Introduction: DIY Corner Bass Traps (Acoustic Treatment)
This is my first instructable, so bear with me….
I have a small home studio in my basement (Blue Feather Studios) and I've decided that the recording/tracking room needed a little audio cleanup. I've also built some other sound absorbent panels already, and if I build some more I'll do another instructable on that too. I mainly do recording for artists for my record label, Badly Bent Records, and some recording for friends, so it didn't need to be world-class, just needs to sound good.
Now, this is acoustic TREATMENT, I.E. 'sound absorption'. It is NOT sound PROOFING. That, is a whole other complicated (and expensive) enchilada. Since bass frequencies tend to build up in the corners of a room, I added these to the treatment arsenal, and it's made quite a difference.
Also, the word 'bass' is referring to frequencies. If you're reading this looking for a way to trap 'bass' the fish, this ain't it :)
Step 1: Materials & Tools
**All materials were purchased at either Lowes or Home Depot**
- 3'x3' of 1/4" Fir Plywood (some call it the 'hobby size')
- Box of #8 screws and drywall anchors (combo pack)
- Roxul Safe N' Sound Insulation. How much you'll need will depend on the size of the traps you're building.
- #6x 1/2" Wood Screws
- 1-1/2" Corner Braces (2 packs of 4 each)
- Some Spray Paint (colour of your choosing)
- 6 Washers
- Measuring Tape
- Skill Saw and/or table saw (or hand saw if not available)
- Serrated Kitchen Knife (buy a couple from the Dollar Store - you'll wreck em cutting the Roxul)
- Drill, Drill Bits and Driver Bits (Drill bit sizes , Driver bit #2 Phillips and #1 Robinson)
- Staple Gun and Staples (Staple Size)
- Table Saw (or Skill or hand saw if not available)
Step 2: Cutting the Plywood Shelves
The size you wish to make the bass traps will determine the size you need to cut the plywood.
I cut the plywood shelf a larger size then I was going to cut the Roxul. There are a few reasons, which I will explain in further steps.
The plywood shelf I cut as a triangle with 15" sides. The Roxul I cut as triangles with 12" sides.
Personally, I like to work with templates. I'll be honest that I can't visualize this kind of stuff in my head. So, I took some scrap construction paper and cut the15" and 12" triangles and held them up into the corners, to make sure it would fit and look okay. Everything fit great!
Using the construction paper template I traced it on the plywood, and cut it out with my Skill saw. Do this twice and you'll have both shelves. Make sure you use a knife or sandpaper or something to take all the little splinters off the edges you cut. Your fingers will thank you later when you're not digging tiny splinters out of them….
Test fit it into the the corners to make sure everything fits.
Step 3: Installing the Shelf Brackets and Plywood Shelf
This is the part where you're judgement will come into it.
Play around a little with how high you want these. Because I have a small cabinet up against that wall, and have a stereo speaker that currently sits on top for re-amping, It couldn't come right down to the cabinet. It IS important that if at all possible it go to the ceiling however, as those pesky bass frequencies can REALLY build up in the upper and lower corners where the floor or ceiling meets 2 walls. So, figure you're going to go from the ceiling down to….as far down as you'd like. Ideally it would be floor to ceiling, but do what you can.
Measure down from the ceiling to the point where you want the bottom of the trap and mark it on one of the walls in the corner, 4 inches OUT from the corner. Do the same on the opposing wall.
**I installed the corner braces ABOVE the plywood, so the plywood sits on them, however they do not protrude below the plywood on the wall. I did this for aesthetic reasons only though.
Place a level on the piece of plywood shelf and hold it up to the marks on the opposing walls - make sure it will be level. If not, adjust one of the marks accordingly.
Screw the brackets in place.
For the third bracket, pick a wall - it shouldn't matter which one you do. Set the plywood shelf so it's resting on the two installed brackets, and slide the third one in place, about 3 inches out from the corner, supporting the shelf. Place your level on the shelf, and mark the wall on the bottom of the third bracket when it's level. Take down the shelf and install the third bracket
Set the plywood shelf in place to make sure it's all level.
Place the plywood shelf on the brackets, and from underneath, mark where the bracket holes are on the plywood.
Remove the plywood shelf and pre drill the holes with an appropriate size bit.
Place the plywood shelf back on the brackets, and screw up through the bracket into the plywood.
Step 4: Cutting and Installing the Roxul Safe N' Sound
What is Roxul? Roxul is a Canadian made mineral wool. It's similar to the pink fibreglass insulation we all know and love, with a few important exceptions.
- It's not as dangerous to breathe
- It's not as dangerous to handle
- It has better sound absorption properties (ESPECIALLY THE SAFE N' SOUND)
- It's woven from ROCK……which is awesome!
***Even though the rock wool is a lot less nasty than the pink fibreglass stuff, I would still HIGHLY recommend using a mask and gloves, and doing the cutting in a well ventilated area.*** There, ass covered…..
Using the 12" paper template, cut a 12" template out of the plywood. Trust me, you'll want a WOOD template for cutting the Roxul.
Place the template on the Roxul (cutting through ONE batt at at time for me worked the best - trying to cut through two or more tended to distort the cuts - for me anyways)
THE best way to cut this stuff is an electric turkey carver with serrated blades, but I didn't have one, and didn't want to go buy one. Any serrated knife will work - you can buy the serrated kitchen knives from the Dollar Store. Boxcutters, Olfa style knives, razor blades, butterfly knives or switchblades won't work very well. Serrated is the key.
My batts in the photo were remnants from the pieces I had cut to make my broadband absorbers, which is another reason I went with the 12" pieces - I could get 2 from each remnant.
Cut as many triangles as you need to in order to fill the height requirement for your corner traps.
Next comes the easiest part - stack up your triangles on your plywood shelf until you reach as high as you want to go. In my installation, a full piece on top was pushing the acoustic ceiling tile up, and so I cut one down to half height to fit. Because we cut the shelf larger than the Roxul, there will be room for a little bit of an air space between the Roxul and each wall, and behind it. Air spaces are important for sound treatment.
Step 5: Installing the Brace for the Front Piece
The front piece needs something to attach to. I was originally going to use hinges so I could open the panel when necessary for even more mid-high frequency absorption, but I decided not to go that way in the end.
Measure across the front of the plywood shelf, and cut a piece of 1"x3" wood furring strip, MAKING SURE THE ENDS ARE CUT AT 45 DEGREE ANGLES. This is very important if you want the bracket to fit snugly on the wall.
Drill through the bracket and into the wall, one at each end. This bit is a little tricky, as it has to go through the bracket at an angle, but straight into the wall. I had to rout the drill holes in the bracket out a bit so the screw would fit.
Place a wall anchor into the drilled hole, and screw the bracket into place into the wall anchors.
**You may want to paint the bracket a dark colour if you're using pegboard and not covering it in fabric, as the wood bracket shows through the holes quite well.
Step 6: Adding the Front Piece
From what I've read/heard/seen one of the main things that differentiates a bass trap from a broadband absorber is that the bass trap has a plywood front. According to people who have degrees and doctorates in such things, the bass frequencies hit the plywood and cause it to vibrate, turning the sound energy into, um…..vibrational energy I guess. This also reflects the higher frequencies so you don't end up with a completely dead room, which contrary to popular believe, is not such a good idea.
A lot of people, including acoustics guru Ethan Winer, in a small room it's best to combine bass traps AND broadband absorbers. It's also cheaper than building several different pieces if you can combine them.
Instead of using plywood for the front, I'm using pegboard. This will still have most of the vibration-absorbing characteristics, while still allowing some high frequencies to pass through the holes and be absorbed, but the majority of them will be somewhat reflected back.
Measure across the front of the plywood shelf to get the width for the pegboard piece, then measure the height you'll need.
***Because I used pegboard, which has holes, I measured the pegboard to the ceiling and then added an extra inch - this will allow it to come a little bit below the plywood shelf, so the plywood shelf doesn't end up viewable in the holes. makes it just a little more pretty.
Using the table saw, skill saw or whatever saw you have, cut the pegboard to size. After you make sure it fits, paint er up! Because I was using a fairly 'bright' paint, I painted the panel front white first, before the sea foam blue. Makes it it pop a little more. I didn't paint the back at all.
**If you don't like being able to see the holes, an alternate finishing idea is to use broadcloth or other linen or fabric to cover it, and staple it in the back. You can pick up some REALLY cheap, neat fabric from a thrift store. Alternately, you can do what I did, and paint the bracket flat black, so you don't really see it through the pegboard.
I used small washers to better hold the pegboard in place because pegboard isn't the sturdiest of materials, and didn't want the screws to go right through.
Viola, bass traps.
Hope this has helped someone along the way, and if anyone has any questions, feel free to email me at badlybentpub @ yahoo. ca for clarifications.