Coil-driven planar

[bentl]

Hi,

I have been playing with the idea of building a "planar" speaker with a flat esl-type diapraghm tensioned in a frame...and moved by a voice-coil/magnet.

I was thinking of using 6my Hostapan left over from a ESL project

As I see it; i remove the problems of coating, stator openness, spacer distance and transformer and powersupply setup.

The diaphragm obviously will be driven from the center, not a disperced force like a esl.

Has this been tested before? I think i can recall having seen something like this done in a magazine 20 years ago..


Regards

Bent

[Illusus]

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[Calvin]

Hi,

oh of course it has been tested.....billions by billions. It´s called dynamic speaker *lol*
Driving force is applied to the ESL membrane over its complete area by an homogenous electrical field. Since each and every point of the membrane is driven the same, there´s no need for mechanical stiffness. That´s the reason why we can use a soft thin membrane material in first place. As soon as the driving force is distributed unevenly over the membrane (as a ring -->voicecoil) we either need a very stiff membrane that ideally should move in a pistonic fashion, or we need a very soft membrane without any mechanical tension within but lots of damping (bending wave transducer, Manger). As we know, no material is so stiff that it works in a pistonic fashion over its complete bandwidth. From a certain frequency range on the membrane behaves as if it were soft, leading to breakups. With a soft thin stretched film there´s hardly any stiffness, so the membrane works in breakup-mode over its complete bandwidth. On the other hand it doesn´t behave like a bending wave transducer, because of the stretching forces within the membrane.
In short, the membrane behaviour is rather chaotic.....not at all what we want, eyhh?

jauu
Calvin

[andyr]

Originally Posted by bentl

Hi,

I have been playing with the idea of building a "planar" speaker with a flat esl-type diapraghm tensioned in a frame...and moved by a voice-coil/magnet.

I was thinking of using 6my Hostapan left over from a ESL project

As I see it; i remove the problems of coating, stator openness, spacer distance and transformer and powersupply setup.

The diaphragm obviously will be driven from the center, not a disperced force like a esl.

Has this been tested before? I think i can recall having seen something like this done in a magazine 20 years ago..


Regards

Bent

Haven't you come across Maggies? They've only been going for over 35 years ... see here:
Stereo Speakers, Home Theater Speakers, High Fidelity Audio - Magnepan, Inc.

Regards,

Andy

[LineArray]

Hi bent,

be carefull, you will most likely end up in the bending
wave loudspeaker thread then ...

What can be expected is that your system will be a bending
wave loudspeaker with soft membrane and a high coincidence
frequency (possibly located above the audio range).

A corresponding transducer already patented and commercially
available is the Manger transducer.

Manger Schallwandler

So the good news is, that a quality transducer based on that principle
is possible.

Another good news is that one can spend his whole lifetime without
problems in developing and optimiting those constructs.

Best regards

[Ron E]

Google Museatex or Melior, and look for posts on diyaudio by moray james.

[reverber]

I immediately thought of BES loudspeakers from the 80s(?) when I read your post. A little digging shows that Sonance now owns what was BES.
IIRC, they used a molded styrofoam panel as the driver, which was excited by a standard magnet/voicecoil motor assembly or two.

Picture

Cody

[mkstat]

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-m

[godfrey]

Originally Posted by bentl

I have been playing with the idea of building a "planar" speaker with a flat esl-type diapraghm tensioned in a frame...and moved by a voice-coil/magnet.
[snip]
Has this been tested before? I think i can recall having seen something like this done in a magazine 20 years ago..

I remember that too. The reviewer was surprised to find it actually produced good bass. The drive was asymmetric, though. i.e. The voice-coil needs to be off-center somewhere to break up the resonance modes.

[amp-guy]

Another one from the past was polyplanar, they consisted of a block of styrofoam with a roll suspension and a voice coil attached, they made sound I wouldn't call it good sound though.
Also more recent is the NXT design, which I don't much care for either.
Something with less mass might have potential though, what about woven silk with a Dammar coating?