An Introduction and Some Questions about Exponential Horns

[fran604g]

Welcome to the forum! In regard to producing/reproducing specific horn designs, there's a guy on the HiFi Haven forum who has experimented extensively with 3-D printing various old horn designs for use in modern speaker systems. If for no other reason than one of interest, you might find his insight valuable in your pursuit(s).

https://hifihaven.org/index.php?threads ... mpts.5480/

Best regards,
Fran

[Lucius1958]

Here's a possible idea:

Instead of molding the horn as a single unit, how about making a mold for one section, or "petal", at a time? You might be able to use foam blocks for the mold (in my theatre group, we have used it for building large props; and you can cut and shape it to the correct profile & radius). You can then build each piece up to a good thickness; then join them together, and reinforce the outside with more layers. This might help if you're planning a more complex shape, as on the EMG/Expert horns.

-Bill

[emerson]

Hey, Where in Pa. are you----close to the NJ border?

[Ethan]

Hello again, and thank you all for your kind welcome to the forum! (I’m sorry that I haven’t replied sooner; I’ve been busy finishing up a Lego castle that I’ve been working on so that I’ll have some clear floor space for my phonograph-in-planning, and yesterday I was making and testing a cardboard “tractrix” horn—more about that soon.)

@ Orchosol, or anyone else who may happen to know—

How does the volume of an EMG machine compare to the smaller exponential-horned HMVs? I have one of the early straight-horned Orthophonics, which I’m guessing would sound similar to the HMVs (the horn is about 40” from soundbox to mouth, with mouth dimensions of just over 14” by 12”, although there may be a several-inch constant-bore section just after the tone-arm), and with an extra-soft tone needle inserted just enough to be grasped by the thumbscrew, it’s just barely tolerably quiet with the horn doors open.

Does the Mark VIII have the “holographic” effect of the larger EMGs? I thought that I read in another thread that the effect is less noticeable on the smaller machines, but I think that the Mark IX was the lowest number to be mentioned.

I had already seen the thread by “emgcr,” and found it quite interesting, although the methods, unfortunately, are mostly beyond my means.

Is there currently an equivalent to sugar paper that can be obtained easily and fairly inexpensively?

Also, how might one make the curved part of the horn? The second of my two most likely plans is similar in shape and size to the Mark X, although with a detachable mouth section—rather like the various “export” models—but the only way I can think of to make the curved back portion is the sawdust-filled-fabric mould, which, as mentioned above, seems likely to give inferior results.

This question may be slightly off-topic, in a way: In my initial post, I said that I would be making another post specifically for my questions about whether EMGs were meant to be placed in corners; would it be better to post it in the “Machines” section, as I’m in Pennsylvania and, sadly, don’t anticipate building my horn across the pond, or in the “British and European Machines” section, as it relates to a British horn design?

@ shoshani, your points about matching the soundbox to the horn all make sense; I’m just wondering whether, for a given soundbox and tone-arm (in my case, both are from Orthophonics, so they should already be matched), the only matching that needs to be done is to design the horn with the same diameter throat as the outlet of the tone-arm—I’ve read Modern Gramophones’ chapters on horns and soundboxes multiple times, and it seems to me that, as long as the horn’s cut-off is no lower than the tone-arm’s, this is all that is required; but it could be that there is some important point that I’m missing, especially in the soundbox chapter.

@ Lucius1958, the foam blocks sound like a promising idea—easier to shape than wood blocks, but not as likely to turn out as distorted as the sawdust-and-fabric—although I’m not quite sure that I’m picturing what you mean when you say “a mold for one section, or ‘petal’, at a time”; are you thinking of something like a paneled morning glory horn? I was already planning on making the horn in two sections, one for the straight mouth and another for the curved part between the mouth portion and the throat, but it sounds to me as though we may be thinking of different types of sections.

@ emerson, I’m on the other side of the state, near the Ohio border.

[Lucius1958]

Hello again, and thank you all for your kind welcome to the forum! (I’m sorry that I haven’t replied sooner; I’ve been busy finishing up a Lego castle that I’ve been working on so that I’ll have some clear floor space for my phonograph-in-planning, and yesterday I was making and testing a cardboard “tractrix” horn—more about that soon.)

@ Orchosol, or anyone else who may happen to know—

How does the volume of an EMG machine compare to the smaller exponential-horned HMVs? I have one of the early straight-horned Orthophonics, which I’m guessing would sound similar to the HMVs (the horn is about 40” from soundbox to mouth, with mouth dimensions of just over 14” by 12”, although there may be a several-inch constant-bore section just after the tone-arm), and with an extra-soft tone needle inserted just enough to be grasped by the thumbscrew, it’s just barely tolerably quiet with the horn doors open.

Does the Mark VIII have the “holographic” effect of the larger EMGs? I thought that I read in another thread that the effect is less noticeable on the smaller machines, but I think that the Mark IX was the lowest number to be mentioned.

I had already seen the thread by “emgcr,” and found it quite interesting, although the methods, unfortunately, are mostly beyond my means.

Is there currently an equivalent to sugar paper that can be obtained easily and fairly inexpensively?

Also, how might one make the curved part of the horn? The second of my two most likely plans is similar in shape and size to the Mark X, although with a detachable mouth section—rather like the various “export” models—but the only way I can think of to make the curved back portion is the sawdust-filled-fabric mould, which, as mentioned above, seems likely to give inferior results.

This question may be slightly off-topic, in a way: In my initial post, I said that I would be making another post specifically for my questions about whether EMGs were meant to be placed in corners; would it be better to post it in the “Machines” section, as I’m in Pennsylvania and, sadly, don’t anticipate building my horn across the pond, or in the “British and European Machines” section, as it relates to a British horn design?

@ shoshani, your points about matching the soundbox to the horn all make sense; I’m just wondering whether, for a given soundbox and tone-arm (in my case, both are from Orthophonics, so they should already be matched), the only matching that needs to be done is to design the horn with the same diameter throat as the outlet of the tone-arm—I’ve read Modern Gramophones’ chapters on horns and soundboxes multiple times, and it seems to me that, as long as the horn’s cut-off is no lower than the tone-arm’s, this is all that is required; but it could be that there is some important point that I’m missing, especially in the soundbox chapter.

@ Lucius1958, the foam blocks sound like a promising idea—easier to shape than wood blocks, but not as likely to turn out as distorted as the sawdust-and-fabric—although I’m not quite sure that I’m picturing what you mean when you say “a mold for one section, or ‘petal’, at a time”; are you thinking of something like a paneled morning glory horn? I was already planning on making the horn in two sections, one for the straight mouth and another for the curved part between the mouth portion and the throat, but it sounds to me as though we may be thinking of different types of sections.

@ emerson, I’m on the other side of the state, near the Ohio border.

I was thinking of the bell section there: the curved neck might be possible, if you make a 2 part mould, and once again, piece the halves together.

-Bill

[Orchorsol]

How does the volume of an EMG machine compare to the smaller exponential-horned HMVs? I have one of the early straight-horned Orthophonics, which I’m guessing would sound similar to the HMVs (the horn is about 40” from soundbox to mouth, with mouth dimensions of just over 14” by 12”, although there may be a several-inch constant-bore section just after the tone-arm), and with an extra-soft tone needle inserted just enough to be grasped by the thumbscrew, it’s just barely tolerably quiet with the horn doors open.

I think the volume between types is roughly in the same ball park, but it's only an impression. It sounds as though you want really low volume compared to the output of most gramophones, and to some extent I believe you won't get all the sonic benefit of a large and well designed horn system that way. A lot of us EMG enthusiasts find that they give of their very best when they're driven hard and loud!
By the way, I might be wrong here but isn't "straight-horned Orthophonic" a contradiction in terms?

Does the Mark VIII have the “holographic” effect of the larger EMGs? I thought that I read in another thread that the effect is less noticeable on the smaller machines, but I think that the Mark IX was the lowest number to be mentioned.

To my ears it certainly does, possibly even more than the larger models, due I think to the purity of its design (largely straight).

Is there currently an equivalent to sugar paper that can be obtained easily and fairly inexpensively?

I have no idea I'm afraid, and I'm not even sure exactly what sugar paper is or was (sorry for a possibly useless comment!) except I believe it was a strong, coarse paper used for paper sacks (sacks of sugar in the old days?).

Also, how might one make the curved part of the horn? The second of my two most likely plans is similar in shape and size to the Mark X, although with a detachable mouth section—rather like the various “export” models—but the only way I can think of to make the curved back portion is the sawdust-filled-fabric mould, which, as mentioned above, seems likely to give inferior results.

Again I really don't know Ethan, except to say I have a stub of an EMG Mk IX horn to restore one day (the IX being a poor design structurally - many sagged and some even broke in two - the rest of this horn has been lost) and I'm probably going to make moulds by lining an intact horn with a plastic bag and pouring in builders' polyurethane foam. Moulds plural (actually maybe 'formers' is the word since they will be inside rather than outside the finished article) - because I'm not confident of one entire piece withdrawing reliably after the papier applique horn is formed, so I'll do it in stages.
Going back to the sugar paper, at some point when I can get the remains of this horn out of storage I could send you a piece of the interior paper layers for reference.

[dennis]

download/file.php?id=24180

My apologies if someone already referenced this but I didn’t see it.

[shoshani]

I have one of the early straight-horned Orthophonics, which I’m guessing would sound similar to the HMVs (the horn is about 40” from soundbox to mouth, with mouth dimensions of just over 14” by 12”, although there may be a several-inch constant-bore section just after the tone-arm), and with an extra-soft tone needle inserted just enough to be grasped by the thumbscrew, it’s just barely tolerably quiet with the horn doors open.

The sound of Orthophonics and HMVs will be similar, but not identical. Victor used wood for most of their exponential horn body, while HMV used zinc. The metal horn is more resonant and probably transmits higher frequencies a bit more efficiently. (HMV machines in general tend to be designed with resonance in mind, which I think is one of the secrets of why their portables, especially the 101, sound so good.)

@ shoshani, your points about matching the soundbox to the horn all make sense; I’m just wondering whether, for a given soundbox and tone-arm (in my case, both are from Orthophonics, so they should already be matched), the only matching that needs to be done is to design the horn with the same diameter throat as the outlet of the tone-arm—I’ve read Modern Gramophones’ chapters on horns and soundboxes multiple times, and it seems to me that, as long as the horn’s cut-off is no lower than the tone-arm’s, this is all that is required; but it could be that there is some important point that I’m missing, especially in the soundbox chapter.

I don't know if anyone has done a study on Orthophonic tonearms, to see whether they were the same length regardless of horn opening. I know that HMV, in their pre-Orthophonic-style "New Gramophone" did use tonearms of different lengths, usually between 8 and 9.5 inches, depending on the horn, size of the cabinet, and other factors. I should grab my copy of "His Master's Gramophone" and check the tonearms on the HMV re-entrant machines.

[OrthoFan]

I don't know if anyone has done a study on Orthophonic tonearms, to see whether they were the same length regardless of horn opening. I know that HMV, in their pre-Orthophonic-style "New Gramophone" did use tonearms of different lengths, usually between 8 and 9.5 inches, depending on the horn, size of the cabinet, and other factors. I should grab my copy of "His Master's Gramophone" and check the tonearms on the HMV re-entrant machines.

Based on the three models I've owned -- the Credenza (8-30), the small Consolette (4-3), and the mid-sized VV-4-40, the tonearms differed. For both the Credenza and the 4-40, the taper of the tonearms is more gradual, compared to the Consolette. The Consolette's tonearm is somewhat shorter than the larger, folded horn models. As for differences in length, if memory serves me right, the Credenza has the longest tonearm of the three.

It would be interesting to see a comparison chart with photos showing the tonearms of various Orthophonic models.

OrthoFan

[Ethan]

@ OrthoFan, as it happens, I was already considering making another post specifically about the differences in Orthophonic tone-arms, partly to help me decide which tone-arm would work best for my project, and partly just as a useful resource for anyone interested in variations between models—I only have two tone-arms to contribute, myself, but others might be able to share photos and dimensions of their tone-arms, as well.

I believe you won't get all the sonic benefit of a large and well designed horn system that way.

Unfortunately, that’s just about the same conclusion that I’ve been coming to—I think that I’ll just have to make the best design that I reasonably can, given my limited space and designing experience, and then experiment with different locations in my room, needle types, and probably also materials to stuff in the horn mouth if all else fails. (Also, while I’m on the subject of loudness, do you happen to know the average decibel level, for a given needle, type of music and recording, and distance from the horn mouth, of the external-horned EMGs? I have read various descriptions of the sound and volume, but very few actual measurements.)

A lot of us EMG enthusiasts find that they give of their very best when they're driven hard and loud!

This is something that I’ve heard multiple times before on this forum, but have never quite understood, as, from what I have read, exponential horns should require a quieter input than non-scientifically designed horns in order to produce the same output volume—Does it have something to do with the way in which louder sounds interact with the room?

By the way, I might be wrong here but isn't "straight-horned Orthophonic" a contradiction in terms?

I don’t believe that “straight-horned Orthophonic” is contradictory; I’ve gathered that “Orthophonic” was just a marketing term used to describe the whole system of electrical recording and matched-impedance reproduction—The first four models in the Orthophonic range were the Consolette, Colony, Granada, and Credenza, of which the first three all had the same straight horn and only the Credenza had a folded horn, so it seems to me as though the straight horn started out as the standard “Orthophonic horn,” with the larger, folded horn only used in the top-of-the line model, but then Victor began introducing smaller folded horns even in tabletop Victrolas, so the straight horn became the economy version.


I tried finding “Armchair Phonatics,” but I only found one result, which only got as far as plotting out the horn’s radii on a piece of paper—it looks as though the plan may be for a Wilson horn, given the 48” length and 24” diameter mouth; but at any rate, the cut-off frequency appears to be about 166 Hz., which is higher than I would like, although I suspect that, because I use extra-soft-tone needles, a good treble response is more important than a good bass response for me.

I think, however, that I may have found a solution to the problem of making a mould/former; I was talking about my designs with my father over the weekend, trying to think of a way to make the former for the curved section of the horn, and he found a description of how to make a former at a site called Inlow Sound—the method won’t work for a curved horn, but it looks as though it could work very well indeed for a straight horn, so I should be able to use it either for most of the Mark VIII-like horn or for the mouth section of the Mark X-like horn.

If I use the Inlow Sound method for the straight section, will fabric-and-sawdust (or sand) work well enough for the former for the narrow-diameter curved section? I’m fairly good at simple sewing—I made myself a frock coat from an adapted morning coat pattern a few years ago, although I wouldn’t ask anyone other than myself to wear it in public—so I ought to be able to get the shape right; the two main problems that I can see are lack of rigidity, because the filling will probably be able to shift around a little, and removal of the former—Might it work to coat it carefully with plastic wrap, then, when the horn is dry, empty the filler and peel out the fabric and plastic wrap? (I might be able to whip up a sketch, if anyone is having trouble picturing this.)

To join the straight section to the curved section in the Mark VIII-type horn, would it work to place the finished curved part in place on the end of the former, then build up paper layers over it as the straight section is being made? (See my sketch, below.)

For the joint between the horn and the internal conduit, should a socket made from ¼” aluminum tubing be strong enough to support the weight of either a roughly four-foot-long horn or a Mark X-like horn with a plywood “keel” along the inside of the large curve? I’m thinking that the throat of the horn will have a piece of tubing built into it, such that an inch or two protrudes and can slide into another tube at the end of the internal conduit, as shown on a Mark VIII-type horn in the lower left pane in my sketch.

Should I be planning on making some kind of external support for the Mark VIII-like horn, to prevent the horn from breaking under its own weight or unbalancing the cabinet? To keep the cost and complexity fairly low, I’m planning on making a cabinet similar to the sort used on the later EMGs, but with the horn coming up towards one side, such that cabinet can be placed against a wall while still allowing the horn to be swung clear of the lid; but it seems as though the horn might unbalance it when swung to the side.

Also, would it make it any easier to read my posts if, instead of saying “Mark VIII-like” or “Mark X-type,” I use my own horn design designation and attached a couple of scans from my design notebook, showing sketches of the two designs with their designations? (The Mark X-like horn, for example, is Type B, No. 16, or simply “B-16,” in my notebook, which might be easier to read.) It occurs to me that my posts are a trifle—er—lengthy, and might be easier to read with a simple designation and reference sketch, instead of a comparison to the nearest EMG horn.