I just finished up what turned out to be quite an investment in time... haven't had a chance to fully install & test them, yet, but hopefully will this week.

I'm a home theater guy with 12X17X8 dedicated room - 7.1 surround. I wanted to add in some trapping for some boomy bass. But I also wanted to tackle the back wall (which has 2 side-by-side windows) about 4 feet behind the primary seating position. Not ideal - but it is what it is.

I originally posted here, looking for some diffuser help. After some discussion, my take was that the distance between the primary seating and the back wall wasn't ideal for traditional diffusion... to make this short, a back-and-forth with Boggy led me to design my own modified binary slat diffuser with absorption. The overall impact won't be as robust as a traditional diffuser, yes... but it's better than nothing!. It's total size is 6'X5' - 2" thick 703 insulation - and it is rigged to hang from the ceiling in front of the windows.

In terms of the bass traps, because of the size of the room, wall constraints, and the current placement of speakers and built-in component cubbies (many of which have wires run to them through the walls, etc., I tried to make the traps as tall and thick as possible to fit within my room. They definitely ended up being a custom creation - trying to get as much as I could out of them. I created four corner traps that are 54" tall and 24" wide - 8" thick 705 insulation, one corner trap that is 33" X 24" - 8" thick 705 insulation, and one wall mounted trap that is 48"X24" - 4 inch thick 703 insulation.

Now, I know that there are minimalists out there that don't believe in heavy framing for their traps. From a performance standpoint, the less frame the better... and from a cost/time standpoint they are DEFINITELY WAY EASIER TO MAKE! But, I wanted something that was going to look good without sacrificing too much performance... so I spent quite a bit of time and money making frames.

My supplies are fairly straight forward. I found a distributor in Maryland that sold JohnsManville 703 insulation board and Knauf Ecose 705 insulation board. The primary wood I used was Pine #1 (I did use Pine #2 for the base of the frames and for the sides that aren't visible). If you ever plan on using/staining this kind of wood, plan on many MANY many hours of sanding and prepping the wood. Otherwise, your efforts will be for not. For the slat diffuser I purchased furring strips. And, of course, loaded up on tons of other supplies, countersink drill bits, screws, block sanders, stapes, brad nails, wood glue, sand paper and stain and material (Cloth) and finishing strips. In terms of tools, I relied heavily on: a drill (with a 3 1/2" hole saw bit), a power miter saw, an orbital sander, a jig saw, a Dremel (sanding and wood removal attachments), a pneumatic nail gun (both finish nailer and brad nailer), a staple gun, and a cabinet making Bessy Clamps. Honestly, making these without those core tools would be almost impossible.

For the cloth, I purchased "utility speaker cloth," burlap, and quilting cloth (which is nice because it is relatively thin like muslin BUT comes in lengths of 108" and can be purchased in a multitude of colors)... all at JoAnne Fabrics. Just as a word to the wise, if you're in the market for cloth, search the net for coupons for JoAnn Fabrics. I purchased all of my cloth with 50% off coupons... which saved me a ton of $.

For the bass trap frames, I opted to drill 3"+ holes into the framing... for those of you interested in doing this... there are several things you should know. First off... you need a solid drill with a ton torque. A cheap cordless drill will suffer and a low amp will flame out and die (believe me, it happened to me)... I suggest a good 9 amp or better drill (this is the one I used). Secondly, the drill and the hole saw bit make a nice hole, but they are rough on the wood and the resulting holes require a lot of sanding (note, MDF board might not have this problem... I chose pine though, because I wasn't comfortable using MDF due to some of its carcinogenic properties... especially when it is airborne with dust particles... also I've read it can smoke and release fumes when heavily drilled). I used various dremel sanding bits and then leaned on a randomly orbiting sander to finish off the smoothing of the outer rim of each hole. Talk about time consuming (and very tedious work!). If you're wondering how many holes I drilled... this board says it all:



Here are a few photos of the frames during assembly. You can see I counter sunk exterior screws... and added some bracing on the inside.






Here's a shot of the slats after being sanded and one round of staining...




For the bass traps, I stapled the cloth onto the face, trimmed, and then attached finishing strips with a brad nailer (and wood glue). The holes were covered by stapling material on the inside of the frame. I used a lot of staples on the inside to make sure the material wouldn't slip when I inserted the tight-fitting rigid insulation.






Also, for the traps going in the back of my HT room, I faced them with kraft paper (front top and sides)... to attach the craft paper I used a spray rubber cement that the insulation contractor sold me. Very sticky stuff!



Here's some shots of the finished frames...





Once the frames were finished and the insulation was installed, I covered the backs with cloth and tight fitting burlap. Here's some shots at the finished product (again, lots of staples):







As for the modified, slat diffuser... I made the frame (note, instead of wood screws I used heavier hex-bolts)... then stretched material over furring strips that I brad nailed to the inside of the frame... Here is a pict looking at the back of the frame. This will give you an idea of how I stretched the fabric and affixed it to the frame by pinning it between a furring strip and the frame. I used an adjustable slide ruler to make sure the depth of the furring strip was uniform over the whole frame. Once installed, the material was placed in such away that it gave me about 2 1/4" of space on the backside (room for insulation) and about 3/4" space on the front for the slats and finishing touches!



On the backside of the material, I installed two 2 1/2" thick furring strips (notched to fit around the firing strips holding the material) horizontally... spaced about 2 feet apart. I don't have a photo of them... but they were installed to help hold the insulation AND to give me a place to nail the slats in the middle. In terms of sequencing for the slats, I used a binary sequence that Boggy provided in another thread to dictate the distribution of slats on the diffuser.

The furring strips holding the material and the two larger firing strips running horizontally across the mid section of the frame gave me 4 solid points attach the slats with a brad nailer. Here's the finished frame without insulation...



Adding 703 insulation in the back (behind the material) was straight forward. It bulges just enough to touch the backside of the slats. This is hanging from the ceiling about 3 1/2 feet behind the primary seating position. This is a really bad picture that does it no justice... but here is a crummy shot. It actually looks very warm and inviting... and isn't as intrusive as it appears in the photo.




Anyhow, those are the finished products born from some discussions on gearslutz. Perfect? By no means. But, once I have the time to measure and calibrate, I'm hoping that I will be one step closer to sonic goodness!

Great job soundoff!

For others, using "biscuits" and ordinary wood glue for joining frames (which is better) causes needs for frame clamping and mitered edges.


Also, circular holes can be much prettier with router and circular holes jig, Jasper Tools or similar. I use piece of transparent plexiglass similar to Jasper Tool, then I drill all necessary holes, so I built this tool by myself.

CAUTION:
If you aren't skilled with woodworking router, please don't use it, because it is probably one of most dangerous woodworking power (hand) tools for beginners, that exist today.

If you are unsure, use circular drill saws as is described in soundoff post.

Soundoff, I'm not sure that I find in your writings, what you exactly use for coating/staining your wooden elements... It's looks beautiful. heh

Thanks... Very good points about a router. I didn't think in those terms - but should have (in hindsight!!). The hole saw bit on a drill is definitely a much rougher cut and your advice is right!

The stain is a red mahogany color made by Cabots. I didn't add any coating on top of it.

Just as a side note - I think that slat diffuser works. I tinkered with it some last night and the dialog from my center channel was noticeably tighter!

A hole saw bit can be dangerous too, one can be seriously injured by a drill kick back, if saw bit get stuck in the wood, which is not uncommon at all.

Well, I would rather pre-cut an about circular hole using a jig saw, its diameter being one or two millimeter smaller than the one you want, and then use a router with a copy bit to remove the extra millimeters, letting the copy bit follow a hole template attached to the woodpiece.

This way, very few wood needs be removed by the router, so this is quick and safer

if not familiar with using a router, simply sand the millimeters off !! slow but very safe.

Even better than biscuits, Festool domino .. Easy and quick to get very accurate results, much more than with biscuits and dowels. Only issue, tool is expensive, but once you try it you won't use anything else.

I agree.

When we work with router, most dangerous is his bit rotation speed (may be even 20000 rpm), if someone try too hard and possibly break the bit, it can fly like bullet in any direction then possibly make serious injury to worker or anyone that stand near.
I don't know any power (hand) tool that is extremely safe and that may be used without any care, all of it may be used very carefully but there are some of it that is more dangerous...
That is a problem with Festool domino system.
After biscuit joiner patent period expires, many (and sometimes cheap) companies appear, that build routers for biscuits, not only Lamello AG (they still exist, they still make this excellent tool but it is still expensive!), so this tool become acceptable for amateurs.

EDIT:
I recommend to watch Lamello video clips, http://www.lamello.com/en/downloads/...ng-system.html .... there are valuable informations about how to work with biscuits, and build nice frames.

Yes indeed, that's why it is always better to minimize the wood thickness to be removed by a router: pre-cut as much as you can (if you can), else do it in many passes meant each to remove a few millimeters.

The other issue with a router is the direction in which it is run against the wood (when routing that circular hole, do it clockwise when router rests over the woodpiece). That ensures that routing bit and router are not forced away from wood, due to the forces existing between bit and wood during the cut.

i like the overall design and side holes. nice stuff

@mhch:

You are absolutely right... hole saw bits can cause a drill to kick back and bite. Anyone reading this that isn't familiar with using these tools in tandem should be aware of that --- especially if you have a drill that produces a lot of torque. I had a couple instances when drilling (I believe I drilled about 111 holes!!! Crazy, I know!) where the drill caught in the wood or kicked back - it was so powerful... almost scary.

So, please, everyone, proceed with caution. If you do use a hole saw, start drilling the holes at a very VERY slow and controlled speed. Once the saw gets in the wood, it becomes more manageable you can run your drill at full speed. Eye protection and hand protection are a must -- and don't skimp on your tools or work set-up... make sure you have everything to do the job safely and efficiently. Cutting corners is bound to lead to an injury.

Be safe!

Just an update: the addition of these traps and the slat diffuser have radically (and noticeably so) improved my HT. I'm still working on dialing in my sub with a house curve... But I've calibrated the rest of the set-up.... WOW! It has completely opened up the sound stage presented by my center, left and right channels. The sound now seemlessly floats around like it never did in the past. The harshness that once existed is also gone. The biggest impactive noticed, though, has to do with what was my primary complaint: the center channel. It often sounded hollow and nasally and VERY narrow. The speaker had no breadth or wideness to its sound. That is 100% completely gone. I'm assuming that the slat diffuser/absorber behind my seating and the absorption I put on the front wall are to credit for this... But because I didn't add the treatments in piece-meal, I'm not sure.

I had once read an article saying that acoustic treatments were the second biggest bang-for-your-buck improvement that you could make in a HT (first being your speaker selection)... this article was rather basic and not overly technical, so it made me wonder. But, now I must say: I'm a believer - wasn't totally a believer before... But I am one now and I'm glad I put the $ and time into it. Most of you probably know this... But I'm reiterating it for those of you who might be reading this and are on the fence about treatments!

Thanks, again, Boggy. You inspired some of this!

By the way, for any of you HT folks out there... Another awesome bang for your buck with big dividends are Aura bass shakers. All I can say about them... Sweet!!! If you want some info, PM me.

I'd make a case for flipping those two even.

Nice work!

I learnt from real life experience too

The best way to use a hole saw bit on a drill is to use a drill press, wood piece being securely clamped. Many advantages, #1 being increased safety
- neither drill nor woodpiece can start spinning and hurt you
- Bit plunge speed is accurately controlled by the drill press handle action, instead of by body forces directly applied to the drill
- The overall operation takes less time, because bit plunge control is easier