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Old 5th October 2009, 02:59 PM   #391
el`Ol is offline el`Ol  Germany
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At that time the usual "Freischwinger" electromagnetic drive units had very low excursion and drove quite large paper full-cones. Probably worked in bending-mode over the larger part of the spectrum.
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Old 5th October 2009, 04:29 PM   #392
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To be more precise, the above "Tonspiegel" device is a Distributed Mode Loudspeaker,
comprising a flexurally rigid flat membrane, which is excited punctually
using an electromechanical exciter ... more than 60 years before the
base patent used by NXT.
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Old 5th October 2009, 04:35 PM   #393
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Quote:
Originally Posted by el`Ol View Post
At that time the usual "Freischwinger" electromagnetic drive units had very low excursion and drove quite large paper full-cones. Probably worked in bending-mode over the larger part of the spectrum.

I agree totally. In those early days there seems to be
little distinction between "piston acting" and "modal
acting" devices.

But the "Tonspiegel" , "Sound Mirror" used a flexurally
rigid flat membrane which was made of wood.
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Old 6th October 2009, 12:59 PM   #394
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do you think the 'f' have some involvment in sound? the 'opere sonore' use some circular holes along the panels
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Old 6th October 2009, 02:18 PM   #395
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I guess, the openings contribute by some kind of Helmholtz resonance.

But in principle the device would also work without it, i am shure.
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Old 6th October 2009, 03:11 PM   #396
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Since the device is excited from the center,
the f-holes may also contribute to a more
asymetric shape and a more even distribution
of modes over the frequency range.

Who knows ? One has to build one and make some
measurements. But i am convinced, that the holes
are not needed for the device to work as a
transducer.
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Old 6th October 2009, 06:42 PM   #397
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Helmholtz resonance? do you think the devices also has some kind of load like a BR?
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Old 6th October 2009, 08:29 PM   #398
pol_bct is offline pol_bct  Reunion
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Quote:
Originally Posted by LineArray View Post
... more than 60 years before the
base patent used by NXT.
Should we think the patent is "ungültig" ?

POL
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Old 7th October 2009, 12:48 PM   #399
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Quote:
Originally Posted by human.bin View Post
Helmholtz resonance? do you think the devices also has some kind of load like a BR?
I am not an instrument maker, but AFAIK every violin has
a range of resonance, where the enclosed air is involved.

IMO there must be helmholtz resonance, when you have
a ported enclosed volume. But we have to keep in mind,
that the membrane/cabinet does not necessarily move
in phase as a hole body.

So i would not call it "BR" in the sense we use the
term today, where a pistonic acting woofer is used.

Maybe someone should copy the device and analyse it ?
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Old 7th October 2009, 12:49 PM   #400
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Quote:
Originally Posted by pol_bct View Post
Should we think the patent is "ungültig" ?

POL
No.

We have to keep in mind, that NXT has done a lot of research and
development in the field of DML. The researchers published many
articles which contribute to the understanding of the DML
principle and they developed many special offspins of DML.

AFAIK the base Patent by Dr. Ken Heron comprised a honeycomb core
material, which was at that time evaluated for application in
an aircraft.

The ability to radiate sound well, was unwanted for the application
in an aircraft. But it was found, that the material could be used
to make a bending wave loudspeaker.

Such material was unavailable in 1923 AFAIK. The "Tonspiegel" device
seems to have its roots in the traditional making of a musical
instrument.

In fact the soundboards and bodies of pianos and violins can be seen
as a kind of bending wave transducer.

In my eyes, the new basic idea was the application of an electromechanical
exciter - driven by a music signal - on a flexurally rigid soundboard or body,
which makes up a new kind of loudspeaker.

This kind of loudspeaker evolved "naturally" from musical instruments,
similar like cars developed from coaches.

A device based on that principle is patented more than 60 years
before the patent by Dr. Heron, which uses the same effect nowadays, but
is based on recently available materials, that is all i want to say.

I do not want to evaluate the validity of any patents for i am not
skilled to do that and i have no interest in doing that.
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