Horn shapes

[anchorman]

After visiting Ahmed and Andy in the UK, and hearing Grahams wonderful horn at Andy's house, along with the various machines that Ahmed has, I've decided that I can't live without a large horned machine in the long term But given their scarcity here, and given that I don't think I can afford to import one of Graham's stunningly beautiful reproductions, I'm probably going to have to make my own.

Can we discuss the merits of an internal horn machine vs external? If I build an external horn machine, would it be best to build an adapter for the EMG/victor size horn connectors (I think they are the same?), or the Larger Expert ones? For expediency, I think I'm going to need to make the first horn rectangular in cross section, as I don't foresee making many multiples as Graham has done, and the effort of a plaster or wooden form for fibreglass or Papier-mâché would be wasted on my first experiments. The advantage I see in the external horns is that they can relatively easily be separated from the rest of the machine, and they can be positioned to aim towards or away from the listener as needed. an Internal horn can be more compact built into the base of the machine.

Regarding taper: I know there is a lot that will come into play, and tone/response will be affected not just by the horn, but also by the length, size and shape of tone arm, the soundbox's characteristics, etc... for the horn itself, should I aim for exponential, hyperbolic, tractrix, some other shape?

Could someone share the standard sizes fittings used for various external horn machines? It would be nice to be able to do my experiments in such a way that they could potentially be tried on machines other than my own.

[epigramophone]

As to the merits of internal vs external horns, one of the advantages of the external horn is the height at which the sound emanates.
The centre of the horn mouth of my Expert gramophone, standing on a record cabinet, is approximately five feet above floor level. This is about the height at which a singer standing in the room would be heard. Most internal horn machines play at about half that height.

The internal horn machine was introduced purely to be more acceptable as a piece of furniture in the home. Acoustically it was a step backwards. No matter how fancy they look, most pre-1925 examples are nothing more than table models with record storage beneath.

Things improved with the Orthophonic Victrola and it's imitators but the makers of EMG and Expert gramophones regarded their folded horns as a compromise, no matter how scientific their designs claimed to be.

[emgcr]

Jon, here are a few sketches which you may find helpful as you go along ? EMG had to use bronze for strength whereas, with their larger diameters, Expert were able to get away with brass. Conduit material (for mine) is LM 6 with no heat treatment---ie inert for extraneous resonance and acoustic purposes. The actual EMG material was pretty similar as far as I can tell. I could also measure the spigots for Expert Junior and Minor if you need such. Have fun !

[emgcr]

If you are considering a square horn, it occurs to me that you may not know about the great Douglas Fitzpatrick gramophone (PDF file attached below) whose horn is actually trapezoidal. You will find much correspondence and discussion here on the TMF. The performance following restoration is now extremely impressive although different from EMG/Expert due to diffusion from a larger mouth---more akin to the ubiquitous or comparatively non-directional output from an HMV 202/203. Three dead bats were found in the conduit during restoration which were impossible to see at the time our report was made ! It was really amazing that any sound emerged at all.......!

[epigramophone]

On a smaller scale you may find this square/trapezoidal horn of interest :

viewtopic.php?f=11&t=53177&p=316213&hil ... ll#p316213

[Sidewinder]

https://www.youtube.com/watch?v=pFEB0chiuJA

Has some horn theory

[Orchorsol]

... for the horn itself, should I aim for exponential, hyperbolic, tractrix, some other shape?

Hi Jon! I'd say definitely Wilson's "modified exponential". There's a chapter in Modern Gramophones and Electrical Reproducers by Wilson & Webb dealing with this, also a couple of articles he wrote in The Gramophone magazine entitled Armchair Phonatics if I remember correctly. I believe you can find all these online.

[Steve]

Q. How do bats make new friends?

A. With a sound wave.

Here's the obvious evidence!

[Ahmed]

It was great meeting you Jon, and looking forward to seeing how your project comes along!

I'd also vote for an exponential horn with a standard spigot like the one Graham shared. Makes for easy mixing and matching of horns/machines as needed

[anchorman]

thanks all! I will find those books/articles and have a read so I can start planning while I finish up some other projects.