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Multi-Way Conventional loudspeakers with crossovers

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Old 19th March 2008, 02:49 PM   #3221
JoshK is offline JoshK  Canada
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Dr. Geddes,

Could you comment on whether there were errors from the perspective of the Webster style theory? What I mean is if one didn't use your more modern approach to horn theory, and only viewed it from the older more basic approach is the information still riddled with errors? (kind like from the perspective of newtonian mechanics versus modern physics)

I have never read any thing on this subject before, so I found it enlightening. Especially since some of the math was hinted at (I took a few PDE courses in school). I would find it useful to understand what aspect of it you find flawed generally.
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Old 19th March 2008, 03:08 PM   #3222
gedlee is offline gedlee  United States
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Quote:
Originally posted by JoshK
Dr. Geddes,

Could you comment on whether there were errors from the perspective of the Webster style theory? What I mean is if one didn't use your more modern approach to horn theory, and only viewed it from the older more basic approach is the information still riddled with errors? (kind like from the perspective of newtonian mechanics versus modern physics)

I have never read any thing on this subject before, so I found it enlightening. Especially since some of the math was hinted at (I took a few PDE courses in school). I would find it useful to understand what aspect of it you find flawed generally.
I just finished my rebuttal paper for AudioXPress and maybe I'll post it on my web site after I send it out (in case its too inflamatory and they won't print it).

The Newtonian analogy is not appropriate. Newtonian Physics is completely accurate for our everyday real world experinces. Websters equation is not. It is not accurate in 90% of the cases where it is applied.

The paper is accurate in that it accurately reflects the thinking at the time, as erronious as it was. But then when he gets to my work the errors are quite distinct and do not correctly reflect my theories or others works coincident with mine.

Hope this helps till my more complete discussion is available.
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Old 20th March 2008, 02:36 AM   #3223
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Quote:
Originally posted by Lynn Olson
OK, enough metaphysics for now. Hey, Magnetar, what was your quick impression of each of the compression drivers you tried? You must have listened to each for at least a few minutes, what did you think - or maybe feel - about each one? Not so much a good, better, best thing, but more of an overall impression of the sonic character of each "flavor".
Sorry but this is a loaded question. It is impossible to correctly answer because there are just too many variables. Many, many, variables ranging from the horn, to the mating of the lower range driver, to what I ate for breakfast to the room, to the crossover, to the amplifier, to the piece of music to......
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Old 20th March 2008, 09:45 PM   #3224
gedlee is offline gedlee  United States
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Quote:
Originally posted by JoshK
Dr. Geddes,

Could you comment on whether there were errors from the perspective of the Webster style theory? What I mean is if one didn't use your more modern approach to horn theory, and only viewed it from the older more basic approach is the information still riddled with errors? (kind like from the perspective of newtonian mechanics versus modern physics)

I have never read any thing on this subject before, so I found it enlightening. Especially since some of the math was hinted at (I took a few PDE courses in school). I would find it useful to understand what aspect of it you find flawed generally.
I have posted my response on my web site www.gedlee.com check it out. Its too big to attach here.
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Old 23rd March 2008, 01:15 AM   #3225
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Dr. Geddes, you've written an very interesting and illuminating letter to Ed Dell. I have no idea if it will be reprinted in AudioXpress magazine, but I am deeply appreciative we can read it for ourselves on your website.

I always like to read a good patent - your Phase Plug with Optimized Shapes, Patent #7095868 is a good read, along with the referenced 1936 classic by Wente (Patent #2037817), and Henricksen's 1977 "Tangerine" variant (Patent #4050541).

I fully agree that diffraction and internal reflection is the primary problem in traditional, Webster-theory horns, and impulse measurements with substantial amounts of stored energy confirm that - and very likely the reason that impulse measurements are rarely seen in the horn literature, while they are much more commonly seen with direct-radiators, going back to the mid-1970's.

It is significant that 1950's-era Altec and JBL high-efficiency loudspeakers have complex, diffraction-inducing acoustical paths - phase-plugs exits with a 50% reflective metal-mesh bug screen a short distance away, a mismatch between the flare rate at the exit of the compression driver and the entrance to the throat of the horn, and in the more notorious JBL designs, another diffraction grating at the mouth of the horn, in the form of an "acoustic lens". Two decades later, more diffraction in the Altec Manta-Ray and JBL Bi-Radial horns for theater and studio-monitor use.

Plainly enough, time-domain performance was not a design consideration, with such a casual approach to intentional induction of diffraction. The attitude in professional designs circles seems to have been that any problem can be equalized away, and if the time domain is further degraded, it doesn't really matter all that much. This is the part of the prosound legacy that needs to be discarded.
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Old 23rd March 2008, 05:57 AM   #3226
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Near the bottom of page 4 of his letter to Audio Express, Dr. Geddes states that a spherical cap that vibrates radially does not exist.

Would not the Murata 80mm piezo-electric midrange dome qualify? It operates from 350 Hz up to around 15 kHz in this design:
http://www.murata.com/speaker/es024.html

The "super tweeter" by Murata, which has a bandwidth extending to 100 kHz on axis, has what is described as a "breathing" motion on its surface. This is their attempt to describe a radial vibration, I think.

quote from their information page: "... Another unique feature of the ES103 diaphragm is its unusual vibration mode. With conventional speakers, the diaphragm generates a front-back piston vibration. But the semispherical ceramic diaphragm in the ES103 expands and contracts like a balloon--a "breathing" vibration mode that actually realizes the point-type tone generation ideal for a speaker. This unique vibration mode offers wide directionality, enabling ideal listening from a wide range of positions. ...."
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Old 23rd March 2008, 02:09 PM   #3227
gedlee is offline gedlee  United States
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Quote:
Originally posted by Russell Dawkins
Near the bottom of page 4 of his letter to Audio Express, Dr. Geddes states that a spherical cap that vibrates radially does not exist.

Would not the Murata 80mm piezo-electric midrange dome qualify? It operates from 350 Hz up to around 15 kHz in this design:
http://www.murata.com/speaker/es024.html

The "super tweeter" by Murata, which has a bandwidth extending to 100 kHz on axis, has what is described as a "breathing" motion on its surface. This is their attempt to describe a radial vibration, I think.

quote from their information page: "... Another unique feature of the ES103 diaphragm is its unusual vibration mode. With conventional speakers, the diaphragm generates a front-back piston vibration. But the semispherical ceramic diaphragm in the ES103 expands and contracts like a balloon--a "breathing" vibration mode that actually realizes the point-type tone generation ideal for a speaker. This unique vibration mode offers wide directionality, enabling ideal listening from a wide range of positions. ...."
As I said, in theory such a thing is possible and indeed this MAY be one. But it would have to be measured to see just how accurate it is at pure radial motion. Piezo is generally a very low displacment process which works well in high impedance medium like water, but not very well in air. So, yes, there is a candidate, but surely an unproven one in terms of cost and performance effectivness.

And then there is the point that the spherical cap must subtend the same angle as the waveguide. The one shown would only work in a flat baffle (a 180 waveguide), not a waveguide of some finite angle. So in reality, a real "waveguide" source still does not exist - but certainly could be made. But piezo-electric is just not a very good material for an audio loudspeaker.
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Old 23rd March 2008, 02:16 PM   #3228
gedlee is offline gedlee  United States
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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.
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Old 23rd March 2008, 06:36 PM   #3229
Killjoy is offline Killjoy  United States
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Default high excursion musical instrument driver

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.
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Old 23rd March 2008, 06:40 PM   #3230
SunRa is offline SunRa  Romania
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Quote:
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.
I think the efficiency might be too low for this project, although I didn't seend the complete datasheet...
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