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In Reply to: RE: very valid points posted by David Aiken on December 04, 2010 at 11:55:06
Unfortunately, this room is "semi-dedicated", meaning my 2 boys have a small entertainment center with a tv, dvd player and wii in it. And my chair is actually our old sofa, 7 1/2' long.
I measured the room this morning. The 2 walls with the slanted ceiling (facing each other) are 19 1/2' apart. The other 2 walls are 17' apart. One 19' wall has the entry hallway coming through it.
While this is not what most would consider to be a small room, when it comes to accommodating both "systems", placement becomes very limited. Keep in mind ac outlets, cable outlet, long sofa, computer desk, doorways (entry and closet) and the ability to be able to face one system at one moment, and the other system another moment. The only way to do that is to have them set up perpendicular to each other. So my system is set up along a 17' wall, the tv/wii along a 19' wall. The sofa is shared between the two systems.
Treating the side reflection areas would be relatively inexpensive. It's the slanted ceiling and all of it's nearly 120 sq ft that has me concerned. My idea is to build 2 partitions, about 4' wide each. They would be based on Risch's bass traps, but rectangular or oval in shape. Build them about 6' tall, and place them behind the couch while I am listening. A "mini-environment" if you will.
As far as cost and results goes, that seems like the most reasonable solution. I was hoping a fellow inmate had tried something similar and had some input. Thanks for the input thus far!
Follow Ups:
Sorry for the delay in replying—I missed seeing your post.
As I've said, I think with your current setup as described, the sloping wall may well not be a problem.
I can appreciate the space constraint issues and the inability to use part of the total room area because it's used for other purposes.
I don't think dividers, at least ones such as you've described, will do much for you. If you build them based on bass traps, they really won't provide effective bass trapping placed out in the open in the locations you describe. Bass traps work best close to room boundaries where pressure is highest. If you're going to make something to use as room dividers, then simply make ones similar to the panels you would use on walls at first reflection points. Since you won't get effective bass trapping at those locations, simply go for panels that work well at mid to high frequencies and experiment with their placement.
My preference would probably be not to worry with the dividers unless they serve a useful purpose in defining the respective room surfaces. If you do make them, I'd make 4 x 2' wide units rather than 2 x 4' wide units. You'll get the same amount of benefit and have more flexibility in how and where you place them. I recently experimented with putting 2 panels between the 2 I already had at the first reflection points on my front wall. That actually created a solid 4 panel wide expanse since the gap between the original 2 panels was almost exactly 2 panels wide. I found that while the really wide expanse helped in some ways, it "blanked out" too big a space in others and the results I got by moving the 2 panels from between the original 2 to positions outside them, closer to the corners and leaving an open space between each panel gave what I regarded as significantly better results. Smaller panels placed with space between them can give better results under some circumstances than the same area of larger panels.
David Aiken
David,
When I originally posted, I really didn't have a certain freq band in mind. And believe it or not, the bass really has not been an issue as I thought it would be with rear-ported floorstanders rated down to 24 cycles.
When I play tracks that are not too "busy" at moderate levels, the presentation is really good. Sitting closer, in a more intimate setting, is allowing me to hear subtle details I was not picking up on in the bigger room.
But I am a R&R fan, too. And it's the beaming highs that are fatiguing. I used my Rives Audio test cd the other day for some experimentation. I had the RS meter setting on the couch back cushion, so I was behind the couch and under the sloped ceiling. As the freq's got higher, the more fatiguing it became. But I also cannot help but think that these mid-high reflections are having an affect on the imaging/soundstaging on the mellower listening sessions.
The partitions I tried to describe would be made from pieces of 2x8 in the form of a component rack, wrapped with wire mesh and then some sort of acoustic material (mineral wool, recycled cotton panels, fiberglass or foam). I would place them behind the couch during listening sessions, diffusing and absorbing first-arrival, and reflections that are making their way back to the listening position from behind.
The downside to panels is that they would be taking up floor space while not in use. The upside is that they would be less expensive. Treating the walls will require more acoustic material, but it would be a permanent installation up off the floor. I am leaning more towards the permanent install.
So here is where my plan stands for now: buy 2'x4' panels of acoustic absorption material. Choices in descending order of cost are wedge foam, recycled cotton, fiberglass, mineral wool. That is misleading though as the fiberglass and mineral wool would require fabric covering, bringing the cost up to the cotton and foam level. Buy some 4'x8' sheets of coroplast from the local FastSigns franchise, cut it to a 7' length, and glue 3 panels to it spaced equally apart. Remove the excess coroplast from between the panels except for some "tabs" for mounting to the sloped ceiling. The goal is a mounting secure enough for an "upside-down" installation with minimal intrusion to the drywall.
I could also put single panels at first-reflection points, and more importantly, the entry hallway coming into the room. The hallway acts as a waveguide, making the sound just as loud if not louder outside the room. I installed a solid-core door and weather stripping, but any listening done after bedtime requires low volume levels. It would be nice to be able to turn it up a little louder without worrying about too much of the sound making it's way past the door.
Coroplast comes in black, as does the cotton and foam. The room is painted burgundy including the ceiling, so black will blend in and be less visible with the lights low.
Again, thanks for your input. Let me know if you detect any flaws in my plan. I would like to move forward with this project immediately following the holidays.
High frequencies actually get absorbed by air though the amount of absorption depends on air volume, and also tend to get absorbed a bit by a lot of room surface materials such as plasterboard. Your room size should be working for you here because of the increased air volume so if you've got a high frequency problem my guess is that you have a lot of reflective surface area in the room which are reflective at high frequencies, things like uncovered glass window areas, a hard reflective floor surface with no floor covering, stone walls, and possibly even a lot of glass or similar surfaced furniture.
The excess mids/highs could have an effect on imaging/sooundstaging if they are coming from the first reflection points so I'd map those points out and see what kind of materials you have at those points.
If it's the nature and size of the reflective surfaces in the room that is the problem, I'd start with things like curtains, a rug between you and the speakers, removing any highly reflective furniture I could, and so on. If you have reflective furniture providing first reflections, then I'd move that furniture elsewhere in the room if I couldn't remove it. TV screens are reflective at high frequencies and can be covered with a blanket or quilt during listening sessions. If that doesn't tame things enough, then adding absorption for the mids to highs would be necessary. When adding panels I'd start with first reflection points but you may need to add some elsewhere if that doesn't do enough to suit you.
You said you couldn't move the listening chair to test out other placements because it's a sofa. If that's the case, leave it where it is, grab a lightweight chair and experiment with other locations to see if you can find one that works better, with or without some speaker position adjustment as well. When you've found a location consider whether you can move the sofa there. If not, then consider using a comfortable, easily movable chair at that location for listening sessions.
David Aiken
Walls and ceiling are textured drywall, not smooth drywall as is found on the east coast. Floor is plush carpet. There is a maple entertainment center on the left, same arrangement as in the old house in the bigger room.
I did not realize that drywall was capable of absorbing highs. Getting a center vocal image that stood out from the rest of the soundstage required a hard toe-in of the speakers. I have since tweaked my rig and improved the sound a tad, so perhaps less toe-in will still give me a good center image while not directing the highs at me?
My concern with the speakers facing more forward with less toe-in is that they will be facing that 7' long by 16' wide sloped ceiling surface. But experimentation will determine whether or not that concern is a valid one.
I will play with speaker placement as time permits. Like I said, I wasn't going to move forward with treatment until after the holidays, giving our credit card a chance to cool off. I will experiment and keep you posted. Thanks again...
Drywall doesn't absorb much at high frequencies but it absorbs some and is less reflective at those frequencies as a result.
Toe in depends a lot on room and placement. If you have the speakers pointing right at you, you'll hear more high frequency content in the direct sound than if you have them pointing straight ahead down the room and are listening off the tweeter axis. Is the high frequency balance more to your liking with the speakers firing straight ahead rather than pointing at you? If so, then I expect that you may find that leaving them that way and using absorption at the first reflection points solves your high frequency problem and gives you your centre image. You need to experiment. You can also experiment with intermediate amounts of toe in.
If you simply change toe in with the speakers in their current position and face them down the room, what you're going to do is move the direct sound more off axis and the move the side wall first reflection more on axis compared to the situation with them toed in facing you. That will reduce the high frequency content in what you hear but you say it weakens your centre image. Moving the speakers closer together will move them further from the side walls. If you face them down the room in that position you'll get the same axis changes as facing them down the room in their current position, but to a slightly different degree for the direct sound and the reflected sound, and you may get a stronger centre image because you're also shortening the direct sound path and increasing the first reflection path, weakening that reflection relative to the level of the direct sound. That may give you an acceptable high frequency balance and strengthen your centre image without the need to treat the side wall first reflection points. That's also worth trying but you may find you prefer the speakers further apart. You really need to try these sort of changes out to see what the result is and whether it gives you what you want.
The sloping ceiling may or may not be a problem. I think there's a fair chance that you won't get a first reflection from it but checking that is going to be awkward. What you need to do is sit in your normal listening position facing backwards so you can see the ceiling and get someone to slide a mirror over the ceiling surface. If you can see the drivers in the mirror at any point you've identified a first reflection point. Trying to do a scale drawing and seeing if you can find a reflection path that way is going to be very awkward because of the fact that the reflection plane will itself angle over the sloping surface at an angle and you'd really need 3D modelling software to try and plot the path theoretically. My feeling is that because the slope peaks behind you, you won't get a first reflection from it. For that reason I'm not as worried by the sloping surface as you are and I think it may even be a plus for you rather than a negative. I don't think toe in will affect the reflection paths from the sloped surface.
I wouldn't try treating reflection points until I'd explored placement options. Get the best sound you can without treating reflection points and then refine that result with treatment if necessary.
David Aiken
I will definitely play with speaker positioning before forking out the bucks for treatments.
In my old room, I had a system that could do lots of different music right. Jam sessions with R&R were not fatiguing, and quieter sessions had a nice soundstage w/a holographic center vocal. But as stated earlier I was missing some details that I am now picking up on in a smaller room with closer proximity to the speakers.
I dread the thought that perhaps this system in this room is not suited to the jam sessions. I do not want to change my listening habits, but I accept the fact that high-end systems can be best suited to some types of music and listening styles as opposed to others (Maggies and jazz, for example). Perhaps my current set-up is incapable of accommodating all of my music to my liking? Only experimentation and time in the listening position will tell.
I will keep you posted on findings as time permits. Thanks again!
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