Does Qms, Qes, and Qts explain a driver? - diyAudio
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Old 20th February 2004, 05:10 AM   #1
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Default Does Qms, Qes, and Qts explain a driver?

So do these three parameters explain a drivers abilities?

I mean can you tell a good driver just by looking at these three parameters, or at least get a good idea of a driver?

Consider the following drivers;

Driver1 6"
Qms 5.56
Qes 0.49
Qts 0.45

Driver2 7"
Qms 1.77
Qes 0.46
Qts 0.36

Driver3 7"
Qms 7.00
Qes 0.38
Qts 0.36

Driver4 6.5"
Qms 3.47
Qes 1.15
Qts 0.86

Now just considering these parameters can you get an idea of which would be better or which would be worse? Some have high mechanical Q, some have high Electrical Q....does it make a difference?
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Now to see how well you guessed, I'll devulge the names of the drivers. I'm not trying to say anyone brand is better than the other I just tried to find different examples from different price points.

Driver1 = (HiVi M6N) $45
Driver2 = (Vifa XG18WH00-08) $93
Driver3 = (Focal 7W4411) $151
Driver4 = (Goldwood) $17

Just wanted to include a wide range of prices and specs.


I know this will probably spark some debate. I know these must mean something. Someone on here once said that Tang Bands were not good drivers because they were not physically made to the same standards that traditional European drivers are, yet those numbers don't seem to reflect that. If anything Focal has horrendous Qms values when compared to their prices, while Scan Speak long known as a "great" brand has high prices, but values that are more in line with everyone else.
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Old 20th February 2004, 05:42 AM   #2
SY is offline SY  United States
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You skipped to the second question without asking the first- how do you define "good"? A driver which is fine for design A may be lousy for design B.
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Old 20th February 2004, 05:54 AM   #3
cm961 is offline cm961  Canada
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I think it depends more on how honest the company is when they quote their specs. They can put anything they want. Perhaps if the TB drivers aren't made to the same quality, its not that the overall parameters are worse or better, but the drivers may not come out the same off the production line... Ie. greater variance in production.

Pete
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Old 20th February 2004, 06:28 AM   #4
sreten is offline sreten  United Kingdom
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Default Re: Does Qms, Qes, and Qts explain a driver?

Quote:
Originally posted by Hybrid fourdoor
So do these three parameters explain a drivers abilities?
If anything Focal has horrendous Qms values when compared to their prices, while Scan Speak long known as a "great" brand has high prices, but values that are more in line with everyone else.
If anything you are paying for the high Qms in the Focal.

Seems to me you don't understand what Qms is.

Qts is the result of both Qe and Qms.

Qms tells you something........ but hardly the total picture.

sreten.
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Old 20th February 2004, 07:23 AM   #5
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Just keep in mind these figures will give you a prediction in physical behaviour of the drivers, but NO information about sound quality. It's comparable to distortion figures in amplifiers: high feedback gives nice figures but sound dull.

A correct tuned enclosure is only a beginning...
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Old 20th February 2004, 08:01 AM   #6
Svante is offline Svante  Sweden
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Default Re: Does Qms, Qes, and Qts explain a driver?

Quote:
Originally posted by Hybrid fourdoor
So do these three parameters explain a drivers abilities?

Nope. If you have Qts, Fs and Vas, you are closer. With these three parameters you can evaluate if you can design the frequency response you want, and what box volume you need.

On top of that, there are a *bunch* of other parameters that will determine the end quality of your system, like Xmax, Power handling capacity, cone breakups etc.

Qts=Qes*Qms/(Qes+Qms), and it is only Qts that is important. Well, almost.
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Old 20th February 2004, 09:08 AM   #7
navin is offline navin  India
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of course there are other parameters (just ask hunter audio) but i think the question here is how far do Qes and Qms go to explain the driver. i dont know where i read this but somewhere in te back of my head a little voice tells me to keep Qms under 5 and Qes under 1 (preferably under 0.7).

i cant remember where this recomendation was posted or typed.
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Old 20th February 2004, 10:34 AM   #8
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Quote:
Well, almost.
That's it. If you want to have low mechanical losses (i.e. a high Qms) you have to make some efforts (low friction or airflow resistance, Kapton formers instead of Aluminium...). There are people saying that drivers with the same Qts but larger Qms would give more accurate bass reproduction (often cited by the two German DIY speaker mags).

Regards

Charles
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Old 20th February 2004, 11:51 AM   #9
Svante is offline Svante  Sweden
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Quote:
Originally posted by phase_accurate


That's it. If you want to have low mechanical losses (i.e. a high Qms) you have to make some efforts (low friction or airflow resistance, Kapton formers instead of Aluminium...). There are people saying that drivers with the same Qts but larger Qms would give more accurate bass reproduction (often cited by the two German DIY speaker mags).

Regards

Charles

Why would low mechanical losses be important? Are they worse than electrical?
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Old 20th February 2004, 01:05 PM   #10
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Why would low mechanical losses be important? Are they worse than electrical?

they are not worse but mostly related to the fact that efficiency is traded for a more flat response. In most cases suspension stiffness and freq-response-behaviour is chosen to modify or smooth out some peaks in overall freq-response.

This can cause a 'foggy' ie. less grainy response.

That's the main reason I personally tend to prefer pro-drivers.
Frequency-response smoothed-out electronically by means of a dsp is far better than damping the whole speaker response.
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