An Introduction and Some Questions about Exponential Horns

[Ethan]

Hello,

As the topic title suggests, this is my first post on the forum, so I will begin with a brief (-ish) introduction—
I first became interested in phonographs about two years ago, when my tenth-grade U.S. history teacher shared an on-line article about music during the Great War, with links to some recordings of contemporary Victor records—I rather liked some of the music, and part-way through eleventh grade, I bought a 1915 VV-VIII, so that I could listen to original ragtime and ragtime-esque music (roughly pre-1920) as it was originally meant to be heard—But, along with the VV-VIII came a few acoustic Paul Whiteman records and one Orthophonic fox-trot from 1930 . . . and I started to become more interested in dance music from the ’20s as well . . . but I couldn’t adjust the VV-VIII’s soundbox to my satisfaction . . . So I began trying to find information about horn design . . . and learned about the Orthophonics and E.M.G.s . . . and bought a VV2-55, mostly for its relatively stable soundbox . . . then started buying more Orthophonic dance music . . . then made a cardboard 150-Hz. modified exponential horn for use with the VV2-55’s tone-arm and soundbox . . . then bought a Victrola Alhambra, as the brighter sound of the straight-horned Orthophonics seemed preferable to the somewhat muffled sound of the folded-horn models . . . but it doesn’t have nearly the bass or treble response of the cardboard horn . . . so I decided that, if I wanted a phonograph with reasonably flat and wide frequency response, I should make something along the lines of an E.M.G., using an Orthophonic soundbox and tone-arm (a real E.M.G. gramophone would be far outside my price range).
So far, I have come up with numerous horn designs, ranging from a 90-Hz. wooden folded exponential horn to a 150-Hz. straight tractrix horn—But there remains a major problem before I can choose a design and start construction: The only large exponential-horned phonograph that I have heard in person is the Credenza in Debence Antique Music World, in Franklin, PA, which, as I recall, rattled, although whether the origin of the rattle was a dirty record, a worn record, a worn needle, an out-of-condition soundbox, or an unsealed horn, is a mystery. I have read the relevant sections of Modern Gramophones and Electrical Reproducers, a couple of more recent technical articles that I only half-understood, and numerous discussions about horn design on this forum; but even so, I have mostly only read about, not heard, the different sounds of various sizes and types of exponential-horn phonographs—So, I decided that it was about time to join the forum and ask some questions directly, instead of just reading other somewhat-relevant discussions.

First, I will say that I am aiming for the best sound possible, given my means and space available (which is rather lofty goal to reach for); but, at the minimum, my final design should sound at least as good as a Credenza, the best-sounding phonograph that I can reasonably hope to afford—otherwise, I’ll probably just start saving my allowance and looking on Ebay and Craigslist.

My first few questions are (or at least I hope are) fairly simple—

Of the E.M.G Marks VIII through Xb Oversize, which machine is quietest, for a given record and needle? My room is small—about twelve feet by fourteen, with a roughly six by four-and-a-half-foot alcove—so quieter is better.

How does a Mark VIII compare to a Credenza, in terms of both frequency response and “that magical E.M.G. quality?” One of my more reasonable designs is for a roughly-133-Hz. straight horn, which has a mouth angle of about 42° and mouth diameter of about 28”, and which I presume would sound similar to a Mark VIII, owing to the similar shape and size.

And now for the trickier questions—

Does anyone have any suggestions for how to make a mould? I have gathered that E.M.G. used wood disks, stacked, cut, and sanded to the correct shape, but this sounds rather complicated; and I have read of making a fabric mould, stuffed with sawdust, but this seems as though it would be hard to use for anything but a straight horn, and even then prone to irregularities in the contour of the horn.

What sorts of paper would work well for the horn material? My current plan is to use torn sheets of packing paper, for no other reason than that it seems reasonably cheap and easy to find.

What kind of glue should be used? I read of someone on this forum using “white glue,” and wondered whether something easily obtainable, such as Elmer’s, would work—Also, this person diluted the glue; does anyone have any idea how much glue should be used for a given amount of water?

Should each layer of paper be allowed to dry before adding another (which might take rather a long time), or should new layers be added before the older ones have dried (which might prevent the inner layers from drying)?

And now for the trickiest—in other words, technical—questions—

Is an Orthophinic soundbox, properly rebuilt, suitable for use with a non-Orthophonic horn, such as those used by E.M.G.; or for use with a horn larger than the Credenza’s? I have read several posts on this forum that indicate that the Orthophinc soundboxes are designed specifically for a certain size of folded Orthophonic horn, but I have been unable to find any scientific articles or analyses to support these claims.

Does anyone know, from first-hand experience, whether constant-bore sections at small diameters—say, under two inches—substantially affect the frequency response of a horn? Modern Gramophones says that they should not, but some forum members—I forget which—have said that maintaining the exponential expansion throughout the entire length of the horn is critical, except where the taper is so slight that a conical section is practically the same shape.
Is there a scientific or mathematical relationship between the diameter of a horn, the radius around which it is bent, and the frequencies that will be filtered out? Modern Gramophones says that tight bends should be kept at diameters below about two inches (indicating that loose bends can occur safely at larger diameters), but does not specify when a bend is tight and when it is not.

Were E.M.G. gramophones designed specifically to face straight out from corners of rooms—that is, 45° from each wall? E.M.G. horn mouths have always seemed to have too small a final angle, to me; but while researching horn design, I came across an article that—I believe—suggests that, for a given rate of taper (cut-off frequency), a horn designed to play out of a corner not only can, but should, have a smaller mouth than the same horn as designed to play perpendicular to a wall, if a smooth frequency response is desired. (I will be posting another thread specifically about this fairly soon, as I am not at all sure that I interpreted the article correctly, but this post is already a trifle lengthy to ask here.)

Should anyone happen to have any useful advice or information, I thank you for your time, and for your patience in wading through my post—I have been researching and trying to design horns for some time now, so I have several months’ worth of questions.

- Ethan

[startgroove]

It is known that larger horns tend to respond well to the lower frequencies, while very small horns tend to sound "tinney" or more trebley. Some of Helmholz Theories apply well to horns. That means that a good broad frequency response cannot be achieved by the horn alone (reproducer, horn material and other factors have influence), or by a single horn. Two horns, one large one small, can broaden the response.

Your other question about the continuous taper of horns can be answered by calling attention to Cheney phonographs. That brand purposely included expanded chambers and non-tapering sections within the horn. Cheney phonographs were and are generally considered to have good sound.

[VanEpsFan1914]

Hello Ethan, welcome to the T.M.F.!

Well, your room is bigger than mine and I had some wonderful results in a tiny room with a variety of different phonographs. For the electric records I've never tried a different size than a portable, but I have a Grafonola portable 202 that is a step above the Victrola Orthophonic 2-65 I had--and the 2-65 was wonderful, though it met its demise when the case came apart due to old age.

The records I play are mostly acoustics so I can't answer for the full scale Orthophonic-style machines, but if you want nice sound, go and get a Brunswick Panatrope and quit worrying about it. Viva-Tonals are nice as well. The Orthophonics sound good on the Victor scrolls but the Panatropes & Viva-Tonal machines will just about play anything, including doing a much better job on acoustics.

There are two people on the forum about your age: Martin & David though David is a bit older. (Mormon S and dzavracky.) Anyway, they're very much interested in maximizing sound quality, but with regular phonographs. Both have gotten hold of some fine post-1925 machines, including 2 examples of the famous Brunswick Cortez phonograph--the best Panatropes ever manufactured. They have no surface noise, put out sound as good as anything you'd hope for, and don't have saggy horns like the EMG but best-quality spruce instead.

Wyatt Markus is still making the Orthophonics (and everything else)new again, he just did some Edison cylinder parts for me & they're on the way back; & Walt Sommers still has some great spare parts on eBay.

Nice to see more folks near my age in the hobby-- College has crimped my collecting down to nothing but that's given me time to fine-tune & enjoy the present collection. And no, they don't have to sound perfect for me so maybe I'm not the one to ask about audio fidelity, but I think any decent phonograph properly adjusted will give acceptable results.

Charles

[shoshani]

Orthophonic soundboxes were designed to "match" to the exponential horn taper; part of that equation involves how the soundwaves are generated, their plane, and whether they travel in a flat wave front, or curved. I realize that's overly simplistic, but I'm not sure how to word the abstract in my head...

Most soundboxes of the electrical era, from the No 4 onwards, were designed to work in conjunction with various shapes, tapers, etc of both the tonearm and the horn. The idea was to provide a free and clear path for the sound waves, not just for clarity but also for care of the record. If the soundwave is impeded, it can affect the action of the diaphragm, and thus the needle, causing unnecessary wear. (This is information mostly taken from British writings of the mid to late 1920s.)

With a proper adapter, the Orthophonic can be used on an earlier tonearm/horn, but it's almost pointless since the designs involved will not give the optimum development of the soundwave projection, if that makes sense? I can tell you from observation that the tonearm and horn assembly designed for HMV's No 4 soundbox was very different from the one used with their 5A and 5B soundboxes, which were basically a hybrid of the spider, diaphragm, and backplate fitting of the Orthophonic with the straight pivot needlebar of the No 4 - yet both reproduction chains were exponential in design. They only differed in the execution.

(There was also a school of thought among British gramophiles in the late acoustical era - which lasted much longer there than it did here - that it was beneficial to have the beginning of the soundpath untapered - focusing the soundwaves at the beginning for better projection in the tapered section. The Internet Archive has a book from 1929, "Modern Gramophones and Electrical Reproduction", that goes into detail on this, with mathematical formulae. It was written by two major contributors to The Gramophone Magazine, Percy Wilson and George E. Webb.)

[startgroove]

shoshani makes a good explanation, and a good point. "Orthophonic soundboxes were designed to "match" to the exponential horn", I'll add that by saying that the horn loads the reproducer with an air column. A perfect match between the reproducer and the horn, is when the mass of the air column can be fully actuated with undistorted sound waves. Too small a column and lower frequencies sound mushy and attenuated (assuming a recording which has good low frequencies is the source), and if too large a horn, the high frequencies are attenuated and unwanted harmonics and other noises could result.

One big difference between an Orthophonic reproducer and the earlier reproducers, is that the Orthophonic reproducer diaphragm moves about the same amount across most of the surface of the diaphragm, while in the earlier ones, the most movement is at the center of the diaphragm and tapers off proportionately away from the center. There are other differences, increased compliance, reduced mass of the armature and diaphragm system, and of course wider frequency response.

[Orchorsol]

A very warm welcome to the forum Ethan and you pose some very well-informed and intelligent questions!

Of the E.M.G Marks VIII through Xb Oversize, which machine is quietest, for a given record and needle? My room is small—about twelve feet by fourteen, with a roughly six by four-and-a-half-foot alcove—so quieter is better.

They will all be approximately similar in volume - there will be some differences in character of sound and of course bass cutoff frequency. Similarly when people first see a large EMG they usually say "That must be really loud!" - not really, just extremely high quality.

How does a Mark VIII compare to a Credenza, in terms of both frequency response and “that magical E.M.G. quality?”

I only have experience of HMV re-entrants which are broadly similar to Credenzas. EMGs and Experts have a holographic or 3-dimensional quality to the sound, whereas with the re-entrants the soundstage is more in a plane.

Does anyone have any suggestions for how to make a mould? … What sorts of paper would work well for the horn material? … What kind of glue should be used? ... Should each layer of paper be allowed to dry before adding another?

Search for a thread by 'emgcr' here on the forum about re-creating the largest EMG horns. He did it extremely accurately as a serious and very costly engineering project. Sad to say I think most "makeshift" approaches might disappoint, but no doubt you can find a way if you're determined! Glue and paper: I've used slightly diluted white wood glue and brown Kraft paper in repairing and restoring an EMG horn, but I a stronger paper would undoubtedly be better for building from scratch. The firms that made the horns for EMG and Expert used fairly heavy sugar paper amongst other things. Yes, I let every layer dry before adding another and my intuition says that might be important structurally.

Is an Orthophinic soundbox, properly rebuilt, suitable for use with a non-Orthophonic horn, such as those used by E.M.G.; or for use with a horn larger than the Credenza’s? I have read several posts on this forum that indicate that the Orthophinc soundboxes are designed specifically for a certain size of folded Orthophonic horn, but I have been unable to find any scientific articles or analyses to support these claims.

Shoshani's points cover this really well. You can probably get very pleasing results swapping soundboxes between types, but I think the answer and the science is implicit in Percy Wilson's writing and theories - in terms of acoustic impedance matching and mathematical modelling of waveform generation, that the soundboxes were designed/evolved to match each particular horn design.

Were E.M.G. gramophones designed specifically to face straight out from corners of rooms—that is, 45° from each wall?

Not that I know of - I think we EMG devotees would have come across advice from the firm before now if they had.

You might also try to track down a couple of Percy Wilson's articles in The Gramophone, titled "Armchair Phonatics". They give directions for constructing exponential horns of a slightly earlier iteration than the one in Wilson & Webb. I was about to start making one myself, so I can really appreciate your enthusiasm and dedication - then I was unexpectedly offered an Expert Junior and bought it! Talk about timing...

[dzavracky]

Hey Ethan,

From my paper mache experiments, I have found that a mixture of flour and water makes EXCELLENT paste. look it up on youtube. The last horn I made with this combo was so hard, I would actually go as far to say its as hard as my metal horn. IT also sounds almost just as good

I have been planning on making an EMG horn as well.... PM me if you want to discuss it!


David

[Inigo]

Davzracky... How did you make the moulding for your horn? I had an old idea, which was to make a structure from wicker, making several rings of adequate diameter, then fixing them with other perpendicular wicker bars along the rims, forming the horn perimeter tractrix curves, and you can place them to give the shape of a curved horn like the Experts. Then I would wrap this skeleton with paper strips, inside and outside, or maybe only outside, if the wicker structure can be disassembled and extracted after the paper born has been hardened.

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[epigramophone]

Returning to your query about positioning the machine, I have found that across a corner suits my Expert Minor best and maximises the "holographic" effect already mentioned by others.
Another factor which has not so far been mentioned is the height from which the sound emanates. I am convinced that this is where the external horn really shows it's superiority over the internal one. The late George Overstall, who supervised the installation of machinery at EMG during WW2, spoke of HMV Re-Entrants "playing to the carpet".

[dzavracky]

Davzracky... How did you make the moulding for your horn? I had an old idea, which was to make a structure from wicker, making several rings of adequate diameter, then fixing them with other perpendicular wicker bars along the rims, forming the horn perimeter tractrix curves, and you can place them to give the shape of a curved horn like the Experts. Then I would wrap this skeleton with paper strips, inside and outside, or maybe only outside, if the wicker structure can be disassembled and extracted after the paper born has been hardened.

1592730393756.png

I haven’t made the mold yet. Although it’s construction is relatively simple. The biggest question is of course, how do you part the mould with the horn after it’s done? I’m hoping to make the mould soon so I can start pasting paper on it. With such a big horn I expect the pasting part to take forever

When I finish my horn I will make a post about it for sure as with most things you can’t always expect the first one to turn out perfect. But hopefully I can make the first one really good

David