# Emkay's HT Bunker Build



## Emkay (Nov 16, 2012)

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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## ALMFamily (Oct 19, 2011)

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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## Emkay (Nov 16, 2012)

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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## ALMFamily (Oct 19, 2011)

Wow - that looks like a serious project!


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## Wardsweb (Apr 2, 2010)

ALMFamily said:


> Wow - that looks like a serious project!


You can say that again!


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## Emkay (Nov 16, 2012)

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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## ALMFamily (Oct 19, 2011)

Sure, what would you like the title changed to?


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## Emkay (Nov 16, 2012)

Lets go for:- Emkay's HT Bunker Build


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## ALMFamily (Oct 19, 2011)

All set mate!


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## Prof. (Oct 20, 2006)

This looks like a serious project with a nice size theatre..:T
I'll be following along with interest..


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## Emkay (Nov 16, 2012)

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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## NBPk402 (Feb 21, 2012)

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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## Emkay (Nov 16, 2012)

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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## Emkay (Nov 16, 2012)

Still progressing, but slower than planned because of wet weather.


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## ALMFamily (Oct 19, 2011)

Looks like a great start mate - hopefully, you get a stretch of dry weather so progress can be faster!


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## Emkay (Nov 16, 2012)

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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## mcascio (Dec 5, 2010)

Emkay.

Looks like you are going to have a really nice space to work with.

Where are you planning on putting all your media components? Like amplifier, receiver, bluray player, etc.


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## Emkay (Nov 16, 2012)

mcascio said:


> 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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## ALMFamily (Oct 19, 2011)

If it were me mate, I would go ahead and do the second layer on the ceiling. That is going to be the weak point anyway - with all the footsteps above, it will help keep sound out as well as in...


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## Emkay (Nov 16, 2012)

ALMFamily said:


> 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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## MrAngles (May 1, 2012)

I noticed the same metal vibration after putting my first layer of drywall up on the ceiling, even sometimes when walking on the floor above. Putting the second layer up completely got rid of the noise.


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## Emkay (Nov 16, 2012)

MrAngles said:


> Putting the second layer up completely got rid of the noise.


And it seems to have done the trick for me, too. I guess I will only be sure when the system is eventually fired up, but it certainly doesn't make that noise when I thump it now. We finished up with 16mm + 13mm Firestop on the ceiling (total: 23.5 kg/m2) and 2 x 13mm Firestop (total: 21 kg/m2) on the walls, both with Green Glue in between. Total GG used was two 5 gallon pails + ten tubes, which is pretty close to the '2 tubes per 8x4 sheet' standard rate.

Pics show 1) the cross-section through the doorway wall,
2) the same wall from inside the room - ready for paint this week after plasterers' return for their final sand,
3) the end wall with the window. I was forced to include the window by building regs, as it is classed as a habitable room, but I intend to put a plug into that space after final inspection, hoping that it will be ínvisible and inaudible after that. 

But I have many questions about appropriate audio treatment. I have attached a rough drawing of the anticipated speaker and listening/viewing positions. Floor will be heavily carpeted. The main speakers are Magnepan 3.7s, see:
http://www.magnepan.com/model_MG_37 These are dipole speakers, radiating as much sound from the back as the front and requiring significant distance from the 'front wall' behind them. I am inclined to install floor-to-ceiling bass traps in each corner and some mid-high frequency absorbing panels at main reflection zones on front, side and rear walls, but I am concerned that I could easily overdo this for these dipole speakers. Perhaps diffusion on the front wall, rather than absorption? Does anyone have any experience with them in rooms like this, and can advise on likely appropriate amount of acoustic treatment?

I also thought that I might need some absorption on the vertical faces of the ceiling bulkheads?

And I had intended to defer buying a projector and projection screen, and make do' with my 50' plasma panel for a while. But I am concerned that the plasma panel sitting between the maggies might interfere with the creation of the wonderful 3-dimensional sound stage that I know these beauties are capable of. Í will use this room as much for stereo music listening as for HT, so I would appreciate comment on the likely effect of that plasma panel there.


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