Concert Double Soundbox

[jamiegramo]

Some of you will have seen this Soundbox that just finished on ebay. I wonder if anyone knows more about it? It has a patent date of '209786' which appears to be early 1925 although you would think that 'Duophone' would already have a similar patent. Apart from the word 'Liverpool' it has a monogram of 'JH' or 'HJ'. Perhaps there is a connection to The Johnson Talking Machine Co. of Liverpool that made Academy gramophones. This may have been an accessory to 'upgrade' a machine. Another quasi-scientific idea that never caught on...

Any ideas? Thanks, Jamie

http://www.ebay.co.uk/itm/DOUBLE-CONCER ... Swx6pYodn5

[CarlosV]

Interesting gadget, seems conceived to increase the sound volume. The acoustic design would be quite tricky, though, to prevent cancellation of the pressure waves inside the conduit. Looks awfully heavy, though, certainly not kind to records. It is indeed similar to the duophone, but I believe the duophone diaphragms were of different diameters, connected to a V-shaped needle arm.

[jboger]

I find this sort of contraption very interesting and wish I had one. However, I don't see a problem with a cancellation of the separate sound waves so long as they are propagated down parallel paths that join at the same point and same distance from the needle point, as is the case with this interesting item. As you point out, Carlos, a sound wave is a pressure wave. It propagates through air with regions of compression and rarefaction. In this configuration, a compressed region of the wave from one reproducer would arrive at the union point at the same time as the compressed region from the other reproducer, both being set up by the vibration of the same needle; t_0 and distance travelled are the same for both. Ditto for the rarefied regions. It would be a problem if the arrival times differed due to different pathways, one being longer than the other, such that a rarefied region combined with a compressed region; they would add but there would be a partial cancellation. My guess, the designers of the interesting item thought there would be a doubling in amplitude when the separate waves combined. But I don't think it's quite that simple because of vibrational losses due to the split pathway from the single needle to the separate reproducers. Want to think about that last statement a bit more.

[Lucius1958]

I think that cancellation of the sound waves would be more of an issue on soundboxes that collected them from both sides of the diaphragm, as on the ill-starred "Wonder".

The Kalamazoo "Duplex" tried to solve this problem by using two diaphragms and horns: but as the soundboxes were set opposite one another, rather than in tandem, the phase cancelation would still apply.

Bill

[Odeon]

The inventor:

Julius Harris

More about this Soundbox here: http://grammophon-platten.de/e107_plugi ... .php?41631

[CarlosV]

I find this sort of contraption very interesting and wish I had one. However, I don't see a problem with a cancellation of the separate sound waves so long as they are propagated down parallel paths that join at the same point and same distance from the needle point, as is the case with this interesting item.

Yes, you are right, I was thinking about small differences in the two paths caused by gasket and manufacturing non-uniformities, but such differences would be negligible: a 1-kHz tone has about 30 cm wavelength, so small differences of some milimiters would not make any difference. As to doubling the pressure,if the needle and its holder would be completely rigid, the record groove would impart the same displacement to both diaphragms, but since the needle is damped with springs the response becomes more complex. It would be fun to hear the results on a real test ...

[jboger]

Carlos: You hit exactly on the problem I was unclear about with regards to the rigidity of the needle and needle bars. Thanks.

[jamiegramo]

Many thanks to Odeon for the information! I could not find this and it just shows how great a forum like this can be. I also thought this device would be awfully heavy but it is surprisingly light-weight. Infact when the postman passed me the parcel I thought the sender may have forgotten to enclose it. Apparently Julius Harris must have given this concern consideration as it is constructed mainly of aluminium. The attached photo shows the bifurcated tube at the back. The partition extends right down to keep the channels separate. I'm not sure this is necessary if attaching to a normal tonearm or whether he had a bifurcated tonearm and horn in mind.

[Odeon]

Very interesting back end of the sound box! Looks really like this had been built for a bifurcated tone arm and/or horn. Most of the “obscure” Patens I found, never achieved it to a “real thing!