Acoustically absorbant materials

[Fandu]

Question: I'm looking to try and reduce the noise both into, and out of my dorm room. I have a big stereo to start with, and I like my base nice and loud. So my primary goal is to reduce the amount of low frequency noise escaping my room. The secondary goal is to reduce midrange frequencies (voices, etc) both into and out of the room.

I don't really want to cover the entire room with a sound absorbing material, I was thinking more of a 12-18" ring around the top of the room, and a 20-30" ring around the bottom of the walls. The ceiling is also fair game, but I am unsure of how effective that would be.

Now to the problem I've run into, most of the sound absorbant materials I've found are quite thick (2-4") and they are rather ineffective at reducing SPL below about 250Hz. The best absorption coefficient I've found at 250Hz is .6, but that is a 4" thick foam that sells for $50 per m^2. I was hoping to find something like a fabric that was effective, but the best I've found is also very expensive, and is only has a coefficient of .2 @ 250Hz.

Any experience or suggestions for reducing the noise would be very helpful. Ideally I would like to reduce the frequencies below 250Hz more than above, but I'll take whatever I can get.

 

[bizmark]

I'm no acoustical engineer, and I've only experimented a little bit with this sort of thing, so take everything I say with a grain of salt, but I think it makes intuitive sense.

First, I think that you're essentially fighting a lost cause. Sound transfer to/from a room depends on a lot of things, some of which you can't control in a dorm room, including crawlspaces above/below the room, the material in the walls and its resonant frequencies, the dimensions of the room and the overall room layout, and the placement of the room within the building (e.g. in the corner, along a long hallway, etc.).

The first thing you should mess with is the placement of your speakers within the room. I know that you probably have limited options as far as this goes, but you can go a long way to avoiding pissing off your neighbors by simply placing the speakers in the right places (although this might not be completely possible). Also, ask your neighbors if they'd be willing to compromise by moving their furniture too. My first year in school, my next door neighbor had his small computer speakers placed on a shelf on the wall between our rooms. I could hear the music that he was playing PERFECTLY when I laid in my bed at night. He wasn't playing the speakers very loudly at all. I would walk in his room and ask him to turn it down, and it would sound approximately as loud in his room as it did at my bed (across the room from the shared wall). (In the bass frequencies in particular -- I obviously couldn't hear the vocals very well through the wall!) I asked him to move the speakers out from the wall a couple of inches, and this change in placement did a lot to change how much of his sound I heard. I couldn't completely eliminate it, though, without simply swapping my position in my bed, placing my head at the other end. I couldn't hear a thing.

This year, I have an apartment, and a similar thing occurred. By moving my bed, my roommate's speakers went from keeping me up at night to a minor nuisance that I could overcome by placing my pillow over my head.

This is completely anecdotal and non-scientific, but I think that it speaks to a truth in acoustics: You can never predict what the hell is going to happen, so you've just got to move sh!t around until you come across a livable solution. So ask your neighbors to sit in their rooms, at their desks and laying in their beds, and crank up your stereo. Ask them how much they can hear it. Then move your speakers around somewhat. Even just putting them slightly skewed to the axis of the room could do a lot to affect things.

Really, this is more of a social problem than an acoustic one. Even with tweaks, there's no way your loud bass won't disturb your neighbors. Just talk with them and maybe you can arrange a system. They're all gone from 3-5 in the afternoon? Great, that's your "pump-it-up" time, and the rest of the time you need to keep it to a moderate level. They like loud music too? So maybe you can all set an "anti-bitch" policy and agree that you can all turn it up as loud as you want anytime you want. Or, just have an "open-door" policy whereby you play your music how you want, but all of your neighbors feel completely free to tell you to turn it down if they're sleeping or studying.

Might I also suggest a nice pair of Sennheisers?

 

[Shalmanese]

Well, you could fill the rest of the dorm with a complete vacuum, VERY effective sound barrier but probably not going to go down well with your neighbours not to mention expensive. Or you could just wear headphones.

 

[Demon-Xanth]

Check with McMaster Carr, they have acoustical sheets that you can hang, as well as various other types of foams and materials.

 

[DRGrim]

Try placing the foam just under your speakers. That would reduce the sound being conducted through the floor to other rooms.

 

[Ju1cyJ]

get a bunch of old matresses and put them on all the walls, works wonders

 

[highwire]

Sadly, foam, fiberglass, heavy curtains will not attenuate low freq bass sounds much at all. But thick stone walls work great, i.e., a rigid diaphragm between point A and point B is about all that will work for low freqs. The heavier the better. And, best no holes.

I got a lot of sound data from a professional plasterer's handbook - a thrift store nugget I latched on to a while ago. I had some misconceptions myself about the magic of fiberglass, etc. Soft surfaces will deaden the higher freqs in a room, but won't help much to keep sounds in/out, particularly low freq bass.

 

[Fandu]

Originally posted by: highwire
Sadly, foam, fiberglass, heavy curtains will not attenuate low freq bass sounds much at all. But thick stone walls work great, i.e., a rigid diaphragm between point A and point B is about all that will work for low freqs. The heavier the better. And, best no holes. I got a lot of sound data from a professional plasterer's handbook - a thrift store nugget I latched on to a while ago. I had some misconceptions myself about the magic of fiberglass, etc. Soft surfaces will deaden the higher freqs in a room, but won't help much to keep sounds in/out, particularly low freq bass.

I've been experimenting with some 3" thick 'eggcarton' foam. And your right, it cuts down the mid and high freq's not too bad, but it doesn't stop the low stuff at all.

I see some stores selling lead sheets that are layered with foam. They have an outer layer of foam, and two inner layers of lead, seperated by a layer of foam. They weigh about 50lbs per square yard (~meter^2), and your suppost to hang these sheets on the walls. Their only about a 1/2" thick, so that's a major plus, but the weight, the cost (~$300 per yard), and I'm not sure that I want my walls covered in lead. But does anyone know how well the stuff works?

 

[Shalmanese]

Have you thought about shielding your speakers rather than your room?

 

[Fandu]

Originally posted by: Shalmanese
Have you thought about shielding your speakers rather than your room?

Hu? Doesn't that defeat the purpose of a Hi-Fi Loudspeaker, or am I misunderstanding you?

 

[Smilin]

I did some network admin work for these guys once, check em out:

http://www.earsc.com/

They make earplugs and sound shielding for everything from stereo's to jets.

The company name is EAR (energy absorbing resin). They make the yellow foamy ear plugs you've probably seen, especially if you've served in the military.

These guys have materials that will do just about anything. They even have this one sound attenuator/ear muff that allows low volume sounds like speech to get through but muffles high energy sounds like gunshots...made with no moving parts or electronics.

They also make this gag-gift as a promo...it's a golf ball that's made with energy resin...drop it from about 10 feet and it hits the floor like a magnet...no bounce at all and without losing it's shape like clay. Supposedly the golf ball will take the head off a club if you hit it hard enough...never seen it happen but gawd it rings your hands with vibration bad when you hit it.

 

[bizmark]

wow... that EAR company is awesome. I remember a few years back when I went to an airshow and got some E-A-R earplugs... very cool stuff. From their site:

In probably its most demanding application ever, ISODAMP® C-1002 material prevents a detonated warhead from exploding seven neighboring shells.

:Q:Q

Also, they say their E-100SM absorbing foam (one inch thick) has a .81 coefficient at 250Hz. It drops to .20 at 125Hz, though. Still, very impressive stuff. They don't list prices, but I'm betting that it's very expensive. It's sold in rolls.

 

[Fandu]

Originally posted by: Smilin
I did some network admin work for these guys once, check em out:

http://www.earsc.com/

They make earplugs and sound shielding for everything from stereo's to jets.

The company name is EAR (energy absorbing resin). They make the yellow foamy ear plugs you've probably seen, especially if you've served in the military.

These guys have materials that will do just about anything. They even have this one sound attenuator/ear muff that allows low volume sounds like speech to get through but muffles high energy sounds like gunshots...made with no moving parts or electronics.

They also make this gag-gift as a promo...it's a golf ball that's made with energy resin...drop it from about 10 feet and it hits the floor like a magnet...no bounce at all and without losing it's shape like clay. Supposedly the golf ball will take the head off a club if you hit it hard enough...never seen it happen but gawd it rings your hands with vibration bad when you hit it.

NICE! I like the Sound Barriers that they make. 0.10" thick, and has a 15db transmission loss @ 125Hz. They also have a 0.20" thick one.... I wonder how you go about getting some of this stuff to try out.?

LOL, I've got to get me a couple of those golf balls, would make great practical jokes.