Homemade Exponential Horn Project

[anchorman]

I guess I won’t worry at the moment too much about what is happening before the horn itself, and try to design the horn to be as long as reasonably possible from the standard EMG spigot to the mouth of the horn, and make an attempt at having tonearm and conduit expand appropriately as I have the ability to do with improved tone arms, etc. the thing that bugs me most about the arms I have is the geometry is not consistent as the soundbox is lifted up and down. The needle would only be perpendicular to the record surface at one perfect needle length. It looks like the swan neck arms used by EMG compensate for this. I’ve got a couple of goose neck Victor arms that I could use to adapt to a more gentle taper that also have closer to proper geometry in their ability to swing the soundbox up and down

[Watanabehi]

Hideki, I surrendered years ago to your charming achievements in gramophone things, your yt videos, your singing, and all that. On me you have an unconditional fan. I already knew your emg-esque handmade gramophone, and it's great! Probably by one of your videos playing it...

Hi Inigo,

I hope these videos work to project the sound.

Hideki

[Ethan]

Sometimes, tone-arms seem like the hardest part of making homemade machines (which is funny, as they aren’t even the part that needs to be made from scratch!)—the HMV arm that I used has good tracking alignment for the right needle length, but it has the same problem with other lengths. Have you considered making your own out of papier maché/appliqué, so that you can design it to have good tracking alignment regardless of needle length, and a single flare from the soundbox all the way to the horn mouth?

As far as I know, extending the horn before the conduit (I’m assuming you mean having a tapered tone-arm followed by a constant-bore conduit?) shouldn’t have any effect on the taper, because the constant-bore tubing should—I believe—be able to pass all frequencies, so anything that made it through the tone-arm should reach the horn proper, in which case the horn’s cut-off frequency just needs to be the same as or higher than the tone-arm’s. It's probably actually more complicated than that though, especially if the horn or conduit materials are very resonant; but as Inigo says, horns do seem to be fairly forgiving at smaller diameters.

Watanabehi, your machine sounds wonderfully clear! Have you ever tried measuring its frequency response? And what did you use to make the internal plumbing and the metal(?) portion leading out of the cabinet to the base of the paper section?

[anchorman]

If I make a tone arm, it would probably be brass, but now you’ve got me thinking that there are other options. I’m just realizing that I could use the existing metal pivots and do the rest with fiberglass or carbon fiber or laminated wood veneer or even papier-mâché…

Ethan, I think I missed a bit of information somewhere: what is the point of keeping the connecting conduit constant bore? Ease of manufacture? Or is there a reason to do that for sonic qualities? What I was referring to was calculating the taper of the horn using the tone arm opening as the start of the taper vs calculating the horn using the output spigot diameter of the conduit as the start of the taper, and letting the small diameter before that simply be whatever the tonearm was.

[Watanabehi]

Sometimes, tone-arms seem like the hardest part of making homemade machines (which is funny, as they aren’t even the part that needs to be made from scratch!)—the HMV arm that I used has good tracking alignment for the right needle length, but it has the same problem with other lengths. Have you considered making your own out of papier maché/appliqué, so that you can design it to have good tracking alignment regardless of needle length, and a single flare from the soundbox all the way to the horn mouth?

As far as I know, extending the horn before the conduit (I’m assuming you mean having a tapered tone-arm followed by a constant-bore conduit?) shouldn’t have any effect on the taper, because the constant-bore tubing should—I believe—be able to pass all frequencies, so anything that made it through the tone-arm should reach the horn proper, in which case the horn’s cut-off frequency just needs to be the same as or higher than the tone-arm’s. It's probably actually more complicated than that though, especially if the horn or conduit materials are very resonant; but as Inigo says, horns do seem to be fairly forgiving at smaller diameters.

Watanabehi, your machine sounds wonderfully clear! Have you ever tried measuring its frequency response? And what did you use to make the internal plumbing and the metal(?) portion leading out of the cabinet to the base of the paper section?

No, I have never thought about making my own tonearm. But I could have used HMV re-entrant horn version longer tonearm, since it has better tracking than orthophonic tonearms. In order to compensate the tracking error, I moved around the turntable position to have a better tracking, but still it is not perfect. If I can find HMV longer tonearm, I should replace the existing one to the better one. It is clear that HMV longer tonearm is better, since I have HMV 202 and Orthophonic Credenza. As you can see on the video, I use a longer susudake fiber need. If I use thorn needle or steel needles, it is too loud.

I never thought about the conduit. I just used PBC pipe which can fit for my project. The issue that PBC pipe has it is flexible, so it can bend, as you can see on the photos. As a result, the front part of the bell sags. If I can find, I should use metal pipe. Obviously PBC does not have exponential shape.

Thank you. I don't have any instrument to measure the sound. I used PBC pipe to connect the tonearm and the horn. The horn bell is a copy of my EMG Xa horn. I used layers of decoupage paper and wood glue to make the horn. Everything is based on the trial and error process. I appreciate if you can provide any information on the better materials. Thank you.

Hideki

[Ethan]

Anchorman, I used a constant-bore conduit because starting the taper right after the tone-arm would have made the bends through the conduit and swan-neck much tighter, which could have caused worse internal reflections and decreased the treble response—a narrower tone-arm with the same cut-off frequency or a lower cut-off (i.e., slower flare) with the same tone-arm outlet diameter would have fixed that, but the HMV large-bore swan-neck style seemed like the best compromise of tracking alignment, cut-off, and price.

It would theoretically be best to start the exponential flare at the tone-arm outlet, so that the conduit and horn have the same flare, but the consensus seems to be that it isn't extremely important--there’s a video on YouTube of an EMG Xb Oversize horn on an HMV 31 base, and I believe whoever posted it said the sound wasn’t much different from a complete Xb Oversize, even though the horn, conduit, and tone-arm had mismatched flares.

Hideki, does the Credenza tone-arm you’re using have the post-1928-recall crook? I believe they’re supposed to improve the tracking alignment, although it still might not be as good as the HMV re-entrant type.

Can you get Audacity on your computer? It’s a free audio editing program, and it has a spectrum analyzer feature, so if you can get videos or recordings on your computer, you should be able to import them into Audacity and measure the frequency content—it wouldn’t be perfect, but it might at least give an idea of the response.

I’m looking for better materials, myself—I suspect that the Elmer’s glue I used is too resonant and flexible to pass low frequencies effectively. What kind of wood glue did you use? And have you tried water-flour glue? I’ve heard that it can be quite hard, but also prone to mold and bugs if not done right.

[anchorman]

If you want stiffer glue, try using hide glue, or maybe a layer of hide glue after wallpaper paste. I’ve considered using PVA (Elmer’s etc) glue, but it has a tendency to creep over time, which I imagine would lead to sagging.

I’ve been concerned about finding acid free paper to use, but my friend rightly pointed out yesterday, that so long as you put a good coat of lacquer over everything to seal it, you’ll prevent moisture from getting into the paper. Acid needs moisture to destroy the paper over time.

[Ethan]

I’ve considered using PVA (Elmer’s etc) glue, but it has a tendency to creep over time, which I imagine would lead to sagging.

Definitely—for a while, I supported the horn by resting the joint between the two halves on top of a bridge lamp, but even with that, the weight of the bell bent the neck a little bit—I’ve since added more layers, so the neck is just over ¼” thick now, but I still have it held up by the lamp, although I’ve moved it closer to the mouth, so that it’s more balanced—I haven’t noticed any more sagging with the new arrangement.

I’ve wondered about acid-free paper, too—my horn is just made from packing paper and grocery bags, so I doubt very much whether it’s acid-free—once it’s finished, though, I’m planning to give it a layer of shellac.

Have you thought about using fiberglass instead of paper? I’m considering it as a possibility if I do make another horn, although it might require different materials for the former—but it should be much less prone to sagging, and I believe it’s supposed to be acoustically inert.

[anchorman]

I’ve considered, but I hate hate hate working with it. Toxic resin, regardless of whether it’s polyester or epoxy, and then when you go to sand it, itchy itchy itchy. If I had a perfect design worked out, I might consider it.

Regarding the sagging, I think that’s probably pretty common with no support structure. The bigger horns like Graham Rankin made tend to have a metal casting for the base of the elbow. If you look at his pictures of how he made his, the former is much easier to deal with since the unsupported fiberglass doesn’t go down so narrow and around so many curves. My goal is to try to do something similar with that part, so it’s not reliant on a mold/former. I’m not sure if you’ve seen pictures of any of Ahmed’s horn attempts, but he 3D printed the lower portion that Graham had cast in aluminum. I may try 3D printing, or try to find another way to tackle that part. I think your initial idea to add a plywood keel was pretty good.

One way that can work surprisingly well is to build up on something easily removed like clay or styrofoam, then cut the whole part in half (or even just cut open one side. Remove the former, and piece the part back together, adding more layers to cover the seam and make it sturdy.

Regarding acid free materials, the originals were not made from particularly special paper (unless old phone books and the like count as special paper?). If one keeps them away from moisture and humidity, they’re probably going to outlive us easily.

[Watanabehi]

Anchorman, I used a constant-bore conduit because starting the taper right after the tone-arm would have made the bends through the conduit and swan-neck much tighter, which could have caused worse internal reflections and decreased the treble response—a narrower tone-arm with the same cut-off frequency or a lower cut-off (i.e., slower flare) with the same tone-arm outlet diameter would have fixed that, but the HMV large-bore swan-neck style seemed like the best compromise of tracking alignment, cut-off, and price.

It would theoretically be best to start the exponential flare at the tone-arm outlet, so that the conduit and horn have the same flare, but the consensus seems to be that it isn't extremely important--there’s a video on YouTube of an EMG Xb Oversize horn on an HMV 31 base, and I believe whoever posted it said the sound wasn’t much different from a complete Xb Oversize, even though the horn, conduit, and tone-arm had mismatched flares.

Hideki, does the Credenza tone-arm you’re using have the post-1928-recall crook? I believe they’re supposed to improve the tracking alignment, although it still might not be as good as the HMV re-entrant type.

Can you get Audacity on your computer? It’s a free audio editing program, and it has a spectrum analyzer feature, so if you can get videos or recordings on your computer, you should be able to import them into Audacity and measure the frequency content—it wouldn’t be perfect, but it might at least give an idea of the response.

I’m looking for better materials, myself—I suspect that the Elmer’s glue I used is too resonant and flexible to pass low frequencies effectively. What kind of wood glue did you use? And have you tried water-flour glue? I’ve heard that it can be quite hard, but also prone to mold and bugs if not done right.

Ethan,

The tonearm is the earlier Credenza's model. I downloaded Audacity. I used a glue called "Harder-than wood". No, I have not tried water-flour glue.

Hideki