A simple resonance-damper for mica sound-boxes

[Menophanes]

I have just read a posting in the 'Machines' section about something called a Morse clarifier, whose purpose is apparently to suppress unwanted resonances. I have no idea what this device looks like, but here is something which seems to operate in the same area: – In the days when I used mica-diaphragm sound-boxes with exposed needle-arms, I always found it advantageous to take a cube of rubber (cut from an eraser) measuring about ½ inch in each dimension, cut a slit in it to about half its depth, and push the cube onto the needle-arm just where this turns through a right-angle to meet the diaphragm. I discovered this by chance when, frustrated by the blasting and booming in a certain frequency-range from an Exhibition box, I tried pinching the needle-arm between finger and thumb. I am no acoustician, but I believe this works by preventing the arm from setting up extra vibrations at its own natural frequency while still allowing it to respond to those which are legitimately emerging from the diaphragm. One needs to experiment a little with the size of the block and the depth of the slit – if the pressure is too great the sound will become pinched and nasal, while if it is too little there will be almost no benefit – but at best it can clean up the sound to a remarkable degree with only a slight loss of volume. Obviously the principle cannot be applied to boxes which are covered in at the front.

Oliver Mundy.

[Orchorsol]

There was also a little device, whose name escapes me, which clipped onto the needle bar in a similar way. They turn up on the likes of eBay from time to time; sellers often mistake them for some kind of tweezers for picking up needles.

[Menophanes]

I thought I could not have been the first to conceive this idea!

Herewith are two drawings: one showing my damper as I actually used it, while the other shows a slightly less crude version, allowing for adjustment of the pressure, which I designed long ago but had no means of fabricating. I may possibly have posted these before, but not recently.

Oliver Mundy.

[Curt A]

If it clips onto the needle bar, maybe something like a small size (½" wide) binder clip - lined on the inside with felt, would work...? A cheap, easy to make and easily removable option that might solve the problem... possibly worth experimenting with.

[Curt A]

Maybe something like this...

[Pathe Logical]

See viewtopic.php?f=2&t=43415 for several pics of a Phonomute attached to a Victor Exhibition reproducer.

Bob

[JerryVan]

I posted here, some years back, about pushing an eraser, (pulled out of the end of a pencil), over the needle, with just enough of the tip protruding, to reduce noise/hiss. At the time, I was called crazy, (which was, and still is, mostly accurate ). However, perhaps the ideas shared here are a similar, but maybe more effective, attempt at the same thing?

[OrthoFan]

My only concern would be the mass and possibly weight added to the needle-bar. If, by resonance, you mean that ringing tone associated with the Exhibition sound box, another option is to use softer gaskets.

My Exhibition sound box was rebuilt nearly 30 years ago by the late Bob Waltrip. Instead using a pair of the white tube gaskets then available, he made a gasket out of non-hardening silicone calk (GE brand) for the back and a conventional white tube gasket coated with a fine film of clear silicone (diaphragm side) for the front. The result is, an overall fuller sound, but without the ringing tone on louder/higher pitched notes.

OrthoFan

[Roaring20s]

Thought this would be a nice addition to this thread...

James.

[poodling around]

I still use Blutac, which to me, improves the sound very well - and comes in different matching colours of course !