Sketch For Bending Transducer (Prototype already built)

[LineArray]

edit: of cause i do not think midrange coloration is positive ...

[LineArray]

the panel seems to have a wide dispersion pattern,
even in the highs, even when listening about 45 degrees
of axis there is not much loss in brillance (if any ..).

Uniform dispersion and good output at the upper
end seem to be possible advantages compared to a
conventional fullrange speaker of same membrane area.

Even at that premature stage impulses like
attack from piano drum beats etc. were rather crisp
and realistic.

Listening to strings was awful sometimes, still too much
coloration.

[el`Ol]

Originally posted by LineArray
the panel seems to have a wide dispersion pattern,
even in the highs, even when listening about 45 degrees
of axis there is not much loss in brillance (if any ..).

This is exactly what I experienced with this design:
Motor-based planar speakers-can it be done?
Measurement gave a slower CSD than expected, so my conclusion was that it works like a DML speaker a'la NXT.

[Paul Burton]

I discovered this thread via jzagaja who emailed me with some questions about NXT's BMR technology and how it related to my own Sumo Aria panel speaker (over 20 years ago now) and the Podium panel.

I haven't had time to read the whole thread - it is quite long now. But it does look like you are embarked on something quite interesting.

I used to be NXT's Intellectual Property Manager, and I thought you might like to look at a patent application which I suspect you may not know about, particularly as it has a very uninformative title, designed to avoid getting the attention of competitors as far as possible.

It is all about in-plane compression drive of panels, and techniques to transform the compression waves into transverse bending waves which radiate sound. It was based on a serious piece of empirical research and modelling by Denis Moorcroft (of DNM fame) and Dr. Nick Hill, one of NXT's senior scientists.

If nothing else, it may give you some pointers going forward.

Details: WO 03090496 "Acoustic Device" Azima, H., Hill, N., Moorcroft, D.

Enjoy!

Paul
Rountree Acoustics Ltd
www.rountree-acoustics.com

[jzagaja]

Thanks to Paul and Neil Charris I've found missing connection between travelling wave and bending wave. Direct link to the said patent:

http://www.wikipatents.com/gb/2400264.html

[jzagaja]

Below link kindly provided by Christien Ellis shows directivity of a DML:

http://tinyurl.com/d3jl8d



Sorry for a typo - not Neil Charris but Neil Harris.

[LineArray]

Hello,

@Paul Burton: Thank you for the information, i am currently
reading the patent.

@jzagaja: The animated polar plot is very instructive and
matches my experience with my own DML panel.

Now proudly like to present: The ugliest speaker built ever:

[LineArray]

Now a quick measurement.

Around 1m distance about 45 degrees off axis.

Free air resonance of the driver is about 55 Hz, dependent
on suspension.

Time frame is too short to evaluate the bass response
of the speaker, but due to high Qts it sounds a bit
"fat and boomy".

Sounds different than a conventional dynamic fullrange
driver.

Sound does not change very much with listening position.

Listening is OK even at larger distances.

After some tweaking i can listen even to strings and voices
without getting hurt.

I have not expected to get that far with this prototype ...

[Elias]

Hello,

What is the efficiency of this proto? And what it can be in practise if implemented carefully?

- Elias

[LineArray]

Hi,

i currently have no calibrated setting to evaluate
efficiency properly.

I would estimate in comparison ro other speakers
i own, that efficiency is below 80dB/W at 1m.

The proto's motor has an air gap which is 8mm wide ...
It was just designed for experimenting/development.

Next Proto will have a different motor:

- Air gap will decrease to ca. 1mm
- Stronger Magnets of double volume
- Double length of wire in the magnetic gap¨

Furthermore mass of diaphragm and stiffness
of suspension will be optimized.

I expect that efficiency will be in the range of
conventional dynamic speakers of same diaphragm
area (active area around 400cm^2).

A "high efficiency" version will be possible regarding
stiffness of suspension. There will be the same
compromises as with conventional dynamic speakers.

But it is difficult to have a conventional fullranger
of that size, having an upper frequency limit of
around 20 Khz with excellent dispersion up to the
top ...


Kind Regards