Wooden Re-Entrant horn

[kirtley2012]

In a similar vein to Alistair's thread on his homemade Balmain horn, here is the start of an idea I've had in mind for a while which is to make a huge Re-entrant horn, the width is probably about the same width as a HMV 202 horn, but it's quite a bit taller, and of course wooden, in the large chamber anyhow, the horn hardware will likely be made of fiberglass, I'm unsure whether to make the first fold of the horn out of fiberglass yet or make it from wood, I haven't fully designed the first fold yet so I'll see how that turns out, just went to the DIY shop yesterday on a whim and this is the result thus far.

I'm unsure what I'm doing for the tonearm or motor yet, I'm trying to fid a long narrow bore tonearm, and for motor I haven't quite decided, might go for a decent double spring Garrard or Collaro, I'd thought about looking for a quad spring HMV motor, but the last one I re-built wasn't too fun!, I have a HMV 32 motor with no spring barrel so maybe if a barrel is found that could be pressed into service

[epigramophone]

An EMG/Expert tonearm would be ideal but they are virtually impossible to find. Perhaps the next best narrow bore choice would be an HMV Swan Neck as used on their "Saxophone" horn models.

As for suitable motors, if I was starting a project from scratch I would look for an electric Collaro or Garrard in unit with a mounting plate and turntable.

[old country chemist]

Hi Alex, thanks for the picture of the start of your horn, and the description. I wish you well. I was told in the past that you can use a tone arm of parallel bore up to 12 inches long before it starts to expand. As Roger says, a "saxophone " type H.M.V. tone arm would be admirable. The big problem is the exponential bit connecting the tone arm in a ball bearing cage to the start of the horn, whilst incorporating a suitable sound proof seal. Philip Knighton used in a smaller machine he made years ago, a cut off spout from a zinc watering can. He said it fitted well, between the tone arm and the start of the horn, and Roger and I can confirm the machine was very good.
George Overstall made a 203 gramophone c 1930. I remember him showing me a photograph of it. Massive, and the horn was also made of formed plywood. I cannot remember what he said regarding the quality of reproduction though,
Good fun Alex! Keep us posted on the progress.

[Inigo]

Good! How do you design the horn shape? Do you use pure exponential formulae or tractrix? What parameters do you fix? Cutoff frequency, etc? It must be difficult when the design is of a folded horn. I've tried myself to design one much smaller but I got stuck in the graphic design of what I've calculated using an excel sheet, step by step. My project is for enhancement of an old conical short horn, and my new folded horn must fit inside the older one... having its mouth inside the old horn mouth. A very complex affair!

[CarlosV]

Good! How do you design the horn shape? Do you use pure exponential formulae or tractrix? What parameters do you fix? Cutoff frequency, etc? It must be difficult when the design is of a folded horn. I've tried myself to design one much smaller but I got stuck in the graphic design of what I've calculated using an excel sheet, step by step. My project is for enhancement of an old conical short horn, and my new folded horn must fit inside the older one... having its mouth inside the old horn mouth. A very complex affair!

Iñigo brings up an excellent point: the orthophonics or reentrants sound good because they were designed based on mathematical models, and not empirically like all the previous designs. The best way to undertake this, Alex, is to construct a theoretical design that predicts the horn response - for instance, the low end cut-off frequency is directly determined by the dimension of the bell, and there are practical dimensioning guidelines that deviate from both the tractrix and the exponential curves - see Percy Wilson's bible. This way you will end up with a more predictable performance once you are done with all the woodwork, and best of all, you will be able to test the horn response against the theoretical model.

[kirtley2012]

Inigo, I do fear you’ve over estimated my ability with computers, my designing with anything goes as far as a great big piece of paper and a pencil.
The exponential components of this horn were borrowed directly from my EMG horns, with a template being made from it and then large full size plans made of the internal shapes of the re-entrant, it’s more of a crazy experiment than anything, but it should yield a pretty good sounding horn

[gramophoneshane]

If you'd prefer a spring driven motor, I'd go for a Garrard super motor.
They're a good strong motor that run silent and smooth, and it has a mounting plate the same as used with their electric motors, which would make upgrading to an electric motor later if you chose to, much easier.
Another option if you can find one might be a Paillard motor as used in Sonora's period Deluxe models, which look stunning being gold plated, are superb quality, and are capable of playing 12-20 records when fully wound.
Having to replace a spring in one of these might be difficult though, both financially and physically.

[kirtley2012]

If you'd prefer a spring driven motor, I'd go for a Garrard super motor.
They're a good strong motor that run silent and smooth, and it has a mounting plate the same as used with their electric motors, which would make upgrading to an electric motor later if you chose to, much easier.
Another option if you can find one might be a Paillard motor as used in Sonora's period Deluxe models, which look stunning being gold plated, are superb quality, and are capable of playing 12-20 records when fully wound.
Having to replace a spring in one of these might be difficult though, both financially and physically.

I'd love to fit it with a Garrard super, finding one may be problematic though, I never see them come up for sale, I know they were occasionally fitted to cheaper cabinet gramophones, but even if I found one of those I'd never have the heart to part it out, I'd certainly like to go with spring, an electric motor would be easier to fit but I've got a few electric machines already, and this gramophone will likely wind up living in a summerhouse type thing I plan on building which likely won't have power, at least not at first, so it being spring would save trailing an extension cord out all the time

[HMVDevotee]

Here is the internal manifold that looks like a Victor fabrication. If it is, it's most likely built on the Bell Labs/Western electric design. Perhaps it would be useful, if not in its current dimensions, but as a pattern to enlarge or even as bones to build upon to fit your existing outer horn.

https://www.ebay.com/itm/284239811428?h ... Sw931gZDh1