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.
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.
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.
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.
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
Thanks for your suggestions.
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.
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.
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
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).
I'm willing to accept holes. They can be patched, and I need to repaint
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).
HomeOwnersHub.com is a website for homeowners and building and maintenance pros. It is not affiliated with any of the manufacturers or service providers discussed here.
All logos and trade names are the property of their respective owners.