The science of silence

I’ve “soundproofed” three rooms since I’ve lived in Seattle. I use quotes because nothing is really ever proofed. Some amount of sound always escapes, so it becomes a question of how far you’re willing to go to bring down the sound levels outside of a room. In the case of our new house, I’ve gone pretty far down the rabbit hole with two primary goals:

1) to make sitting upstairs enjoyable for Brangien when I’m making loud drum, keyboard or guitar noise in the basement

2) not piss off the neighbors

I’m actually confident that #2 will be achieved. In my last house on Capitol Hill I built a rehearsal space that allowed Maktub and other bands to rehearse at full volume. My closest neighbor told me she could hear the kick drum in her living room (about 15 feet from the back studio wall), but not enough to bother her. Someone walking by the side street could hear the muffled sound of a band rehearsing at a low volume as it bounced off the brick wall of Immaculate Conception church. Again, never a complaint … but some amount of sound always finds it’s way out of the sound maze you try to construct as a barrier. In particular, bass guitar and kick drum frequencies are hard to contain. People with subwoofers in the trunk of their car (note: I was once one of those people) don’t realize how loud the boom is a block away. Same goes for subwoofers in home or movie theaters when you hear the intestinal bass tones from the blockbuster next door.

As for #1, I’m not so sure. In my last studio, a person sitting upstairs would hear just about everything downstairs. It wouldn’t be as deafening as the actual studio, but it was not possible to quietly read a book or even consider napping while rehearsal was going on downstairs. A person upstairs was pretty much in attendance by proxy for rehearsals downstairs.

I’m not an expert of any sort but I do have real world experience building, and therefore living with, a studio of my own design for a few years. This has reinforced my understanding of the weakest link concept: soundproofing is only as good as it’s weakest barrier. For example, with the last studio I went to the trouble of insulating, decoupling sheetrock with Z channel, caulking, etc … but there was a big air vent in the studio wall. Sound entered the vent, went up the heating ducts and back out through the vents upstairs. Not good!

Which brings me to the science-ish part. There are two concepts that come up when soundproofing: mass and decoupling. Mass (e.g. a thick cement wall) is required to dissipate sound and there’s no cheating the mass math required to reduce, say, a bass guitar or kick drum. However, decoupling is often overlooked by people like me building studios in their home. Here’s a common progression for sound nerds: band rehearses in garage and it sounds “harsh” so you cover the walls with egg cartons. That seems to soundproof things, but your neighbor complains and you realize that does nothing for containing the sound, it just deadens things inside the room. So you add some mass by insulating and maybe hanging sheetrock. That definitely helps but it doesn’t matter how thick you make the walls, a lot of sound still escapes (particularly bass and kick drum). Next you hear about “decoupling” and you get fancy enough to hang sheetrock on Z channel. That helps some, but the vibrations are still reaching the wall studs and that transfers into the rest of the house turning it into a speaker for those vibrations. If you dig a little deeper you start to understand the science and art of decoupling and mass.

Here’s what I did to reduce sound in my previous rehearsal space:

  • caulked all the gaps in the ceiling and wall framing
  • insulated every wall and ceiling cavity with standard R19 insulation
  • installed Z channel (aka resilient channel) between the framing studs and joists, and the ceiling and wall sheetrock in an attempt to decouple the vibration between sheetrock and the rest of the house
  • installed double-pane tempered glass windows with laminated exterior glass
  • installed sealed storm windows in addition to the double-paned glass
  • installed an exterior grade sliding studio door with a tight seal around the perimeter of the door

What I learned from living with that rehearsal room for 7 years:

  • soundproofing is only as good as the weakest links (in this case: big air vent & Z channel)
  • Z channel is good in concept, but is almost always short-circuited by sheetrock screws during installation (even when pros install it) and it passes along vibrations
  • adding a third pane of glass to the window bays resulted in an amazing decrease in sound levels outside the house (an air chamber separated by a window or door is probably the most awesome sound reduction tool)
  • all-in-all this room worked well for my needs—upstairs in the house the sound of a band rehearsing was loud, but outside the house it was low enough in volume to keep the neighbors happy

In the new house I decided to pull out most the stops and spend the time and money necessary to truly decouple the basement studio from the upstairs. I asked Seattle Sound & Vibration for help in designing and choosing all the sound reduction materials and enlisted the studio construction talent of Brouwer Contracting.

Here’s what I’m doing to reduce sound in the basement studio of our current house:

  • installed double-pane tempered glass windows with laminated exterior glass (if required, I’ll add a third pane)
  • floated the one framed wall in the basement on compressed fiberglass with rubber bushings between the lag bolts and framing
  • installed a spring-suspended ceiling with one layer of 5/8″ plywood followed by two layers of 5/8″ sheetrock
  • used isomax clips for areas where springs weren’t possible
  • sealed the 1/2″ gap around the ceiling membrane with sound foam and acoustic caulking
  • installed 3 heating duct silencers (with rubber clamps) on each air duct run to reduce sound as it enters the air system
  • installed 5 exterior grade solid-core doors with full sound sweeps for all the basement closet doors and an exterior grade solid-core door at the top of the steps and one double-paned exterior grade window door at the base of the stairs
  • installed three layers of sheetrock (2 on the front, 1 inside the closets) on the single framed wall in the room
  • caulked every gap in the door frames
  • packed fire-proof putty in all the gaps and holes of the light switches in the wall to prevent sound leaks
  • installed sconce lighting instead of ceiling cans, to prevent unnecessary holes in the ceiling membrane

I won’t know how well this works for about another week. Mudding and taping is occurring as I type and we’ve still got to do the final caulking seals around the perimeter of the wall, ceiling and windows. Once that’s all done I’ll close the airtight doors, crank up a guitar amp for starters and see how it works.

Before we started this project Brangien and I could have a conversation without raising our voices while she was upstairs and I was below her in the basement. Since the ceiling, walls and doors have gone in we can’t hear the radio downstairs but we can still yell and hear each other. Keeping with the weakest link theory, I have faith that the final seal around the ceiling, windows and doors will reduce the sound even more.

Before:

Cleared the closets and clutter, moved the heating ducts to the crawlspace, sandblasted the floor and walls, acid etched the floor, installed new gas furnace:

Installed three silencers (connected with rubber clamps) in series for each of the two air duct runs:

Framed the walls with walmatt and anchor isolator rubber bushings:

Used rubber isolated ceiling springs and metal channel to hang 3 layer ceiling:

Three layer ceiling consists of 5/8″ plywood and two layers of 5/8″ sheetrock:

Isomax clips for attaching ceiling to furred out section under fireplace:

I’ll add more pictures and report back on how the sound levels behave directly upstairs and outside the house. A couple other nerd things to mention:

I’ll likely add Indow Windows to the inside of the window frames if the outside noise level is too high. In my last studio I was amazed at how much an extra chamber of air reduced sound. The two exterior grade doors (which just means they’re solid-core and thicker than interior doors) with sound sweeps reduce sound traveling up the stairs, and the large air space (in this case the length of the staircase) between the lower door and the upper door helps to reduce noise levels. That air space is where a lot of the sound dies out.

One other great advantage I have to soundproofing this room is that the basement is underground and surrounded by cement walls. Basically, it’s a bunker. Concrete and earth = mass. So I’m focusing my efforts on the suspended ceiling, floating wall, doors and windows. The bunker should take care of the rest of the sound escape routes on its own.

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9 thoughts on “The science of silence

  1. This is excellent. I love projects like this. You’ve come a long way since the garage box over on Magnolia. 🙂 Keep up the good werk and I look forward to the next update.

  2. Ha! Two sound nerds comment on my blog … what a day! I’ll post final pictures soon, Snap & Cozzi. Painting happened today and tomorrow it all gets put back together. Exciting!

  3. It looks great. Nice shot of the different layers in your ceiling! Very helpful. I look forward to seeing the finish product and to finding out how well it blocks the sound. Cheers!!

  4. I’m looking into doing something similar for my detached 2-car garage. Do you mind giving a rough estimate on the cost including design and the actual construction? Did you do any of the work yourself?

  5. Hi Dan,

    I had a contractor do the actual construction. My brother and I did the deconstruction. It’s hard for me to separate out the costs because lumped into my vague memory of the price tag is the sandblasting and floor coloring (aesthetic decisions) along with the new furnace and moving the vents and utilities to the crawlspace. So, it’s a hard number for me to back into a year after construction. The actual soundproof materials (springs, sound mat, screw w/ rubber bushings, acoustic caulk, etc.) really aren’t crazy expensive: maybe $1,000? It’s the installation (you need someone who has done this work before or is willing to spend the time necessary to learn) and the additional sheetrock and plywood (3 layers in total) and the extra associated hours for framing, decoupling and hanging the extra sheetrock and such. How’s that for a non-answer answer?

  6. Now I’m second-guessing my cost estimate on the springs—it might be a bit more than $1k for all those supplies (but not too much more). Note that you need a pro to design the spring layout as you’re hanging hundreds (if not thousands) of extra pounds of sheetrock and plywood (it’s a three-layer cake) from those springs and they need to be able to handle the weight. The layout is super important and shouldn’t be guesstimated.

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