Hello,

I asked for advice here in the past year about building my own bass traps and a lot of nice folks helped me out, so I figured it might be of interest to document this little project. Here are a few pics taken today. I used two 2'x4' sheets of OC 703, 2 inches thick, the first one facing the room is foil reinforced. Behind those two sheets, triangular layers of Roxul Safe and Sound.

NICE JOB!! I would move forward and keep building more.

Thank you Glenn! One down, seven to go. One thing I had not accounted for as you can see in the second photo is that those 16 pieces of Roxul - 3 inches thick - would get compressed. So to actually get 48 inches in thickness I'll need to fit one or two more pieces of Roxul in the frame. Oh well...

What tool do you use to cut them.. utility knife or something else?
Good job on framing

Hi Edin,

I used a bread knife to cut the Roxul. A regular knife tends to shred it a bit. Long and slow strokes with the bread knife will do a nice job.

I cut the OC 703 with a big sharp kitchen knife. I goes in like butter. I had to finish the job with an exacto on the foil reinforced sheet.

As for the frames, I designed them but had someone build them for me. It took him 8 hours while I would have spent 2 weeks on them...

Well worth the $200 he charged me.

Cool, so good sharp knife should do it.. I thought they might be all over the place, glad to hear not. Thanks

...I've used a "reciprocation electric bread knife" to cut the "insulation" and it's cheap...works great...hth.../s~

I had a serious bass problem in my basement (control room). I got some advice from a fellow AES member that worked quite well.

I bought 5 bales of Roxul (large) dense acoustic fiberglass. I did not take it out of the packaging. Repeat - leave it in the plastic.

Three bales were stacked at the front of the control room and covered with a sheet. It looks like a couch. The other two were placed in the front two corners behind the wide-band absorbers.

Bass problem solved.

Hello,

Here are a few more pictures of my bass trap project.

Please let me know if you have any questions.

Next step: getting some fabric on them. Any suggestions? I was thinking about black burlap but it seems the smell can be annoying.

Next step part 2: before and after tests with Room EQ Wizard.

Have a nice weekend!

Dramis

These look great so far. Good job with them.

Thank you! It's a lot of work and hopefully worth it.

I'm still looking for an affordable fabric. This "olyfun" material made of polypropylene - the fabric for reusable grocery bags - seems interesting:

Oly*fun-10 Yard Bolt - JoAnn | Jo-Ann

Has anyone tried it? It's not expensive and appears to be quite resistant based on those grocery bags I've been using for quite a while.

Thanks for your input!

I just used burlap but am unimaginative and did not test any other fabric. There may be less expensive, more-fit-for-purpose fabrics for all I know. Burlap isn't necessarily expensive, but if you buy enough burlap then it ain't cheap either. My "minimal materials count" absorber projects probably spent as much money on burlap as on wood framing or the pink fluffy or safe'n'sound mineral wool. IOW, especially with cheap big pink fluffy bass traps, maybe the cost got equally spread between wood, insulation and burlap. I asked the fabric store lady about it. She said that nowadays big fancy weddings buy lots and lots of burlap for decorative purposes in the ceremony or reception. Too arty for me. When I was a kid they used burlap for feed sacks and cotton-picking bags.

If you need to be fire-rated then burlap or other non-fire-rated fabric needs spraying with commercial or homemade gunk to make it fire-******ant. Dang I don't know why this forum always spells ****** with asterisks. I suppose Fire ******ation is somehow politically incorrect. Maybe "Fire Special Needs" is a more desirable and accurate engineering terminology!

I didn't bother with that. If the office catches fire when I'm in there then I'll just have to be either quick or dead. However the space is for personal use so it is unlikely that there will be numerous dumb customers hanging out who need to be shooed out like cows from a barn if the office catches fire.

My burlap faced absorbers are 2 or 3 years old and none of the fabric has shown signs of sagging. Maybe tomorrow they will all decide to sag all at once, but so far they remain tight as a drum.

Maybe because I have a somewhat obsessive compulsive, belt-and-suspenders personality. I routinely twist the heads off bolts making sure that they are tight enough.

I would stretch the burlap real tight using about 1 staple per inch. Electric staple gun staples are cheap and the finger doesn't get sore pressing the trigger. Then I glued down each seam where the burlap touches a wood frame edge.

At first I used Titebond III wood glue to glue down the seams. The titebond III works great but turns brown after it dries. So it is ugly as sin unless all seams and glue drippings are covered by decorative wood strips.

Then I discovered an adhesive easy available in USA (dunno other countries) Loktite Power Grab. It comes in caulk gun tubes and several formulations, though the cheapest interior-use version seems to work fine for burlap. It dries fast and completely clear, but so far as I can tell seems "chemically in the same family" as good aliphatic glues such as Titebond.

I would staple all the burlap on an absorber, then run a bead of Titebond or Power Grab down each wood strut. Then take finger and "rub in" the glue so it soaks into the burlap fibers and underlying wood. After about an hour of drying, all the burlap fibers are glued so good to the wood frame that you could pull all the staples and the fabric would remain tight in place.

Thanks for your input jcjr! Your detailed account on how to glue burlap will be very useful, whatever fabric I choose.

Also, it might depend on the batch or its origin but I read that burlap can have an annoying smell that will make a studio smell like a barnyard...

Urban legend maybe?

Thanks gain!

I got a bunch of nice looking burlap at 1/5 the cost from the clearance section of ATS acoustics' site:
Clearance Items

They say it may have imperfections, but all 50 yards I got look perfect to my eye.

Used this fireproofing spray:
https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1

Hi Dramis

I bought the burlap from Hobby Lobby and it didn't seem to have a strong smell. Maybe "dusty smell" would be descriptive or maybe not. I don't notice smell from the burlap, safe'n'sound mineral wool, or owens-corning fluffy attic insulation in the office. So far as I recall the insulation also had a bit of odor fresh out of the shrink wrap, but not excessively strong to my nose. It seemed to air out quick enough. Decades ago I worked with pink fluffy for attic and wall insulation, rather unpleasant to handle, smelly and itchy. The modern-manufactured pink fluffy seems improved, less irritating to skin and nose.

One caution about over-aggressive fabric stretching-- I built the frames "as light as possible" while being strong/rigid enough to get the job done. On the first couple of absorbers I managed to stretch the fabric tight enough to warp the frames. Learned the lesson and on the other absorbers avoided pulling the fabric so tight that it warps the frame.

Hmmm-- If it is true that large amounts of burlap are somehow used for wedding decorations (dunno what-- Table cloths? Hangings?)-- Wonder if all that burlap gets tossed in the dumpster after a wedding? If the stuff gets tossed out along with the empty bottles and dirty paper plates, then maybe slightly used burlap could be acquired cheap or free from wedding contractors?

Wow, quite a deal! Thanks for the input. I'll definetly look at the burlap option!

I know what you mean by dusty smell. A smell of "dust and slight humidity" if I recall correctly when I bought the stuff to cover shrubs in the fall.

My frames are light also, so good point about overstretching!

Thanks again for your advice jcjr!

Hello jcjr, considering the above quote, I figured you'd be the ideal person to answer my question. I bought the fabric to cover my bass traps (the stuff reusable bags are made of, i.e. polypropylene), an electric staple gun and some 1/4 inch staples. But I now have doubts about the staples. Are they too short? I guess the pressure on the fabric will be minimal but still, should I use 5/16 or 3/8 instead?

Thanks in advance!

Hi Dramis

I have used in the ballpark of half-inch or a little bigger but maybe quarter-inch would work fine. Dunno.

Never was very skilled at stapling. For years used manual stapler with not so satisfactory results, occasionally tacking up insulation into walls or putting naugahyde on stage speaker cabinets etc. It was hard on the hands but I was too cheap to buy an electric stapler.

Got better results when I finally got a Stanley electric stapler that runs on AC power, but still am not so good at it. This model from a few years ago was about $80. The only stanley I see for sale today is about $30 with mixed reviews. Maybe I could do a better job with a better tool, though the fault is probably in the workman rather than the tool. Some folks seem to staple fine with any old stapler.

Also got a Ryobi battery stapler that works OK. The stanley probably works better when it is convenient to trail an extension cord plugged into the wall. There are enough bad reviews of the current $30 stanley claiming it is not strong enough, but maybe those reviewers are (like me) just not very good at stapling and they are blaming the wrong part of the process.

Maybe an air stapler would be a better buy. Even the cheap air tools I've bought (too cheap to buy anything expensive) seem durable and work good.

Most air staplers seem built to drive crown staples (woodwork and such) rather than the square flat staples but never went shopping for an air stapler.

My technique problem mainly involves not holding the stapler firm enough against the surface to adequately drive the staple all the way in. But perhaps a stronger tool would make this less of a problem. I have a couple of electric or air nailers, and it isn't rocket science to hold an air nailer firm enough against the surface to drive the nail all the way in. So maybe a more powerful stapler wouldn't be so finicky.

Covering absorbers, I had a good percentage of the staples not driven all the way in, but that was easily enough solved with a hammer.

With my staplers, which in my hands need a lot of pressure to set the staples "mostly all the way in", it was a little fiddly stapling to the big fluffy fiberglass absorbers built out of very light struts. I would use a piece of 2X4 or whatever to brace behind where I was stapling to make it easier to drive staples without the thin wood "springing" away from the staple recoil.

I built the big absorbers as lightly reinforced frameworks of 3/4 inch square pine sticks. Like a big balsa wood model airplane framework. Ripped the sticks out of the cheapest 1 X 4 or 1 X 6 pine planks I could find. Build a big absorber out of a few bucks worth of wood. They are strong enough for purpose, but if I make any more absorbers maybe will use slightly thicker struts. 1 X 2 (3/4 X 1.5 inch) possibly overkill, but OTOH 3/4 X 3/4 maybe a little too risky of accidental breakage if one of the sticks happens to have a weak spot. I didn't break any of the thin struts, but maybe it was more luck than skill with thin struts ripped out of the cheapest wood I could find.

Ha! I knew I'd get an exhaustive answer from you! Very much appreciated jcjr.

But darn, I just bought the cheap Stanley you mentioned for $40 CAD, without reading reviews first. Oh well...

That's the reason I opted for shorter staples though, figuring I'd be able to drive them completely in, since I also suffer from limited handyman skills...

I'll give it a try on one of the bass traps and see how it turns out. I'll keep you posted.

Thanks again for your very helpful tips.

Have a nice weekend,

Dramis

Hello,

I finally finished my corner bass traps a year later. Yes, I procrastinate a lot...

I have two of them stacked in each corner of the room, for a total of 96 inches in height and 16 inches at their maximum depth per corner.

I tested the room with Room EQ Wizard before I had them up, and will do another test soon. In a year or so, I guess...

But I could tell the difference right away upon listening to a song with a lot of heavy bass in it:

1) stuff doesn't rattle and shake in the room anymore;
2) the bass sounds much tighter and isn't muddy anymore;
3) high and mid frequencies are much clearer now that the bass is under control.

The cost of building them myself was around 800 canadian dollars ($650 US) and included labor (I had someone build the wooden frames I designed), lumber, Roxul and OC 703, bread knife, fabric, staple gun, staples, wood glue and beer!

I'll post the before and after REW test results when I get to it.

Note: When stapling on the fabric, I made the mistake of working outside in full sun, so the wooden frames and fabric expanded. It looked perfect but when I brought the bass traps in my studio where it was much cooler, it contracted back and the fabric got very slightly flabby. Oh well, lesson learned.

Have a nice day!

Congrats Dramis. Glad you like them. They look good!

Thanks jcjr! Being a bit of a perfectionist myself, I thought I'd remove the fabric and start over again. My wife said I was completely nuts... she was right. I don't even notice the tiny little folds in the fabric anymore.

Nice! Do you have any pictures?

Nice! Do you have pictures?

Sorry its taken me so long to post a picture.
This is the front end of my room. The room is too narrow and too deep. There was a real bass problem at the front. Its not perfect, but it works ok.

The lighter grey is wide-band covered by acoustic fabric and a white frame, the black fabric under the TV and on the floor to the left and right are bales of insulation still in the plastic (please excuse the cat hair - unfortunately they like to sleep up top in the ceiling sound treatment . . .). Behind the cabinet under the TV there is another bale of insulation. I used Roxul Safe'n Sound (around $30 a bale).

Against the wall there are two Helmholtz resonators (you can tell by the carefully drilled front). They used to be flat on the ground with the speaker stands sitting on them. Turned out that wasn't a good idea as the speakers started using them like the hole in the body of an acoustic guitar - howling.

You can also see some commercial foam behind the speakers in front of the wide-band. These were expensive and are no better than homemade wide-band IMHO.

This looks awesome. Thanks for posting

Come on, man!

REW after results!

I'm very curious to see how just absorber bass traps do the work.

Because I started to believe, they should not be effective on very low end as physics does not let them to be. A low frequency wavelength could be as large as 8 meters.

All my readings led me to believe a membrane bass trap is the only way to go to handle low end.

I really like this design!! Do you find the foil on the 703 prevents all the highs from being sucked out by the roxul ?

Hey dramis,

Cool craftsmanship. I like how you put everything neatly.

I am about to build my own corner bass traps. Why arent you using less denser products for corners? Over at John Sayers forum they ar strong advocates of using as less dense products as possible for low frequencies. I have read Ethan Winers report on OC measurements and seen the graphs and waterfalls. But still guys over at Sayers forum keep their point.

As for the facric - I will be using locally produced flax. It is actually linen material and the guys here produce it in very different specifations. I would reccomend any good quality fabric that you can blow air through with your mouth without much effort.

ANother question for the SLUTZ:
What if one would also add wooden slats on the face of this type of corner bass trap at a sequence to reflect even more highs back into the room? Would it lower the effectiveness of the bass trap significantly? I guess since modes build up in the corners anyway - it would not do much harm and some liveness in the room is never a bad thing.

Thanks for your input.
Cheers,
AM