Wednesday, April 27, 2016

Moving Day Part 4: Acoustic Treatments are a Component, Not an Accessory

The finished product. Read on to learn how I got here...
The fundamentals of ANY audio system performing it's best are:
  1. Dedicated AC lines and proper power conditoning
  2. Optimal speaker placement
  3. Acoustic treatments
Skimp on any one of these and you are cheating yourself out of the best possible sound for your dollars spent. One can spend a lot more money trying to get around doing any one of these through component purchases, cables and tweak purchases. Without the proper foundation, you are just putting band-aids on the sonic problems.


The new listening room was coming along. The electrician finally installed the dedicated lines and wired them with Audience 10 AWG in-wall cable. Man, what a difference! I had (and still have ) a 14 AWG dedicated line in the same room. The Audience cable allowed my system to be quieter, more dynamic, and have way better bass. A great investment.

The Room

The room looked like the intersection of two rectangles, with the entry way and stairs in the middle along one long wall. The total useable area of the room is 39 feet by 14 feet. The first rectangle is 14 feet wide by 29 feet long, this intersects with a rectangle shaped area 20 feet wide by 10 feet long.
The speakers are placed along the 20' wall,  8' apart, 38" from the back wall and firing into the large area. 

The speakers themselves are a controlled directivity design with single 12" front firing midbass drivers, waveguide loaded air motion transformer high frequency drivers (80 degree dispersion horizontally, 30 degrees vertically), and 2 opposing powered 12" subs per speakers. At 98dB efficiency they easily fill the space with powerful sound.

Room Acoustics

So it was time to focus on room acoustics. In the most general terms, one wants the right combination of surfaces that absorb sound (absorption), as well as scatter it (diffusion). What one does not want are flat reflective surfaces that sound "bounces" off of and arrive at your ears with enough delay to "smear" the sound coming directly from the loudspeakers themselves. You want the directly radiated sound and not so much of the reflected sound.

To start, the wall behind the speakers should have a combination of diffusion and absorption, for the side walls I prefer mostly diffusion, and the walls behind the listening position mostly absorption. To my ears too much absorption results in an overly "dead" room. It sucks the life out of the music and makes the room feel small. Too much diffusion and the room is still too "live". You don't get so much slap echo, but the midrange can have too much energy and sound artificial.

The Problem with Room Treatments

The problem lies in finding the right placement of treatments, as well as the ratio of absorption vs. diffusion. This is difficult because placing acoustic treatments on a wall is like hanging art. It leaves holes in the wall and is a pain in the arse.  So how to hang acoustic treatments in a way that 1) does not damage the walls every time you swap or move an acoustic treatment, and 2) allows one to experiment with placement.

I came up with a pretty slick solution for the particular treatments I was using. I incorporated a rail system used for hanging art, and "McGyvered" the acoustic treatments so that they could be hung by cables and slid along the rails of the picture hanging system. This system also allowed me to adjust the horizontal and vertical placement of each treatment. Perfect!

The Hanging System

I used the Stas Mini Rail picture hanging system found here.  It consists of a small rail that is installed along the length of the wall (or as long as you want). Cables with hooks on one end are then hooked into the built-in rail and can be slid along it's length. Spring loaded hangers are placed on the cables and hook on to fasteners installed on the acoustic treatments by me (more on that later). This enables one to move on the horizontal or vertical plane, and it allows you to easily swap absorbers and diffusors. Limitless experimentation, at least for the walls in your room.
Mini Rail hung 2" from the ceiling with cable installed.

The Absorbers
Sonex Whisper Wave hung from the ceiling.

I chose the Sonex Whisper Wave 24" x 48" panels for my acoustic absorbers. I liked the shape and the light weight. They are perfect for hanging from the rails and will get the job done. A set of  4 24" x 48" panels in unpainted white is $248 plus shipping. That should be plenty for most rooms.

The Diffusors

I chose the GIK Acoustics Grid Fusors for my diffusors. Again they were light weight, and looked aesthetically pleasing. The surface was also paintable. They came in sets of 4, 24" x 24" panels and the cost was $214 per set. You may need more than one set of Grid Fusors, as a set of Grid Fusors covers about half as much surface area of  your walls as a set of Whisper Waves.

Modding the Acoustic Treatments for the Rail System

I needed to install something on the acoustic treatments to accomodate the hooks that will hang from the cables. It had to support the weight of the treatment, be durable ( I often bump into things when I am working behind my system). I decided to use some heavy duty self drilling drywall anchors. They were large enough to not pull out of the treatments and could hold the "screw eyes" (yep, that's what they are called).
Self drilling drywall anchor

Drywall Anchor with screw eye installed on a GIK Grid Fusor

Drywall anchor and screw eye inserted into the Sonex Whisper Wave
These worked out perfectly.  I installed the hangers on the tops of the Sonex Whisper waves, and on the tops and bottoms of half of the Grid fusors, while the other half just the tops. My plan was to hang two Grid Fusors beside one Whisper Wave, that would make both the diffusor surface area and absorber surface area nearly equal. Making for a tidy display along the wall.

One Whisper Wave panel hanging from the rail.

Bass traps

Let's not forget bass traps. A great way to even out room response in a mechanical way. I had 4 bass traps from Acoustic Geometry's Curve system. They consisted of the corner trap plus the Curve diffusor. 2 were placed in the corners of the wall behind and outside of the speakers. 2 more were stacked in the corner opposite the left speaker in the 20' wide section of the room. The picture below illustrates placement, with the bass traps indicated in red.

Acoustic Geometry bass trap (Stein Harmonizer on top).

GIK makes bass traps as well. They are available in a wide variety of colors, and start around $229.

Getting More Creative

I had also made a DIY absorber out of 1" thick remnant pieces of industrial felt that I glued to a piece of Baltic birch ply. For those more inclined to DIY their room treatments, this was super easy and looked pretty cool when finished. Cost was about $100.
My kids love this piece because the "dots" are not glued down. They can move the dots around to create different patterns. The colored dots are simply spray painted felt pieces. They lose some of their absorptive properties when spray painted, so I left the majority of them their natural color.


The results, so far, have been outstanding. Imaging has improved, the soundstage has more width and depth, and it doesn't smear nearly as bad as it did before. No smearing at low to moderate levels, with a slight bit of smearing and echo when the volume goes up. Which tells me there is more work and experimentation to do. My next installations will most likely be on the ceiling, which right now is the largest reflective surface in the room.
Standing at the back wall, behind the listening chairs. Three absorbers and two sets of two diffusors currently behind the speakers.  Off to the right side are 2 more sets of 2 diffusors. To the left, one absorber. This is how it currently is, but could change at any moment. :)  I feel I need to experiment with the ceiling next. Perhaps another blog post.
Taken from the right corner, you see the bass traps in the opposite corners. The shape of the room makes the bass a little boomy at around 30 and 60 hz. The bass traps help immensely, but DSP will help further.

From the right corner, facing out into the room. To the left, my felt "art" that acts as an absorber, and on the far back wall, two Acoustic Geometry absorbers on either side of the double doors. The length of the room takes care of a lot of slap echo problems, but as one turns the volume up, the need for absorbers on this wall makes itself evident.

From the left speaker, facing out into the room. You see the entry into the listening room, with the "horn-shaped" opening.

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