Hello All. First off, I want to say how impressed I am with the generosity of all on this forum for offering advice. Thank you in anticipation and in advance!
I have a dedicated listening room, 14.5’x18’ rectangular with a ceiling that slopes up from 8’ to 14’ from the front (speaker) wall to the rear wall. A side-view cross-section schematic is shown below:
The rear wall is a floor-to-ceiling masonry fireplace. When I first moved into the room, there was considerable slap echo in the upper regions between the fireplace and upper ceiling, so I installed 2” thick 703 home-made absorbers on both the ceiling (hanging, both sides exposed) and the upper fireplace (hanging, one side exposed) as shown above. That took care of the slap echo. Out of the 14.5 feet width, the fireplace occupies about 10.5 feet of the rear wall (the remaining 4’ holds a door well), and it has three 2’x4’ absorbers across it. The ceiling has two 2’x6’ absorbers offset in alignment to the gaps between the wall absorbers. Below the fireplace mantle (i.e. < 6’ height), the fireplace surface has no treatment, but has 4 upholstered dining chairs sitting on the stoop up against the fireplace (rear legs sawed off: stoop = rear legs). The chairs likely provide some additional absorption. Also important: this side view schematic shows a ceiling beam crossing the width of the room, extending about 10” down from the ceiling. A photo of the beam, fireplace and associated panels is shown below (chairs missing):
The right side wall (looking forward) has a window in the forward position (shown on schematic) which is covered with thick velvet drapes, and a fully-loaded record shelf in the rear position (shown on photo above). The left wall has a continuous run of built in cabinets and a door. There are no longer any treatments on the side walls – though I think the window curtain occurs at the first reflection point.
The front wall has a French door in the middle (also covered with thick velvet drapes), and on either side are 2D quadratic diffusors (3’x5’, home-made with balsa wood, maximum block depth 5”). I put them on the front wall because I was previously using quads and maggies, and wanted to break up the backwave.
All corners have home-made ASC tube traps (12” and 16”), plus I’ve got extras to move around the room as needed. On the ceiling (forward of the beam) are three skylights, each in their own well. I’ve installed hinged “shutters” in each well (to block out light during movies), and one shutter in each well has a small 1” thick absorber that helps control reflections within the well.
The room sounds pretty good, but it’s not quite as alive as I’d like and I’d like to get better resolution and imaging. I’m now using Avalon Eidelon Diamond speakers, so I no longer have the backwave issue. I am considering the following three modifications:
1. DIFFUSION ON REAR WALL: In order to make the room more alive (and to be consistent with “common wisdom”) I am thinking of replacing the 3 absorption panels on the upper rear walls with diffusion. This diffusion would be balanced out be the two larger absorption panels that are hanging from the ceiling, angled toward the fireplace (see schematic). I likely cannot add diffusion to the lower half of the fireplace, as the upholstered chairs need to stay there (for movie viewing events in the room). Although the chairs break up the flat surface of the lower fireplace, I would guess that they predominantly add adsorption.
2. COVERING THE BEAM WITH A CURVED SURFACE: I am guessing that the beam causes reflection in both longitudinal directions: from front-to-back and from back-to-front. I’m thinking of affixing bendable plywood to the ceiling on either side of the beam and to the beam itself to make a curved, smooth “speed bump” that covers the beam and doesn’t cause reflection. I could stuff the “speed bump” with insulation. It would be hard to get a perfect seal on it though because there are cables that run along the ceiling that must go “through” the “speed bump”.
3.COVER FRENCH DOORS WITH AN OUTWARD CURVED SURFACE. This would be easy to do with bendable plywood. I could use 2x12 to create a form and attach it to the floor and the 6”-deep ceiling ledge (shown on schematic) and rap the plywood around it, attached with Velcro so I could pull it back if I wanted to get stuff through the door. I might be able to make this an airtight seal if that would benefit, and/or I can stuff the space with bags of insulation or batting.
I would like people’s opinions on which, if any, of these modifications would be most beneficial. If they are all worthwhile, or only some, or if some of them are not worthwhile or even a bad idea.
Also, if I replace absorption with diffusion on the rear wall, what style of adsorption should I use? 1D or 2D? If 1D – horizontal or vertical. Note that the listening position is maybe 6 feet in front of the fireplace, but several feet lower than where I would mount the diffusion. I would likely build the diffusion myself using either wood or foam. Because I don’t want to penetrate/damage the masonry, I would likely mount a sheet of plywood against the fireplace between its acute angle with the ceiling the mantle - and then mount the diffuser structure to the plywood. As for diffuser depth, I’d prefer ≤ 6”, if possible (for aesthetics sake). Finally, if I add diffusion to the rear wall, should I exchange the difffusors on the front wall with absorbers, or is it OK to have diffusion on both front and rear walls (my aesthetic preference)?
Thank you, Peter S.
PS – I’m anticipating advice that I should have absorption at the first reflection points on the sidewalls. I think I already have that on the right sidewall (window drapes), but the left sidewall has all these cabinets and doors that need to open – I’m not sure how to do that except to place an absorptive base trap there (which I can move around as needed).
