Homemade Exponential Horn Project

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Ethan
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Re: Homemade Exponential Horn Project

Post by Ethan »

The nearest I’ve come to a Balmain-reentrant comparison is a 150 Hz. corrugated carboard tractrix horn compared to the Alhambra—the tractrix horn was pivoted and had an elbow to hold an Orthophonic soundbox and the Alhambra just has a curved horn, not reentrant, so the difference probably wasn’t as noticeable as it would be with a true Balmain and reentrant, but the tractrix horn did seem to have more treble, although part of that could have been because it didn’t have a proper lid to block sound from the face of the soundbox.

I finished the final structural layer of the mouth this morning and removed it from the former this afternoon—fortunately, it came out after striking the narrow end repeatedly with a mallet, so dissolving it wasn’t necessary. It looks as though I’ll have to trim off a little bit from the mouth, where the paper shrank unevenly, but for the most part, the rippling-when-re-wet hasn’t caused any major problems; just a couple of spots that could be filled in with paper mâché paste if necessary.
The paper pulled away from the end of the former, creating a discontinuity in the final flare, which will probably have to be cut off.
The paper pulled away from the end of the former, creating a discontinuity in the final flare, which will probably have to be cut off.
The next step will be fastening the next mounting ring to the curved part of the horn, then building up the thickness another ⅛”—but I couldn’t resist the temptation to rig up something to hold the two parts together for a mid-construction test:
The whole horn, with the mouth held in place by a makeshift scaffold.
The whole horn, with the mouth held in place by a makeshift scaffold.
There’s a rather sizeable gap between the neck and the mouth, but even so, the paper horn’s sound is much better than the Alhambra’s; there is more bass, although presumably not as much as there will be when the two halves are sealed properly, and it sounds generally clearer and fuller—it even makes my one Brunswick Light-Ray electric sound almost good.

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dzavracky
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Re: Homemade Exponential Horn Project

Post by dzavracky »

WOW! Fantastic job Ethan... I am very impressed.

David

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Inigo
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Re: Homemade Exponential Horn Project

Post by Inigo »

That looks wonderful!
Inigo

poodling around
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Re: Homemade Exponential Horn Project

Post by poodling around »

Ethan wrote: Mon Jul 26, 2021 9:23 pm The nearest I’ve come to a Balmain-reentrant comparison is a 150 Hz. corrugated carboard tractrix horn compared to the Alhambra—the tractrix horn was pivoted and had an elbow to hold an Orthophonic soundbox and the Alhambra just has a curved horn, not reentrant, so the difference probably wasn’t as noticeable as it would be with a true Balmain and reentrant, but the tractrix horn did seem to have more treble, although part of that could have been because it didn’t have a proper lid to block sound from the face of the soundbox.

I finished the final structural layer of the mouth this morning and removed it from the former this afternoon—fortunately, it came out after striking the narrow end repeatedly with a mallet, so dissolving it wasn’t necessary. It looks as though I’ll have to trim off a little bit from the mouth, where the paper shrank unevenly, but for the most part, the rippling-when-re-wet hasn’t caused any major problems; just a couple of spots that could be filled in with paper mâché paste if necessary.

Misshappen horn mouth.jpeg

The next step will be fastening the next mounting ring to the curved part of the horn, then building up the thickness another ⅛”—but I couldn’t resist the temptation to rig up something to hold the two parts together for a mid-construction test:

Whole horn with makeshift support.jpeg

There’s a rather sizeable gap between the neck and the mouth, but even so, the paper horn’s sound is much better than the Alhambra’s; there is more bass, although presumably not as much as there will be when the two halves are sealed properly, and it sounds generally clearer and fuller—it even makes my one Brunswick Light-Ray electric sound almost good.
Very good indeed.

Ethan
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Re: Homemade Exponential Horn Project

Post by Ethan »

More progress—I filled in the ragged end of the neck with paper mâché paste, added a couple layers of paper over the whole section, glued the wood mounting ring in place, fastened the horn together for some more testing, and cut off the uneven edge from the mouth. Technically, the horn can support itself, but it’s rather unbalanced on the small cabinet and the wooden keel isn’t in place yet, hence the bridge lamp holding it up.
The horn neck with paper mâché paste to fill in around the rough rim.
The horn neck with paper mâché paste to fill in around the rough rim.
The whole horn in place on the test cabinet--the uneven mouth has been trimmed, but the neck still needs a few more layers of paper and the wood keel.
The whole horn in place on the test cabinet--the uneven mouth has been trimmed, but the neck still needs a few more layers of paper and the wood keel.
The bass doesn’t go all the way down to 100 Hz.; on electrical records, there isn’t much below about 130 Hz., and using an electric speaker in place of the soundbox, a sweep from 10,000 to 0.1 Hz. shows a low cut-off around 156 Hz., but possibly peaks that might be audible below that. (I don’t have a soundproof room for testing, so some of the lower frequencies could have been from sources other than the horn.).

Interestingly, one of the cut-off frequency-determining methods I’ve found is that the mouth diameter needs to be roughly equal to the wavelength of the lowest frequencies to be passed through the horn; my horn has a 27” diameter mouth, which means roughly an 85” perimeter—and that corresponds approximately to the wavelength of a 160 Hz. tone, which is roughly where the measured cut-off is when using the electric speaker. I do think that the neck isn’t thick enough yet, as I can feel it vibrating while playing, but perhaps the mouth isn’t close enough to the corner of the room for corner-loading too work properly. I’ll be adding at least a couple more layers over the next few days, so it will be interesting to hear whether the frequency response is any different afterwards.

Here are a few videos of the gramophone playing, prior to having the horn rim trimmed:

https://www.youtube.com/watch?v=d-HhS72m0Mg

“Kansas City Stomps” by Jelly-Roll Morton’s Red Hot Peppers—late-’20s Victor electric sound with a quiet Columbia-type laminated surface.

https://www.youtube.com/watch?v=-eHVF9TN6_8

“Copenhagen” by the Benson Orchestra of Chicago—typical late-acoustic Victor sound.

https://www.youtube.com/watch?v=Hkkj-HdB3gw

“Positively – Absolutely” by Mal Hallett and His Orchestra—Columbia Viva-Tonal.

https://www.youtube.com/watch?v=nFMtq1jKeV4

“To-Night’s My Night with Baby” by the Broadway Bell-Hops—acoustic Harmony.

https://www.youtube.com/watch?v=Zv9KzT12gzk
“Clarinet Marmalade” by Fletcher Henderson and His Orchestra (1926)—one of the best-sounding records in my collection, as well as one of my favorites.

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Jwb88
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Re: Homemade Exponential Horn Project

Post by Jwb88 »

From what I can tell this thing sounds FANTASTIC! This is obviously well-worth your efforts. Nice job! Now finish it off well!

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dzavracky
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Re: Homemade Exponential Horn Project

Post by dzavracky »

Boy Ethan that really turned out fantastic! Congrats on a successful project... I am looking forward to seeing the cabinet you make for it.

David

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Orchorsol
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Re: Homemade Exponential Horn Project

Post by Orchorsol »

An over-used word in this day and age, but truly AWESOME! Congratulations, it's fabulous!
BCN thorn needles made to the original 1920s specifications: http://www.burmesecolourneedles.com

Youtube channel: https://www.youtube.com/channel/UCe4DNb ... TPE-zTAJGg?

old country chemist
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Re: Homemade Exponential Horn Project

Post by old country chemist »

Hello Ethan, I have listened to parts of our recordings on youtube (something I seldom look into).
The clarity seems exceptionally good, and the overall "open horn" effect is most noteworthy. Have you tried some other reproducers? I suppose you are tied to the Orthophonic box which fits your tone arm. Perhaps it would be possible to fit an adapter, and try other soundboxes if you have any? If you had one, I would recommend trying an Orchorsol soundbox. or a No4 mica diaphragm soundbox which can give surprisingly good results coupled to an external horn.
I wish you well with the finished gramophone. Great pleasure can be obtained from an acoustic machine, and yours looks and sounds as if it will be a favourite machine to play your wonderful jazz and dance records.
As an aside, I have never found an electric "Harmony record. I have several and they always amaze me at the volume and quality of reproduction from an acoustic record. A pity that here, in Britain, there are few to be found, sadly.

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emgcr
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Re: Homemade Exponential Horn Project

Post by emgcr »

Brilliant Ethan---many congratulations---the horn looks very good indeed. The shape would appear to be spot on and the sound is wonderful only lacking a little in the bass department at present. You are rightly concerned about mechanical strength, particularly as there is no metal swan-neck. Mk IX and X EMG horns were too weak and many quickly drooped/broke as I am sure you are well aware.

When adding wall thickness you will be killing two birds with one stone, firstly by increasing mechanical strength where it is especially needed around the bends to resist/prevent future drooping and secondly by increasing resistance to unwanted resonance by producing a very strong and stable sound conduit unable to vibrate. Both considerations are very important for top sound propagation. It is hard to tell but it would seem from the photos that you have achieved a slightly forward lean at the bell mouth which is a good thing as a vertical stance will give the impression of leaning backwards.

I wonder if you could include a very thin layer of something like Kevlar or carbon fibre at the high stress points before the final cosmetic finishing paper ?

You have cleverly positioned the whole phonograph in the corner of the room but you may find that the skilling (angled) ceiling might produce some strange sound reflections. It might be worth experimenting in a fully right-angled corner if you have one available ?

Superb work.

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