Wood panel piston-ic speaker

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#21
VaNarn said:
I have the feeling that once put together,the means of re-opening would have been a mystery.In the pictures presented so far,it seems that the original rear panel has been pried away if the black strips(rubber or felt) were what held it in position.The leads to the front panel are the voice coil leads and I would think the magnet is compliantly mounted in the sub-frame in such away that it can be aligned with the v.c. but be reasonably free to to move back and forth.A mechanical crossover system is suggested by the 5 foam pads that are spaced on the magnet rear surface and these would have driven the original rear panel.The bamboo 'thing' appears to be a ring in.
Click to expand...

That's the part I'm having a hard time wrapping my head around. I am assuming the motor magnet has a pole piece...and the voice coil attached to the wood panel must be aligned to sit within the pole piece gap but failing having some form of suspension system on the edges of the panel...how would this beast stay aligned?😕
 
#22
I can only make presumptions about this intriguing design as I am unaware of any detailed specification or measurement that is readily available.The front panel,which appears to be of thin plywood together with the voice coil would have a high moving mass and it would be expected to be of a very low compliance.As the effective area is large the excursion would not have been required to be high (at least for the standards of the day) and this is of great help in aligning the coil to the magnet pole gap.A normal suspension would not be needed.It is feasible to contend that the magnet assembly could be held in place with foam rubber or neoprene in the sub-frame.This then would allow lateral movement and a restoring force.Again, a high excursion would not be required. I would also think the original rear panel was of the same material as that of the front one, although driven over a limited frequency range.Maybe Roger Russell could be prevailed on to contribute to a better understanding of the working principle.
 
#23
Yes it would be great if roger could add his observations and memory of this technology...there's a tantalizing hint here:

http://www.roger-russell.com/ml1cpg.htm


"...He mentions the effect of solid angle seen by the speaker: "It would seem to be a good idea for someone to design an equalizer network to provide variable bass boost to compensate for this effect on performance due to change in solid angle." No patent had been filed. The behavior of speaker radiation into various solid angles is common knowledge. It is explained in detail in books such as Acoustics by Leo Beranek published in 1954 and Hi-Fi Loudspeakers and Enclosures by Abraham Cohen published in 1956. While at the Sonotone Corporation, I spent the day once in the early 1960's with Abe and ran response curves for him on his Bi-phonic Coupler speaker system..."

Anyone have a copy of this book?... Cohen, Abraham B. Hi-Fi loudspeakers and enclosures. New York (480 Canal Street) : John F. Rider, Publishers, Inc., 1956. 368 P

Perhaps A Cohen covered this coupling speaker in it. Although the printing date seems to precede the unveil of this speaker by several years.
 
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#25
mid 60's univ model

Stumbled on this just now.
 

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#29
What a wild bunch of stuff!

Today, I skimmed Cohen's 2nd ed and there was no mention of these contraptions. There is only a very small section on acoustic doublets but not even a hint about these particular implementations.

Might've read somewhere that he was gone from University before the time that these (circa '63-4) came-out. Must have licensed them (?)

Contemporaneously, they used some pretty viscous goop on surrounds (called "moving seal" in catalog) in the "mini-flex" which was a 0.4 ft3 box with a 6" W that was advertised to hit 40Hz.

I too would like to see under the magic cakepan.
 
#31
grindstone said:
What a wild bunch of stuff!

Today, I skimmed Cohen's 2nd ed and there was no mention of these contraptions. There is only a very small section on acoustic doublets but not even a hint about these particular implementations.

Might've read somewhere that he was gone from University before the time that these (circa '63-4) came-out. Must have licensed them (?)

Contemporaneously, they used some pretty viscous goop on surrounds (called "moving seal" in catalog) in the "mini-flex" which was a 0.4 ft3 box with a 6" W that was advertised to hit 40Hz.

I too would like to see under the magic cakepan.
Click to expand...

I believe it was only mentioned in the 1956 First Edition according to someone who remembered seeing the original article.

I find the concept an interesting one...worthy of further investigation particularly because Cohen was no audio troglodyte. Whether or not it was truly Hi-Fi is secondary to my interest in understanding the principle and design particulars.
 
#32
DrBoar said:
There was a HiFi speaker that was tested in HFN&RR in the 80 that had a oval flat piece of wood as speaker cone.
The Swedish guitar builder Georg Bolin made a speaker for his instruments so not a hifi speaker per se.
Vintage Guitars, SWEDEN - 1970s Georg Bolin Tonbord
I also found this contraption

http://elderly.com/images/vintage/130U/130U-8316_front.jpg
Click to expand...

Thanks Dr. This utilization fits with what I believe this type of driver might ultimately be best suited for...although I would like to hear/build a home audio version myself and see where the experiment leads me.
 
#36
Looking at the photos and reading the article it does seem much like the NXT distributed mode speakers with many of the same problems, fixes and advantages. I'm not clear on the magnet mounting though. Is it held rigidly by the box in the center?

The cane backing seems to be used the control the rear wave.
 
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