Modman's discreet inwall atmos home cinema remodel

Modman2017

Standard Member
Good evening folks,

I've posted this to get some ideas / critisim and guidance from likeminded enthusiasts. This is the first time ive undertaken a big project like this and to tell the truth in abit over my head.

Currently in the middle of a project turning my living room of a 1930's semi into a discreet home Cinema, with the aim of creating a Dolby atmos 5.1.4 setup. The main tv wall is a centrally located chimney breast which we have boxed out with studding to create a recess in which the tv (Samsunng 49" Q7F hopefully) will sit in along with 3 LCR speakers from Kef (ci4100's) will be left right and centre (below tv for better listening ear height).

The studding is backed with an acoustic rubber against the existing chimney breast and secured to the wall with 90 degree acoustic brackets to decouple. The builders opening for the fireplace has been brought forward so the new cast iron arched gas fire place is flush with the soon to be plasterboarded studding. I've read somewhere that to get a 'live' sound from the tv wall i shouldnt instulate it, whats the consensus on this if any?

After seeing many amazing builds in the forum ive decided to go the whole hog and install an acoustic ceiling with genie clips furring channel 19mm soundplank plasterboard and 15mm acoustic plasterboard with some tecsound membrane sandwiched inbetween the two layers of plasterboard (alternatives welcomed ,not sure on the whole green glue thing) floor above is 18mm pine T&G. The reason is two fold, to stop sound escaping into the room above and as the joists link to the party wall protect the low frequency noise from annoying our elderly neighbours.

I wanted to know if the ceiling joists would be able to take the weight of all this plasterboard without sagging. The joist dimensions are 7"x2" spaced on average 300mm apart with a span of 3.4m, the wood species is not know .

Ive ripped down the lath and plaster ceiling, sealed underneath the floorboards with AC50, stuffed in some rockwool RW3 100mm 60kg/m3 between the joists leaving an air gap above, put in some cross members to strengthen and stop the joists from twisting any more than they have.

My next job is to work out my 4 height speaker positions based on Dolby's recomendations. Im thinking two in the centre of the room and two rear heights just slightly behind/above listening position. Speakers will probably be Kef CI200RR-THX's.

With the current ceiling design would an acoustic speaker hood work well or would a speaker box (kef recommend 0.71 cubic feet)made from some marine ply&chipboard work better? with the thickness of all the plaster board i think id have to modify the dog legs on the speakers to accomate it all.

Another part of the build would include an underfloor subwoofer with tubes and vents underneath where the sofas will be as we have a raised floor with about 1 1\2ft gap. Possibly a buttkicker in the sofa itself for extra oomph . Has this been done before ? help or ideas are welcomed on this.

Oh and i've got my work cut out, missus wants it completed before Christmas....2019.
 

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derekhansen

Active Member
With regard to the ceiling bearing the plank and acoustic plasterboard layers, your combination of joist depth and spacing sounds ok especially as you have removed the lath and plaster which is pretty heavy. If still in doubt try talking to a building control officer at your council or get a structural engineer to give their opinion.
 

Modman2017

Standard Member
Thanks Derek,

Appreciate your comments mate, yeh I'm glad we decided to rip down the lath and plaster although it was a messy job. General consensus from a few ppl is that the ceiling joists are adequate. I'll crack on and post a few more pics with progress.
 

Ronski

Well-known Member
I'm sure you're joists will be fine, 300mm spacing is quite narrow, as is 3.4 meter span.
 

Modman2017

Standard Member
Thanks Ron trying to replicate what you achieved, what a headache the furring channels are trying to get them square when all the walls seem to be out, but I'll get there. After using green glue on your build would you recommend it over the tecsound type membrane? Thanks for your earlier advice btw
 

ash23t

Active Member
If you don't mind me saying, you are going to a lot of trouble for a 49" tv.

What is the shape of the room? Can you get a projector lift/ceiling mounted projector one side and a projector screen the other? That would do true justice to your efforts.

if not then a larger TV (can use a tv lift/picture lift etc to hide if needed).

Also are you soundproofing the alcoves on each side of the chimney? I would also check for any blown plaster and remove it and re-do to make the brick walls airtight.
 
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