An Introduction and Some Questions about Exponential Horns

[phonosandradios]

This is the video I’m basing my project of of

You’ll see in the comments he responded to me gave me all the measurements

Good luck with your project - I hope that you will post the results of your experiment. It looks like it will be a very time consuming one based on the comments made by the you tube poster. Although this is something I will put on my "I want to do" list I am currently deep in the middle of the restoration of my VE-9-55 which has to be squeezed in between day to day life / work etc. We are also about to start major house renovations and all that involves so I suspect the horn project, for me, may be a retirement project and that is still a number of years off yet!

[Ethan]

Hello,

Phonosandradios, I had actually seen this video a while ago, before I had any serious thoughts of making my own horn; but it seems as though it would be hard to make the exponential flare accurately with the bubble-wrapped portion. The flexible former does, however, sound like a very good idea for extraction from the finished horn, as does plastic wrap for a releasing agent—I had heard of using Vaseline, but it seems as though this could soak into the paper of the horn, possibly with structurally-detrimental consequences.

I did try making a fabric mould for a plaster former, but I only got as far sewing five of the eight panels together; I couldn’t get the seams even enough to follow an exponential flare—or, for that matter, any particular flare at all; I think that if I had continued, I would have ended up with a very irregularly-shaped horn indeed. I may try one more time, but sewing by hand instead of machine, and using a sturdier, less-slippery fabric.

I do have another idea that might work; I was thinking back to Lucius1958’s suggestion of foam blocks, and I’m not sure that it would be all that difficult to carve the former out of a suitable type of foam—at any rate, it doesn’t look any harder than any of the fabric-and-filler ideas that I’ve had, so if my second fabric former turns out as poorly as the first, I’ll probably order some blocks and start trying to carve a former.

- Ethan

[phonosandradios]

I was thinking a bit more about this today and about how the process could be improved. The horns in those you tube videos all seem to have a very wrinkly inner surface and I assume this is a by product of using cling film and that as the paper drys it distorts to form those wrinkles. A possible way around this would be to use something like tin foil instead of cling film to line the former. Then it could be sprayed with something like photo mount which would leave a slightly tacky surface against which you could put the first layer of paper. The foil would only be tacky on the sprayed surface and once the horn has been built with multiple layers of paper using normal glue the non tacky side of the foil should allow the whole thing to slide away from the former. As photo mount just creates a tackiness the foil can be pealed away from the first layer of paper once it is removed from the former. A finishing layer of paper then may be glued to the inner surface of the horn to finish it off. I think this way you would be able to achieve a smoother finish on the inner side of the horn.

I am just pondering this at the moment as I am not going to have time to either experiment or actually build it in the foreseeable future to see if using foil would over come the wrinkle problem. Another way forward to create a former would be, as you say, to use foam blocks and carve the former for the bell part of the horn - for me the difficult part of that would be the noise of the carving. Like fingernails down a chalk board

[Ethan]

I assumed that the wrinkly inner surface of the horn in the video was due to the different papers used for the innermost surface versus the outer layers, as he says that he first applied two layers of “white paper” followed by fifty layers of “strips of newspaper”—if the outer layers of newspaper shrank more than the inner layers of white paper as they dried, the innermost layers might have been constricted by the outer layers, forcing them to pucker and wrinkle. (I could, of course, be completely wrong about this, although I seem to recall the horn’s creator mentioning somewhere that the wrinkling was due to to different shrinkage rates.)

Foil might actually work quite well, although it may work better to glue it permanently to the former—peeling strips of foil out of the finished horn might be tricky in my case, as the curved portion in my design is fairly long and narrow (about 31.75” long through the center and only about 1.25" in diameter at the throat); but the paper will be wet when I apply it to the former, so it shouldn’t need anything to help it stick.

At any rate, I have some glue and scraps of paper, foil, and plastic wrap, so I can test how easily glued paper separates from both foil and plastic wrap—although I suspect that, even if both work equally in tests, plastic wrap might work better in practice, as its stretchiness could make it easier to apply on a curved surface.

- Ethan

[fran604g]

The same fella who I earlier referenced doing the 3-D printing, is working on a very interesting horn replica again at HiFi Haven - the WE KS-6368. Lots of great ideas that may help envision replicating other exponential horns.

https://hifihaven.org/index.php?threads ... 6368.5826/

Best,
Fran

[emgcr]

I have just been informed that this magnificent and definitive tome is now available for $150 as follows :

https://www.parts-express.com/high-qual ... s--500-032

[Ethan]

Hello emgcr, I’m glad to hear from you! I looked at the link you gave, and from what I’ve heard, the price doesn’t seem too bad as far as technical, textbook-type books go, especially considering how much information is in it (“magnificent and definitive” looks like just about the right description); I’ll definitely keep it in mind for future horns. My current design is pretty much settled, if only because it seems fairly close in shape to a real EMG horn (specifically, the Mark X’s) and it looks, based on my drawings, as though it fits reasonably well in the space available. I’m away at college right now, but if you (or anyone else) are interested, I can start a new topic and post pictures of my progress once the semester is over.

- Ethan