad thing?
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Old 1st November 2004, 09:21 AM   #2
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I believe that Qms and Qes are irrelevant in normal (voltage driven, reasonably thick and short cable/negligible series resistance) applications, only Qts matters. However, some others may believe that Qms should be low to indicate good mechanical damping and say that it makes things sound better
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Old 1st November 2004, 11:44 AM   #3
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High Qms is indicative of a stiff suspension, most often seen in woofers intended for large enclosures or even no enclosure IB applications. As with all specs it's not necessarily a bad thing, just part and parcel of the overall package.
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Old 1st November 2004, 07:48 PM   #4
Ron E is offline Ron E  United States
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Woofer low freqency design is based on Qts, which is the combination of Qes and Qms. There are an infinite number of combinations of Qes and Qms that will give you the same Qts. High Qms happens when non-conductive formers are used. and it is an inverse measure of losses in the suspension. High Qms means low losses and low Qms means high losses...

The only effect on bass frequencies according to modelling is that drivers with higher Qms have higher Impedance peaks - which does not matter for solid state amps and matters only some for tube amps......

Contrary to what others have said, I believe the golden eared crowd tend to favor High Qms drivers because they have less damping and they believe they sound more dynamic. I think that because high enders are the ones more likely to use tube amps nowadays, they are hearing the FR bumps caused by their amps' high output impedance, and they like it.
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Old 3rd November 2004, 01:23 AM   #5
madinoz is offline madinoz  Australia
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For what it's worth, I have heard a number of respected speaker designers state that they prefer high QMS designs with low QES. They theorise that there is more dampening occuring within the suspension.
A high BL factor is also a consideration.
Listening to a driver is the final determining factor as figures can only tell you so much (but they are a good starting point).
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Old 3rd November 2004, 07:05 PM   #6
Ron E is offline Ron E  United States
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Quote:
Originally posted by madinoz
For what it's worth, I have heard a number of respected speaker designers state that they prefer high QMS designs with low QES. They theorise that there is more dampening occuring within the suspension.
A high BL factor is also a consideration.
Listening to a driver is the final determining factor as figures can only tell you so much (but they are a good starting point).
Qms is related to the dampening in the suspension. A High Qms means low damping in the suspension relative to the mass.

Qes is related to the dampening in the motor system - which is related to Bl/Re. High Bl factor in itself means absolutely nothing at all.

Do a search for Joachim Gerhard of Audio Physik.
http://www.speakerbuilding.com/content/1039/
He is the only "well respected designer" that I know of that has spoken out about this parameter that I know of - and he makes comments that completely contradict what you say regarding the amount of damping in the suspension. He also makes comments that contradict himself. Q is a measure of energy stored divided by energy dissipated, meaning that higher Q means more energy storage "Dissipated energy" is loss.

Quote:
.words of JG...
Later, in the 80's, manufacturers started to add more mass, they added more damping, and they made surrounds with high loss. That gave an extremely flat frequency response, but also a lot of energy storage. This compared, the old drivers were much quicker. They had some resonances, but you could get rid of that in the crossover. It was this run for flat response that gave a lot of modern drivers this dull, uninteresting sound. And you can also measure higher second and third harmonic distortion in some of them. If you compare the on-axis response between an old and new driver; you will see that the energy in the treble is far higher than in the new drivers. These so-called "modern" drivers often has a Qms of maybe 0.8 or 0.6. The old drivers had Qms values of maybe 5 to 7! We found that drivers with a very high mechanical Q sound more open, more clean and dynamic. And when you look at it, you find it is very simple, because they have less loss. The surround is easier to move, the spider is better constructed, they have better air flow, higher sensitivity. So a high mechanical Q is a very good indicator of energy storage behavior. This is one of our secrets. One of the many!
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Old 4th November 2004, 10:36 PM   #7
mike.e is offline mike.e  New Zealand
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Well i used to think that there was no possible way for there to be a sound difference-but perhaps this is true.Im no golden ear!

Klippel.de article


Klippel.de article

Variance of t/s parameters with excursion


The total loss factor QTS considering all system resistances and the resonance frequency fS are important parameters for the final alignment of the loudspeaker system. Both parameters vary with the displacement if the motor and the suspension are nonlinear.

The instantaneous value fS(x) is proportional to the square root of stiffness KMS(x). Operating the driver A,B, C, D, F and G at xmax where Cmin=25% the resonance frequency is shifted one octave higher then at the rest position x=0.

An increase of the resonance frequency fs also leads to a higher mechanical loss factor QMS and has also an effect on the total loss factor QTS. However, the electrical damping usually dominates and variations of QTS(x) can be neglected if the motor is sufficiently linear.

Contrary, the electrical damping of the system will vanish with the squared force factor variation. For example, if the force factor variation goes down to Bmin= 25% the electrical loss factor QES(xmax) increases by factor 16 and the remaining mechanical damping will determine the total QTS. Operating driver F at xmax the total QTS is 10-times higher than at the rest position giving more acoustic output at fs. However, the generation of a distinct resonance peak and the shift of the resonance frequency by one octave are usually perceived as a spectral coloration of the sound (booming bass).
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Old 5th November 2004, 02:24 AM   #8
Ron E is offline Ron E  United States
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Quote:
Originally posted by mike.e
Well i used to think that there was no possible way for there to be a sound difference-but perhaps this is true.Im no golden ear!
Certainly T/S parameters change with drive level, but how is this relevant to driver selection based on Qms, which was the original question?
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Old 5th November 2004, 02:28 AM   #9
mike.e is offline mike.e  New Zealand
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Well i posted all that rubbish,because it seems to say that at high excursions Qms can become dominant-because the Vc is not being controlled by the Magnetic circuit (low bl state)

Cheers!

Contrary, the electrical damping of the system will vanish with the squared force factor variation. For example, if the force factor variation goes down to Bmin= 25% the electrical loss factor QES(xmax) increases by factor 16 and the remaining mechanical damping will determine the total QTS. Operating driver F at xmax the total QTS is 10-times higher than at the rest position giving more acoustic output at fs. However, the generation of a distinct resonance peak and the shift of the resonance frequency by one octave are usually perceived as a spectral coloration of the sound (booming bass).
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Old 5th November 2004, 09:40 PM   #10
Ron E is offline Ron E  United States
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Quote:
Originally posted by mike.e
Well i posted all that rubbish,because it seems to say that at high excursions Qms can become dominant-because the Vc is not being controlled by the Magnetic circuit (low bl state)

Dumax rates Xmag at 71% Bl, and at that point they claim there is about 10% Harmonic distortion due to that nonlinearity. So by the time you are moving far enough to get to the 25% Bl point, I would say that Qms is the least of your worries.

I was really just poking you to see if you understood what you had posted. Maybe we should all be buying woofers with a Qms of 0.2 so that when we factor in the doubling of Fs at high excursions and the neglectible contribution of Qes we get a reasonable Qts for our speaker design....
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