HT reconstruction: lively but not boomy. Thoughts & concerns

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HT reconstruction: lively but not boomy. Thoughts & concerns

Postby Jacob b » Thu Apr 22, 2010 12:14 pm

I am planning the acoustic treatment of a rebuilt 7.1 home theater, which will serve a secondary purpose of 2 Ch listening room.
I have attached pictures of HT before rebuilt and the bare room after modification. Room dimensions: 20' x 13' x 8'. Beams in ceiling are 4" high

For sound insulation purposes, I have added 2 xtra layers of ½" drywall to the ceiling and walls, with green glue. On the sloping ceiling I added 10cm/4" of insulation for energy purposes, making the room slightly smaller. On the floor, I put 10mm rubber mat and 2x16 mm OSB with green glue.
The window will be covered up with a removable panel made of 2x ½" OSB with green glue, with 2" fiberglass behind - mounted flush with the frontwall.

My old room had what I now realize was crude diffusion on the short side walls, made out of 3½" wide and 3/4" thick wooden strips mounted on two horizontal 1"x1". There was also book shelves on the right side (diffusion, but no symmetry). All side walls and sloping ceiling had Jute hessian tapestry. The room sounded a little dead as well as boomy. I never liked the sound of music in there, but movies, including dialog, was ok. I suspected the hessian tapestry to absorb somewhat in the high freq.
Jacob_HT_old picture.JPG
Old HT room
Jacob_HT_old picture.JPG (75.09 KiB) Viewed 2599 times


I want the new room to be lively, yet have clear dialog on the movies. Of course no boomyness. The new room will have a false screen wall with SMX acoustic transparent screen, and two rows of Berkline 090 HT chairs with leather, 2nd row on 20" riser.
Front wall_HTv2.JPG
Modified HT room
(96.41 KiB) Not downloaded yet


I have read the FAQ. I have read the Acoustic master thread on AVSforum.com. I am confused on primarily 1st reflections as well as the use of diffusors in my small room.

Planned treatment:
1st reflections:
The plan was originally to treat front wall with 2" OC703 and sidewalls front 2/3 of room and 4' up with 1" OC703 for 1st reflection treatment. The 1st reflection points for 2nd row will have 1" treatment up to 5½'
Ceiling to be treated with 1" OC703 at 1st reflection point (between 3rd and 4th beam on picture). This plan seams ill adviced now, but reflected the general wisdom at the time on the AVSforum.com (plan made spring 2008).

Combined RFZ, bass trap and crude diffusion:
On sloping ceiling, 6"x 48" 2" OC703 panels framed with 3½"x1" wooden panels, leaving 1½" of air behind OC703. These panels will be placed vertically and spaced with 8" between them (and they are 8" wide including framing). I plan to cover the 8" wide empty slots with GOM FR701 to match the panels, to create a homogeneous look.

Bass traps:
All 4 lower tricorners with 17"X17"x24" superchunks up to sloping ceiling. In addition, the front wall will have 1' x 1' square bass trap along the floor-front wall corner.
Furthermore, 4" OC703 between the ceiling beams bordering the front and rear wall, to cover the two- and tricorners related to the ceiling and front/rear walls. On the front wall I will add standard corner absorbers (4" OC703) on sloping ceiling as well as ceiling-front wall corner.
To counter ringing at the primary seating position, I plan 4" OC703 between beams right over head (primary) 1st row, as well on the side walls right next to the row, and on the center rear wall at ear height.

I HAVE TWO FEARS:
1. The room will be too dead for my likening. Especially since all walls and ceiling will be covered with GOM FR701.
2. I will mess up the tonal balance of my speakers by absorbing too much high freq.

MY FRONT SPEAKERS (three identical) use a concept called "sound stage enhancement", which uses two venting ports on the back to send high and mid freq backwards for front wall reflection. Front wall treatment will kill the purpose of this concept, and I don't know what I gain instead. :( :?
See http://www.audiovector.com/technology.html# and picture:
s3backlcoseup.jpg
s3backlcoseup.jpg (6.67 KiB) Viewed 2594 times

My Surrounds are MK SS150THX tripoles, if that has any influence on the plan.

Possible solutions (some can be combined):
A. Change the side wall 1st reflection design to 4" or 6" OC703 panels, and try to cover the majority of the seats with only two 2'x4' panels on each side wall.
B. Change ceiling treatment to 4" treatment at 1st reflections.
C. Change ceiling treatment to include 4" treatment between ALL BEAMS, but cover some or all with a thin membrane underneath fabric, like plastic glued to the OC703, or a perforated 1/8" massonite sheet.
D. Add membrane or perforated 1/8 massonite sheet to sidewall and rearwall treatments.
E. increase distance between the 8"x48" frames on sloping ceiling to accommodate DIY polys and don't cover with GOM here.
F. Add diffusors on the rear wall (2½ feet from 2nd row, 8' from 1st (primary) row). Polys or QRD types? And I still want absorption in the center, right? Can I use RealTraps Diffusor for this purpose?
E. Don't know about front wall:
1. keep 2" treatment
2. remove completely (keep basstraps of course)
3. make 4" treatment right behind each front speaker and leave rest of wall untreated (this will leave 33 % untreated horizontally and 25 % untreated
vertically, when including the corner bass traps in the calculation)

I would really appreciate any comments and help, as the knowledge here seems awsome - and you are not trying to sell me something... :D

Cheers,
Jacob b
Denmark
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Re: HT reconstruction: lively but not boomy. Thoughts & concerns

Postby Jacob b » Mon May 10, 2010 9:36 pm

Come on, take the bait :D

Seriously, I would really appriciate a few comments.

Jacob
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Re: HT reconstruction: lively but not boomy. Thoughts & concerns

Postby Scott R. Foster » Mon May 10, 2010 9:38 pm

fewer thicker panels - then stop and listen
SRF
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Re: HT reconstruction: lively but not boomy. Thoughts & concerns

Postby Jacob b » Mon May 10, 2010 9:40 pm

Thanks scott!
Jacob b
 
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Re: HT reconstruction: lively but not boomy. Thoughts & concerns

Postby Scott R. Foster » Mon May 10, 2010 9:45 pm

ubetcha!
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