Homemade Exponential Horn Project

[Inigo]

Alastair, it is what they're saying... To install the border reinforcement ring and then cover it with the last layers of paper. Your idea of it being rough, so the paper adheres better to it, is the thing to do... I was thinking more about choosing a perfectly smooth ring, and installing it at the end, over the paper, so the ring was the finishing at the border.

[Ethan]

Thank you emgcr, Inigo, and Alastair for your suggestions!

This wouldn’t be the same as hearing it in person, but I could try to make a video of the gramophone playing once it’s complete; it might at least give some idea of the sound.

I did some brief and not-very-scientific tests this morning with a cardboard tractrix horn and some foam pipe insulation inserted over the edge of its mouth, and I couldn’t hear any difference with or without the insulation, although there might be more of a difference with an exponential horn’s smaller mouth angle.

At any rate, I don’t have any suitable hoses at the moment, but I do have some wood, so to start, I’ll try something along the lines of the Expert ring embedded in the horn, but made from wood instead; when I apply the first layer of paper, I’ll let the ends near the mouth overhang by a few inches, then add the ring, build up the rest of the layers over it, and then fold the loose ends of the first layer back over the ring and final layers.

[Ethan]

The former is now completely removed, after being partly dissolved with D-limonene, partly pushed out from the throat (once most of it was dissolved), and partly scraped out by hand; now I can attach the wood mounting ring at the large end and continue adding layers over that.

While I was waiting for the former to dissolve, I started work on the internal conduit, and began removing its former as well; it seems to be coming out more easily, so if I can make a wood ramrod that reaches all the way around the curve, dissolving it shouldn’t be necessary.

The interior of the horn, looking into the large end.

What better time to use up the hot pink cardstock that was left after all the other colors were used than when making a horn...? It isn't as tear-resistant as the paper bags and it leaves the glue pink, but it speeds up the process, and I can always add a layer of brown paper over it at the end.

[Inigo]

Seriously, that intermediate brown paper layer you added at some point would be ideal for finishing. It looked exotic, like the skin of something... Because of cutting it into small pieces, and the pva glue outside made it look as varnished. This pva glue, diluted, is also used as a clear coat on top of wax drawings and other children's works...

[Ethan]

Seriously, that intermediate brown paper layer you added at some point would be ideal for finishing. It looked exotic, like the skin of something... Because of cutting it into small pieces, and the pva glue outside made it look as varnished. This pva glue, diluted, is also used as a clear coat on top of wax drawings and other children's works...

Well, I may not have any more of that particular paper, but I have plenty of other packing papers that I’ve been saving for the project, so I can certainly test some to see if they give similar results. My original intention was to use off-white paper for a finishing layer, but the brown color has been growing on me—from a distance, the color is reminiscent of the reptilian paper used on some EMG horns, and the mottling is a very interesting effect.

I started work on the mouth section, and just added the third layer (fifth and sixth, counting individual sheets) to-day; I mismeasured when cutting out the wood ring for the mouth—gave it a 12.75” radius instead of 13.75”—but then realized that I can just cut off the extra paper from each layer before adding the next, and fold a final layer over the cut edge after the horn is off the former.

Once the lower layers have dried, adding more wet layers on top makes the first layers expand, so the mouth keeps expanding and rippling as paper is added, but so far, it seems to shrink back and pull tight against the former—Could this be why homemade paper horns tend have wrinkly inner surfaces? And if so, has anyone else noticed it happening and found a way to prevent it?

Rippling from first layers expanding when re-wet while applying second layers. The rippling wasn't as bad when I applied the third pair of layers, so I'm hoping that it keeps becoming less noticeable as layers are added.

Horn progress as of yesterday--the paper had dried and pulled tight at this point, and the rough ends had not been cut off yet.

With the formers for the neck and internal conduit removed, I was finally able to hear the horn (or half of it, at least) in action, and for as small as the mouth is, it sounds surprisingly good—compared to my only reference, a Victrola Alhambra, its bass is rather lacking (and the Alhambra has the small, straight Orthophonic horn, so even it doesn’t have much bass) and the frequency response sounds slightly peakier, but it seems indescribably “less flat”, “less restricted,” and “more open”—it’s a difference that I’ve noticed with some experimental horns, and I usually attribute it to a better treble response, but it could also have to do with the shape of the emerging wave-front, as the Alhambra’s mouth is rectangular while the half-horn’s is round.

The half-horn in place on the cabinet--a metal tube at the throat fits into a wood socket in the tone-arm board.

[Inigo]

Boy, this project of yours looks fantastic!

[RefSeries]

I am lost in admiration. Well done!

Keith

[Curt A]

What a great project. Just an idea, which may or may not be a good one: for the outside finished layer, why not use decorative metallic or marbled book binding papers? Since this is an original horn design, why not have a truly one of a kind? https://www.talasonline.com/Japanese-Metallic-Papers

I'm sure there are many suppliers in the UK.

[Ethan]

Thank you all for your kind words!

Since Wednesday, I’ve added just over two more layers of paper to the mouth, for a total of four and part of the fifth—my current plan is to stop at six layers, so it should be able to come off the former soon—and I installed the wood mounting ring.

The horn mouth as of yesterday--four layers (eight individual sheets) thick, with the mounting ring glued in place and the rough edges trimmed off.

A decorative marbled paper is a good idea—when I began the project, I wasn’t at all sure that it would turn out well enough to warrant a decorative finishing paper, but based on how just the half-horn sounds, I think it will…When I tested it Wednesday, I used my not-as-good Orthophonic soundbox, but after taking my better soundbox from the Alhambra and putting it on the homemade gramophone, the sound quality is much better; the frequency response is less peaky and the “more open” quality is more noticeable—for records in good condition, I would say that it sounds better than the Alhambra at this point. Interestingly, worn records sound more worn with the half-horn than with the Alhambra, even with the same soundbox and type of needle—Perhaps the narrower frequency response of the latter filters out more of a worn record’s surface noise and high-frequency distortion?

[Inigo]

The full sound of big horns help masking the needle scratch. These horns are bigger in mid and low registers than in treble. A smaller horn has less mid and bass, so the treble are more prominent. Nevertheless, to gain a very clear and powerful high range, I've always felt that the secret is in the soundbox, but also in the horn. The treble is what suffers most from the sound tube curves and deflections. Maybe a Balmain type straight horn would render a better treble register using the same soundbox than a curved one (as emg/expert and all the reentrants). Has anyone ever tried such a comparison?