Adding soundproofing to existing walls?

[PTRAVEL]

We've just bought a 120+ year old Victorian in San Francisco. Our house was built as the middle one of three townhomes, all of which share common walls (we knew this going in). Our neighbors are great people, and we rarely hear them (actually, I fear they hear us more often). Still, when they have a party, it's as if we were there, and I've set up a home theater in one of our basement rooms, and I'm afraid to crank up the sound too much.

I know the standard technique for soundproofing requires two walls without common studs. This isn't practical here for a number of reasons. First is the cost -- far too much to rebuild 75 feet of walls on each of 3 levels. Second is the difficulty -- our first and second floor have ten foot ceilings with elaborate original-plaster crown moldings. Tearing down the walls and recreating the moldings would be far too large a project.

So . . what else can we do?

Is there anything we can inject into the wall space that would help deaden sound transmission? I was thinking about that expanding polyurethane foam which is used for insulation -- does it have enough of an effect on sound to justify the cost, as well as drilling all those holes?

For the home theater in the (fully finished) basement, I'm thinking of just putting up acoustic tiles on the common walls. I also need a solution for the ceiling, which has flush-mount built-in lights.

Any suggestions would be greatly appreciated.

Thanks!

[wayne]

heavy drapes will help you could glue cork to the walls anything soft will help to absorb the sound

Wayne

[Joseph Meehan]

It is difficult to suggest any single thing. Sound transmission is a complex issue. I will try to suggest several common issues and suggest:

As a source for ideas and materials.

In general you want to block air exchange. Air caries sound very well. (Try opening your car's window as a train is going by.)

Next you want weight. Heavy things (drywall lead sheets etc.) block sound well. An additional layer of drywall can help a lot, but, in your case the walls may already be heavy with real plaster. If the walls in question are dry wall, I would suggest an additional layer of drywall.

You also want to prevent any direct solid connections. Stagger wall studs or use special isolation devices to keep the sound from traveling through the wall (remember the two cans on a string (well wire actuarially worked) you want to break the wire). However this seems to have been ruled out in your case.

Filling in wall cavities with sound absorbing materials (acoustical fiberglass bats) will do a little.

The frequency of sound makes a difference. High frequency can generally be traced to air transfer and can be controlled by absorbing materials and more attention to things like HVAC vent and returns. Low frequency sound is usually going through solid materials and needs separation or more mass in the dividing wall.

[m Ransley]

Foam increases transmission of certain frequencies . I put foam on my exterior now I can hear my neighbors kids running up their stairs. Blown in cellulose may help, wall hangings or sound panels on the walls finished with art. The best way is dual walls which you have ruled out.

[SQLit]

I had my block home injected with foam in the walls. I did it for thermal reasons. I will say that the home was much quieter that before.

The holes are not all that big of a deal.

[PTRAVEL]

Thanks, I'll look.

Most of the common walls are lath-and-plaster, though of a recent vintage. It also wouldn't be possible to add drywall, because of the crownmoldings and base shoe.

Yes. I'm trying to find a solution that doesn't require tearing down and rebuilding half the house. Whatever I do has to be something I can place between the walls, preferably by injection. (Someone else suggested drapes -- I can't run drapes down a 75 foot wall).

That's what I was wondering. I assume that injectable foam, which has air pockets, just like the fiberglass, would work, too

Ha! This is an antique victorian -- there is no HVAC! ;)tually, there is, kind of. There are heater ducts that run from a furnace in the attic (actually the 4th floor). However, these ducts, fortunately don't run through the common walls, and aren't shared with my neighbors. Incidently, anticipating a comment, the attic isn't common -- the houses are on a hill, so the attics are staggered and each is isolated from the other, so the attics aren't transmitting sound.

I was afraid of that. That's going to be an issue for the home theater, though I have a little more leeway downstairs -- it's a single room and I could, if neceesary, build a second wall that's isolated from the common wall.

Thanks for your suggestions.

[PTRAVEL]

Blown-in cellulose sounds interesting -- it's not an expensive solution. Thanks for the info on foam increasing high-frequency transmission. Except for the home theater, it's the higher-frequencies that are the problem, i.e. music and voices.

>

[PTRAVEL]

I'm willing to accept holes. They can be patched, and I need to repaint anyway.

I'll have to research foam, as some are saying it increases high-frequency transmission, and some are saying it helps deaden sound. Blown-in cellulose sounds like a good solution (and has the advantage of being considerably cheaper than foam).

[Edwin Pawlowski]

Check out Owns Corning web page. They have been touting some material for soundproofing that may help you.

Maybe a combination of things. Some rooms may be better treated with some sort of wall finish, like cork. Carpeting is supposed to be good, but I doubt it would look good an any room.

The second wall may be best for the home theater wall as that is probably the one room you'll make the loudest noise. Drapes may be enough for the bedroom where the noises are not loud, but you'd rather not be heard anyway.

[Joseph Meehan]

PTRAVEL wrote: ...

I don't think adding another layer would help much anyway. However, while it is a lot of work, it can be done.

I would vote for the Blown-in cellulose. The hard real plaster walls are different than drywall and I believe the cellulose may help a fair amount in your case. I suggest you get someone who knows what they are doing as it is easy to get part fills due to the keying of the plaster. Some foams may also work well.

[PTRAVEL]

Damn, I didn't even think about that until you mentioned it. Now I'm really going to be paranoid. ;)

Thanks for the Owens Corning tip. I'll check it out.

[PTRAVEL]

If I go with something blown or injected into the walls, I'll definitely hire a sub to do it. I know my limits. ;)

Thanks!

[m Ransley]

I did not say foam increases high frequency transmission. footsteps are low frequency. as the music and voice are low mid. Understand sound waves , and sound first. High frequency 6000 hx and up , cymbals etc have short waves. The higher a frequency the shorter the wave, the less power is needed to make it and stop it. The waves may be inch long and can be absorbed by carpet. Low and mediun frequency require more power to produce and stop-absorb. Low bass waves go to 4 feet in length , require the most power to make and stop- absorb. That is why you hear Bass out of cars and houses not cymbals and high frequency. To stop sound you are turning sound energy into mechanical energy by absorption into the proper material, density and depth. or by separation as floating walls provide. As you need to stop certain mid- low , low frequencies, Not high, you must understand sound , sound wave lengths, power needed to produce certain frequencies, and what material and design will work best or your money wont be well spent. Think of this, in a Tri amp stereo the high frequencies- above say 6000 hz go to the tweeter, mid to 700 hz to the main and below 700 to the woofer . The tweeter needs 10% of the power, the mid 40% , the bass or sub 50% , longer waves need more energy to make and stop. My numbers are not accurate but my point on wave length and absorption are. Ask a pro , get pro equipment if you really want to reduce your sound. A db sound meter and book at Radio shack is advisable for you to track and learn about your project before you waste money not fixing your problem. Talk to sound proofing pros

[p_j]

Is there such a thing? My impression was that modern plaster walls were typically built with that metal mesh.

Danger is expansion of the foam. Watch out. It can deform things. Also, if there is a small opening on the other side of the wall, it will foam out there and ruin any finish it lands on.

[PTRAVEL]

Actually, you could be right -- it might be mesh. I haven't been inside them yet, I only know they're plaster.

If I go with foam, I'll have it done by a professional who, I assume, will account for such things.

I have a very good relationship with my neighbors, so I'll let them know what I'm planning. Since I'll be hiring a pro, it will be his liability (and I always insist on proof of insurance for these kinds of things).