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Old 23rd March 2008, 07:01 PM   #3231
gedlee is offline gedlee  United States
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Default Re: high excursion musical instrument driver

Quote:
Originally posted by Killjoy
I've been lurking on this site for a while just trying to get caught up. There is a lot of good information. But when I saw the BOM 12 I just had to chime in.

This site has an interesting musical instrument driver using Dan Wiggin's XBL2 motor tech. Perhaps it may be worth considering for the OB that Lynn is designing.

http://www.acousticdev.com/html/products__adi.html

It has over 16mm of linear stroke. Might this work? If so it would require a group buy since they tend to want to sell to OEMs.
The flat diaphragm is ideal for use on a waveguide - the first test that I did used a flat diaphragm driver.

But I am not a fan of XBL2 and excursion is seldom an issue in waveguides. I have my doubts about 16 mm in a driver that size, but thats simply a waste of BL when one will only use a few mm. Is such a driver available with normal voice coil drives?
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Old 23rd March 2008, 07:04 PM   #3232
KSTR is offline KSTR  Germany
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Quote:
Originally posted by gedlee
And Lynn thanks for your kind words. Its nice to know that people actually read and appreciate what one does. In other forums I would have been crucified for what I say in that letter.
Dr. Geddes, this isn't just a letter, it's the most logical and most understandable (little math involved ;-) introductory yet profound text on what a horn essentially does or should do today, that I've ever come across, really eye-opening. Big thanks for this!

- Klaus
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Old 23rd March 2008, 07:34 PM   #3233
gedlee is offline gedlee  United States
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Quote:
Originally posted by KSTR
Dr. Geddes, this isn't just a letter, it's the most logical and most understandable (little math involved ;-) introductory yet profound text on what a horn essentially does or should do today, that I've ever come across, really eye-opening. Big thanks for this!

- Klaus
Thanks kindly.
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Old 23rd March 2008, 08:05 PM   #3234
jzagaja is offline jzagaja  Poland
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Quote:
The flat diaphragm is ideal for use on a waveguide - the first test that I did used a flat diaphragm driver.
Excluding ribbon driver?
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Old 23rd March 2008, 08:55 PM   #3235
JoshK is offline JoshK  Canada
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I hope that AudioXpress does publish the letter as I too found it enlightening. It was easy to read and gave you a big picture view on the subject and the comparison between horn theory and waveguide theory.
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Old 23rd March 2008, 10:17 PM   #3236
Killjoy is offline Killjoy  United States
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Default Re: Re: high excursion musical instrument driver

Quote:
Originally posted by gedlee


The flat diaphragm is ideal for use on a waveguide - the first test that I did used a flat diaphragm driver.

But I am not a fan of XBL2 and excursion is seldom an issue in waveguides. I have my doubts about 16 mm in a driver that size, but thats simply a waste of BL when one will only use a few mm. Is such a driver available with normal voice coil drives?

Hello Gedlee,

Can you add some more thought to why you are not a fan of XBL2?

Also can you comment on why there aren't any large compression drivers used in waveguides. I'm talking about a 12" driver using a 2 or 3:1 compression and run through a waveguide to reproduce low frequencies--kind of along the lines patent--US5537481.


BTW, were you referring to the BOM 12 (musical instrument driver) or the LAW subwoofer with the flat diaphragm? I noticed the BOM 12 has a 4 inch voicecoil (assumed to be a single voicecoil).
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Old 23rd March 2008, 10:24 PM   #3237
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Hello Earl,

I just read you response to the A-ex article. Well written, but if I may I would make one suggestion that may improve the odds of publication. I found the opening paragraph somewhat confrontational. Having served as a reviewer for technical journals in the past, I might suggest that you "depersonalize" the opening some what. "Having spent the better part of my life studying these devices I was anxious to learn how they worked." in particular seems a rather sarcastic way to open the discussion.
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Old 24th March 2008, 12:07 AM   #3238
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John Atwood has been kind enough to pass along the first constant-directivity horn paper, written by Abraham B. Cohen of University Sound in 1952.

The primitive nature of horn theory in the 1950's is all too evident - but remember, modern crossover filters using Butterworth functions and the first paper by Neville Theile (in Australia) was still more than a decade away when this was written.

I find the Lansing and Hilliard 1945 Theatre Speaker article more inspiring. The 515 and 288 drivers became the foundation of movie theatre sound for more than 30 years, and were used in more than 12,000 theatres across the world. Most notably, the 70mm Technicolor widescreen moves of the 1950's and 1960's used three fully discrete mag-track Altec A2 and A4 systems behind the giant curved screens.

The 515, 416, and 414 midbass drivers all use underhung voice coils, which resulted in notable midrange linearity due to well-controlled magnetic geometry in the gap. (It is much harder to control the linearity of the field lines with the more common overhung voice coil structure. Voice-coil cooling is less efficient as well, since the portion of the VC outside the gap is not in close proximity to the much cooler magnet, which acts as a heat sink for the voice coil.)

The 288 compression driver replaced the corrugated surround of the 283 Shearer-horn compression driver with tangential suspension, resulting in substantially lower distortion in the midrange. The 515 and 288 drivers represent good solid engineering that still has merit today - indeed, the titanium diaphragms and the JBL diamond surrounds used in modern theaters are arguably a step backward, with resonances starting at lower frequencies (4 kHz instead of 7 kHz), and far more aggressive use of HF boost equalization in the region where the driver is breaking up.

(The optical sound tracks of 1945-era movies rolled off above 8 kHz, thus not requiring the 10+ dB of boost EQ mandated by the modern THX specification. I strongly disagree with the idea of boosting power to a driver in breakup mode - that's what supertweeters are for.)
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Old 24th March 2008, 01:10 AM   #3239
gedlee is offline gedlee  United States
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Quote:
Originally posted by john k...
Hello Earl,

I just read you response to the A-ex article. Well written, but if I may I would make one suggestion that may improve the odds of publication. I found the opening paragraph somewhat confrontational. Having served as a reviewer for technical journals in the past, I might suggest that you "depersonalize" the opening some what. "Having spent the better part of my life studying these devices I was anxious to learn how they worked." in particular seems a rather sarcastic way to open the discussion.

John - off all of the lines in that paper, that was the one that I was most concerned with. I can't help but to try and have some fun when writtng those kind of things (they can be so dry) but I didn't mean this personally. I will strongly consider your point, but this is not a professional journal by any sense, so I might be more liberal with the attempted humor. (So you weren't offended by "evolution"? I'm surprised that slipped through.) As I told one editor I intended the tone to be "a bit sarcastic, but polite". I really do think my work was seriously short changed in that paper. Sarchasm has no place in a professional paper, but this was not intended to be a professional paper.
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Old 24th March 2008, 03:37 AM   #3240
gedlee is offline gedlee  United States
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Default Re: Re: Re: high excursion musical instrument driver

Quote:
Originally posted by Killjoy
Can you add some more thought to why you are not a fan of XBL2?

Also can you comment on why there aren't any large compression drivers used in waveguides.


I don't believe that cone excusion is anything more than a marketing scam. Its not a big factor to me, except in maybe a sub and even then my deisgns are not that sensitive to nonlinearity. The XBL2 seems to me to be simply a lot of add mass with no real net benefit.

Large drivers have very limited HF usage and as I said in my paper, I don't see the advantage of a horn for low frequencies. So there doesn't appear to me to be any advantage to a large diaphragm.
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