12-10-2006, 01:17 PM
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Frank Pirz
Member
Join Date: Dec 2006
Local Time: 12:09 PM
Local Date: 11-18-2008
Posts: 1
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Construction Started, Need advice on speaker placement to Continue
The Room
I've started finishing a basement room. I'm at the point where I need to finalize speaker
positions so I can place wiring in the walls for surrounds, lighting and outlets.
Included in this posting are several drawings (floor plan, side wall, front/screen wall)
http://www.avsforum.com/avs-vb/attac...chmentid=69686
http://www.avsforum.com/avs-vb/attac...chmentid=69688
http://www.avsforum.com/avs-vb/attac...chmentid=69689
of the room. Overall the room is 13'11" x 21'3". The rear wall is the concrete foundation
wall. It has been covered with conventional 2x4 studding and fiberglass,primarily for
thermal insulation. The left and right walls conceal steel columns that support I-beams.
I used 2x6 studs for the header and sole plates and 2x4 studs for the walls placed on
alternate centers for isolation. 6" thick fiberglass insulation was woven between the
studs for sound proofing. The rear wall is conventional 2x4 construction with 3.5"
fiberglass insulation. My floor joists are wooden I-beams on 20" centers. I'm using 24"
wide 6" thick batts of fiberglass insulation placed between the joists.
There is a return air duct along the right hand side of the room. That will be enclosed
in an insulated soffit. The spaces between the joists above each if the I-beams have been
blocked off on both sides and filled with insulation. We went beyond what was required to
meet fire code in an attempt to minimize sound leaks. The soffit will be constructed from
MDF (Medium Density Fiberboard) and painted. For aesthetics, a second soffit will be
constructed on the opposite side of the room. The soffit does not extend to the screen
wall, but could be. I felt it would be better if I did not have to box in the ceiling
area near the screen. A hung (Drop) ceiling, using acoustic quality tile, will be
installed 6" below joists.
False Front Wall
There is no convenient place to locate an equipment rack in the room. I've chosen to
create a false front wall located 2'3" out from the rear wall [to align it with a ceiling
joist]. The wall will be constructed with a minimum of framing and with removable panels
covered with cloth. I've attached two designs showing different front wall layouts. In
the first there are two equipment racks located in the bottom corners of the wall. In the
second design the equipment bay is moved to the space below the screen, the Center
speaker is aligned with the L/R speakers behind the screen. The subwoofers Are moved to
the corners of the room. In either design, the equipment bay will be fully enclosed and
positively ventilated using quiet 120mm fans. The exhaust air will be ducted to basement
rooms on either side of the theater that are not used when the theater is in operation.
The wall is constructed on a false stage. Really false since I only intend to cover over
(floor) the 9 inches that sticks out in front of the false wall. The part behind the
false wall will be open framing.
Screen
For the first design I've chosen a 52" x 92" Da-Lite Cinema Contour Screen in fixed
frame. It has a 106" diag (nominal). That's a 16x9 format.
For the second design I'd have to use a Cinema-Perf screen, or go with an SMX screen
since I'm placing a speaker behind the screen.
The Da-Lite frame adds 3" all around the screen giving a 58" x 98" frame dimension.
The frame is mounted in 6" deep shadow box with 3" around the frame for clearance
giving 64" x 104" shadow box inside dimensions.
Speakers
A local dealer was offering a HDTV "Package" for a room that
is approximately the same size as the one I'm building.
The speakers they used were:
B&W VM1 L/R/C Front 20.6h x 4.8w x 3.7d
B&W CCM-20 Surround (discontinued) 8.9dia x 2.9deep
(2) B&W ASW300 Subwoofer (100w@) 16h x 13w x 14.8d (add +2d)
For no particular reason, I've used the following (larger) speakers in this layout.
B&W DM604 L/R Front 39.1h x 9.3w x 15.7d
B&W LCR60 Center 6.9h x 18.1w x 12.2d
B&W CCM-50 Surround (in place of the CCM-20) 7.9dia x 3.1deep
Choosing speakers is a topic for a separate discussion. The design can accommodate a
range of sizes with the current placements.
Surround Placement
Because of the Soffits on either side of the room, my headroom is limited to
7 foot in the area where theater goers walk into the theater. Mounting the
Surround speakers on the wall would create "head bangers". Instead, I've chosen
to build false columns and use speakers recessed into the columns. There was
not enough room to put them into the soffit with the return air duct. Putting
them into the hung ceiling would move them too far into the room. The columns
are 12" wide and 6" deep and will be made from MDF and filled with insulation.
For aesthetics, there is a third set of columns in the room. Column spacing breaks the
wall into three equal sections. I'm thinking of putting wall sconces on the front two
columns.
My Questions:
I created the first design (center speaker below screen) because I was concerned
About moiré patterns when using a digital projector on a screen with holes.
The subwoofer placement will not be in the corners of the screen wall because of where
the equipment bays are. The center speaker is below the screen centerline by 3'3". While
it can be angled to point it up towards the listening position I'm not happy with it that
far out of alignment from the L/R speakers. The second row of seats does not have a
direct sound path since the first row of seats blocks their line of sight to the center
speaker. While I've seen some designs with the Center speaker above the screen that's not
an option here because of limited ceiling height.
The second design uses a Cinema Perf screen, or an SMX screen, and puts the center
speaker behind the screen. I've moved the equipment bay to the space directly under the
screen which permits the sub-woofers to be moved to the corners of the screen wall.
I'm not happy with the surround speaker placement, which is the same in both designs,
but don't see any reasonable way to do much better. The back row of seating puts the
person closest to the wall directly under the 7.1 speaker. That can't be helped.
So which design do you think is better?
Speaker behind the screen (design 2) or speaker below the screen (design 1)
How much weight do I give Subwoofer placement in the two designs? I've heard that corner
placement is better. Is that true?
In practice, is Morie a problem? The SMX website says no (assuming I tilt the axis of the
weave).
Should I place the surrounds differently? Should I ignore aesthetics and use a different
column spacing to give different (presumably better) placement angles?
Frank Pirz
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