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Old 7th June 2006, 06:00 AM   #11
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Default Highwood Audio

Highwood Audio designed and manufactured the Sumo "Aria" loudspeaker which is exactly what you discribed a voice coil mounted to a tensioned mylar diaphragm. This is the speaker which later became the Museatex loudspeaker (when Highwood Audio and Museatex merged). The speaker design worked very well. You need to use a very low inductance single layer voice coil as well as a copper sleeve on the motor pole piece and shorting rings at both the top and bottom of the pole piece. Aside from this you need to deal with diaphragm damping especially edge termination to effectively deal with reflections. The design can be made to work very well and present a very easy load to the amplifier. You will need a cone for the coil and if you can find some the type used for piezo tweeters are excellent (paper) I have some of these.
Quote " by using a voicecoil you raise the moving mass of the driver greatly, which defeats the main purpose of the planar/ribbon design (excellent transient response)." sorry but you are very wrong! Have you ever measured the actual mass of a maggie? You will discover it is far mor than most heavy cone speakers. The moving mass of our speaker with coil, dusy cap (cone) and tinsil leads is 2.2 grams. That's about as good as any tweeter out there. Our voice coil is a 1.25 inch custom made unit but if I were you and wanted to experiment I would go with a one inch tweeter motor assembly (very modified) and note that you will also need ferro fluid to act as a liquid bearing/spider replacement. Any attempt to use a spider will generate far too much noise otherwise. I hope that this helps you good luck and have fun. Very best regards Moray James cofounder coinventor Highwood Audio.
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Old 7th June 2006, 06:49 AM   #12
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Default Re: Highwood Audio

Quote:
Originally posted by moray james
Highwood Audio designed and manufactured the Sumo "Aria" loudspeaker which is exactly what you discribed a voice coil mounted to a tensioned mylar diaphragm. This is the speaker which later became the Museatex loudspeaker (when Highwood Audio and Museatex merged). The speaker design worked very well. You need to use a very low inductance single layer voice coil as well as a copper sleeve on the motor pole piece and shorting rings at both the top and bottom of the pole piece. Aside from this you need to deal with diaphragm damping especially edge termination to effectively deal with reflections. The design can be made to work very well and present a very easy load to the amplifier. You will need a cone for the coil and if you can find some the type used for piezo tweeters are excellent (paper) I have some of these.
Quote " by using a voicecoil you raise the moving mass of the driver greatly, which defeats the main purpose of the planar/ribbon design (excellent transient response)." sorry but you are very wrong! Have you ever measured the actual mass of a maggie? You will discover it is far mor than most heavy cone speakers. The moving mass of our speaker with coil, dusy cap (cone) and tinsil leads is 2.2 grams. That's about as good as any tweeter out there. Our voice coil is a 1.25 inch custom made unit but if I were you and wanted to experiment I would go with a one inch tweeter motor assembly (very modified) and note that you will also need ferro fluid to act as a liquid bearing/spider replacement. Any attempt to use a spider will generate far too much noise otherwise. I hope that this helps you good luck and have fun. Very best regards Moray James cofounder coinventor Highwood Audio.
Mind explaining that to me in more simple terms?

(Where'd I put my copy of "Advanced audio terminolgy for dummies..)

It sounds to me like you're thinking of using a standard motor, with a metal insert that goes through the coil's center.

I was actually thinking more along the lines of simply using a magnet on each side, with nothing at all through the center of the coil. Although the magnets would need to be extremely powerful, you would'nt really need any bearings or supports; the coil would be held in place by the mylar. (Or were you suggesting something else?)

I'm also not opposed to using a high-powered tweeter (which would normally be unable to reproduce bass due to size) connected to the panel through a pushrod. Not elegant or fancy, but it would give acceptable performance, especially with a pull-pull system. (Just put one tweeter on each side, and have a piece of wire going between the cones. Attach the film to the center of the bit of wire.)


Thanks for the help-I think I'll try my hand at a pair of these as soon as I'm able.
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Old 7th June 2006, 04:13 PM   #13
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Default Start here

Go to your library and get a copy of an article that I wrote on this design some years back. That should get you up and running. Ask for "Audio" June 1992 the article was titled "A New Type of Speaker, A Shere of Sound".
Quote - I was actually thinking more along the lines of simply using a magnet on each side, with nothing at all through the center of the coil. Although the magnets would need to be extremely powerful, you would'nt really need any bearings or supports; the coil would be held in place by the mylar.
This idea will not generate anywhere near enough force on the diaphragm. At the point in time the above article was published the business had been working on this design for almost four years. Voice coil stability in a design like this is critical and yes you will need to use ferofluid in the coil gap to keep the coil from rocking under large pulses and very loud playback. Check the patents under Babb as these are expired and they would offer excellent voice coil control. We would have liked to use this idea at the time but it was protected. We took out a US patent around 88-89 but I have forgotten the number but you could check under the company name of Highwood Audio.
I wonder if you had considered building an electrostatic loudspeaker? That project would prove a lot easier than the road you are going down now and a lot less expensive. Just a thought. Good luck Moray James.
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Old 7th June 2006, 05:45 PM   #14
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Default Re: Start here

Quote:
Originally posted by moray james
Go to your library and get a copy of an article that I wrote on this design some years back. That should get you up and running. Ask for "Audio" June 1992 the article was titled "A New Type of Speaker, A Shere of Sound".
Quote - I was actually thinking more along the lines of simply using a magnet on each side, with nothing at all through the center of the coil. Although the magnets would need to be extremely powerful, you would'nt really need any bearings or supports; the coil would be held in place by the mylar.
This idea will not generate anywhere near enough force on the diaphragm. At the point in time the above article was published the business had been working on this design for almost four years. Voice coil stability in a design like this is critical and yes you will need to use ferofluid in the coil gap to keep the coil from rocking under large pulses and very loud playback. Check the patents under Babb as these are expired and they would offer excellent voice coil control. We would have liked to use this idea at the time but it was protected. We took out a US patent around 88-89 but I have forgotten the number but you could check under the company name of Highwood Audio.
I wonder if you had considered building an electrostatic loudspeaker? That project would prove a lot easier than the road you are going down now and a lot less expensive. Just a thought. Good luck Moray James.
Why exactly is ferrofluid needed around the voice coil, as opposed to some other damping material?

I'm not building an ESL for a good reason: They're expensive, fragile, and use very high voltages.
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Old 7th June 2006, 08:54 PM   #15
dnsey is offline dnsey  United Kingdom
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Many years ago I owned a pair of Planax 3 speakers, made by (or more likely for) Goodmans.
They used an expanded polystyrene diaphragm about 30 X 20 X 1 inches, flat at the front and moulded at the rear into LF and HF areas. Each area had its own motor, of a conventional design, and the entire diaphragm was mounted in a hardwood 'frame', resulting in a dipole transducer.
They didn't sound too bad - the bass was a bit flabby, and the treble rolled off quite early, but the basic design seemed sound and capable of further development.
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Old 7th June 2006, 09:02 PM   #16
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Default It's like this

if you build a driver like the Sumo Aria which was a 1.25 inch dia voice ciol mounted directly to a mylar diaphragm and then drop that into a motor assembly then the diaphragm will act like a huge top suspension to hold the coil in place. There is how ever nothing to act as a bottom suspension to prevent rocking and that is what the ferro fluid does for you. Any kind of conventional spider will generate output of its own which will sing straight through the mylar diaphragm so that is a non starter. I mentioned the Babb patent to you as it is out of date now. Babb designed vertical teflon ribs into the pole piece to act as a bushing so the coil cannot rock how ever ferro fluid would still be beneficial to reduce friction and improve thermal dissapation. Your motor top plate will need to be 3/8 inch thick or better to obtain wide band width with level. Type five neo magnets will help shrink the motor size, we used type seven ceramic as neo's were not commercially available at the time at competitive prices.
Quote:
"I'm not building an ESL for a good reason: They're expensive, fragile, and use very high voltages".
Since you have no experience in building the kind of motor structure that I am discribing and since I have built both this design as well as ESL's I will tell you again that an ESL project (one off basis) will cost you less that this project will. We spent just under two million dollars in the first year and a half getting ready for production of the "Aria" which was distributed by Sumo of California. An ESL is far les exensive to build especially if you purchase a set of say used Acoustats to use the interface and high voltage supply. I will also strongly dissagree with you that ESL's are "fragile" this is absolutely wrong. Jim Strickland of Acoustat boasted that they never had a single field failure of a panel in all the years of production. Failures were due to physical damage to the panels or connecting wires or missuse of the interfaces. Yes ESL's use high voltages but they are confined to the interface box and for all intent and purposes are a non issue. Last night I auditioned a new cable design (my own) on a set of 20 plus year old Acoustats. The panels are dead stock while the interfaces have been modified for improved performance. These speakers (0ne plus 0nes) sound spectacular. At the time that I developed the Highwood Audio speaker my reference was a set of similar Acoustats. Combined with a set of good super tweeters and stereo subs these speakers can give anything you like a serious run for thier money and better most.
So if you want to build a magnetic planar like the Highwood speaker you should at least know that you will have to design and build the motor structure prototypes all from the ground up as there is no cmmercial driver designed like what you will need. No off the shelf parts are going to get you where you need to go. You will need to design and build a very strong frame to hold the motor (magnet assembly) in place with perfect alignment. You will need to have precission machined jigs to both align and punch the voice coil hole in the diaphragm as well as similar jigs to align and mount the voice coil to the diaphragm. If you honestly believe that a project like this will be less expensive than a home brew ESL then you have never done either and I am sorry again to say that you are mistaken. I would be very happy to see you go the planar route as it is a good design and can work very well. You should know that it is really more like a tweeter with the worlds biggest suspension than a planar magnetic like a maggie. Because this speaker generates spherical wave fronts off the diaphragm (a mechanical version of the Quad 63) you will have to deal with both side wall reflections as well as floor and ceiling bounce so they need to be well away reflective surfaces as they are so non directional. This is a problem which does not exist with a line source ESL design. If you are truly interested in this project pull the Highwood Audio and the Babb patents and get familiar with what has been done and was successful (Highwood died due to business reasons not a bad design). I would be happy to share my experience on such a project. If however this is simply an arm chair design excercise I think that I have contributed about as much as is useful. Good luck and please post your progress on the speaker. Best regards Moray James.
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Old 7th June 2006, 11:36 PM   #17
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Moray,

I am confused by some things you posted in this thread.

How is there any difference between the mass of a "maggie" style speaker and one where the same diaphragm is driven from a single, or even multiple "standard" voice coils??

Are you saying that the differential in mass is the applied conductors' mass?

Then what about the single point drive to a mylar diaphragm acting like a point source with a very very unstiff and very large suspension - ie. like a jump rope being waved??

The first "planar" run with voice coils that I recall was (iirc!) the Beostatic?? Or something like that out of Italy I think. Expanded Styrene diaphragm...

The original Magneplanars did use wire attached to the mylar with adhesive. They looked like a paper run through a shredder, if you put too much power in or had a parasitic oscillation! Heat + mylar = electric knife.

I agree with Moray, building an ESL is a really good way to go to build a planar speaker with excellent results for not too much money. The "high voltage" is high, but is very very low current when done properly. Modest care is required. Less than with the typical tube amplifier.

There are numerous threads in the archives here on building magnetic planars and real ribbons of various sizes and shapes...

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Old 8th June 2006, 12:17 AM   #18
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Default Hey Bear

As I said the Sumo "Aria" had a diaphragm of 150 gage mylar driven by a single point source voice coil. The entire miving mass not countint the diaphragm was 2.2 grams. In a maggie you are driving all the wire of the heavy voice coil (intentional mass especially in the bass section to lower the diaphragm resonant point) as well as all the adhesive. Maggies are for the most part fairly high mass drivers when you measure the mass per unit area that is actively being driven. It is like comparrring the mass of a large heavy woofer to that of a tweeter assembly the difference is huge.

Quote: Then what about the single point drive to a mylar diaphragm acting like a point source with a very very unstiff and very large suspension - ie. like a jump rope being waved?? Not sure that I understand what you are getting at here? The diaphragm in a driver like this has to be tight to give you efficiency. The speaker that you are referring to is probably the Bertangi (sp) which was a styrene moulded diaphragm. That diaphragm was ment to be still and rigid. Manger had to actually put off patent application as Highwood Audio had allready received a patent in the USA on a traveling wave speaker. My speaker was intnded to have waves travel across the face of the diaphragm (like the ripple in a pond effect). The traveling wave combined with the initial central pulse generater spherical wave fronts launched off of a flat diaphragm.
I hope that spasticteapot gives this design a go but I felt that he needed a heads up as to what would be involved. A handy diyer with a home machine shop could do the job. Regards Moray James.
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Old 9th June 2006, 03:08 AM   #19
Nanook is offline Nanook  Canada
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Default maybe all on this thread...

should realize that Moray designed the Aria loudspeaker (If my poor old neurons are firing across my equally aging synaptic gap correctly). And yes, doing some reading prior to throwing out the idea may help.

As far as the development of the loudspeaker goes, believe me, Moray would be the one to ask. If he suggests that ferroid fluid is needed, he knows.

and recall Sony's attempt, the apm series several years ago.
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Old 9th June 2006, 04:44 PM   #20
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Quote:
Originally posted by Spasticteapot
Hmm...interesting.


Also, could someone explain how the "personal planars" speakers work? I can't figure it out.

I wish I was'nt going on a !#$!$!@#$ vacation in three days.

Looks as if they worked by inflation. I ask myself why they don`t use compression drivers.

Does anybody know something about this planar?
http://www.sonus.de/php/p_produkte.php?produkt_id=347
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