Does Qms, Qes, and Qts explain a driver? - Page 3 - diyAudio
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Old 21st February 2004, 08:26 AM   #21
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that's the point where 'motional feedback' comes into play. This is the most effectif way combined with dsp. Because the real movement measured is better than the 'predicted' movement.
(non-linearities change when using the driver, be it by change of voicecoil-temperature, fresh or used suspension, etc)

G-sensors not only for women
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Old 21st February 2004, 08:33 AM   #22
Svante is offline Svante  Sweden
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Agree. Feedback is a good way to linearise a non-linear system. But I don't think that the nonlinearities in Rms is the biggest problem.
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Old 21st February 2004, 08:43 AM   #23
sreten is online now sreten  United Kingdom
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Quote:
Originally posted by Svante
So, sreten, you are basically saying that a high Qms is desirable, because this means that the mechanical losses are low, and that low mechanical losses is good since they mostly are nonlinear and hysterical (or whatever the adjective should be )
Did I get you right?
I am not saying mechanical losses are mostly non-linear, just
that they are not perfectly linear and may have hysterisis effects.

At least one manafacturer, Audio-Physics states that high Qms
is desirable for a bass/mid, interview excerpt :

Quote:
- Many "old" paper woofers still sound astonishingly good compared to modern drivers?

- Oh, yes. We have not always went to the better. What many driver manufacturers have done the last years, is to increase the damping to make the frequency response more flat. But some old drivers, like the famous 6,5" paper woofer that Jan Paus at Seas made several years ago, (The Seas CA 17 RCY, ed. note) was optimized for low loss. So they made a compromise between frequency response and sensitivity. This driver was very good, and was used by Wilson Audio for many years. 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!
Well I for one can't find a driver with Qms below 1.5.
And it does smack of commercial manafactures pseudoscience hype.

All I'll say is a driver with a lowish Qms needs to designed very
carefully.

And there's no such thing as a horrendously high Qms.

sreten.
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Old 21st February 2004, 08:43 AM   #24
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I'm the happy owner of fairly big speaker systems, wich I don't use for more than 10% of it abilities, but when you drive those little shoe-box-like systems to 70 or more % of their capacity, ......

I agree with sreten, playing with suspension characteristics is a janus play: if you don't do it right it's horrible (wich it is most of the time)
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Old 21st February 2004, 09:11 AM   #25
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Quote:
Originally posted by sreten



And there's no such thing as a horrendously high Qms.

sreten.

Your always knocking me.


So, based on what you guys have said, why are these figures even important then?
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Old 21st February 2004, 09:30 AM   #26
sreten is online now sreten  United Kingdom
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Quote:
Originally posted by Hybrid fourdoor


Your always knocking me.

So, based on what you guys have said, why are these figures even important then?
Sorry if that appears to be the case,
it wasn't intended to be read that way,
just as a clarification.

Most of the time Qts is used for designing the bass alignment,
Qms and Qe are the two parameters that determine Qts.

sreten.
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Old 21st February 2004, 12:43 PM   #27
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Let's discribe it in another fashion:
Most, if not all instruments who produce low frequencies in a natural way are fairly big in size, agreed?
If you want reproduce this same sound out of a little housed speaker, you have to bring some tricks in play. Non-linear amplification (playing with equalizer knobs) or damping the natural frequencies of a system to relatively enhance response outside this optimum ie. to widden the optimum range.(with the optimum at a lower level !!!)
All 'tricks' are more or less a trade-off (bass-reflex versus closed box, suspension as discussed above, etc.)

As with all tricks: only few magicians, artists are really 'GREAT' in everything they do, most of them have a great performance now and than, but they often don't even know themselves why it was great.

Most great autopilots are great feedback loops, most gentlemen-drivers are not, what makes them bad racing-systems, despite the potentionally performing cars.
Brute horsepower requires 'handling' skills to lead it into victory. Most of the time a trade in horsepower/ torque gives better but average results, but the better pilot chooses for the brute force.

This is what makes following names great:
auto-racing: Walter Rorhl (naturally talented, put him in your wives car and it's a race car, suddenly)
music live band: Rolling Stones(give them 3 notes and they'll propose 20 hitsongs)
guitar: Jimmi Hendrix (extreme: the system in the system, could make 1 note hitsongs)
ampllifier design: Nelson Pass (yeah, bet this forum is one of his feedback loops). Give him 1 transistor, 1 resistor and a choke...he could even ask you why he would need all that...hehehe
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Old 21st February 2004, 04:11 PM   #28
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I know a well known guy who reckons that high Qms subwoofesr sound 'muddy'

Personally=
A low Qts is desired
Cms linearity will be dominant BELOW fs , so its not the major worry!

its BL linearity that i worry about first!

Cheers
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Old 27th March 2013, 12:59 AM   #29
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Interesting thread, thanks to all.

But could someone please just provide a list of the following and what, to them, is a good value ? And applicable can you mention whether higher is better or worse for each one.
What i don't get is this: if this info is of no value, why is it even provided in the first place?

Resonant Frequency (Fs) Hz
DC Resistance (Re) ohms
Voice Coil Inductance (Le) mH
Mechanical Q (Qms)
Electromagnetic Q (Qes)
Total Q (Qts)
Compliance Equivalent Volume (Vas) ft.
Mechanical Compliance of Suspension (Cms) mm/N
BL Product (BL) Tm
Diaphragm Mass Inc. Airload (Mms) g
Maximum Linear Excursion (Xmax) mm

The above criteria was taken from a product page on Parts Express.

Thanks a lot. I am sure this, if even possible to state, will help a considerable amount of total rookies like myself.
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Old 27th March 2013, 01:02 AM   #30
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Hey, looks i have found something pretty much in line with my request !
Speakerplans.com
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