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Soundstage/Imaging and The Room

I'm encountering an interesting phenomena.
I moved to Connecticut from California. When in California, I had a 10 x 13 x 27 room, dedicated outlets, the works. I had no problem with imaging,soundstage, etc. Now, here in Connecticut (I know! the geography counts for beans, but I wanted to give some background), I'm temporarily in a basement in the family home. The basement ceiling is 8' , with joists (planks that support the structure and hold up the floor) hanging down from the actual celing and spaced every two feet. So, in essence, with the 7" joists (planks of wood) hanging down, the height is about 7'5" and I notice that there's NO imaging whatsoever. I had even installed dedicated circuits (2) for the time being.
What's your take on minimum ceiling height for imaging? By the way, the basement is open, so it's 23' x 40' (give or take 5 feet). I can hear low level detail when music is playing, but the actual imaging is fascinatingly absent.
Equipment is a First Presence preamp, a Marsh A400s amp, Arcam FMJ23, Shunyata power cords, PS Audio line conditioner (and power cords) and Nordost interconnect with Synergistic speaker cable.
I've actually tried the setup two different ways: with the speakers set up so that they are aimed parallel to the joists, and setup so that they are aimed perpendicular to the joists --- no difference in imaging, but the sound is more "distant" when they're fired perpendicular to the joists. The music loses some "intimacy."
I'm finding this interesting. In a couple of months, I'll have a dedicated room added onto the house, but still, what are everyone's views on how the room's ceiling height affects imaging -- and soundstage boundaries? I'm wondering if all the ceiling joists hanging down interrupt and reflect the sound back onto the concrete floor and walls, and confuse the ear/brain into not "seeing" imaging. Especially since it makes it seem like a "low ceiling" effect. What do you think?
gbmcleod
jaytor's avatar
jaytor
747 posts
 
I agree with those that feel it is most likely the room acoustics. The large room size will, in general, help you, since it will reduce the frequency of the primary bass modes (although the low ceiling height is a bit of a problem here). I agree with Rives, though, that the construction of the ceiling is more important than the height.

If you've got hard concrete walls and floors, you need to do something to tame strong reflections. Make sure you have some acoustic absorption at the first reflection point on the side walls and floor. If the room is excessively bright, you can add more absorption on the wall behind the speakers, then on the wall behind the listener. Be careful about adding too much absorption, though. You don't want to make your room too dead. Substituting diffusion for absorption works well with less effect on reverberation time, but is more expensive to implement for a comparable effect.

Very hard walls will also increase the Q of the room, causing the bass modes to be narrow and strong. It doesn't sound like it's bass boominess you're complaining about though so this may not be as big a problem in your room. If it is, then some use of bass traps (RPG Modex is probably the best if you don't want to make your own) and low frequency equalization will help a lot.

Regarding your ceiling, I agree with Rives that diffusion can make a big difference, particularly with such a low ceiling. You can make polycylidrical diffusors that will fit up between the joists fairly easily. If the heavy blanket trick suggested by Buscis2 helps at all, then a broad application of diffusors will help significantly more. If you need help figuring out how to make the diffusors, let me know.

Good luck.
- Jay

http://www.jaytorborg.com
buscis2's avatar
buscis2
468 posts
 
Gbmcleod, The blanket concept is simply a temporary "fix it".

I don't know exactly how long you will be using this temporary listening area. My suggestion would be, if you are going to be using this room for any extended period of time, buy a few sheets of 4x10 x 5/8" sheetrock and a couple of rolls of "fully encapsulated" (such as Owens-Corning "Miraflex") insulation, maybe R-19 or R-30. About 1-2 hours time and some sheetrock screws will yield much better "temporary" results. Insulate the "bays" between the floor joists over your listening area and screw the sheetrock to the floor joists to create the ceiling.

Hang a blanket from the ceiling down to the floor about 3-4 feet behind your listening position. A little more work but much better results.

The "lack of openess" is probably the fact that the majority of the high frequency and "bloom" is being absorbed by the blanket. Again, I'm not sure how much time, work or money you are willing to invest, but about $75.00 and my aforementioned procedure will bring much better results. My original suggestion, I would of hoped, would bring you max results for minimum effort.

Maybe a trip to Home Depot is in order?
gbmcleod OP
430 posts
 
Guys, I appreciate the ideas. Please keep in mind, however, that this is an empirical experiment, not one where I need to be concerned about the materials or the reflection. It's simply a way of finding out how much any given material works. I wouldn't refer to myself as a novice in this arena, although I always appreciate good advice.
Buscis, as for the blanket absorbing the 'bloom' and high frequencies, I assure you it's not. The high frequencies are MORE present, not less. The blanket, being porous, wouldn't likely be sufficient to damp the highs, given that sound would go 'through' the blanket. In fact, the blanket 'softened' the ceiling and allowed the highs to be heard more clearly. The lack of bloom is likely a combination of the low ceiling and the other room nodes, and I made a decision to limit the amount of work I was going to do, given that this is a family home, but my presence in it is for only a few years. Don't misunderstand: I like your suggestions, but I'm pretty aware that, if I need to make changes, I can do that with the 40 tube traps I'm bringing back from California, and I've been working with tube traps for 14 years now, so I know how to set them up.
And Jaytor, thanks for your input also; I've already damped the first and second reflection points with the Armstrong acoustic ceiling tiles. That would be the first thing I'd do. Again, this is an experiment. I hope I made it clear that this is more a fascinating experiment, not a source of consternation. I was in the euipment manager for an audio magazine for a while, so I have some understanding of necessary room treatments, although more info is better!
I'm in the process of having a 10x14x19' barn
being assembled. If I'm going to acoustically correct something, it'll be the barn, as that space is completely mine to do with as I please.
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