ALUMINIUM DIAPHRAGMS.

[leels1]

I’d be interested to see other people’s experiments.

I've had a go at making aluminium diaphragms:

https://youtu.be/mK1bGhanqf4

as part of experimenting with 3D printed soundboxes

I've also tried flat metal:

https://youtu.be/aMrX8tn-tYI

And various types of plastic

https://youtu.be/XqAlJVpN3ZM

Very interesting topic of experimentation and great to see lots of other people investigating it too!

I love to watch your videos, the ingenuity of your experimentation is great!

[leels1]

in your opinion, is there a tangible difference between the design of the edges on a 5a vs a 5b... and if not, why might they have change the design?

In my opinion, the change between 5a and 5b was not drastic. In the diaphragm I've only noticed the different edge corrugations. The triangles in the 5b provide the same effect, but seem more easy to die-press than the tiny corrugations of the 5a, so maybe the change was only for technical production matters. I've always tempted to think that the 5a is more flexible, but this could be a biased opinion due to the fact that my 5a diaphragms were old, while my 5bs were brand new. I never noticed any change in sound between both.
Apart from that, the only other difference I've found is that the metal front cover of the 5b has four support points beside the screws (acting as tiny legs) that the 5a didn't have. I suppose they are made to improve the cover support when you screw it thoroughly. The old design tended to bend it down when screwed tight.

Some people swear there is a difference... I've not heard it myself, but I have noted variances between different 5a and 5bs when compared to each other. I guess time, pot metal swelling, pivot bar setup etc all play a part.

[leels1]

Also, if EMG are considered the "pinnacle" of sound reproduction, I wonder why they kept a relatively simple diaphragm design compared to the orthophonic? The 5a/b design is supposed to be balanced with with a re-entrant horn, but they also used them on exponential horned machines which theoretically has no extra benefit?

I believe that the EMG mostly relied on no-compromise metals and an excellent design of the needlebar pivot. I never had the chance to put my hands on an EMG as they are so scarce, but gramophone enthusiasts that own both an EMG and a 5a/5b and that I look on as honest listeners, won't swear on either of the two, but basically report that any of the two sounds slightly better than the other depending on the gramophone on which it is installed.

Coming to your second point, I'm not really sure that I get your question. Re-entrant horns also happen to have an exponential profile: there is no difference form this point of view, and I don't think that 5a/5bs were specifically designed with re-entrant horns in mind, also because re-entrants don't have any specific parameter or figure that would tell them apart from their straight horn equivalent when seen from the throat of the duct. Re-entrants were basically designed to save space and fit a huge and long horn in a comparatively small cabinet, once it became clear that horns happen to be surprisingly tolerant (I would rather say almost unbelievably tolerant) to sharp bends, splits, quadrisections, and re-joins. However, the 5a/5bs were also widely deployed, obviously with the same success, on many "normal" folded horns, on portables like the highly regarded 102 (which in turn is equipped with a folded but not re-entrant horn), and so on.

I'm not convinced with the needle bar pivot on the EMG, I only have one, and yes, it's adjustable etc and well made with option to "tune" but there are others such as the Meltrope (ii better than iii) and an interesting one that seems scare called "The Lenthall" that provide a fantastic sound and are also adjustable too. I never really found the adjustable ring on the EMG/ Meltrope's makes that much of a difference when it's tighter or looser but that might be my lack of a discerning ear!

Re the horn point, I had thought the "orthophonic" soundboxes were designed with a direct correlation to the re-entrant horn's length (with some mathematical formula no doubt) to provide the best sound (that said, is orthophonic really a thing, or it is really just a well designed aluminium diaphragm as Inigo has described earlier) so putting a 5a on a portable for example defeated the object of its design.

[Marco Gilardetti]

Re the horn point, I had thought the "orthophonic" soundboxes were designed with a direct correlation to the re-entrant horn's length (with some mathematical formula no doubt) to provide the best sound (that said, is orthophonic really a thing, or it is really just a well designed aluminium diaphragm as Inigo has described earlier) so putting a 5a on a portable for example defeated the object of its design.

Orthophonic is indeed "a thing" and it's the name given by HMV to an entire new range of gramophones (not only to the diaphragm, then) that were for the first time stricly designed by following settled and understood scientifical principles, and not "by ear" or "by trial and error" as was customary before. The switch from a mica to an aluminium diaphragm is part of the road that led to a much improved sound (as we partly covered in this thread). Designing an exponential horn of the correct shape that would well impendance-match and correctly load the soundbox is another side of the "orthophonic thing". Another is designing a tonearm that would on one hand interface perfectly with the horn, and on the other hand minimise the tracking error - a thing that in turn begun to be finally based on solid geometric considerations around the same years.

If you think of the difference in size between HMV models 156, 163, 196 and 202 you will immediately get that re-entrants differ much in size one to another, and that the 5a/5bs couldn't have been designed specifically for any of them, but mostly all of these horns were designed to match well with the soundbox. On the other hand of the scale, the tiny but mighty 102 portable is there to clearly show that even a relatively small folded horn, if well designed, can match very well with 5a/5bs. So definitely no: applying a 5a/5b to a small portable will not, by any means, defeat the object of its design; the 102 is unanimously reagarded as one of the best (if not "the" best) sounding portable units.

[CarlosV]

Re the horn point, I had thought the "orthophonic" soundboxes were designed with a direct correlation to the re-entrant horn's length (with some mathematical formula no doubt) to provide the best sound (that said, is orthophonic really a thing, or it is really just a well designed aluminium diaphragm as Inigo has described earlier) so putting a 5a on a portable for example defeated the object of its design.

If you think of the difference in size between HMV models 156, 163, 196 and 202 you will immediately get that re-entrants differ much in size one to another, and that the 5a/5bs couldn't have been designed specifically for any of them, but mostly all of these horns were designed to match well with the soundbox. On the other hand of the scale, the tiny but mighty 102 portable is there to clearly show that even a relatively small folded horn, if well designed, can match very well with 5a/5bs. So definitely no: applying a 5a/5b to a small portable will not, by any means, defeat the object of its design; the 102 is unanimously reagarded as one of the best (if not "the" best) sounding portable units.

Just to complement Marco's post, originally the large re-entrants (the commercial name that HMV used to refer to the Victor orthophonics) utilized the number 5 soundbox, which is the HMV counterpart of the orthophonic, and identical in all aspects, except for one: differently from Victor, HMV never made a brass back soundbox, from the start all production was pot metal. After a short while, I presume for cost reasons, HMV developed the 5a, which was an adaptation of the number 4 that utilized a similar diaphragm to the orthophonic, in aluminium and with a spider. The later production of the large reentrants carried the 5a, and the 5 was retired. Not many number 5 soundboxes survive today in operational shape: I have a couple that I use in the 202, as well as some orthophonics, they provide a better sound than the 5a to my ears. In conclusion, for HMV the orthophonic (number 5) and the 5a soundboxes were interchangeable for use on the large reentrants, and from my experience the number 5 is a better fit to the 202.

[anchorman]

once it became clear that horns happen to be surprisingly tolerant (I would rather say almost unbelievably tolerant) to sharp bends, splits, quadrisections, and re-joins. However, the 5a/5bs were also widely deployed, obviously with the same success, on many "normal" folded horns, on portables like the highly regarded 102 (which in turn is equipped with a folded but not re-entrant horn), and so on.

interesting that you say this, because the EMG/expert people seem to think that horns are not at all tolerant of sharp bends and such. It would be interesting to hear the same size horn, same basic materials, but one with tight bends, and one without, and see how much different they really are.

[poodling around]

I'm not convinced with the needle bar pivot on the EMG, I only have one, and yes, it's adjustable etc and well made with option to "tune" but there are others such as the Meltrope (ii better than iii) and an interesting one that seems scare called "The Lenthall" that provide a fantastic sound and are also adjustable too. I never really found the adjustable ring on the EMG/ Meltrope's makes that much of a difference when it's tighter or looser but that might be my lack of a discerning ear!

I agree - my meltrope ii sounds far better than my meltrope iii and my Lenthall soundbox even better than those.

[Marco Gilardetti]

interesting that you say this, because the EMG/expert people seem to think that horns are not at all tolerant of sharp bends and such.

It's in turn "interesting" that they say so, as the horn duct of EMG/experts begins with nothing less than a 180° bend, followed by a sharp 90° intersection (!!!), then followed by other five 90° turns.

[Inigo]

Yes, and Percy Wilson wrote that sharp turns aren't dangerous while maintained in the narrow zones, where they impair the waves of similar wavelength to the diameter of the pipe. But the last bends of the EMG/Expert horns occur in places certainly wide... A wavelength of 8" corresponds to a 1720 Hz sound, well in the middle of the spectrum... !

[Hoodoo]

What about the flat sections as found at the bends of some Columbia portable machines and modern hi-fi speakers in these photos, do they work as well as a bend?
A big EMG-type horn would not look as elegant with the flat bits instead of smooth curves, but would it perform as well?