Hi,
as far as I know the TS-parameters are just correct for small signal conditions and a small frequency range around the driver´s Fs.
The relevance of Rms as it was stated in the DIY-magazine was just an assumption of this journalist. It couldn´t be proofed as a rule. In fact, many people think that the assumption is wrong.
I admit that I never spent much attention to the Rms-factor, when choosing a bass driver and nearly no attention at all to TSPs for midrangers or even tweeters. When choosing a midranger tapping and slightly scratching the membrane tells me more than those numbers.
jauu
Calvin
as far as I know the TS-parameters are just correct for small signal conditions and a small frequency range around the driver´s Fs.
The relevance of Rms as it was stated in the DIY-magazine was just an assumption of this journalist. It couldn´t be proofed as a rule. In fact, many people think that the assumption is wrong.
I admit that I never spent much attention to the Rms-factor, when choosing a bass driver and nearly no attention at all to TSPs for midrangers or even tweeters. When choosing a midranger tapping and slightly scratching the membrane tells me more than those numbers.
jauu
Calvin
Calvin said:
Many people think the hard edged, glassy, sterile sound of much of the "audiophile" recordings and associated "high end" equipment is the "real thing" (things like metal cones and high order slope crossovers).
I have developed so many different loudspeakers, I have lost the count but I have yet to hear a woofer with high mechanical losses (high Rms or low Qms) that would sound fast, detailed and with impact. Perhaps "clean" but not lively.
I don`t claim Rms is the sole factor, but it is a very important one.
http://www.loudspeakers.we.bs/
Qms, and therefore Rms, is strictly defined only at resonance and can vary with frequency. Rms is not a reliable indicator of "speed", whatever that is. 😉
Ron E said:
Of course not, it is just a strange coincidence.
Whew, the beauty of scientific approach!
Member
Joined 2004
Hi,
I just started continuing the interview series Pjay did with several driver and loudspeaker designers. His series can be found on Helarc
One of the questions i added to the list was. What about Qms & Rms? First driver designer to answer the question was Allan Isaksen from Wavecor.
I hope Bernd from Hobby Hifi will answer the questions too. Heres the new serie of interviews. Speaker Gurus
Commercial and on topic.
Kind regards
Roland
I just started continuing the interview series Pjay did with several driver and loudspeaker designers. His series can be found on Helarc
One of the questions i added to the list was. What about Qms & Rms? First driver designer to answer the question was Allan Isaksen from Wavecor.
I hope Bernd from Hobby Hifi will answer the questions too. Heres the new serie of interviews. Speaker Gurus
Commercial and on topic.
Kind regards
Roland
fivestring said:
The Selenium unit I use in Altec A7 boxes has a Qms of close to 14 yet has tremendous impact. The drivers I am comparing with ie: Eminence and JBL have 1/2 or less the Qms yet offer no more punch so I guess YMMV.
http://www.parts-express.com/pe/showdetl.cfm?Partnumber=264-425
EDIT: Oops, I just reread the quote, my bad.
At the 2008 Munich audio fair I talked to Allan Isaksen about these very issues.
I know I am not deaf and I know what I hear. It is sad how people and especially some manufacturers underestimate this problem.
I know I am not deaf and I know what I hear. It is sad how people and especially some manufacturers underestimate this problem.
Some more things Allan Isaksen said in that interwiev:
"At Wavecor we strongly believe this is the right direction and you will usually see that Wavecor drivers have higher Qm than most. We can easily hear the difference but it’s a little frustrating that we can’t easily prove our point in terms of measurements – at the same time as most reviewers and “experts” mainly rely on measurements like the conventional frequency response curve."
Any tips to know if a driver is good or bad on paper?
"For a woofer I would look for the T/S parameters to make sure it fits my application in terms of cabinet volume and –principle. Check the frequency response as well to make sure it’s not impossible to work with. Other than that, of course, look for woofers with low mechanical loss."
Tony Gee:
How about mechanical resistance in loudspeaker drivers. QMS and Rms. Important or overrated?
"Very important, one of the first things I look at when choosing an appropriate woofer. It increase dynamics and low level detail. All tg-acoustics designs use drivers with extremely low mechanical resistance. For example, the large 15-inch woofer in our up-coming reference speaker has mechanical losses normaly only found in small midwoofers!"
"At Wavecor we strongly believe this is the right direction and you will usually see that Wavecor drivers have higher Qm than most. We can easily hear the difference but it’s a little frustrating that we can’t easily prove our point in terms of measurements – at the same time as most reviewers and “experts” mainly rely on measurements like the conventional frequency response curve."
Any tips to know if a driver is good or bad on paper?
"For a woofer I would look for the T/S parameters to make sure it fits my application in terms of cabinet volume and –principle. Check the frequency response as well to make sure it’s not impossible to work with. Other than that, of course, look for woofers with low mechanical loss."
Tony Gee:
How about mechanical resistance in loudspeaker drivers. QMS and Rms. Important or overrated?
"Very important, one of the first things I look at when choosing an appropriate woofer. It increase dynamics and low level detail. All tg-acoustics designs use drivers with extremely low mechanical resistance. For example, the large 15-inch woofer in our up-coming reference speaker has mechanical losses normaly only found in small midwoofers!"
Member
Joined 2004
The same low Rms sounds good view is shared by the editor of the German Diy loudspeaker magazine Hobby Hifi.
It's still not the most important parameter. But comes in handy judging drivers. I tend to "forgive" metal coned drivers for their slightly higher rms if the result is a flatter, more easy to work with freq plot.
It's still not the most important parameter. But comes in handy judging drivers. I tend to "forgive" metal coned drivers for their slightly higher rms if the result is a flatter, more easy to work with freq plot.
I agree it is not the most important parameter, perhaps even more important is the question of the cone material but this I believe has nothing to do with mechanical resistance and mechanical losses.
Either soft or hard cone woofers can be made with low Rms/high Qms
properties.
Either soft or hard cone woofers can be made with low Rms/high Qms
properties.
Member
Joined 2004
A suspension with a little bit more loss can flatten out some freq. problems in a cone. Paper, metal or ceramic. It's a small part of a bigger whole. I know.
Would be cool if some driver designers joined in this discussion. I know some about it. But barely enough to make bald statements. Or to get a full grip on these matters.
Would be cool if some driver designers joined in this discussion. I know some about it. But barely enough to make bald statements. Or to get a full grip on these matters.
Once, an engineer from a pro loudspeaker manufacturer gave me the following formula:
Rms=(2Pi x fs x Mms)/Qms
where we see a correlation between (high) Qms and (low) rms. I've mentioned this equation in another thread and some people don't find it fully convincing. See http://www.diyaudio.com/forums/multi-way/131739-low-rms-woofers-your-experience.html
and for what it's worth: Ciare has some woofers with particularly high Qms. For instance this one http://consumer.ciare.com/?altoparlanti=pw396&lang=en&output=pdf where it is 24,73 ; despite the relatively high moving mass and the not particulalrly low resonant frequency, we may get an Rms value not far from 1 (for a 15" woofer).
Rms=(2Pi x fs x Mms)/Qms
where we see a correlation between (high) Qms and (low) rms. I've mentioned this equation in another thread and some people don't find it fully convincing. See http://www.diyaudio.com/forums/multi-way/131739-low-rms-woofers-your-experience.html
and for what it's worth: Ciare has some woofers with particularly high Qms. For instance this one http://consumer.ciare.com/?altoparlanti=pw396&lang=en&output=pdf where it is 24,73 ; despite the relatively high moving mass and the not particulalrly low resonant frequency, we may get an Rms value not far from 1 (for a 15" woofer).
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The impact of Qms parameter is defined like this:
Qts=(Qms*Qes)/(Qms+Qes)
Very easy and informative is to check with a box simulator.
Any change of Qms changes Qts, so the response changes too.
Qts=(Qms*Qes)/(Qms+Qes)
Very easy and informative is to check with a box simulator.
Any change of Qms changes Qts, so the response changes too.
I would definitely take lowish qms and a flat response over high qms and resonances. There is too much emphasis on face peeling overly detailed sound nowadays.
Not one single parameter will determine how a driver will perform. High or low Qms per se doesn't mean anything.
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Qms is important if you are using a current amplifier… lower the better. Rarely seen, but Qms<1 would be nice.
dave
dave
Tang Band W8-1772 has Qms = 1.02
I played it in a Brines box with current source amp based on LM1875. Very nice!
Maybe it's a bit utopian at first glance, but i think the ideal dynamic loudspeaker driver have the following T/S parameters: Fs=0Hz, Qes=0, Qms=∞, Mms=0, SD=∞ and at the same time 0, Le=0, BL=∞, only to mention the most common parameters, but you see the tendency here.
Of course such a driver don't exist, but this will be the only driver that follows the electrical input signal properly from T/S point of view.
So the Qms needs to be infinite to get zero Rms (mechanical resistance). If the Rms is not zero, the drivers mechanical resistance changes the electrical input signal, slows the driver and converts a portion electricity into heat and the output will be not the same as the input.
The aforementioned ideal driver is not possible, but the closer we get to the parameters without the loss of other parameters, the higher the objective quality of sound reproduction is possible.
So what about Qms? I think, if we have high enough electrical damping (low enough output impedance from the amp and low enough Qes from the driver), then higher Qms is better objectively.
Of course such a driver don't exist, but this will be the only driver that follows the electrical input signal properly from T/S point of view.
So the Qms needs to be infinite to get zero Rms (mechanical resistance). If the Rms is not zero, the drivers mechanical resistance changes the electrical input signal, slows the driver and converts a portion electricity into heat and the output will be not the same as the input.
The aforementioned ideal driver is not possible, but the closer we get to the parameters without the loss of other parameters, the higher the objective quality of sound reproduction is possible.
So what about Qms? I think, if we have high enough electrical damping (low enough output impedance from the amp and low enough Qes from the driver), then higher Qms is better objectively.
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Unfortunately a bit on the coloured side — but the current amp might clean some of that out. Measured Qms=1.7. Which Brines box — i expect it adds some LF impedance bumps.
Alpair 10..3 and 12pw have (specified) Qms ~1.45
dave