Hey All,
Let me preface this thread with the following: If due to "domestic pressures", your current gear is jammed up against one wall of the livingroom with the TV set projecting forward of the speakers which straddle it- Stop reading this thread now! Hit the back button and go about your business...
Still there? Great, there is hope (and help) for your system! So if you are here then there is a high degree of likelihood that you've taken the first steps to great sound already. I'm referring here to having put some time and energy in placing your speakers and listening chair in the best spots possible within your room. With that out of the way, lets move on.
So as one can pretty clearly surmise from my recent rather lengthy
thread on my experience with room acoustics, I think room treatment is absolutely essential to great sound. I'm certainly not alone in that regard but I really don't think that the higher-end AV community (retailers and consumers) grasp how big a deal it really is. Over the years I've become pretty convinced this a function of just how expensive most
effective commercial room treatment products are.
And no Virginia, "egg crate" foam panels are not effective room treatment! Acoustic foam only soaks up high frequencies, unpleasantly deadening our rooms. Now in the case of simple 3" or 4" thick 2' x 4' compressed fiberglass broadband absorber panels like those in the foreground below, even commercial wall panels tend to be pretty affordable. Mine are DIY and more affordable still. They also have built-in diffusive features that no commercial broad band absorber panels I'm aware of share. Typically one hangs these on the walls at all primary reflection points. One should avoid over-deployment of wall-mounted broad band absorption as it can over deaden the room,
Proper bass traps, another key room tuning element, are rather pricey if bought commercially. IMHO, ASC Tube Traps are
the best stand-alone bass trapping product made. Did I mention they are freakin' expensive?!? Better still, unless you live near Portland Oregon, the shipping bill is gonna hurt too. Though often referred to as "bass traps", the wall panels above
most definitely are not! The small 11" diameter traps in the background of the above photo are DIY. In the picture below of the back of my listening room, the 14" diameter 6' tall traps sitting atop the 16" x 3-1/2' ASC Tube Traps are my DIY creations too. Can you tell the difference? They work the same too. Details of how they were built are found
here on the Teres Audio site. A simpler design for an effective bass trap is found
here on the Studiotips site. These are built-in affairs though. Unless your speakers have very limited low frequencies, the bigger the better is the rule with bass traps. You want 'em in all 4 corners and ideally from floor-to-ceiling.
What happens After you've bass trapped your room corners and damped the side wall reflection points
but still have an annoying slap echo {like me}? Then you add diffusion to the mix so as to break-up and scatter strong reflections harmlessly
without sucking the life outa' your tunes! Diffusion is the final element necessary to coaxing the best possible sounds from your gear.
If your current listening space serves other more pedestrian purposes (a living or family room perhaps?
) You likely have diffusive elements already present within the room. The catch is they are unlikely to be in the ideal spots. Bookcases with shelves full of randomly sized and arranged books or heavily foliated house plants are examples of "naturally" diffusive objects. Commercially manufactured diffusers tend to offer more predictable results than "winging it" with household objects. Poly cylindrical diffusers along with the more complex QRD "phase grate" diffusors will offer diffusion over a fixed bandwidth offering consistent randomized scattering of reflected sound, predicted by mathematical formulas used to model them. So a properly designed diffuser, founded in "good" mathematics is a good thing. If commercially made, its also an expensive thing. And that folks, brings us to the subject of my build thread.
A DIY "Skyline" 2D QRD Diffusor
'Cuz I'm basically a lazy person, I went looking for examples of DIY QRD diffusers that others had already done the heavy lifting on. That being the crazy mathematic formulas that these things are based on. The DIY model my build is based on is found at the
PME Records site here. In this specific instance, I wanted to use a diffuser on the back wall at ear level, 5' behind the listening seat. I'm not gonna get into in detail here but due to a number of factors (my high ceilings and the listening seat's proximity to the proposed diffuser amongst others), a 2D (two dimensional) "Skyline" diffuser was the better solution. Below is a photo of the PME Records design borrowed from their how-to page.
There is nothing really earth shaking about either building one of these things, or the couple of small modifications I made to the PME Records design. If you have the requisite tool(s)- an electric chop saw at minimum (and for my design modifications, a modest table saw, a jigsaw, an electric drill, and a staple gun- preferably pneumatic), and a significant chunk of free time, then you are good to go.
**Note that I'm assuming that you thoroughly read through the link I posted to the PME Records design. I'm not gonna go into a great deal of detail re-hashing what they've written. Most of my comments and instructions will focus on where my version diverged in the interest of ease of manufacture, secure mounting, and appearance.
My design modifications diverge from the PME Records plan pretty much immediately. Rather then cutting all my four lengths of wood blocks from 2"x2",
I used ripped down 2"x4" wherever a pair of identical length stakes were found side by side. There are a lot of paired block lengths when you are building multiples of this 18" square panel design. I'm building a 3' square array of 4 panels and using ripped down 2"x4" in place of paired 2"x2" where possible saves a lot of additional chop saw cuts! Counter-intuitively, 2"x4" lumber is more than twice the width of 2"x2" lumber. Hence the need for a table saw to rip your lengths of 2"x4"s to the precise width of a pair of your 2"x2"s.
As I stated, I'm building a 4 panel array. With the stock PME Records design using exclusively 2"x2" material this requires:
152 pieces 1-7/8" long
152 pieces 3-3/4" long
160 pieces 5-5/8" long
60 pieces 7-1/2" long
For
a grand total of 524 accurately measured pieces.
Using my modification of the PME Records design we get:
80 pieces of 2"x2" @ 1-7/8" long
36 pieces of 2"x4" @ 1-7/8" long
48 pieces of 2"x2" @ 3-3/4" long
52 pieces of 2"x4" @ 3-3/4" long
64 pieces of 2"x2" @ 5-5/8" long
48 pieces of 2"x4" @ 5-5/8" long
44 pieces of 2"x2" @ 7-1/2" long
8 pieces of 2"x4" @ 7-1/2" long
For
a grand total of 380 accurately measured pieces,
almost a 30% reduction in the number of required cuts. When building multiple panels this savings really adds up!
You'll need about 90 board/ft of 2"x2" and 55 board/ft of 2"x4" for the 4 panel build. Make sure that you're 2"x4"s
are the same thickness (approx 1-1/2") as your 2"x2"s! There can be some variation between one mill and another.
Fortunately I figured this out prior to cutting all my material or ripping my 2"x4"s down to a 3" width.
If you intend to otherwise follow the PME Records design and paint your creation, make sure you are using a sharp 80 tooth (my saw has a 12" blade) carbide cross cut blade in your saw to get the smoothest end cut possible. Otherwise, you'll be sanding your a$$ off and it'll look like crap.
Another time saving tip is to clamp a piece of 2"x4" to your chop saw fence exactly the required length of your block from the blade. This means you only measure once (to set your "jig" up) for each block length and every block is precisely the same length. When performing this little trick, hold the blade down after completing each cut, release the switch, and allow the blade to spin to a stop prior to lifting the blade and removing your cut block. Otherwise the spinning blade picks up your freshly cut block and chews it up. Pictured below is my pile o' neatly stacked blocks completed earlier this week.
The next place where my design diverges from the PME Records diffusor is the back panel. Rather than attempting to wall mount a 100 pound 3'x3' panel through the pseudo-randomly placed "0" spots on the panel where there is no glued block, I've lengthened my back panel 2.5" top and bottom. This permits me to drill holes and run sturdy screws with washers through the 3/8" thick sheet of hardboard anywhere along it's width, top and bottom. A 3' wide panel ought to engage a minimum of two studs in the wall behind it, possibly three, as they are typically on 16" centers. My walls are actually on 12" centers so three studs top and bottom is a piece of cake. Now I'll sleep better! Photos to come...
The final place where my design differs is in the use of a frame wrapped around the diffusor array. After a single panel test layout of the blocks, I realized two things: Getting into all the crazy nooks and crannies to paint this thing, even with an air sprayer, would be a horribly frustrating task, and thoroughly sanding, then priming, then sanding each individual block prior to assembly and final paint, would be a horribly time consuming task! Did I mention I'm basically a lazy person?!? I'm gonna cover the entire contraption with the same Guilford of Maine FR701 acoustic fabric used on all my other DIY and commercially made room treatment. The wrap around frame is made up of 4 pieces of 5/8" birch ply cut in 8" wide strips. My back panel has been widened and lengthened to accommodate the thickness of the ply. Using my drill and jigsaw, I'm going to then remove sections of the left and right hand sides of the wrap around frame. I'm basically cutting out large windows to ensure that even reflections coming in from extremely oblique angles can still access the diffusor. Photos to come...
Today's crap weather drove me inside preventing further progress
on my other diffuser project- 70 sq ft of "polys" for high on my side walls. So today after 2 more test layouts of the blocks, I trucked up to the new Rona Superstore (with their brand new, still accurate panel saw) and got the back panel cut to size. I then glued and screwed the 8" high birch ply frame to the back panel
and test fit my block layout one last time... 
Woohoo! the blocks fit precisely within the frame.
Well thats all until Monday for the Skyline diffusor. As soon as the wife returns from her current TV shoot with the camera flash card dongle I'll post additional pics. I've got some sorta free time this weekend (watching our wee one) so I should get a bunch of the sanding and priming done on the mdf "poly" diffuser framework providing we have at least one dry day. That parallel project will shortly have its own build thread.
To be continued...
Happy Trails!
Vince@Freewheelcycle.com
Login
Register
FAQ
Search
Members
to make room for the diffusor array...
I drove out of my parking lot late for an appointment 
Back tracked and reported it to the local police but no joy and no pile of electronic wreckage along the roadside. Fortunately I had a "Time machine" back-up of my drive contents from a day or two prior.
