Room Acoustic Treatment Devices

Introduction

The one component that is almost universally taken for granted and acknowledged as being a major factor in the quality of sound reproduction, the listening room, is largely ignored. Following on from some of my earlier contributions on system set-up, this article describes the construction of room acoustic treatment devices. The idea for these devices came from a glowing review of products manufactured by "Roomtune". Some friends of mine were also using them and were impressed by the results. As I understand it, they break up resonances in the room by reflection and absorption. These devices do not damp a room so if your system is bright it will remain so. I am not a fan of room damping or any other devices that damp the sound.

All rooms I have heard these devices in have benefitted, regardless of the type of system and remarkably in the same manner if not to the same extent. In my and others' opinion, by using the materials specified here, we thought the results superior to those using Roomtune products. We did not audition covering material or reflector material.

To first try out these ideas, an old sofa was butchered and four triangular foam shapes with tinfoil reflectors were installed in the room corners: the Mark 1s. The idea was based on the Roomtune product Cornertune and is used to break up pressure points formed in the room's corners. Results were dramatic. The sound was more open and the room did not seem to overload. I could go on but believe now that the results have to be heard to be appreciated.

A friend had looked inside a "Roomtune Cornertune" and based on what he saw, purchased a selection of fibreglass insulation sheets with foil backing, similar but not the same. The original looks like a floor insulation material backed by builders foil. It is similar in structure to the nylon damping material used in speaker enclosures. I sourced some other insulation material (wall insulation made from surplus wool - a natural product) and made up two triangular cushions with kitchen foil for the reflector.

In the end we compared the Roomtune with cushions made from two different types of fibreglass, three made from long hair wool and one made from the material I had sourced. Much to our surprise the new material produced the superior result clearly bettering the commercial Cornertunes and our other concoctions.

Construction

Based on our listening tests, we concluded that the material should be quite airy, much like slightly teased cotton wool. We found the heavier types of layered fibreglass insulation sheets to be no good. At a pinch, seat cushion foam could be used to get an idea of what can be achieved. It should be about 30mm thick.

I used a cheap off white poly cotton to cover the cushions. It should be acoustically transparent i.e. easy to see the shape of the foil reflector (tinfoil) through the cover.

As there are a number of cushions to be made, I used corrugated cardboard templates for the various pieces; one for the covering, one for the damping material and one for the foil reflector. The three equilateral triangles have sides of 15.5" (No. 1), 12" (No. 2) and 9" (No. 3) respectively. The rectangular cushion templates are 14" by 8" (No. 1), 12" by 6" (No. 2) and 10" by 4" (No. 3)

The damping material I used was too thick so it was split in two once the shape had been cut out using wallpaper scissors and the No. 2 template. If you are using fibreglass, be careful and cover exposed skin. Fibreglass will also no doubt ruin any cutting device.

Two material covers are cut to size using the No. 1 template. I used an iron to fix the edges in place before sewing using the following method.

1. Place the No. 2 template in the middle of the material and fold the material corners in to meet the template corners and iron flat.
2. Now fold the material edges in to meet the template's edges and iron flat. Turn this piece over.
3. Place the other piece of material on top and following the above fold and iron procedure, copy the material shape below which should result in the second face being identical to the first.
4. Place the two inside faces together and sew along two of the edges (two long and one short for the rectangle). Stuff the cushion with damping material. It is easier if the large template is used as a former.
5. Cut out a tin foil reflector about 10mm larger than the No. 3 template. Fold the foil edges in to replicate the template. Fold in the corners about 20mm. Slide into the cushion and position centrally. A dab of glue can be used to keep it in position. It should look like the picture below.
6. Sew along final side. Start near the end of one of the previously sewn edges, sewing over the top of that seam and finish on the other sewn edge, once again going over the previous seam. This prevents the seams unravelling.

Installation

They can be held up with pins but I use Velcro glued to the cushion corners and the wall. If they are an eyesore in your place of listening, then with this method they can be installed and removed quickly. The Velcro need only be 5 mm square as the cushions are so light.

"Roomtune" type cushions shown in corner and first reflection position. Attached by small velcro squares.

The current speaker position may be the best one in an untuned room but may not be right once these devices are installed. These are not necessarily fit and forget devices. I use six triangles at present but may be adding more. Two behind the speaker, two behind the listener and two either side of the chimney breast. They are installed in the ceiling/wall corner with the foil side facing out.

The rectangular cushions are positioned high on the left and right walls at the ceiling/wall interface. Using a mirror placed on the side wall, move it up and down the wall until the speaker drivers can be seen in the mirror viewed from the listening position. The cushion is placed directly above this point, long edge against the ceiling or coving.

There are other devices like these that I will be making, which once again will be based on Roomtune's principles; the basis of another article. And once again, if you are interested in hearing their effect, ring for a demo. I still have the Mark ls (which are big, heavy and ugly) that can be loaned out for those who want to hear the effect in their own room.
 

Andy Nehan had something to say in the same issue.

A follow up

I recently became a convert. Stephen brought round 6 corner tunes and two rectangular panels. The corner tunes and rectangles were fitted up into the joins of the ceiling with the walls. I was convinced within a couple of minutes that they were a winner. OK so I am biased as I heard them before round at Stephen's where they sounded good so I naturally sought the opinion and approval of the management before committing myself to fitting them; any other course of action is not to be recommended. I guess like most wives mine thinks that anyone who claims to hear differences in capacitors is surely round the bend. At a very minimum they are deluding themselves!

The sight of the triangles was not to her liking, they do not actually improve the appearance of the room, nor are they by any means normal accoutrements of a hi-fi room. But being a fair minded person she gave them a listen, the same piece of music with and without the triangles and rectangles. For interest it was the Rachmaninov piano concerto, a piece of music with lots of wellie but at the same time many delicate passages. It was a winner, the triangles etc. got management approval (whoopee). The sound space was described as being less compressed and the bass more extended, just the words Stephen and I had used.

The next job was to make up 14 triangles and 2 rectangles. I cut out the material, thin curtain lining, and the wife machined it. We originally used double sided tape to fix the items up but found that they fell off. The problem was always with the fixing to the material. The only solution was to sew velcro tape onto the material then tape the other part of the velcro to the walls/ceilings. Even this has not proven to be a perfect solution and I am looking at a better way of fixing the velcro to the ceiling.

In the future I want to try some long strip tunes which would extend from floor to ceiling in the corners of the room. These would obviously be unsightly and in order to fix that I would only put them in a limited number of corners. I will let you know how I get on with these.