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Old 17th June 2013, 02:17 AM   #8961
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Quote:
Originally Posted by DBMandrake View Post
But, mass aside, Qms is a direct measure of mechnical energy storage. A low Qms driver has lower mechanical energy storage. So his comment is still backwards. Mass alone does not dictate energy storage.
If I remember my T/S correctly - not so.

Qms is a measure of damping effectiveness. Specifically, it is a dimensionless number - crudely a ratio between energy storage (eg. sprung weight Mms) and energy loss (eg. damper setting Rms).

It tells you nothing about the ability to store energy - the only places to store energy are potential (in the spring eg. 1/Cms) and kinetic - in moving mass (Mms).

Just bumping up Mms will raise Qms. But adding Rms will reduce it.
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Old 17th June 2013, 07:04 AM   #8962
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Quote:
Originally Posted by thoglette View Post
If I remember my T/S correctly - not so.

Qms is a measure of damping effectiveness. Specifically, it is a dimensionless number - crudely a ratio between energy storage (eg. sprung weight Mms) and energy loss (eg. damper setting Rms).

It tells you nothing about the ability to store energy - the only places to store energy are potential (in the spring eg. 1/Cms) and kinetic - in moving mass (Mms).

Just bumping up Mms will raise Qms. But adding Rms will reduce it.
How does any of this contradict what I said ? I said mass alone does not dictate energy storage, as implied by Elias. You've just told me increasing mass increases energy storage while increasing Rms decreases it.

Now go and look at the T/S equation for Qms. See a connection ?
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Last edited by DBMandrake; 17th June 2013 at 07:06 AM.
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Old 17th June 2013, 08:08 AM   #8963
Elias is offline Elias  Finland
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Quote:
Originally Posted by DBMandrake View Post
How does any of this contradict what I said ? I said mass alone does not dictate energy storage, as implied by Elias. You've just told me increasing mass increases energy storage while increasing Rms decreases it.

Now go and look at the T/S equation for Qms. See a connection ?
You don't understand what "energy storage" means. The energy initially stored into a device, and the rate by which it is consumed are two different things.
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Old 17th June 2013, 01:03 PM   #8964
soongsc is offline soongsc  Taiwan
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Originally Posted by pos View Post
Some interesting comments from Joachim Gerhard that cover parts of the discussions we had here last week (high Qms/low Rms, and trend in modern drivers)

SpeakerBuilding.com - Interview with Joachim Gerhard of Audio Physic
It seems that all but the soft dome tweeters are the same way I see it.
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Old 17th June 2013, 03:52 PM   #8965
zmyrna is offline zmyrna  United Kingdom
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http://profesional.beyma.com/pdf/SM-112%20NE.pdf

Beyma SM112 is another high Qms(12.4), low Rms(1.32) 12" driver.

Very reasonably priced as well.

I would love to try this for 100-800Hz on open baffle or nude.

My only concern for OB is the size of the magnet; there is not much breathing space at the back.

So I purchased a pair of second hand Faital Pro 12PR300 neo driver instead. Will see how it works.
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Old 17th June 2013, 09:11 PM   #8966
freddi is offline freddi  United States
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just for fun, I suggest some compression driver owners who use higher xover to roll up a quick Karlson tube from a sheet of paper and some tape - make it 1" inside diameter perhaps 6" overall length, and with scissor cut an ellipse based slot ~5.5" long tapering down to around 1/8". The tube could be used pointing forwards or more typically, elevated up to as much as 30 degrees.
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Old 22nd June 2013, 08:23 AM   #8967
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I'd like to thank LineSource for this recent posting about the alignment that Jean Hiraga might be using for his 604-Duplex loudspeaker. Since Bill of GPA informs me that the GPA 604 and GPA 416 use the same cone and magnet system, whatever alignment that works for the current-production 604 should also work for the current-production 416. (Note the use of the phrase "current-production".)

I should mention that Altec, even back in the Fifties and Sixties, made unannounced production changes to the 416 and 515 that altered the Theile/Small parameters of the drivers.

This went largely unnoticed because the first Neville Theile and Richard Small papers were not published in the AES Journal until 1973, if memory serves, and published measurements of professional Altec and JBL drivers didn't start appearing until a year or so later. That's when people discovered the year-by-year production variations of the Altec and JBL drivers. (Production standards tightened up after Altec and JBL started publishing Theile/Small parameters in the product brochures, since customers could easily check the T/S parameters for themselves.)

It's a little dangerous to design around old drivers, because of magnet aging and production variations, especially in the pre-Theile/Small days. It begs the question ... which 416 or 515, made when?

I've opened up two beautiful cast-aluminum cans for Altec A5 crossovers, and discovered that the caps in each channel were not only cheapest-possible Mylar caps, but not the same vendor between the two different channels, even though the serial numbers on the two crossover cans were sequential. In other words, Altec just used the parts that were the cheapest at the time; I suspect the cast-aluminum cans actually cost more than the parts inside.

Don't be fooled by the pretty cast-aluminum cans; they add nothing to the sound (a plain wood box would be better electrically, since no eddy currents would be induced in the container) and conceal the dodgy parts inside. At least the parts weren't potted; that would be a nightmare to remove, and again, adds nothing to the sound.

The 288 and 515 drivers, of course, were beautifully made, but not as gorgeous as JBLs, which were always champs in the looks department.

It would be interesting to see Stephens Tru-Sonic revived; the old-timers I've met told me that they were the best-sounding drivers and loudspeakers of the early and mid-Fifties. My understanding is that Stephens was part of the Wente and Thuras team at ERPI in the late Thirties, and was the inventor of the multicell horn.

Last edited by Lynn Olson; 22nd June 2013 at 08:50 AM.
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Old 22nd June 2013, 12:43 PM   #8968
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How inmportant is the bass shelf that Line Source designed into his sim. I have heard opposing views about whether to go maximally flat or build to room.

BTW, Here is a sim of my drivers in a down firig box that has a lot of tunability in terms of the LF, by either varying port or stuffing. May try it with linesource's idea.
Attached Images
File Type: jpg Altec Box1.jpg (331.9 KB, 426 views)
File Type: jpg Altec Box4.jpg (291.8 KB, 406 views)
File Type: jpg Altec Box5.jpg (445.3 KB, 399 views)
File Type: jpg Altec Box6.jpg (459.8 KB, 392 views)
File Type: jpg Altec Box7.jpg (230.8 KB, 297 views)
File Type: jpg Altec Box8.jpg (235.9 KB, 19 views)
File Type: jpg Altec Box9.jpg (304.4 KB, 22 views)
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Last edited by buzzforb; 22nd June 2013 at 01:08 PM.
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Old 22nd June 2013, 07:43 PM   #8969
limono is offline limono  United States
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While I'm almost always in agreement with Lynn's writing (the parts I can comprehend) I have to say that I like mylar caps at least some of them like ERO MKT green sqares. I'm not sure the reason but when you look at gear perceived as very musical : shindo , audio note , leben you won't find PP caps only PIOs and mylars. Myself If I have choice between cheap pp cap and mylar I go for mylar . Only if I want to sell something I put shinny poly caps otherwise "morons" would not consider it Rgrds, L
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Old 22nd June 2013, 07:59 PM   #8970
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Limono,
Mylar is just a trade name for polyester film caps. Most regard a polypropylene or polystyrene as the most linear of the film types of capacitor as used in a passive crossover design. You have to also look at the construction methods used as these can be film and foil, metalized and also radial or axial construction. Mylar would be my least used in any of these applications except if I couldn't find a value or was making something that I didn't care as much about like a car stereo application.
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