This title says it all, basically. I explain that acoustic foam does not block sound about 5 times a day to prospective customers wanting to know how to soundproof. The question invariably  comes back, “Why not? Then what the heck is it used for?”It’s not that I’m trying to ruin anyone’s day here – I would love to have foam that could stop sound from going through walls. I would sell a ton of it.  But physics is physics and the fact is that we at Acoustical Solutions are not going to sell anything to someone that has zero chance of meeting a customer’s expectations.Now, a lot of Audiophiles and people very familiar with the nuances of sound will say: “Well if you have a relatively small confined space with a given large sound source the waves will build up and potentially amplify certain frequencies due to modal responses of the shape of container – and therefore adding absorption to the inside of said confined space will indeed reduce overall dB from escaping into the environment

,” but that’s not the point, I say.The point I’m trying to make is that putting a few squares of 2” thick foam here and there on a partition wall in an apartment will not keep someone from hearing the other guy’s TV and sub woofer at 3 AM.  Even covering the wall 100% with 2” thick foam is not going to, to the extent of the person’s expectations, stop that sound from traveling right through the wall. Using acoustical foam is not how to soundproof.For instance, some speakers used to use foam as the speaker grille cover years ago. If foam is that great at blocking sound, then why do that? Or the old earphones on Walkman’s from back in the day (I’m showing my age here) – they had foam right over the head phone to make it more comfortable for the listener. The foam in both of those examples was not blocking the sound in any way. The sound just poured right through. Here’s the deal: absorption and blocking are two totally different things. I explain things better with analogies, if you have read any of my previous blogs you will be used to this by now.

The color white “reflects” all light, right?  And the color Black “absorbs” all light. What we perceive as white is simply just all colors of light mixed together, and what we perceive as black is the absence of all color.  Shine a flashlight at a bright piece of tissue paper and you will register a great deal of reflectivity. Shine the flashlight at a dark black colored piece of tissue paper and you will register very little reflectivity.However, being that it’s tissue paper, you put either the white or black paper up against the light and use a rubber band to totally cover the end of the flashlight with it, and you will register nearly the same amount of luminosity traveling through both colors of tissue paper. Maybe a tiny little less with the black…it’s not a perfect analogy. Splitting hairs aside though, the point is that sound does the same thing: It reflects off certain surfaces and it’s absorbed by other surfaces, in much the same way white reflects light and black absorbs light.

When you look at recording studios that have all this fancy foam all over the place, don’t make the assumption that it’s the foam that is blocking sound from going through the wall. They have added layers of mass and caulk and isolation to that wall first to block the sound from traveling through, then added the foam to reduce echoes in the room for various reasons.camper hvac unitsOne of the main reasons foam, or any acoustically absorbent material (baffles, banners, fabric wrapped wall panels, etc.), are used, is to reduce the average reverberation time in a room. car ac repair beaumont txA good example of a space that will benefit from adding acoustical absorption is a large gymnasium. split unit ac prices in uaeHere is an excerpt from a recent email exchange I had with a customer:ME: “Sound goes out from its source and goes until it has simply gone through enough air that it loses energy and falls below the background noise level or below the threshold for our hearing.

If there happens to be a wall, floor, or ceiling in its way before it has gone through that certain amount of air, the sound will bounce right off and head in a different direction still looking for enough air to go through before it dissipates. The louder the sound, the more air (distance) it has to go through to dissipate. PA systems are a great deal louder than a person’s voice. If the sound hits a surface that is very hard and immobile, it will bounce the sound energy at nearly 100% efficiency, which means the sound from a persons voice over a PA system is literally bouncing around the room for about 5 seconds or so. That five seconds is the Reverb Time, or RT 60, of that room. People speak in a quick succession of vowels and consonants, so if the listener is hearing 5 or 10 vowel sounds still hanging in the air with 5 or 10 consonant sounds….all you hear is garble.  Hanging Sound Baffles work because they are not 100% efficient at reflecting the sound – in fact they are nearly 100% efficient at NOT reflecting the sound.

They are absorbing the sound reflections and therefore reducing the overall average Reverb Time. ”CLIENT: “So Matt, how do I actually go about blocking sound through a wall or ceiling or anything else?” That, unfortunately is a much bigger discussion. It takes mass, or weight, and layers of it that are mechanically disengaged from one another, and sealed up tight 100% with caulk and putties, and…etc. I actually have a previous blog entry that I wrote on the subject.As always, I welcome any comments or questions, feel free to contact me using the information below. Thanks and Happy Acoustical-ing!Contact Me for more information:Matt BoughanVirginia Territory Sales Manager800.782.5742 ext. 111Direct: 804.349.0051Contact Matt BoughanHave an interesting one here for you building science detectives. Existing two story home built in the 1950s – Charlotte, NC (mixed humid) – approx. 3000SF. Existing mechanicals were a furnace in the crawl space with duct work distributed throughout the house and an air conditioner in the attic serving the second floor.

Old batt insulation in the ceiling, wall insulation undetermined (we think none) and batts in the floor. Owner received an energy audit and implemented some of the recommendations. Removed all batt insulation in the attic, removed both HVAC systems and all duct work, performed air sealing in the crawl space and the attic (at the floor and ceiling) and installed 5 ½” of Demilec open cell spray foam on the roof deck. Existing roof did not have a ridge vent - shingle color is a dark gray. Now that everything is installed, there is very high humidity in the attic and condensation on the unit and condensate drain. There are already several threads on open cell vs. closed cell, vented roof vs. unvented and blown-in insulation vs. spray foam insulation so please let’s stay with our fixed variables we have here in our discussion. Here are few readings we took. - 75 degrees and 45% RH. – 89 degrees and 50% RH (low for here this time of year). Attic temp – 84 degrees and 75% RH.

HVAC – we are asking for the manual J and checking the refrigerant charge to be sure the unit is sized correctly and performing properly. Typically in these situations the units are oversized and short cycling which is definitely not the case here – during the hottest part of the day the system is running non-stop and cannot keep up so do not think that the HVAC is the main issue although it could be contributing. Spray foam – one of the problems with spray foam is there is not really any way to do quality control on it. Have read before that if the mix is not correct there will be odors, discoloring and the foam would be extremely hard. We do not see any signs of these issues. I was expecting to see large gaps where the old soffit vents were but it appears to have a tight air seal at the perimeter. We did inspect the foam insulation with a thermal imaging camera – temperature was 84 degrees for 90% of the area. There were several areas where the depth of the foam was not consistent and we saw about a 5 degree difference within the same rafter bay (Installer said this was typical).

A handful of small ½” voids where the temperature got up into the 90s. None of which you would think would allow that much moisture to enter the attic. What else can we look for to determine the quality of a spray foam job? Big question is how did the humidity get so high up there. I do not think it is coming from the house below - that air is conditioned and relatively low humidity - if that air was getting into the attic it would improve the situation. I do not think it is coming from the exterior either - if there was a hole in the foam/roof, the moisture would be going from the attic to the exterior. So how did it get there? I think two things may have happened - the day they sprayed the foam, the attic conditions were probably pretty similar to the exterior and probably even hotter. Let’s say hypothetically - exterior was 90 degrees and 70% humidity - inside the attic was probably 110 degrees with the same amount of moisture in the air as the exterior. After the foam was installed the attic temp.

dropped from 110 to 85 degrees. The amount of moisture in the air remained the same thus the humidity would increase with a temperature drop. Secondly to compound the problem, the blowing agent for the spray foam is water - as the foam cures, offgasses, etc. it released all of the water used to install it so added more moisture into the air. Since the attic is only passively conditioned through leaks in the duct work and the leaks in the ceiling, there is nothing working to remove the moisture from the attic. The only way for the moisture to leave the attic right now is through diffusion through the roof to the exterior and diffusion through the plaster to the conditioned area of the home. Diffusion is a slow and weak force so it could take weeks for the attic to equalize with the conditioned portion of the home. Our plan of attack is to temporarily run a dehumidifier in the attic until we get the RH to match that of the conditioned area below. I think once we get the attic acclimated with the rest of the house the levels will somewhat mimic each other.