Rubanoide Project

Few

Member
2004-04-14 10:51 pm
Maine, USA
Total weight doesn´t matter but weight versus area.

Both the driving force from the voice coil, and the fraction of the diaphragm that is actually driven at high frequencies, must be taken into account as well. I'm guessing that only the portions of the diaphragm closest to the voice coil move in phase with the voice coil in the high kilohertz realm. A look at the off-axis high frequency response might provide a clue about whether this conjecture is true. In any case, I believe the portions of the diaphragm that fold back toward the cabinet are rigidly fixed in place so it's clear that including the entire mass of the diaphragm in the calculation of moving mass is going to be misleading.

Few
 
I've been intrigued with this design for a while, since the other thread "DIY ribbon of a different kind" was posted:

http://www.diyaudio.com/forums/showthread.php?s=&threadid=69450&highlight=

It is interesting, as it would appear to posess some of the qualities of a ribbon/line source, those of a dynamic driver and some attributes in common with bending wave transducers. If this design is implemented well, I can see how the driven area might match smoothly with frequency and perhaps avoid "ringing". If one implemented a graded diaphragm compliance, it might offer further benefits. The gradual transition from longitudinal to transverse excitation, a result of the diaphragm curvature, has achieved this in part (I think).

I was interested enough to make a lash up version out of things on my desk. Diaphragm is a 2"x5" piece of notepaper. 8 "windings" were applied where the paper is folded at the centre. This assembly was taped to a frame made from a small box lid. Magnetic field is provided by 2x 1" square neo magnets with a gap about 1/8". For a small driver with an inefficient motor, constructed from random materials, it plays rather well with no glaring sonic horrors. Of course it's not Hi Fi!

Wish I had more time to play with this idea and make something bigger.

Ed
 

AnthonyPT

Member
2004-10-29 9:23 am
Hi

Having followed the progress of this
"large Linny" (Lineaum) design and
using Linaeum ET6 tweeters I too am fascinated
where this wave bending idea can develop more,
I too like the idea of using an electromagnet
design instead of the neos. How to go about
designing the electromagnet I am not sure.
Would give you a lot of control by varying the
voltage. The best Linaeums used doped silk and
the original designer,Paul Pattock, has been out
there researching new and exotic materials for membranes.
I would like to try silk and maybe Kodak Estar film if available
in a suitable size. Consistancy is maybe the main issue
and perhaps the tweaking allowed with an electomagnet
might be beneficial,

Regards
AnthonyPT

Wonder if the Gallo tweeter is a cousin and if the
Nearfield design has ever been reviewed
http://www.nearfieldacoustics.com/S7monitor.html

amsci99 Please email me! I have notes and pictures!
 

Few

Member
2004-04-14 10:51 pm
Maine, USA
Wonder if the Gallo tweeter is a cousin...

Unless I'm mistaken, the Gallo tweeter is unrelated. It uses a piezoelectric film made of Kynar. Since the film is piezoelectric, if you place a voltage across the thin metal electrodes deposited on the two faces of the Kynar film the film changes dimensions. You can arrange things so a flat piece of the film expands or contracts in the plane of the film if you lay it flat. If you then wrap the film into the form of a tube the dimensional changes cause the tube's radius to expand or contract depending on the polarity of the voltage you apply. The expanding/contracting tube generates a nearly cylindrical wavefront. There is no voice coil and there are no magnets.

The other devices discussed in this thread are bending wave devices in which a voice coil is immersed in a magnetic field.

Few
 
Actually, the Japanese company Pioneer used this technology in the 1970's and called it a high polymer tweeter. A bit more information can be found here, and by searching for information on Pioneer's HPM series of loudspeakers from the good ol' days. As a student MANY years ago I got a hold of a sample of piezoelectric Kynar and hooked it up to a receiver via a really tiny transformer. I confirmed that it made sound but at the time wasn't equipped to do much more. One complication with the piezoelectric approach is that nonlinearity and hysteresis are hard to avoid if you want a large displacement (by piezoelectric standards) per volt.

Few
 
Few - Thanks for that insight, its rather interesting.

I remember that Audax had a gold domed piezo tweeter at the top of their line a few years ago. Hi Fi world, and their "World Designs" lineup of DIY projects used to feature this tranducer.

I'd imagine that the complex impedance of a piezo material might cause some headaches if one is looking to implement large area radiators.

Ed