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Discussion Starter #1
First real post, and building my first HT which I want to do properly so that I won't need to do it again. Thanks for all the hints picked up already!

Its 7.2 x 4.4m, downstairs, below the main living area. Currently working on the ceiling installation. I intend to use two layers of 13mm fire-resistant plasterboard on furring channels suspended by resilient mounts from the underside of the existing hardwood floor joists. These are 120mm x 50mm, with 19mm tongue and grooved hardwood strip flooring fixed to the upper surface. I will use 50 or 75mm thick acoustic insulation matting between the joists, but i am first installing 4kg/m2 mass loaded vinyl to the underside of the flooring and sides of joists in an inverted wide U. I am attaching the MLB to joists and flooring with foil-fixing clips. I can install closely to the three wooden surfaces, which looks nice and neat and won't let the MLV sag onto the acoustic matting. Alternatively I can cut it a bit over-wide and leave it somewhat saggy. I figure this more limpid state might allow the MLV to do it's job better, but it might touch to upper surface of the matting in places. See photos of the tight and loose options - which should I go for?
 

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Yay for another build thread! :yay:

I am by no means the expert here, but I think tight will work just fine. The main purpose of MLV (as I understand it) is to reflect higher frequencies and allow low end frequencies to be absorbed by whatever is behind it. I do not believe it would matter if it is tight or saggy, so I would avoid allowing it to touch any surface that would allow for transmission of sound (vibrations mostly) to areas you do not want it to go.
 

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Discussion Starter #3
Thanks Joe, and sorry about the long silence. I was hoping to get the MLV fixed before starting excavation, as the former head height was quite convenient for this little job. But contractors arrived and it's been quite hectic with excavation, installing strengthening beams, new steel pillars and preparing footings for block retaining walls and slab - see photos.

In the meanwhile I found installation instructions at The Soundproofing Company's website which quite clearly confirms your opinion that there is little difference whether MLV is taut or limp - so taught it will be, when I can get back to that job in a few weeks time, but unfortunately will be working from a plank! But can't complain, it's all powering ahead here.
 

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Discussion Starter #6
Yes, quite a project. My front lawn has disappeared, I have no front steps and my doors wont shut properly in the process, but a great outcome will justify the effort, disruption, time and $$, as long as decisions taken along the way are good - i.e. with the help of the Forum! .

Can I change the name of this tread to follow the build job through, or should I start a new one?
 

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Discussion Starter #11
Thanks! Here's the overall plan for the new lower floor. The HT 'media room' is only part of it - I needed to include other functional areas to sell the concept! While there is a lot of utilitarian space, access to the HT from the main living area upstairs will be quite direct and quick via the staircase.

The HT room will be 7.17m x 4.38m x 2.64 internally, pretty close to the audiologically desirable golden cuboid ratio of 13 x 8 x 5. I realize the ratio alone won't ensure an ideal outcome, but I am hoping that it will give me a good starting point.
 

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Are you building a basement theater? Looking at the pictures I am confused... You lost your front yard. Was there a landslide or is it just from excavating for the Home Theater?

It def looks like a seriously $$$ project!
 

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Discussion Starter #13 (Edited)
Yes, all that spoil in the front yard has been excavated from under the house. As you can see from the view from the street in the earlier post, the house was built on a sloping block, so that the depth of excavation goes from nothing on the left side to about 2m on the right side, so there was 100+ cubic metres to remove. Reinforcing steel bars for the retaining wall footings are in now, ready to pour:
 

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Discussion Starter #16
Apologies for another long silence. My wife and I were away on a work/holiday trip to Europe for a month. I found it a bit scary leaving the builders unsupervised for all that time, but it has worked out OK and the new downstairs area is now ready to sheet in. Here are a few shots taken in the past week:

1) acoustic box behind power & AV outlets in double wall
2) after adding a bit of fibreglass insulation around the front edge (thought it might be useful as the wall sheeting is attached to Rondo 581 resilient channel: I hope the insulation might at least partially prevent some leakage through the wall from the outlets)
3) mass loaded vinyl between ceiling joists and a little down the wall, also showing the 581 channel
4) Studco resilient mounts suspended from joists, with attached 308 furring channel (to which ceiling will be screwed)
5) boxing and insulation around the beams
6) general view of walls with resilient channel and 11kg/m2 fibreglass acoustic insulation
7) general view of ceiling with 308 furring channel and acoustic insulation
 

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Discussion Starter #18
Emkay.

Where are you planning on putting all your media components?
Planning on having these out in the open on a stacked stand. Not de rigeur for HT I know, but I want to be able to get at everything and keep it cool. I have some serious power in the amps.

But I think I have struck a serious problem. The room was sheeted in yesterday with 'Firestop' plasterboard (drywall) - 2 x 13mm layers on the walls with greenglue between, and 1 x 16mm layer glued and screwed to the 308 channel on the ceilings. The walls are great, solid and not drummy at all. But when I thump the ceiling, I get a sort of metallic vibration. I guess it's the 308 channel moving within the clips of the resilient mounts? Will this be a problem in use? I can't stand the thought hearing some vibration at certain frequencies after it's all done and occupied!

I have already ensured that the current ceiling sheets are hanging fully from the channel, not binding on the adjacent walls. Perhaps I should add another layer of plasterboard (and use my leftover green glue between) - thinking that I might stop any vibration by increasing the suspended weight of the ceiling on those clips.

Will this work? or am I worrying about nothing?
 

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Discussion Starter #20
I would go ahead and do the second layer on the ceiling
Thanks - doing just that, tomorrow. Using 13mm firestop for the second layer, staggered joints, green glue between. More $$ but I'd rather be sure than sorry, and the extra isolation must be a plus whether or not vibration would have been a problem.
 
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