Room Acoustic Treatment

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DrJ-10

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Room Acoustic Treatment
« on: 3 Oct 2020, 07:37 pm »
I am trying to make a room that is not helpful at least to sound reasonable.  It is 9' wide (with a large window on one wall), with an 8' ceiling, and about 40' long with a few minor arches and windows along the way.  The last dimension I think is irrelevant for these purposes.  The floor and ceiling are wood nailed to joists, and the walls are standard drywall.  Along the length, at 17' the floor changes to porcelain tile and the room opens up, but again I don't think this is significant.

The loudspeakers are Beveridge Model 3s, which are cylinders of about 2' diameter and 6'6" tall.  They are a 6' electrostatic line source that terminates into an acoustic lens that gives it about 180 degrees polar dispersion which is pretty uniform though slightly biased to the on-axis plane; the back wave is damped.  Their top and bottom have rather flatulent 10" sealed woofers, and the bottom one is slot loaded.  A traditional way to set them up is to have them face one another, though other orientations work fine too.  Yes, the room is too small for them, but that's what I have to work with.

My initial thought was to put a heavy curtain on the front wall behind the speakers, put a rug with a thick pad on the floor, some tube traps in the corners, and play with the speaker orientation (rotation) with absorption or dispersion at the first reflection plane.  Likely some ceiling treatment will be needed.

I have a minidsp 4x10 that I intend to use to help with the mess that the nearly identical room dimensions will make, but I'd like to try to do as much with the room first before using the filters.  I use REW on a near-by computer, a calibrated microphone with a Focusright unit to provide phantom voltage and to provide a USB signal to the computer.  I'm comfortable with all of that.

I know the room/speaker combination never will be outstanding, but at the moment is really is lousy.  Advice would be appreciated.

Bob Stark

Re: Room Acoustic Treatment
« Reply #1 on: 3 Oct 2020, 10:39 pm »
DR J-10,

Does the wall behind the speakers have ay features?  I have nearly finished with my listening room in the basement--the final iteration.  I like a live sound with no noticeable slap echo.  I have a combination of 8 Synergistic Research UEF panels and 10 dots, along with built in bass traps in the lower half of the front corners, and huge floor to ceiling bass traps in the rear behind a pair of equally large storage cabinets for albums, CDs, and cassettes.  I also put in two GIK 6" Alpha 1 bass trap/diffusors behind the listening couch with a pair of quadratic diffusors in-between them.  The side walls are angled like a theater as is the ceiling with the back taller than the front.  I have a pair of quadratic diffusors at about tweeter level (tweeters are in the middle of my speakers) on the front wall.  The ceiling is Armstrong high articulation ceiling tiles with a Glacier cloud in the middle between the speakers and the couch.  The room is 17 ft. across the front and 20 ft. across the rear.  The sidewalls are about 14 ft. between the angled traps. 

Things I have learned while doing this:  1.)  The quadratic diffusors brought more life to the sound which the GIK Alpha 1s tended to make a little too quiet prior; 2.)  The 4" high density Roxul rockwool boards that made up the corner traps, sometimes in 2 layers with 2" of air between them, actually made the soundstage widen and deepen in addition to tightening the already good bass of my VMPS RM40 BCSE ribbon speakers; 3.)  The SR panels and dots made a significant difference for the better in the live and realistic sound of actual instruments and voices.  I have not finished the cabinets in front of the rear bass traps, but I'm guessing they will liven up the sound and still allow the traps to work--the rear panel of each cabinet is rough pegboard facing the fronts.  I have a 3/4" spacer board in front of the rear panel to allow the sound to pass around the albums and CDs.  There is about 1" above the records and CDs to allow this to happen also.  My speakers are about 5 ft. out from the front wall at the drivers, and are 7.5 ft. apart C/C with about 4 ft. to the sidewalls.  The floors are ceramic tile with a large area rug covering between the speakers and the couch.

Putting at least one Alpha 1 on the wall at the midpoint of your speakers will help with the diffusion and soundstage.   The SR panels and dots have an amazing effect on the sound making it better in all ways with no downsides except cost.  I would try placing the Beveridge speakers out from the 9 ft. wall as far as the bass will allow without it getting too wimpy sounding.  I'd try having them about 18" from each sidewall, and move them an inch at a time until the sound locks in.  Then adjust your chair to the spot where the bass is the best and the soundstage is good.  If you have to, make a rear wall several feet behind where you will sit and see if that helps.  My speakers have mids and highs much like an electrostatic speaker with adjustable powerful bass. 

I won't know what my finished rebuild sounds like for a couple weeks until I get the cabinets built and installed.  I'll let you know if things change--hopefully for the better.

Good luck!  Man, I remember the sound of your speakers--lovely and clear.




DrJ-10

  • Jr. Member
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Re: Room Acoustic Treatment
« Reply #2 on: 3 Oct 2020, 11:05 pm »
Bob,

Thanks for the reply!  I was concerned that no one would have any idea what the Bevs are, since they are very old now.  But they still are lovely, with very unique radiating characteristics.

The only feature on the 9' wall is a fairly large window that is not particularly good, and for WAF reasons that has to stay open.  The compromise was a heavy drape that is easy to open and close.  I will say that in general that MrsJ is very good about stereo "stuff," and loves the music.  The corners are available for treatment.

Currently the speakers are against the long walls facing each other, and about 5' from the front wall.  So most of the frequency spectrum is originating about 2' from the side walls.  The woofers are about a foot from the side walls, and cross over at about 200 Hz, which should roughly be the Schroeder frequency of the room (I've not calculated it yet).  I realize that I will have to play with the spacing to the front wall and to the side walls, and the subtended speaker arc.  And no, I've not measured the room RT60 yet, as without much in it at the moment it would be terribly live.

Otherwise, we have the usual bookshelves that we can use in addition to "real" acoustic materials.

There will be no wall behind the listener(s) -- we just took that out for may reasons.  So nothing will be done for that.  Also, there is little furniture required in the room, so there will be no couch -- free-standing chairs only -- and no coffee tables and the like.

I'll have to look up the GIK terms -- I'm not that familiar with them -- but I figured that this would be the best place to ask my questions.

DrJ-10

  • Jr. Member
  • Posts: 29
Re: Room Acoustic Treatment
« Reply #3 on: 3 Oct 2020, 11:46 pm »
Bob,

It sounds like (pun intended!) that you have a great space to work with.  I wish I did, but our house is very small and has no basement, a downside of living in CA.

I'd appreciate it if you would post some pictures when you are done, or nearly so.  I find I have a hard time visualizing what traps go where and how high they are.  Thanks!

Bob Stark

Re: Room Acoustic Treatment
« Reply #4 on: 4 Oct 2020, 11:59 am »
Give me a couple weeks to finish the area and clean it up so you can see various things a little better and I'll get some pics on.  My brother Steve has been a great help in doing this as he is a contractor and has a small business he runs.  He came in and worked with me on the whole basement build along with the music room for several days and even weeks at a time and we built some very cool things in a basement that I did about 1/3 of the finishing 13 years ago.  I needed much more space for records, CDs and cassettes for storage and future purchases.  I did about 2/3 of this room back then.  I've been researching and talking to some knowledgeable people such as Roy Johnson of Green Mountain Audio (speaker maker) about how to do the combination angled corners with bass traps behind the huge cabinets and trying NOT to screw up what has been very good sound up to this latest effort.  Right now, I'd say the sound is bordering on the too polite side.  I really hope that the cabinets restore some of the live sound that was in the room previously.  It's a funky looking room and very much my space to fool with.  My wife wanted me to keep the stereo in the basement so it didn't mess with the living spaces on the first floor. 

I'll get back to you at the close of this listening room project.
Bob