Coil-driven planar
 

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

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

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

Regards,

Andy

Hi bent,

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

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

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

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

Parts-Express.com:*Sound Advance ST2432D-3D2 2x2 SpeakerTile Cortega | STS2432 Sound Advance Sonance SpeakerTile ceiling speaker background foreground public address drop in panel grid planar suspended ceiling t-bar 70v SA0209 SoundAdvanceTile050109

-m

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.

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?