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
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
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?
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 ...
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
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
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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?
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?
What kind of a coil driver did you have in mind? If you are considering a conventional coil and motor (as in a standard dynamic driver) you will have to make some adjustments. You will require a shorted turn (copper or silver sleeve on the pole piece) on the pole and you will require shorted turns at the top of the motor top plate and at the bottom of the pole. You will need to vent the pole and probably the cavity inside the motor. Build a single layer 4 ohm coil as short as possible with a top plate and magnet as large as possible. You will not be able to utilize any form of standard spider, the best option is a liquid bearing instead, use a medium to medium thick ferro fluid in the gap to centre the coil rather than a spider (will generate talk and distort the sound). You will want to keep the coil driver dead centre to balance tension from the diaphragm. You will also need to use a much heavier diaphragm so save the micron stuff for stats. The diaphragm in this design is your primary suuspension so keep the coil as light as possible. You will want to use a biaxially oriented film to keep things balanced and I would recommend 150 to 200 gage Mylar. If you like I can send you some DuPont HS150 (works very well but heavier gage would be nice if you want to make any real bass). Damping can be applied close to the rear side of the diaphragm and must vary across the diaphragm being heaviest at the outter edge of the film. This will allow you to build a cardioid polar patten which is very usefull. This speaker will radiate high frequiencies in all directions (left, right, up and down). In most cases left to right radiation is not an issue but floor and ceiling reflections are a concern). You may think that the film thickness I have recommended is much too thick to generate any high frequiencies but this design can easily run out to 10 K at the outter edges of the diaphragm. For the last octave you only require a light pulped paper dust cap on the front side of the voice coil. Mount the cap inverted into the pole (machine the pole out to accomodate this) and extend the outter edge of this dust cap outward past the diaphragm surface plane by about a milimetre or so (not flush with the diaphragm) to increase the structural integrity of the cone. All that and a lot of hard work should get you there. Hope that this has been of some use. None of this is made up or just my opinion, this is all based upon real R&D and a sucessful product which made it to market. Regards Moray James.
Many thanks for the insights of Calvin, moray james and others. But what are the "take away" messages?
Going to large surfaces done only as a trade-off when creating drivers limited to small displacements. Light-as-a-feather can't be achieved well without graphene which is light but strong but nothing can possibly be strong enough not to have waves. How to drive a surface broadly (like an ESL or Maggie) using a coil with an enormous diameter.
Just doesn't seem to work generating low distortion piston motion, ESLs excepted.
B.
Going to large surfaces done only as a trade-off when creating drivers limited to small displacements. Light-as-a-feather can't be achieved well without graphene which is light but strong but nothing can possibly be strong enough not to have waves. How to drive a surface broadly (like an ESL or Maggie) using a coil with an enormous diameter.
Just doesn't seem to work generating low distortion piston motion, ESLs excepted.
B.
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