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Electrostatic design - is a round design practical?
Electrostatic design - is a round design practical?
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Old 26th May 2004, 05:02 AM   #11
Pete Fleming is offline Pete Fleming  Australia
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As far as a “pulsating sphere” design is concerned, have a look that the MBL Radialstrahler 101 E. To explain the design, imagine an orange or mandarin with its segments. Now imagine peeling just the surface of those segments and arranging them back so they reform the surface of the orange. What you then have is a hollow sphere made up of the segments. The top of the segments are attached to a rod so they can’t move, a bit like a core going through the centre of the sphere. The bottom of the segments are attached to the voice coil of a relatively standard driver. In operation, as the voice coil moves out the segments flex out, and as it moves back in tension is applied to the segments and they contract in. Hope that all makes sense. MBL use different size drivers for the different ranges of frequencies as usual.

I have heard the MBL 101 and can honestly say it is THE most impressive system I have ever heard. I know it’s a cliché but it truly is quite unlike anything I’ve heard before. It doesn’t have the absolute resolution of an electrostatic for example, but for sheer “I am there” factor this was it.

I would be most impressed if somebody had a go at replicating this driver, I can assure you that if it comes within ten percent of the MBL systems I’ve heard you’ll consider it time well spent. For info the “segments” of the Radialstrahler look like some type of metal however I would imaging any type of material capable of consistent flexing could be used.

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Old 26th May 2004, 06:04 AM   #12
fr0st is offline fr0st
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I wonder - since it's not a stretch for anyone's imagination, who have pictured a "pulsating sphere" - why not mount a large driver, say, a 12" fullrange type driver inside a bandpass-like enclosure, so it's front-of-cone energy were directed through a tube... to the top of the tube, a balloon like orb.
I reckon you could actually use a ballon. I was gonna post the idea but i re read the thread and you already mentioned it. You just have to find a way to enclose a constant volume of air between the speaker and balloon.
I think using an ESL would be near impossible, If you managed to get two half spheres of perferated metalyou still have to tension a constantly curved membrane.
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Old 26th May 2004, 08:41 AM   #13
Alidore is offline Alidore
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Default 360 degree radiation

In a conversation with Roger West of SoundLab, he told me that in experimenting with full-range electrostats he'd tried many different radiation patterns including 360 degrees, but that the 90 degree arc (front and back) sounded the best. So I'm not sure that a full-range 360 degree electrostat would be the best application of that technology.

I believe that RTR made a faceted round electrostatic transducer array, but as I recall it was only operational above 1 kHz.

An array of drivers could certainly approximate omnidirectional radiation, as embodied in the larger Shahinians.

Note that Walsh-type drivers have a donut-shaped radiation pattern at high frequencies - that is, they aren't truly omnidirectional across the spectrum.

The MBL Radialstrahler is probably closer to a true omni with its small tweeter, but the system would be very difficult to DIY.

Henry Wolcott of Wolcott Audio holds a patent (number 4,850,452) for using a 360 degree spherical waveguide structure to approximate omnidirectional radiation. Here's a link to the patent:


This looks to me like the most elegant approach available to the DIYer. The commercial product is called the "Omnisphere", and differs somewhat from the patent application.

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Old 26th May 2004, 11:01 AM   #14
Pete Fleming is offline Pete Fleming  Australia
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The MBL Radialstrahler is probably closer to a true omni with its small tweeter, but the system would be very difficult to DIY.
Actually I'm not sure it would be that difficult to DIY. Matching the performance of the MBL yes possibly, but all it needs is reasonable selection of material for the segments. The segments are driven by a conventional voice coil.

Seeing the extent some go to with cabinets I think it's a very DIY project for some with imagination.
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Old 26th May 2004, 02:37 PM   #15
maik is offline maik  Germany
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You may have a look to


They make omni-directional speakers based on
"standard" dynamic drivers. Looks very interesting.
I never heard them but they won several awards
on Hifi-shows.


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Old 26th May 2004, 06:09 PM   #16
Kensai is offline Kensai  United States
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How about building a sphere from a matrix of alternating mid and high units? Probably have to either customize the frames or research out some more esoteric units to get it to assemble correctly (possibly some of the square framed mid drivers meant for line arrays and then just chopping up the plastic faceplates of some tweeters to fill the spaces inbetween). Then you'd manufacture some sort of bracing rig for the inside, and it would stand on a metal rod attached to that, passing through the bottom. If done correctly, the whole assembly could be sealed, and possibly even finished in a somewhat civilized fashion if one was clever enough, to result in a "globe" bookshelf. Combine with a dipole bassbox or sub, and you should have some room filling sound.

Just a though . . .

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Old 26th May 2004, 11:46 PM   #17
johnkramer is offline johnkramer  United States
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OK, this sounds like fun.

build a square frame out of 1x1's. sized to fit this idea

take two old drivers that you don't care about. Strip them down to just the motors. technically they should be identical drivers

mount the motors on to the frame so that they are facing each other with the voice coils pointing to the center of the frame.

Now take a standard party balloon and blow it up.

stuff the balloon between the two motors so that the voice coils come in contact with the balloon. glue it with whatever to hold the balloon in place.

wire the coils in parallel, hook up some tunes, and have a good laugh. It might actually sound good too!
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Old 27th May 2004, 12:21 AM   #18
Hybrid fourdoor is offline Hybrid fourdoor  United States
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Do a search on Plasma Tweeters. They are probably the truest iteration of what you are thinking about.

However they have drawbacks, such as frequency extension, very high voltage, very little resources available, and they produce ozone.

But they basically use a plasma flame that modulates at the frequency...in <practically> true 360* nature.
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Old 27th May 2004, 12:33 AM   #19
SY is offline SY  United States
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Default The Red Balloon

If memory serves, someone made an omni balloon radiator by attaching piezo film to it.
"You tell me whar a man gits his corn pone, en I'll tell you what his 'pinions is."
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Old 27th May 2004, 02:08 PM   #20
sashua is offline sashua  United States
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I have been digesting all the great ideas you super-geniuses have been concocting. Nearly all of them are known to me but so far only the balloon and plasma ideas are in the right ball park. I am actually using a plasma tweeter in my design (David, you win the stuffed animal!). The problem is that the best all my experimenting has allowed me to hope for is extension down to 1Khz.

The problem is "where do I go from there?" If I am to be true to my project's design principles I will need to get from 1Khz. down into the nether regions where bass loses its directionality and accomplish this by means of a truly omnidirectional radiator. multiple driver arrays are all well and good but if you measure them around the perimeter of the speaker there are dips and valleys that look like a skateboard park. Then, of course, since the plasma is a truly massless design I will also need to match its blinding speed with something equally hellish.

Now do you all see my dilemma? Who among you thinks they have the chops to "think outside the box" (pardon the pun) and come up with a solution?

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