Metal Mesh in sound holes - What it all about?

[melp]

Hi All,

Sorry another one of "those" questions again. This time is about the function of covering sound holes with wire mesh - like the diamond shape holes around the cones on a tricone.

Simple question. Why? Does is have a acoustic function? Is it just for decoration? Is it just practical, to stop foreign objects from falling into the cone?

I guess the most important thing does it make any difference to sound?

Any contributions/thoughts welcome.

Cheers

Mel

[LouisianaGrey]

The mesh over the small soundholes on a dobro can certainly make a difference, but not necessarily - sometimes taking the soundhole screens out changes the tone and volume, sometimes it doesn't. Paul Beard retails soundhole "screens" with no mesh as an option for this reason. It seems more likely - i.e. I've heard an audible difference more often - to make a difference with American soundhole screens, which are slightly smaller and use a closer mesh than the Chinese imports, but it's not always the case. I guess it depends on the body volume and other variables (like internal baffling does too).

[tark]

It's one of those frustrating things - the original designers of those sound holes are gone so I don't suppose we will ever know the exact details of the thinking that went into them. I suppose there may be some surviving Dopyera family members around that might have some stories.

To me it seems they must be both protective and cosmetic. Acoustically they would act as resistances to the airflow and would also reduce the effective size of the resonator port/s, so both lowering the resonance point and reducing its strength. This should mean the cone 'honk' (resonance) would be more prominent. Incidental with a Helmholtz resonator air only flows back and forth through the port at the resonant frequency, at other frequencies it is as though the port is not there. Mind you the resonance of a guitar body isn't usually very narrow or high so there will be some resonance effect and air movement some distance either side of the centre frequency.

[steverino]

Acoustically the mesh screens could be modeled as a momentary partial obstruction to a transmission path, which would have the effect of a low pass filter. In other words, high frequencies above some threshold would be progressively attenuated. I would expect the effect to be very minor due to the small percentage of obstruction, and I have a hard time hearing any difference at all.

Tark the sound holes will allow all frequencies to pass through to a great extent, though their output seems to be all bass due to the broad peak at resonance.

[blueshome]

The most obvious and simplest explanation of the mesh on a tricone is that it is to protect the cones. Whether John Dopyera actually considered the subtle effects on the ultimate sound of the mesh chosen we'll never know as this stage, my guess it's what he had around at the time. We do know changes were made to the original design with the elimination of the diamond holes around the rim and the replacement of the wooden well with metal. I'll leave it to others with greater experience of these instruments to comment on how these changes affected the sound.

With due respect to the theoreticians amongst us, I think the invention of great musical instruments is based on part experience and part luck in knowing when you've hit upon something good.

[steverino]

I had spider bridge reso sound holes on my mind, probably because of continuing discussions about the effects of their mesh grills on the sound. Melp's original question was in regard to the cover plate vents on a tri-cone. In this case the holes exist to let the wide-band sound from the cones out, and my assumption is that they were covered with wire mesh to protect the delicate cones from damage.

[andys]

Reminds me of a thread started by owners of the little Fender Champion 600.

Apparently one one of the most dramatic mods you can do, before you change valves, circuitry, speakers etc, is take out the factory fitted speaker cloth, and replace it with something less sound absorbing!!!

[melp]

Hi All,

Thanks guy's. Have ordered some mesh, not sure if its the right stuff. But will try it with and without and see what happens. Let you know.

regards

Mel