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Old 03-22-2012, 12:36 AM   #16
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Sound attenuation; a surprise about insulation


Some good and not so good info....I like #'s....tends to remove opinions....

Here are some relative thermal conductivity #'s for common materials...expressed as k - W/(m.K)...the lower the #, the more insulating it is.

Air - 0.024
Glass/wool insulation 0.04
White Pine 0.12

Yellow Pine 0.147
Gypsum 0.17
Concrete 0.1 to 1.8 (lite to dense)
Dry Earth 1.5
Glass 1.05
Stainless Steel 16
Iron 80
Copper 400


With that noted....

Sound transmission through materials is a function of several factors...density being one of the most obvious...Freq also plays a significant role. Typically, the more dense the material, the better it will transmit sound. Case in point, sound travels through the ground faster than air or water....as in how oil engineers find oil deposits. The range of freq that get carried is greatly influenced by the material.

We could spend months talking about all the materials...but I believe we are concerned with a basement.

As you can see above...it would appear that there is a direct corrolation between mass and thermal conductivity....with some exceptions....as in stainless steel....poor conductor of heat....and not a very good conductor of electricity.

So, refering to the above....Air is the best insulator....until it moves....so the trick is to not let if move...that is what insulation does....traps the air in small pockets to prevent movement. That is why plugging leaks is so important.

Blocking sound is a matter of preventing sound waves from propogating. A combination of low mass materials with different freq characteristics works best. One of the big sound transmission culprits is the stud or floor beam. It acts as a coupler between walls or between a basement and 1st story floor. If you could install a dead space where there was no mechanical connection, noise would be greatly reduced.

One last point....you know why sealing up a room and preventing drafts makes it feel warmer? Any air movement across the skin causes evaporation on the skin...so it cools you off. In the winter time the relative humidity tends to drop drastically which causes you to feel colder due to evaporation of moisture from your body. Case in point...in the summer time people use ceiling fans to circulate air...a ceiling fan can make a room at 80 deg feel like 75. Conversly, raising the relative humidity above 25% and or reducing air flow will make a room feel warmer.

And floor 'radiant heat' makes a room feel warmer because it warms up the feet.....how many people feel so much colder when their feet are cold even though the room is fine? How many people run the heat in their car on the feet instead of the dash vents?

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Old 03-22-2012, 05:34 AM   #17
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Sound attenuation; a surprise about insulation


one point I would still like to make clear.... the convection in front of a window is not only due to a leaky window. Larger windows will have more convective currents. This is from the colder air in front of the window falling and thus pushing up the warmer air in a conditioned room. And you are also correct that our body heat moves towards the colder surface of the window panes. this is very clear with an infrared camera. You will see your image (heat) perfectly in the glass in front of you. (ghost hunters anyone)

My issues may be more that you offered points that are misleading in the fact that a minor part of the heat transfer is stated to indicate it is the major factor.

But discussions like this help clear up some issues. So many people are posting things that are dead wrong.
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Old 03-22-2012, 01:00 PM   #18
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Sound attenuation; a surprise about insulation


roger that. it is always lengthy and complicated to "talk" this stuff over online, because, for brevity, we don't always say things like "it's there, but it is probably a minor factor", etc. Typing is much slower (on my end, anyway) than speaking. Then, too, if you don't get to your Mac quickly, someone else posts and the discussion flips off on another tangent. I learned (I hope) long ago to be a bit cautious in the words I chose, as I, too, sometimes don't properly read between the lines on what someone says. So, I generally try to post links (but don't store a ton) so people can read and draw their own conclusions. It ain't rocket science, but it IS building science, and there is often a lot of physics in it. c ya.

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