Sagged emginn expert horn fixed

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Burtemg
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Sagged emginn expert horn fixed

Post by Burtemg »

I fixed the sagging horn, not too straight, i like to listen while seated.
I even found a £30 matching table...
Its a keeper!
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Lucius1958
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Re: Sagged emginn expert horn fixed

Post by Lucius1958 »

Luverly! :D

2Bdecided
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Re: Sagged emginn expert horn fixed

Post by 2Bdecided »

Is this the one that went into the shower?!

Would you be willing to explain exactly how you did it? Especially, how did the surface survive so well, and how do you prevent the whole thing from turning into mush?

Thanks,
David.

Burtemg
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Re: Sagged emginn expert horn fixed

Post by Burtemg »

When the horn is soft of the moisture you have plenty of time to shape it
while it's drying... I bent the circle metal ring in the
mouth of the horn into shape and stuck a bucket in the mouth as far as I could to make the innerside
round. Don't know the name but I also used devices to tighten wood parts when you glue wood together.
Support the sagging horn as high as you can until dry (12 to 20 hours)
I reglued most of the inside leatherette but had to
repaint the outside. After a layer of quality plaster i gave the outside a patina using 4 colors of paint
Chocolat brown,chestnut brown, gold paint and a final dark tainted mat varnish.
Some are against painting the horn but thats what they did in the 30's so
I don't mind.
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emgcr
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Re: Sagged emginn expert horn fixed

Post by emgcr »

Very courageous Bert---well done---looks good in the photos. How much plaster did you apply and is it now a little heavier ?

This was certainly a technique sometimes used in the nineteen-thirties but the original plastered ones I have come across are substantially heavier. The problem can be that gravity is always the great enemy in the case of Expert horns as the paper-covered bronze under-gusset does not really adequately support or spread the full load, thus lightness is a real benefit and virtue. Many EMG equivalents suffered from similar problems but the Xa and Xb models are intrinsically far more stable due to the aluminium cygnet castings onto which the bells are grafted.

In my experience, the inside of the horn should never be varnished or unwanted frequencies may result.

2Bdecided
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Re: Sagged emginn expert horn fixed

Post by 2Bdecided »

Thank you for sharing Burt.

Emgcr, do you mean too much treble, or some other resonance?

Thanks,
David.

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emgcr
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Re: Sagged emginn expert horn fixed

Post by emgcr »

About 13 years ago, when I first became interested in gramophones, I found a rough condition paper petal horn---not actually EMG, but one which I partly redesigned to be able to fit a Mk IX outlet. This was my first introduction to what EMGs sounded like. Although, with hindsight, the sound probably was none too good, it was sufficiently startling to make me sit up and listen very carefully---I really could not believe the quality of what I was hearing---I was hooked ! I then, in my ignorance, sought to improve the cosmetics by painting the exterior and varnishing the interior following which the sound was never anywhere near so good again---lesson learned !

A similar experience took place many years later when friends and I excitedly test-played the first new Oversize fibre-glass horn which necessarily had a highly glazed interior surface produced by the gel coat. The acoustic quality was initially disappointing but improved dramatically following abrasion of the surface to produce a matt finish.

Later on, I tested the Nimbus fibre-glass horn with the Decca graduated frequency records and found a few levels at which there were harsh resonances which, again, I put down to a glazed internal finish of the horn.

To me, therefore, empirical evidence suggests that such "bright" finishes are undesirable and that this is one of the more important reasons why EMG/Expert utilised reflectively inert paper at the larger and more acoustically delicate diameters. Easily obtainable and cheap to buy paper was an obvious choice of material in economically depressed contemporary days which promoted and enabled only the disired frequencies from the record itself to be heard as the wave was allowed to evolve and expand in a geometrically perfect and uninterrupted exponential way without being adulterated by unwanted reflections. It is also interesting to note that it would appear to be the actual surface finish which is critically important to good acoustics rather than the material itself. By common consent, the acoustic delivery of horns of similar design made from either paper or fibre-glass (unavailable in the nineteen-thirties) would appear to be identical so long as the surface treatment is matt or non-reflective. Mechanical stability of the horn casing, which must totally resist any form of fluctuation or movement, has also been found to be very important.

From memory, the experiments with the Decca records on horns with shiny reflective internal surfaces showed harsh resonances at several frequency levels between approximately 3,000 and 80 Hz.

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Re: Sagged emginn expert horn fixed

Post by Orchorsol »

emgcr wrote:About 13 years ago, when I first became interested in gramophones, I found a rough condition paper petal horn---not actually EMG, but one which I partly redesigned to be able to fit a Mk IX outlet. This was my first introduction to what EMGs sounded like. Although, with hindsight, the sound probably was none too good, it was sufficiently startling to make me sit up and listen very carefully---I really could not believe the quality of what I was hearing---I was hooked ! I then, in my ignorance, sought to improve the cosmetics by painting the exterior and varnishing the interior following which the sound was never anywhere near so good again---lesson learned !

A similar experience took place many years later when friends and I excitedly test-played the first new Oversize fibre-glass horn which necessarily had a highly glazed interior surface produced by the gel coat. The acoustic quality was initially disappointing but improved dramatically following abrasion of the surface to produce a matt finish.

Later on, I tested the Nimbus fibre-glass horn with the Decca graduated frequency records and found a few levels at which there were harsh resonances which, again, I put down to a glazed internal finish of the horn.

To me, therefore, empirical evidence suggests that such "bright" finishes are undesirable and that this is one of the more important reasons why EMG/Expert utilised reflectively inert paper at the larger and more acoustically delicate diameters. Easily obtainable and cheap to buy paper was an obvious choice of material in economically depressed contemporary days which promoted and enabled only the disired frequencies from the record itself to be heard as the wave was allowed to evolve and expand in a geometrically perfect uninterrupted exponential way without being adulterated by unwanted reflections. It is also interesting to note that it would appear to be the actual surface finish which is critically important to good acoustics rather than the material itself. By common consent, the acoustic delivery of horns of similar design made from either paper or fibre-glass (unavailable in the nineteen-thirties) would appear to be identical so long as the surface treatment is matt or non-reflective. Mechanical stability of the horn casing, which must totally resist any form of fluctuation or movement, has also been found to be very important.

From memory, the experiments with the Decca records on horns with shiny reflective internal surfaces showed harsh resonances at several frequency levels between approximately 3,000 and 80 Hz.
Really good to have this experience and reasoning set out. I've heard the same thing from other authoritative sources too. These observations are also borne out by the maths and acoustic science in the various academic publications on the subject, from historical to recent - as EMGCR indicates, the criticality is negligible at small diameters but increasingly important as the horn flares out wider, where the developing wavefront, optimally spherical, can be disrupted by reflections (which will necessarily be frequency-specific) - hence the potential for spikes in the response curve, over-emphasised harmonics etc which will be heard, subtly or less so, as harshness or colouration.

I recently listened to one of the Decca gliding-tone frequency test records on my EMG Xb and was absolutely amazed how perfectly even the response was (subjectively) down to a sudden cutoff around 80-90Hz.

As mentioned before, maybe a matt varnish inside an original horn would be fine (some say so) but I wouldn't want to take the chance unless absolutely necessary for some reason.
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Steve
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Re: Sagged emginn expert horn fixed

Post by Steve »

the criticality is negligible at small diameters but increasingly important as the horn flares out wider, where the developing wavefront, optimally spherical, can be disrupted by reflections (which will necessarily be frequency-specific) - hence the potential for spikes in the response curve, over-emphasised harmonics etc which will be heard, subtly or less so, as harshness or colouration.
And you claim to not know what two elongated slots in the back of a cabinet we're talking about?! :lol:

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Orchorsol
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Re: Sagged emginn expert horn fixed

Post by Orchorsol »

Steve wrote:
the criticality is negligible at small diameters but increasingly important as the horn flares out wider, where the developing wavefront, optimally spherical, can be disrupted by reflections (which will necessarily be frequency-specific) - hence the potential for spikes in the response curve, over-emphasised harmonics etc which will be heard, subtly or less so, as harshness or colouration.
And you claim to not know what two elongated slots in the back of a cabinet we're talking about?! :lol:
Ha ha, YES! My 111 (just checked) doesn't have those slots and I've never noticed them on others, then again I haven't studied HMV tabletops closely at all. I was confused by others' posts about them too.

On the other hand I've been studying the theory of Wilson etc horns for a long time! Over a period of time I had drawn up plans for a huge modified exponential horn, but that got sidetracked about a year ago when I unexpectedly bought my Expert and got heavily immersed in listening to it relentlessly (even more fun). :lol: Hopefully I'll resurrect the project at some point, although it will probably be back to the drawing board after a lot more academic input.
BCN thorn needles made to the original 1920s specifications: http://www.burmesecolourneedles.com

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