EXPERT two-spring v four-spring soundboxes

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emgcr
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Re: EXPERT two-spring v four-spring soundboxes

Post by emgcr »

Many thanks gregbogantz for your excellent and clear thoughts on the reasons for and advantages of heavier reproducer weights/mass etc all of which make a lot of sense.


With reference to design weights in general, the main section of the EMG tonearm in particular is heavier than most others and is a casting which, being thicker than many, also has a natural resiliance against itinerant and unwanted secondary frequencies. It was always the most expensive part of the whole set-up to make and was not incorporated without reason ! An EMG Mk Xb Oversize (all acoustic) is quite capable of reproducing bass frequencies down to about 80 Hz if not lower. Final bell-mouth diameter is 33 ½ inches.

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Re: EXPERT two-spring v four-spring soundboxes

Post by Orchorsol »

This is such an interesting discussion. It makes total sense to me - high mass/inertia of the whole assembly, but modest (normal) tracking force... Less transmission of low frequencies into the body and arm, and therefore more to the diaphragm.

The same considerations apply to modern hi-fi arms and cartridges, but in a very different arena, as it's possible to design extremely compliant cantilevers and suspension for microgroove styli. Within the audible frequency range, all the energy should be in the moving parts of the cartridge, not transmitted to the arm.

I use counterweights on both my main machines (the first and third of Graham's photos above) and they both work really well, even if the one on my EMG is slightly amateurish in construction. What a strange 'blast from the past' to see my Expert Junior with a Meltrope fitted, before I got my first Expert soundbox! Nowadays I use a Meltrope only occasionally for rough records.
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Re: EXPERT two-spring v four-spring soundboxes

Post by old country chemist »

Many thnaks indeed for posting on the forum the pictures and photographs of the two different weight adjusters.
I will now try to send you all a picture of a George Overstall soundbox which I brought home at the weeekend. It must have taken the old chap a week of full time work to make it from start to finish. Very good bass response fromthe fitted "jam pot ring! gasket.

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Re: EXPERT two-spring v four-spring soundboxes

Post by old country chemist »

Hope it works this time. George Overstall soundbox. My appologies if it does not, as I seem to have forgotten how to upload pictures.
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George Overstall soundbox 1970s 008.JPG

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Re: EXPERT two-spring v four-spring soundboxes

Post by emgcr »

Interesting and seemingly well made item. One or two questions please :

What is the material of the "jam pot" gasket ?

Is there an identical ring on the other side of the diaphragm ?

Why does it need to be so wide ? Surely the reduction in I/D militates against diaphragm flexibility ? If so, is this thought to be a good thing ?

What is your take on the sound produced ?

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Re: EXPERT two-spring v four-spring soundboxes

Post by old country chemist »

Just a few moments to answer Graham's queries re. the George Overstall soundbox.
1."the jam pot ring gasket" is made of Dow Corning siliconised latex. Dow Corning are an American firm that specialised in catheter manufacture,(I well remember supplying them to customers in the past), but they also made other siliconised items. the rings were cut from sheet material, supplied by them.
2.I have not dis-mantled the box yet, so I do not know if there is an identical ring behind, but I do know that George was very keen on a thick flat gasket on one side of the diaphragm, and a tubular gasket on the other side, so when I take it to pieces, then I will know!
3.Another theory of George's (and may have been one from other gramophiles of many years ago), was that a wide gasket would promote the diaphragm to move, if looked sideways, in a piston type action, and not be flexing from the our extremity. I have never been able to fully accept this-but who knows?-others of you will have the answer, I am sure.
4 The sound quality is good. I had to fiddle with the springs somewhat, and tighten the backplate slightly, as this box had not been used since the mid 1990s. I think the diaphragm is a little soft, and too thick, so some of the "top" is missing, but the bass response is good, as I tried it on one of my test discs "ENTRY OF THE BOYARDS" on an H.M.V. AMERICAN RECORDING, by the Bostonm Proms Orch. There are a few triangle notes in this heavily orchestrated disc-good one for needle breakdown! I could hear the triangle, reasonably clearly, and the bass drum was "meatier" than on other boxes I had tried on this disc. It really needs a better diaphragm, and full adjustment, maybe even removing the siliconised ring, and replacement with conventional tubing...? George, being the engineer that he was, used Allen screws in the front plate!. No keeping to originality for him, he just wanted a good usable item. This box would be great for heavy dance record, as fine tonal quality would not be required, as far as I am concerned. Must dash, as I have a four and a half month job of painting pantomime scenery-6 backcloths to paint-all of them 24 feet long and 14 feet tall. and we are only on no 3 at present. Been working on them since start of September with another artist. Keep up the good work, as I will try to look in a little more than I have done in the past 6 months. Great forum, and really encourages comradeship in this wonderful hobby of ours. Kind regards to you ALL, Alastair.

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Re: EXPERT two-spring v four-spring soundboxes

Post by emgcr »

Many thanks Alastair---a very helpful reply which always adds to the mix of experiences/possibilities we all undergo and the knowledge gradually built up. The trick is not to lose this knowledge which has been the problem in the past and is a continuing battle.

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Re: EXPERT two-spring v four-spring soundboxes

Post by Steve »

I have an Expert 4-spring s/box with its original wide and chunky "jam jar" gasket ring very similar to the one pictured above. It also has the bottom corner of the main body of the s/box chamfered off at 45 degrees on the corner that is closest to the playing surface when in use! It's the only one I've ever seen like it and it came from the estate of Phillips! I guess it might have been one of their experimental examples as they didn't even get around to marking it as an "Expert" made by "E M Ginn".

It sounds good so I have not rebuilt it BUT as Chunny has noted it sounds better with two springs removed!

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Re: EXPERT two-spring v four-spring soundboxes

Post by chunnybh »

Scouring through The Hillandale News, another interesting article from October 1966 by a David McCallum. Historically Interesting High Quality Exponential-Horn Gramophones.
A PDF file attached. Hope it is downloadable.
Some very interesting points on soundboxes on page 3 where he talks about mass and air chambers. On page 7 where he suggests "It 1s
possible, but inadvisable to tune the soundbox by" the four springs. But more important to tune the back plate to achieve the bass response. I like the way he talks about a "tuned circuit". Explains why a Meltrope with minimal adjustment can be such a good soundbox. The rubber seals seem to be the most important factor in all this.
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33 Oct 1966 article 3.pdf
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Re: EXPERT two-spring v four-spring soundboxes

Post by chunnybh »

I'm surprised there are no comments on this article. To me, it's a revelation.

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