Do you have a question about soundproofing your theater? Then this is the thread for you. It is a sister thread to the Acoustical Treatments Master Thread
, but for soundproofing questions instead of acoustic questions.
Basic Q & A
Q. What is Soundproofing?
The goal of soundproofing is the reduction of sound leakage into or out of a room.
Q. Do I need soundproofing? I don't have close neighbors and everybody in my home watches movies at the same time!
Soundproofing refers to sound leakage both going out of the room (sound generated by your theater) and
the sound entering the room. Arguably, controlling the sound entering a room might be more important than controlling it from leaving.
Q. Why? Who cares what happens outside the theater?
Sound leaking into the conditioned space of your theater adds to the noise floor in the room. This requires that in order to hear the quietest parts of a movie, you'd need to turn up the volume quite a bit just to hear over the noise from outside the room. How much? This quote by Dennis Erskine says it all:
Q. What's the difference between soundproofing and acoustics?
Originally Posted by Dennis Erskine
The softest sound on a sound track is 22dB. The typical noise floor in a quiet home in a quiet area is 33dB to 35dB. That is in the range of 6 to 7 times louder than the bottom of the sound track. Ok, so for whispers, and other low dB cues and voices on the sound track, that's no big deal...turn up the volume. But, now you run into problems. Normal speech is now 6-7 times louder ... talking is now yelling on the sound track. Next comes the louder sounds ... traffic, bombs, gun fire, etc. They are now 6-7 times louder as well ... too loud for comfort (or realistic listening). With the top of the dynamic range in a sound track at 105dB, that now must be 6-8 times louder. The problem is the vast majority of consumer equipment (amps/speakers) cannot handle that increase on the top end ... blowing out tweeters, clipping the amps, or amplifier distortion as you reach those levels.
Technically, soundproofing is a form of acoustic control, but most people think of them as two different categories. Soundproofing is all about controlling the sound leakage in and out of the room. Acoustics is all about controlling the sound that is in the room. Think echos, reflections, reverberations, and the like. Both are important, if not at the same level. Soundproofing is likely important to many home theater builders -- acoustics is important to all of them.
Q. What are the fundamental basics of soundproofing?
There are four primary elements of soundproofing, roughly in order:
- Adding Mass
All soundproofing methods will involve at least one of those elements.
Decoupling refers to creating gaps between solid surfaces. Sound is just a vibration and it travels very well on direct solid pathways. Decouple the solid materials and the pathway is broken.
Adding mass means to make the vibrating surfaces "heavier." Again, since sound is a vibration, it needs to actually vibrate any substance that it passes through. Heavier materials are simply harder to vibrate than lighter materials.
Damping is all about adding some material (usually a viscoelastic compound) to a surface to keep it from vibrating as much as it normally would. This is a relatively new development in soundproofing, but is so effective that it has become almost ubiquitous.
Absorbing is what you think it is - you add materials that can "trap" air and slow down resonating sound. This is an important step (and critical for acoustics) but for soundproofing, it is not as effective as the other four elements. That is, just adding a batt of fiberglass in your wall by itself will not do very much.
Q. How do I apply those elements, practically?
There are many ways to soundproof a room, and those elements can be adapted to fit many types of situations. Here are some high level thoughts:
First, address your walls. If you are able, consider decoupling them by creating a "room within a room". This is a separate 2x4 wall separated from your existing walls by an inch or so. If space is tight and it is new construction, then consider a staggered stud wall. Another alternative is to float the drywall by attaching the sheets to channels that are separated from the studs via clips. Add mass by layering at least two layers of 5/8" Type X drywall. Damp the drywall by putting Green Glue (or equivalent) between the sheets. Add absorption with insulation.
Then, do the same with the ceiling. Your ceiling is likely connected to either the floor above you or to the shared attic with the rest of the house. Decouple it by "floating" the ceiling, either using floating joists (in a "room within a room" concept) or via clips and channels. The former costs less from a materials perspective, but requires more room and is not always feasible. Add mass, damp, and add absorption the exact same way as the walls.
Now take care of your door. The door is typically the weakest link in the soundproofing chain, since it will be substantially thinner than the walls and will also need to be moveable. At the very least, get a 1 3/4" solid core door. Then add perimeter door seals (like weatherstripping). Consider an automatic door bottom to seal off the bottom of the door. If you need more soundproofing, then try adding more mass to the door using layers of MDF and damp with Green Glue. If even that is not enough, then (assuming you have room), create an "airlock" with two sealed solid core doors. That's the decoupling component.
You might also look at your floor, especially if it is on a concrete slab. Concrete transmits low frequencies very well and so it's possible for vibrations from air conditioning units or freezers or the like to intrude in your theater. Combat this by decoupling the floor via an additional layer of OSB or plywood laying on an underlayment. The underlayment adds mass and some absorption.
Here are two links that give a great introduction to the topic of soundproofing:
Advice from Anthony Grimani (PMI) - Soundproofing 101: How to Keep Your Home Theater Quiet
Advice from Ted White (Soundproofing Company) - 4 Elements of Soundproofing
Quite a few articles on soundproofing quote from the original research done by the National Research Council of Canada. The most quoted white paper is here: Control of Sound Transmission through Gypsum Board Walls
. If you ever hear references to "triple leaf", then this is where some of the key research concerning that was done. It's a very accessible paper.
In general, the articles on the Soundproofing Company website are excellent. The site is trying to sell soundproofing products, but the founder is an AVS Forum regular and the articles are very unbiased. Start with these articles: Soundproofing 101
. Move on to these articles: Soundproofing Articles
This article is from the perspective of apartment buildings, but soundproofing is soundproofing and this is a great intro: Acoustical Considerations for Mixed-Use Wood-Frame Buildings
Interesting Links in this Thread
Using OSB instead of Drywall as an initial layer (Post #4)
Should the "air gap" in a double wall be filled with insulation? (Post #10)
(TL;DR - no)
Essential soundproofing links from BasementBob (Post #20)
Comparing soundproof door solutions (Post #30-50)
Solutions for non-permanently "plugging" a window in a theater (Post #31)
OSB as first layer; Does next layer of drywall need to be screwed into channels or directly into the OSB? (Post #64)
(TL;DR - channels)