soundbox gaskets

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ptjw
Victor Jr
Posts: 39
Joined: Wed Nov 10, 2010 8:54 am

soundbox gaskets

Post by ptjw »

hello all,


i know that soundboxes came with gaskets inside to make an airtight seal, i had a HMV 5b from india that used gaskets made of cardboard (!!) and i did a search online and found that soundboxes had gaskets made of rubber, felt and now even neoprene...i was wondering, does the material that the gasket is made of make a difference?


thanks!

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Henry
Victor V
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Location: Allentown, Pennsylvania

Re: soundbox gaskets

Post by Henry »

As long as it forms an airtight seal and is a good dimensional fit, the material shouldn't make a difference AFAIK. But why not just use the same (or as closely similar as possible) materials as the original? It would probably look better and, given the variety of modern materials available, work better too. I know that the front and back gasket materials on my rebuilt Exhibition do a splendid job!

gregbogantz
Victor II
Posts: 393
Joined: Thu Jan 08, 2009 5:03 pm

Re: soundbox gaskets

Post by gregbogantz »

The gasket material matters on some reproducer designs and not so much on others. The later designs that use an embossed metal diaphragm such as the Victor orthophonic and the HMV #5 are designed such that the edge of the diaphragm is intended to be held securely with no flexing in an airtight seal. The required flexing is provided by the embossed folds in the metal diaphragm. In these cases, the type of gasket material is not so important so long as it clamps the edge of the diaphragm tightly and provides an airtight seal.

However, most of the earlier designs (all of the Edison cylinder models as well as the DD models) and the pre-orthophonic Victors and pre-VivaTonal Columbias are meant to allow the edge of the diaphragm a slight amount of movement. This is usually necessary because the diaphragms are merely flat plates or sheets with no embossing. Flexure of the plate results in very slight radial motion at the edge which must be accommodated. In these designs, the gasket is meant to have some resiliency and flexibility which allows the edge of the diaphragm some slight movement. These gaskets are usually made of a rubber-like material in order to provide this function. The hardness of the gasket material WILL affect the sound in these early designs, as will their thickness and the amount of clamping force used to compress them. It is particularly true in the case of the Edison designs that you can "tune" the sound of the reproducer by adjusting the tightness of the clamping ring that compresses the gaskets on the diaphragm.
Collecting moss, radios and phonos in the mountains of WNC.

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Henry
Victor V
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Location: Allentown, Pennsylvania

Re: soundbox gaskets

Post by Henry »

It's absolutely true with the older sound boxes such as the Exhibition that the front gaskets in particular should be very compliant, as the mica diaphragm flexes across its entire surface from edge to edge when acted upon by the vibrations of the sound waves transmitted through the needle bar. This I can demonstrate with my Exhibition by gently applying suction to the exit end while viewing the mica surface in a mirror; one can actually see the flexing as it corresponds with the application and release of suction. This is also a good way to check on the airtightness of the seals.

ptjw
Victor Jr
Posts: 39
Joined: Wed Nov 10, 2010 8:54 am

Re: soundbox gaskets

Post by ptjw »

I see, I was contemplating about ordering a pair of felt gaskets online for my 5b but they cost around 4pounds and I was wondering what's the big deal for them to cost so much.

if the HMV soundbox diaphragm is not meant to flex at the rim, wouldn't using a harder material result in a better performance? but as far as I know the cardboard ones that came with my 5b are supposedly of a 'lower grade' than the originals that came with the felt gaskets (I'm assuming the originals built in the UK did come with felt/rubber gaskets)

now that I think about it, maybe the cardboard gaskets on mine were replaced by the previous owner,especially since it looks like they were cutout from a cigarette or cereal box!

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