Lead shot questions

Putting metal weights inside a speaker enclosure is obviously a misunderstanding of the concept of weighting down the enclosure by external loading.

But, it brings to mind an idea that I have been kicking around for a while, but never got to try. Carbon dioxide, CO2, is an easily obtained and non-toxic gas that is heavier than air. One could drill two small holes in a speaker, top and bottom, and fill the enclosure with CO2 (slowly from the bottom). After filling plug the holes, perhaps with a cork. The extra weight would not be enough to affect the enclosure structure, but it would change the enclosure loading of the driver, perhaps in a desirable way. If the effect is in the "wrong" direction, one could try Helium, but that gas would tend to leak out (whereas CO2 would not). Has anyone tried something like this?

Distortion...Suggestion. Turn the speakers upsidedown to fill them. CO2 "pours" like a liquid, and if you go slow you will get a good fill. If the port plugs are tight and not permiable the CO2 will hardly leak ar all. (It will stay in an open dish or other depression, and sometimes is a suffocation hazard to workers for this reason).

It would be interesting to hear your observations regarding the speaker performance using air vs CO2, with the plugs in in both cases.

But don't use up all the CO2 so that you can't service the beer kegs!

With regard to "Mass Loading" this term has been used to describe addition of weight to a woofer cone so as to lower its free air resonant frequency. In the old days we used to modify drivers in many ways, but that is not done much today because there are so many drivers available, of every possible characteristic.

Fifty years ago Warfedale (and others) used enclosures with double walls, which you filled with sand after the speakers were set in position. I guess this would be Mass Loading. Other speaker makers may use laminated material to make enclosure walls heavy (I have used wood/sheetrock/wood). However the wall thickness must be taken into account when the enclosure is designed.

In general, if an enclosure is designed with mechanical bracing, excessive wall thickness or weight is not necessary. Weight alone does not do the job. I once made small bookshelf speakers using concrete Chimney blocks for the enclosure walls except for the front and back. Turns out that masonary "rings" and does not work very well. But I have often thought about the subwoofer that you could build using a 1500 gal septic tank.