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Old 20th January 2007, 10:33 PM   #1
Tenson is offline Tenson  United Kingdom
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Default Planar design

Hi,

I have some planar tweeters that I took apart. They only have the magnets on one side and the other has the membrane directly exposed to the air.

Around the sides of the magnets (single line of them) is some absorptive filling which then vents out the back.

All as might be expected then! The interesting thing is that on top of the magnet line and absorptive filling is a lining of thin felt, which, when the unit is fixed together, just touches on the back of the membrane (or so it seems).

What is the point of that? I would have thought that the membrane needs to be free so it can move unrestricted. I guess the slight touching gives a bit of damping but how can it even work right like that lol.

I also have some midrange units by the same manufacture and they also seem to have a very gently touching felt on the back of the membrane.

It should be noted that these are not great drivers, having quite high distortion. however, even with the felt removed so nothing is directly touching the membrane, the distortion doesn't go down.

I guess I am asking if this is common in planar drivers and if so, what is the point of it?

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Old 21st January 2007, 02:03 AM   #2
soongsc is offline soongsc  Taiwan
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These types are made for mass production. Depending on the shape of the diaphrams, you will get various resonances which colors the playback, and are also dynamically limited in the lower frequencies. Work quite well for super tweeters if they go that high. Felts are normally used as an attempt to acoustically damp resonances.
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Old 21st January 2007, 11:50 AM   #3
Tenson is offline Tenson  United Kingdom
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Quote:
Originally posted by soongsc
Felts are normally used as an attempt to acoustically damp resonances.

Yes, but its not just acoustical damping, its actually touching the membrane!

I want to see inside a B+G now
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Old 21st January 2007, 01:10 PM   #4
soongsc is offline soongsc  Taiwan
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Quote:
Originally posted by Tenson



Yes, but its not just acoustical damping, its actually touching the membrane!

I want to see inside a B+G now
On the front side, it would serve as both damping and ristricking travel. But really, they are for the mass production market.
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Old 21st January 2007, 01:25 PM   #5
Tenson is offline Tenson  United Kingdom
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Restricting travel only in one direction though really.

So what would it be like in a non mass production planar design? What is the 'proper' way to buid them?
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Old 21st January 2007, 03:10 PM   #6
soongsc is offline soongsc  Taiwan
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That's really a tough question. Physically, it's really a trade off with this kind of design between frequency response and damping. Some people also call these ribbons. Really not too much you can to since damping is necessary to some the vibration when the music stops. These types have good onset transients, but rely on either damping material or tension to stop it. Increasing tension sort of reduces the resolution capabilities, and damping material may vary with moisture. I think the more proper way to do it would be to have the ends wrap around damping material at the ends. The damping material needs to be high loss material properly matched with the diaphram so that energy can be transferred from the diaphram to the high loss material.
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Old 21st January 2007, 04:34 PM   #7
Tenson is offline Tenson  United Kingdom
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Well, all the planar designs I have seen possess extraordinarily good CSD behaviour, so whatever they do, it works!
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