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Old 10th June 2006, 03:29 PM   #21
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Moray,

I'm not sold/convinced on this "traveling wave" idea in terms of planar speakers.

The Quad concept is a "traveling wave" , but there is only a singleton wave (in principle) which exists, since the diaphragm is energized sequentially with respect to the speed of sound vs distance from the center of the diaphragm (at least that is the idea). Thus emulating as spherical source.

In the system you have just described one gets the "jump rope" standing wave effect, as far as I can see. One gets in phase and out of phase radiation from the diaphragm as the wave travels across the surface, or so it would seem.

Even if you argue that a non-repeating excitation will create a singleton, clearly a sine wave input of some frequency will create a standing wave on the surface, yes?

And, the amplitude of the wave will diminish with time/distance from the center in general. (standing waves being a possible exception)

Just curious,

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Old 10th June 2006, 06:30 PM   #22
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Default think of it this way....

say you are standing behind a large diaphragm and just for now lets assume that there will be no edge termination reflections. If you poke the compliant diaphragm with your finger in the centre (which would be what a pulse with the voice coil does) you will create a forward traveling (in the air) pulse of air on the front side of the diaphragm. The instant your finger is removed the pulse also starts to travel outward in all directions across the diaphragm (like the ripple in the water). The leading edge of that circular (and expanding) wave is pushing air outward from the trailing edge of the central pulse you just generated with your finger. The two seperate wave fronts (one in the air going forward on the central axis and the other in the diaphragm traveling across the plane of the diaphragm) are moving at about the same speed. The combined result of these two actions generates a half spherical wave to expand on the front side of the diaphragm.
Another way to imagine this would be to think of blowing a bubble with a wire hoop that is expandable in size (from small diameter to large) as you blow. The soap film is your diaphragm and your breath is the inital pulse while the expansion in size of the hoop (and then so your bubble) is the wave traveling across the diaphragm. You end up with a great big bubble the size of which is determined by the size of your hoop (or the speaker frame). If you increase the size of the hoop at the exact same speed as the forward traveling pulse you will end up with a spherical bubble. If you expand the hoop size too slowly you end up blowing a hotdog shaped bubble and iif you expand the hoop size to quickly you end up with a flattened out buble.
You may not believe that this works but I can assure you that it does. We had our Highwood Audio speakers measured extensively at the acoustic lab department at the university of Alberta and by the JBL labs in LA and on our own system. We were able to take a 1/4 inch B&K microphone and place it at the outside edge of the speaker (at 90 degrees) and measure 10 K responce try that with an electrostatic panel and see what you measure (we did)!
A lot of hoop jumping has to be done with the diaphragm material and with its tension, diaphragm damping and especially with the edge termination damping to make this all happen and work well but it can be done. I used to like to think of this as a horn loaded speaker with no horn. The diaphragm can be made to act like a wave guide to expand the initial pulse much as a wave guide (horn) does. I hope that this helps some. Best regards Moray James.
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Old 11th June 2006, 01:52 AM   #23
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Forgive me if I'm wrong, I know you've put much work into this.

Quote:
Originally posted by moray james
The two seperate wave fronts (one in the air going forward on the central axis and the other in the diaphragm traveling across the plane of the diaphragm) are moving at about the same speed. The combined result of these two actions generates a half spherical wave to expand on the front side of the diaphragm.
If I think about this in terms of the forward moving waves, I feel as if the result of this linear forward component and a linear lateral component will produce a conical wavefront.

Quote:
Another way to imagine this would be to think of blowing a bubble with a wire hoop that is expandable in size (from small diameter to large) as you blow.
Wouldn't the bubble start as a point (cone) and distort to produce a dome shape due to the air trapped behind it, not at all like a wavefront? I suppose I just feel that there could be a better angle for analogy.
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Old 11th June 2006, 05:37 AM   #24
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Default too sick to think straight

Yes I did say spherical and in truth it is only half of a sphere. Perhaps my discription is poor but the initial pulse of air disturbed in front of the voice coil is essentially the diameter of the voice coil there is a slight amount of tenting happening due to the diaphragm but not much. For arguement sake the forward wave is only as wide as the coil. The rollong action of the wave expanding in the plane of the diaphragm (at approx the same speed as the wave launched into the air) expands the back trailing edge of the forward moving wave and so over time develops a half sphere. As I said polar plots confirm the dispersion. Sorry if my choice of terms may not be the most acurate but I have a flue like infection and don't feel too swift. I don't have technical training in this area so I may not be correct in the use of my terms but I think that you get the drift. All the best Moray James.
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Old 16th June 2006, 03:11 PM   #25
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Moray,

I will take your representation that you measured some 10kHz response at 90 degrees... not sure that is all good or not... but does indicate that the idea works to some extent.

My concern is the anti-phase wave that is created.

I think that you are claiming a "singleton" - that is a wave that is singular, only positive? Sort of like 1/2 of a sine wave, no negative going portion.

In the case of your traveling wave on the surface, it is being "followed" across the surface by an image, negative wave, (of nearly equal amplitude) which is merely delayed in time compared to the initial positive wave. So, I am suggesting that there would be some cancellation taking place at any point in time beyond the initial stimulus??

Then too there is the question of the speed of sound in the diaphragm material playing a role in the shape of the wavefront.

And, I would think that the system is somewhat frequency limited/dependant upon the stiffness of the diaphragm material/ diameter of the VC?? The area of initial "excitation" will determine the volume of air that can be moved, so intuitively a 1/2" VC drive might make a fine tweeter, but doesn't seem terribly useful at lower frequencies since the excursion is limited??

Not sure how this idea translates into a practical speaker with useable sensitivity/efficiency?

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Old 8th January 2007, 10:00 AM   #26
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That was done by the same guy that orig. brought us all the Heil tweeter (in the 70s); see his (old) web site @ http://americanpowerlight.com/lt7/lt-7.html
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Old 8th January 2007, 08:40 PM   #27
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Default No not the same thing...

The heil unit is a piston. My design is with a stretched planar diaphragm upon which concentric traveling waves move. You could think of it as a mechanical version of the Quad 63 concept. Regards Moray James.
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Old 8th January 2007, 10:05 PM   #28
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I would not refer to the Heil driver as a piston (the diaphragm is squeezed on edge; but the planar drivers in the American Power & Light LT7 are stiff/square/carbon-fiber pistons (w/foam sur.). American Power & Light is working on a new variation on the Heil driver.

My post was an attempt to reply to the thread starter (but I couldn't find the quote box).

Is there a we site to promote this new speaker w/concentric traveling waves?

regards,
DK
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Old 9th January 2007, 08:06 PM   #29
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Default I was not clear...

I was referring to the LT7 whic is a piston driver (I had assumed that it was a Heil design and so the reference by name rather than a specific design. I have a Us Patent on the design that I mentioned but will have to look it up for you. The design was manufactured in Canada by my old company Highwood Audio and soold under the Sumo brand name then later Highwood merged (bought) Museatex and distributed under the Museatex "Melior" name. Hope this helps. Regards Moray James.
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Old 9th February 2007, 02:13 PM   #30
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Default Highwood patent details

For those of you following this thread who may want to take a look at the patent, you can view it online at esp@cenet:

The best document is the European application, EP0296139, as it has all the drawings (called "Mosaics" by esp@cenet). The direct link below might work, otherwise you will have to do a number search:

http://v3.espacenet.com/textdoc?DB=E...=EP0296139&F=0

There may have been other IP generated after I left Highwood (I don't know), but this is the original patent.

A strange thing is that this patent actually contains two inventions: A line source and a point source. This is not allowed under international patent law (as I have since learned), but the patent examiners never noticed. Had they done so, they would have required the filing of "divisionals" and there would have been two patents. Had it ever been wheeled into court it would probably have been judged prima facie invalid on this basis.

The line source was never commercialised because it was too inefficient and didn't have enough bandwidth. In other words, it didn't really work... The existence of a patent is no guarrantee that the invention is workable, or useful.

The Sumo Arias were reviewed in Absolute Sounds (Vol. 62, I think) and there was a good explanatory article in Hi Fi News, although unfortunately I have lost my copy, so I can't give the issue number. Anybody got a back collection who could look it up, sometime in the late 80s?

There is also a description in Martin Colloms' book "High Performance Loudspeakers", including the new edition, right next to the section on Manger.

Moray is quite right, the speakers did work well (eventually, after the liberal application of $$$), and produced a flat response from 40Hz to 20kHz, with constant wide directivity. They did this without any form of equalisation or crossover.

He is also correct that they were very hard to get right, and proved James B. Lancing's (JBL) adage that "Loudspeakers are 90% glue" to a greater extent than anything else I've worked on before or since. Not for the fainthearted or shallow of pocket...

So, I'd second Moray: Electrostats have to be a much easier route to high performance home made di-poles.

Bear: As Moray says, travelling wave radiators do work. They are a true low mass "coherent" source, behaving as a virtual point source located behind the panel. You might like to contrast them with their conceptual opposite, the quasi-random Distributed Mode Loudspeaker (DML), which is an "incoherent" defuse sound source. (see the technical white paper at NXTsound.com for an introduction).

The point source is an acoustic radiator who's behaviour is easy to analyse and model, but is damn near impossible to build. On the other hand, a DML is nearly impossible to analyze and model (the maths is extremely complex), but once you have managed to do so, it is really easy to build one.

...And now there's the Balanced Mode Radiator (BMR), courtesy of Dr Graham Bank of Celestion SL600 fame. That's what this forum should be concentrating on, never mind the Heils, Mangers and Arias of 20 years ago. Much more interesting.

BMR patent: WO2005101899.

There is a recording of Dr Bank giving an AES lecture on BMR here:

http://www.aes.org/sections/uk/meetings/a0701.html

He makes it sound so obvious... But it isn't. It's very, very clever stuff. It should by rights transform the industry. But I wonder if it will? Ten years ago, we all thought NXT was going to do that, and look what happened.

Regards,
Paul
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