Let me start this by saying that there is no such thing as a totally sound proof room, but depending on what your needs are and how much you want to spend you can make the space pretty darn quiet. Therefore, this Instructable is actually how to build a sound “attenuated” room.
In my case, my main goal was to reduce the sound escaping from the studio. The original room was a makeshift work shop directly under our master bedroom. Not only were the basement rafters open, there were also two HVAC supply ducts traveling across the ceiling that fed the bedroom.
The situation was such that whenever someone was jamming away in the “studio”, it filled the entire house with sound. When you were in the bedroom, it sounded like you were in the same room with the drums. To keep everyone happy I really needed to address the sound problem. Plus if I want to record, sound coming in from the rest of the house could be recorded as well.
This Instructable covers the design and build of our new “sound attenuated” studio. For the sake of readability, I will use the term “sound proof” just because that’s what most people say.
There is a plethora of information on how each of my choices effect sound propagation. So I will not spend a lot of time explaining how each thing works unless I think it needs more background in this Instructable. But some general principles for reducing sound transmission include:
· Sound propagates in waves of energy – stop the waves from advancing, you stop the sound.
· Make sounds go around corners to lose energy
· Use dissimilar materials (think air pocket to fiber, solid mass to soft mass, etc).
· Decouple the room from the main structure
One thing I found interesting is that most of the basic principles of sound proofing were pretty much standardized by the mid-1950’s.
Just to be clear, my main goals here are to:
1. Minimize the amount of sound traveling to the bedroom above the studio - This was by far the most important goal.
2. Reduce the amount of sound going to the rest of the main floor – hopefully nothing louder than something like a TV in the next room.
3. Minimize the external sounds coming IN to the studio.
NOTE: I created a video walk through of the studio. You might find this helpful as well:
Step 1: Identify Specific Issues and Prep the Area
The first step is to figure out where the main sound propagation points are and develop a plan to deal with each one. In some cases, you might find that when you make a change, it might cause a different problem somewhere else.
The obvious issues were the open rafters and the HVAC ductwork. There were other areas of sound transmission that needed to be addressed, along with the need for electrical, lighting and ventilation in the completed room. Each area needs to be thought of a part of a complete system and how they relate to each other.
After a fair amount of research on sound proofing, I decided on some general approaches I would use.
- The three concrete walls would require the least amount of sound proofing and floor would require none.
- Double drywall on the ceiling and certain walls.
- Decoupling the entire room from the rest of the house.
- Plenty of insulation
- SC3000 (aka Sticky Crap) for sealing joints and between the double drywall sheets
- A dead vent with inline fan for ventilation.
- A sheet of lead for one problem area
- Double door access (2nd door pending at this time)
Specific to electrical issues:
- Dedicated circuits for
- Recording and related equipment
- Everything else
- Absolutely no fluorescent lighting
Specific to venting/climate control:
- Use of “dead vent” to pull air in from and vent out to adjacent room while still minimizing sound transmission
- LED lighting to reduce the amount of heat being generated
- Vent fan on motion detector switch to automatically turn on vent while someone is in the room
Note about order of events: I broke this Instructable down into major sections. But as you will see in the photos, many of these activities take place at the same time, alternating back and forth depending on location and if it was pre/post framing, etc. This entire project required careful orchestration of “what to do next”.
Prep the Area
In this case, the room was a workshop/studio/storage area that had been hodge-podged together for 20+ years. I’m sure many of us have the same room:
- Shelving, cables (Co-ax, Cat5, telephone, speaker, etc) were randomly running across the ceiling and walls.
- Bare concrete walls/floor and various things nailed/glued to the walls.
- A HVAC inlet vent for the shop that shared the same line as one of the bedroom vents.
- Lots and lots of “raw materials” (aka crap) from projects past.
So essentially, the room needed to be stripped of pretty much everything, wires and HVAC ductwork rerouted or updated and any plumbing concerns addressed.
Step 2: HVAC
This was an important step as the HVAC lines were a direct sound conduit for the entire house.
1. The main metal conduit lines were replaced with 6” insulated ducts and hung using nylon straps.
2. Crossover Conduit:
- The crossover conduit (the one that drops below the floor joist) was moved and rebuilt using a combination of insulated ducts and metal angle ducts. I was limited on space and could realistically only use the metal corner ducts on the turns.
- I’m still a little torn over whether I should have left the crossover in it’s original position on the back wall vs. moving it over the door. With it over the door, it utilizes space that probably would not have been used for anything else. If I left it on the back wall, then it would have taken up a fair amount of usable wall space but then the doorway path wouldn’t feel as cramped.
- All connection points/seams were sealed with HVAC tape.
Step 3: Wiring
This was probably the most tedious step. That room was a total DIY cable rats nest from all the cable TV, internet, phone lines, etc. that occurred over the years. Plus there was a series of shop lights that each had their own outlet and were controlled from a single switch. Every single wire of every type had to be removed and/or rerouted to conform to the final room build and layout.
1. AC lines need to be continuous run between the breaker box and outlets. If any splices or splits were needed, they had to be accessible from inside the room (not buried in the walls).
2. Surveillance camera lines, network/Cat5 cable, cable coax cable, telephone wires, TV antenna coax, and doorbell wire/transformer were all redone.
3. During the construction of this room I also ran a feeder line from the breaker box to a new 40 amp sub-panel in my garage – I had professional electricians do the actual hook-up of the line to the breaker box and sub-panel.
4. All lines were run to reduce the number of pass-through holes in the drywall.
a. All the outlets, switches and junction boxes were surface mounted to the drywall so only a small hole needed to be sealed for each.
b. Similarly, surface mounted conduit was run between several boxes/lights to reduce the number of drywall intrusions.
The final AC runs utilized the same two original breakers that previously served the shop area.
Step 4: Sealing Off the Room
The more air tight you can make the room, the better the sound control. You’ll take care of ventilation with the dead vent.
If the previous step was the most tedious, then this step was the messiest. The key materials I used for this step were drywall and SC-3000.
OSI SC-3000 - The OSI SC-3000 was much cheaper than Green Glue and was what commercial sound proofers seem to use. It doesn’t seem to be available anymore and appears to be replaced with SC-175. SC-3000 sticks to absolutely everything and never seems to dry – but that’s the purpose of this stuff. It always remains flexible – even a couple years after I finished this, I would come across a small piece of scrap wood in my garage that has just a little bit of that stuff on it… and it’s still just as sticky as it was on day one.
The SC-3000 was used as a sealing caulk to seal up all cracks and to serve as the sandwiched elastomeric layer between the drywall sheets. Every time I mention double drywall, this means it was the two layers of drywall with SC-3000 squished between.
1. All joist openings were sealed with double drywall and caulked with SC-3000
2. All wire runs through flooring/etc. were sealed with SC-3000
3. The duct work was insulated and double dry walled
Step 5: Framing the Room Within a Room
The framing was constructed in a manner that would not directly touch any other surface of the house (except for the concrete floor). If the bottom plate of the frame was not secured to the floor you could theoretically move the entire room around about ½” in all directions and not touch the rest of the house.
The walls were easy enough, but the ceiling joist and HVAC cross-over area frame were more of a challenge. The ceiling joists were mounted so as to protrude between the floor joist above and not directly touch anything above them. The HVAC cross-over area took a little engineering creativity to get together – one of the big problems was that I was running out of head space for that area and needed to be careful to let the door and ceiling height still meet area building codes.
I used 24” stud spacing at the recommendation of several sources… that maybe were not based on fact. If you think about it, the 24” spacing allows the drywall to vibrate more freely. In fact, several other sources (that seemed more believable) recommended staying with standard 16” spacing. For the decoupled walls, going to 24” doesn’t seem to offer any benefits from a sound proofing perspective.
If I had to do this over again, I would go with 16” spacing to help with mounting shelves/etc. on the walls.
Step 6: Insulating
Once the framing was completed, it was time to start adding insulation. This was straight forward. After this step was completed you could tell how well the room held heat and how important having good ventilation was going to be.
Step 7: Drywall
I utilized the original drywall when I could. The new drywall was the new lightweight material. I wasn’t sure how I was going to like this at first, but after using it I was pleasantly surprised. Much less chipping on the edges, a lot more rigid, it holds screws pretty good… and it weighs a lot less!
Concrete walls are excellent at reducing sound transmission so the outer three walls only had a single layer of drywall.
Double drywall – I used two layers of drywall for the ceiling, dead vent and shared office wall. The only trick here is to try to get an overlapping pattern on the edges (corners, ceiling/walls). The steps were:
1. Hang the ceiling drywall. Be sure to have the wire pass through holes in the correct position.
2. Hang the walls. The first layer of wall drywall will butt up against the ceiling. This will help support the edges of the ceiling drywall as well.
3. Seal the edges with a bead of SC-3000.
4. Hang the 2nd layer of the ceiling. Apply a heavy bead of SC-3000 to the new layer of drywall. Hang the drywall in a different direction so the seams do not line up with the first layer of drywall.
5. Repeat this process for the dead vent and shared walls.
6. You could install a 2nd layer on the concrete walls. But for me, the two “wall intrusions” (circuit breaker box and house water supply shut-off valve) were the weak link in sound transmission on the walls. As it turns out, having those two “openings” did not appear to negatively affect sound control on those walls.
Step 8: Dead Vent
This is one of the most critical systems in the entire room. You need to have air movement in and out, but you want to keep the sound transmission to a minimum.
1. Size of room – air exchanges/hour. My room would usually only hold one or two people, but heat from amps/lighting/etc. can build up quickly and needs to be moved out at a reasonable rate. My goal was to have an exchange rate of about 10 room volumes/hour.
2. Source of air – I have a small office next to the studio. There happens to be a HVAC vent in the ceiling that provides more heating/cooling than needed for the small office area (and is almost closed all the way most of the time because of that).
3. Where the air comes in and where it goes out – and how it gets circulated. Since I’m worried about heat buildup, I put the exhaust (“cold air return”) vent near the ceiling. The supply vent was positioned to push air in from the opposite side and perpendicular to the exhaust vent.
4. In-line fan - that can handle the air exchange rate for the diameter and length of duct in the system. This was wired to turn the fan on when there is someone in the room (including cats) and run for 15 minutes after they leave.
5. The number of baffles and length of the duct runs for both the intake and the outlet – I tried to have about the same number of corners and total length for both sides.
6. Liner material – Air will be moving through this and the amount of potential particles/fibers coming out should be a concern. I used a material made from shredded blue jeans. In the 2 years since building this room, I have not detected any residue from this material on anything in the room. In fact, this room is the least dusty room in the house even though the door is open 99% of the time.
7. Cabinet material – I went with MDF because it’s cheap and was to be buried behind two layers of drywall.
Step 9: Tape, Mud, Prime, Paint
Standard stuff here. It’s a good idea to have an extra fan for ventilation during this step to keep the air fresh and speed up the drying. I even put an extra exhaust fan in one of the basement windows to help keep the fumes and dust out of the rest of the house.
Step 10: The Door(s)
The door is probably the most important barrier to sound transmission. It is literally the “window to the world” when it’s open – and without proper seals, even being closed doesn’t help much. I have this late in the process, but I cannot stress out important this part is. The upside to the door is that it is relatively easy to seal. As you can see in the “Sound Measurements” section, a properly installed door alone can be good for a 35+ db drop in volume (@ 440Hz).
I happened to have a solid core exterior door on the original “studio” and just remounted it. However, this time I carefully built up a rubber seal system to reduce the sound transmission. Properly sealing the outer (office side) door made a dramatic improvement in sound reduction as compared to the original door mount without the seals.
With the heavy door and seal in place, you get a cool sounding whistle for a second as the air is completely shut off from the door opening and has to now exit through the dead vent. If it's not air tight now, it's pretty close.
To complete the studio 100% I will need to add an inner door and that will provide a significant amount of additional sound proofing for the office area. My plan is to basically duplicate the outer door layout… But I am planning on cutting the door in half to open into the studio as two tall skinny doors to reduce its footprint in the studio.
For the sake of transparency, I want to point out that this is currently the weak link in my chain. But the room has proven itself in the rest of house even without the inner door. See the Sound Measurement Section for proof!
Step 11: Sound Measurements
It wouldn’t be much of a sound proof room if it didn’t work! For the measurements I focused on the office adjacent to the studio and the bedroom directly above the studio. The results of the sound pressure levels (SPL) measurements (in db) taken at several different frequencies are presented in Figure 1 (see pictures).
With the help of my wife, I used an online frequency generator though my studio speakers and a Radio Shack sound pressure level gauge (with a fresh battery) set on C weighting and slow response time. We also tried using a Harbor Freight multi-meter that has a built in SLP meter to see how they compared. The Harbor Freight manual declares 40-100 db. And it seemed to be somewhat close to the Radio Shack meter (bottom limit is 50 db) within that range – but not near as stable as the Radio Shack. The Radio Shack is better regarded, so I just went with that one for this test.
The gauge was on a tripod at ear level (about 5’). The base line for the studio with the exhaust fan off was below measurable levels on both the Radio Shack and a Harbor Freight multi-meter (its scary quiet in there with the fan off). With the fan on it’s still below measureable levels on the Radio Shack meter and 35 db or so on the Harbor Freight meter.
After taking the baseline measurements, I started with 440Hz and set the volume to 100 db in the studio. The other frequencies and locations were then run with the same volume levels. I missed taking the 880Hz measurement in the studio. For the studio measurements, I placed the gauge about where I would normally stand, facing the mixing desk. For the office I placed the tripod about 6’ from the studio door and aimed the gauge at the door. In the bedroom, I placed the tripod next to my wife’s side of the bed and aimed at the open door. I didn’t bother to try closing the door because we were already below measurable levels. Closing the door reduces the sound even more.
A few days later I realized I didn’t check the vents specifically. I went back and focused on just the dead-vent intake/exhaust on the office side and the bedroom vents (just at 440Hz). The vents were measured about 12 inches from the vent grills. The results are presented in Figure 2 (see picture).
In both tables (Figures 1 and 2), you can see how well the sound volume was substantially reduced across the board. The relatively high bedroom reading of 62 db at 55Hz is probably because it was actually vibrating the concrete floor… along with the rest of the house. The dead vent is confounding because it’s very close to the office door and the meter is definitely picking up sound from that – because you only hear the tone coming from the door.
I wish I would have taken measurements before the project. I did not have a sound level meter available at the time and didn’t think of it. But based on my memory of the annoyance levels of a drum set in the next room, there is a night and day difference.
Step 12: Other Additions
At this point, the construction of the room in complete (aside from the inner door). The next steps were installing the recording work station, shelving, and my secondary workbench area.
1. For the floor, I used Harbor Freight anti-fatigue foam matting and two carpet runners.
2. The circuit breaker box needs to stay readily accessible. But I covered it with a hinged faux Fender speaker cab front to make it look nicer. The desk top surface runs across the wall in front of the box, but there is a 30” wide insert on the desk top that can be quickly removed to open up the entire area.
3. When you close the door, you are isolated from the rest of the world. You don’t hear anything from the outside –trash trucks, doorbells, and lawnmowers are all silenced. I have a small LCD TV screen that displays the security camera feeds in case someone comes to the front door or driveway.
4. I will eventually add a wireless intercom system to communicate with the kitchen so I know when dinner is ready :-)
Step 13: Closing Thoughts
While I was doing my initial research on this project, I came across a plethora of sound proofing companies and suppliers on-line. I don’t doubt many of the products work as claimed, but much can be achieve (or even better) without these expensive products (e.g., isolation hangers, sound absorbing panels, rubberized sound barriers, etc). Everything I used was purchased from the local home improvement stores.
But the bottom line is that this room was a complete success. The volume levels to the bedroom above was drastically reduced – a full drum set in now about as loud (or less) as having the TV on in a room down the hall. Recording is super easy in here. I turn off the in-line fan during recording because that’s the only source of sound in the room. Between the practicing/recording and using the small work bench for small projects/repairs, I’m in the studio just about every day of the week.
This was a major project and took me several months to complete. But it certainly makes life more enjoyable for everyone in the house.
Please let me know if you have any questions or suggestions!