New HT Project: Construction questions

[DucatiR]

Thank you in advance to all those who have posted and replied before me. Your comments and information have helped me tremendously as I've progressed from the dream to initial design. This is my first post so please be patient with me.

I have listed a couple of questions directly below with additional project details following. Apologies if these questions have been addressed already - I did try some searching first. Appreciate your feedback at this initial stage - I am sure there will be more questions to follow!

Thank you!! DucatiR

1) Room: do I treat 'hipped' ceiling (see attached pic) any different than rectangular room when calculating 'good-sound' room dimensions?

2) Floor: 2x8 joists in pre-built bonus room trusses over garage. Have searched but having trouble finding devices to isolate the theater room floor. Found Hush-Felt products out of UK. Also Kinetics KIP pad at ~$2.50 ea. Not sure I like the performance of rubber - significant worry? Suggestions on floor isolation??

3) Projector noise: Is projector noise an issue? I was thinking of a lift (until I looked at prices ) or a self-contained, exhausted enclosure. Do I need to worry about that?

Existing building:
- unfinished bonus room over garage separated from 2nd floor rooms by ~22' open trusses
- separation from 1st floor rooms ~6' horizontal
- truss dimensions: 12'x32' floor; 54.75" short wall to 'hip'; 46.5" flat ceiling

Current concept (no hardware decisions yet)
- retrofit damping to garage door openers
- new bonus room 20'L x 11.5'W x ~7.5'H seems to work with on-line spreadsheets I found
- front row seating ~70" from back wall
- riser made of mdf on isolation mounts
- 1 layer 5/8" wallboard mounted to RSIC-1(?)/channel with full insulation and acoustic sealant for walls
- minimal wall penetrations except track lighting input, speaker drops, air duct and doors
- air duct baffles and 180 deg duct turns; possible lined ducts
- min solid core doors with weather striping and threshold drop; possible custom self-made doors
- isolation for ceiling wallboard
- false ceiling for fiber optic and rope lighting; suspended conduit for HDMI/etc cables to projector
- 110" AT screen with LCR speakers behind screen; possible curved screen
- possible anamorphic CIH projection
- separate equipment room for hardware, light generator and, er, refreshment refrigerator

[tenzip]

Wow. Very nice blank canvas. Minds me of the "Bat Barn" on avforums.com in the UK, except his is open to the peak. If you go look at that thread, make sure you have a couple of hours to spare. I think it's 70 pages or so.

I'll not comment further, except to say Welcome!

[bpape]

If you're only tied to the garage trusses, it's not likely as much of an issue. You could simply do subfloor, a good iso mat, and then another layer of subfloor.

Slanted ceiling - from a calculation of required decay time, you'll just use the average height. From a standpoint of calculating room modes, good luck. You'll need some very complex software to do it - much more than you'll find as a freebie on the web. Do the best you can with length and width

PJ noise can absolutely be an issue. There are a few of them that are very quiet - not sure what you're looking at exactly. You can certainly do a hush box with one of the cold air returns from the room in/by it.

Bryan

[hddummy]

1) I'm not an acoustics expert, but I would suggest you use the regular L,W,H dimensions of the room regardless of the hipped ceiling. The possibility of a standing wave will still exist between the floor and the horizontal portion of the ceiling. The hips just work to reduce the area of parallel surfaces and, I think, would help reduce the possibility/affect of standing waves.

2)what bpape said

3)what bpape said, except I would suggest trying without a hush box first and see if it bothers you. Otherwise, you could plan ahead so you know how you could add a hush box after the fact with minimal effort.

question: maybe I would need to see a picture of the house from the outside because with that roof shape, I'm picturing a garage as a peninsula off of the house. If so, why put so much effort into sound containment if you are out over a garage and probably only one side open to the rest of the house. If you are trying to keep outside noise out, then I guess OK, but if you just trying to keep theater sound from intruding on the rest of the house, would it really be an issue?

otherwise, welcome to the shack. This looks like it will be a really good project. I hope you can give us regular updates. Also, have you given any thought to doing an IB sub? those areas of space outside of the short side walls are prime targets.

[Prof.]

Looks like it will be a nice project DucatiR..which I will follow closely..and if you look at the "Bat Barn" as tenzip mentioned, you should get some good idea's from that..

Also, If you decide to go anamorphic..we'll be able to help you get setup for that as well..

Good luck with it all..

[MatrixDweller]

1) Non linear surfaces are better for acoustics, so a vaulted ceiling is superior to one that is parallel to the floor. Most calculators you can download don't do the complex stuff like that though.

2) I guess it depends on what's underneath that room. If it's a garage then noise transferring into the garage is not really an issue. It would be more the noise coming up into the theater room. Double drywall on the ceiling below and joists packed with Roxul would be a good start.

A double subfloor of 3/4 plywood or OSB would help also. Use glue and floor screws. You could sandwich some mass load vinyl in between the layers but that would be prohibitively expensive. I'm not sure if Green Glue is recommended, but a viscoelastic layer between the two subfloor layers would help a little bit. Mass is your friend when it comes to soundproofing. Isolation helps but mass is the key. More mpact noise should be attenuated by using good carpet and underpad.

3) Some of the newer projectors are whisper quiet. If noise is an issue then take a look at the specs and choose one that has very low fan noise. You could also build a hush box around the projector, but make sure that the projector is still getting adequate air flow or you'll shorten the lamp and possibly the projector life. Most home theater projectors don't need one in my opinion. You will actually tune out the whisper of the fan (psychoacoustics) for the most part.

[bpape]

Just remember that if you really want isolation, just doing the ceiling without the walls won't help a lot. Sound will flank around to the easiest path - in that case, the walls, and all the associated holes for outlets, switches, etc.

Bryan

[Space]

DucatiR wrote:

DucatiR

Existing building:
- unfinished bonus room over garage separated from 2nd floor rooms by ~22' open trusses
- separation from 1st floor rooms ~6' horizontal
- truss dimensions: 12'x32' floor; 54.75" short wall to 'hip'; 46.5" flat ceiling

Hi DucatiR,

I'm going to play the Devils advocate here. This isn't an unfinished room, this is a truss roof. A gable roof as the picture shows with the flat wall at the end studded up, as gables are. What you are suggesting is not going to be a "doable" project without a lot of intervention.

Please let me explain.

All the metal gang plates on the framing members are designed and calculated for a specific job. That job is to hold the members together. It was not taken into consideration that this area would be used to carry a live load. And it is not recommended.

As the picture shows us, there is a connection with plates on the joists on the left and right hand side, close to the verticle webbing of the truss. This would have to have some support from underneath, and that would come only after your plans were approved by the locals.

Then there is the issue of all the additional weight that isolation requires.

Granted, these things may have already been taken into consideration. If that is the case then I'm just wrong, and it isn't the first time

[DucatiR]

Thanks all for the comments and suggestions. I have a couple of follow-up questions and some more information in response to several of the posts.

4) I've seen a few posts, some by bpape if I recall correctly, suggesting that in-wall speakers can be ok acoustically (more realistic surround pan?). In-walls and IB would represent a significant wall penetration - yes? Or do I build isolation/insulation boxes behind the wall to contain the speakers?

5) IB sounds intriguing and I will research that further particularly after seeing the Bat Barn (nice!). But wouldn't that bass use the entire open space behind the walls and the other attic space as a resonance chamber? Then I have serious LF bass impacting the back side of the 2nd floor living quarters (see attached diagram).

Sounds like I'll just be doubling up the floor with something in between the plywood/OSB without isolation. Saves me some money and work. There is already blown insulation in the entire space. Adding sheetrock to the existing, finished garage ceiling would be very complicated. Good advice to start without a hush box but plan for one just in case.

hddummy asked about the overall house configuration. Please see the attached diagram. The connecting attic space between the 2nd floor of the house and the HT space is open web trusses. 22-24' separate the 2nd floor wall from the nearest wall of the new HT room. I may end up being a little conservative on the build: if my family comes up to the HT and asks me to turn it down then I've wasted a lot of time and effort.

Space brought up a good question re: truss design/loading. When I built the house I spec'd these bonus room trusses but didn't have enough money to finish it at the time. I've already been reviewing some engineering work with the truss company so know the trusses can handle the load.

Thanks - DucatiR

[salvasol]

DucatiR wrote:

Sounds like I'll just be doubling up the floor with something in between the plywood/OSB without isolation. Saves me some money and work. There is already blown insulation in the entire space. Adding sheetrock to the existing, finished garage ceiling would be very complicated.

I don't think is neccesary to double up the floor because is above the garage so you will not bother the cars ... also, if you already have blown insulation in the entire space is okay too, as long as there's no hollow walls or you'll have a resonance problem (that includes de floor too)

.... The connecting attic space between the 2nd floor of the house and the HT space is open web trusses. 22-24' separate the 2nd floor wall from the nearest wall of the new HT room. I may end up being a little conservative on the build: if my family comes up to the HT and asks me to turn it down then I've wasted a lot of time and effort.

Is there any way to build a small room/space between the 2nd floor wall and the HT wall??? ... WHat I mean, is to create an air gap between them to try to isolate the sound. I remember reading that somebody used a double door between the HT and the rest of the house (that in the same wall) and helped with the sound ... in your case maybe you can create a small room