Originally Posted By: tfabris
Originally Posted By: tanstaafl.
The downside is that the entire house is a sounding board. There is NO wood construction, it is all concrete and masonry and steel, and if someone in the basement scrapes a chair moving away from the table, I will hear it quite plainly on the fourth floor.


Very interesting. I would have thought it would be the opposite.

I would have guessed that concrete walls and steel rebar would have reduced vibrations transmitted through the house, by virtue of being stiffer than wood and drywall.

The are two possible origins of noise in your house. Noise by air and noise by contact. Noise by air is the easiest to get rid of. Eg. If a neighbour is playing loud music, just close the window. In a concrete house, the effect of closing the window will be larger (read: the volume will become lower) than with a wooden house, because of the density of the material. Because there is a lot more "air" inside wood (read: the micro "pores" in wood are a lot larger than in concrete), normal noise can travel through it easier than with more denser materials like concrete. Also low-frequency sounds travel better through materials than high-frequency sounds. (everybody who has neighbours with a subwoofer setup knows this)

To understand this, you have to know how sounds travel. We all know here that sound travelling is no more than air that gets moved. Every material our there has pores in it, and thus contains air. With some materials out there, like lead, these pores are so incredibly small, they are hardly noticeable under a microscope. But they are there. This is the density of the material. The less pores/smaller the pores, the denser the material is.

Now, with smaller pores, the material contains less air, and so sound doesn't travel as good though it.

HOWEVER... there is also noise by contact. And here the situation is reversed. Because the material is do dense (and contains extremely small pores and thus little air), noise is able to travel trough the material much like the way electricity travels through copper wire. This is what you get when living in a entirely concrete apartment, and the downstairs neighbour moves a chair without lifting if from the floor... you be able to hear the screeching sound as it it was in your own apartment. (Same with fireworks: lots of air gets moved) The air in wood construction works as an insulator and dampens this effect.

So it's always a tradeoff, materials with of lot of air in them (wood, insulation, ...) are good at dampening contact noise. As a bonus they insulate heat better as well. Materials that are denser (concrete, steel, ...) are good are blocking out air noise. However, they don't insulate heat very good and are bad at blocking out contact noise.

Again, the story of the air. There is no better insulator out there than "non moving air". So if you want to create a good thermal isolator, you need to create a material that is capable of "capturing" as many "little bubbles of air" as it can. The more the material is able to hold, the better the heat insulator will be. So heat insulation materials are no more than plates of captured air. That's why they are so light. They are the worst at blocking out noises though, because the air in them lets everything pass through.

The best noise insulator is actually lead, because of the density of the material. Should you want to create a silent room (for air noises!), and you put slabs of lead on all the walls and ceilings, I can guarantee you the room will become unnervingly quiet. Of course, it would cost you a ton of money and lead is also not the easiest material to work with because it's so heavy. The cell phone/WiFi reception is that room would also suck. smile

The solution: make a combination of both. Eg. Build a concrete house, and put a lot of insulation around it. What also gets done, mostly in apartments, are the so called "floating floors". This means that the floors are not just built with concrete, but in the areas where the floors touch the walls, an insulator is put in between to separate both from one another (and so contact noise cannot travel any further). If it's not done is this fashion during construction and you live with a noisy upper neighbour, you could always eg. create a fake ceiling with insulation in it to get rid of the air noises, but because the ceiling is essentially not separated from the walls with an insulator, you'll never get rid of the contact noise. I hope this makes sense.

Originally Posted By: tfabris

I had always dreamed that someday I would build a house that didn't transmit vibrations and noise the way regular houses did. That way it could have a recording studio, but the other household members wouldn't have to be quiet when tracking. I had always imagined the whole thing would be solid concrete. But from what you're saying, it sounds like that wouldn't work.

As you can read above, it would work. You just have to do it the right way. Concrete is also still my building material of preference, because it's got a lot more benefits than downsides. It's just that blocking our contact noises isn't one of them. But as I've explained, this can be remedied if this is taken into account when the house is getting built. This is crucial, because you'll never be able to fix it to a satisfactory level afterwards, because you won't be able to reach the core of the problem anymore (well, not without tearing it completely down again, that is...)
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