Re: Re: Re: Re: Kleenex and Spit


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Posted by Rick Denney--summarizing on August 18, 2000 at 10:55:25:

In Reply to: Re: Re: Re: Kleenex and Spit posted by Paul R. Ogushwitz on August 18, 2000 at 07:01:55:

Paul, trees are to my liking. But they do take a while to grow, and you can't plant a fully grown tree. I have as many young trees in the area in front of the house as that amount of earth will support. But they will need another ten years or so to really fill in.

I do not desire to absorb the sound, which was the problem you faced with your bedload apparatus. My desire is to aim it towards the back or sides of the house, rather than out the front.

So, let's follow the vibrations. The air surrounding the bell is filled with pressure waves emanating, ultimately, from my lips. Those shock waves excite the materials they reach. Those are: the concrete wall, the floor/ceiling joists, the deck of the first floor, the rim joist (covered by acoustically invisible vinyl siding), which is what closes off the ends of the floor joists, and the sill (on which the rim joist sits).

These materials will in turn excite the materials to which they are connected, including the first floor air, the air outside the foundation wall, the air outside the rim joist, and the air outside the sill. The air in the first floor will excite the wall, which will excite the air outside the house. Each time the sound energy passes through one of these media, energy is absorbed, because it takes energy to get them moving. The heavier the material, the more is absorbed (which means the less sound is transmitted--reflection is a different issue). The more plastic (as opposed to elastic) the material, the more energy is absorbed.

Egg-crate and the like is designed to create traps for the sound. Instead of reflecting back into the room, the sound reflects to another protrusion on the surface, and bounces around until it's attenuated. I don't want that--I want to hear my playing. But sound not trapped will bounce around the room and have more chances to re-excite the surrounding materials.

The concrete wall is too heavy to transmit much, unless you find a resonant frequency so that it gets into a feedback loop. But it's stiff, and it's damped by having dirt piled up on all but the top foot of it, so I don't expect to be able to find resonance. It doesn't ring when I hit it with a bat.

But the joists, decking, and sill are all wood products, which are plastic at higher frequences but are quite stiff and rigid at lower frequences.

The objective with ceiling tile would not be to absorb the energy, but to reflect it back down into the room so that it won't excited the joists, sill, and decking nearly as much. Ceiling tile, though, is also somewhat elastic at those lower frequencies, and would probably have to be isolated by a plastic medium fromt the ceiling. My sense is that there is not plastic medium that is plastic at these low frequencies.

So, my question, now refined by all this quality discussion, is this: What material or design might I use to redirect the sound being radiated out the front of the house to the sides or the rear? I'm looking for something that can be built quickly and cheaply, so that the Hatfields across the street can sleep when they want to without getting my permission first, and so I can play when and how I want to without getting theirs.

Don't I wish moving to the woods was an option right now, but it ain't.

Rick "McCoy" Denney


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