your contractor is full of crap. Containing low frequencies requires mass dampening and isolation his proposed design doesn't have it. Here is my talking point when I meet with contractors
Contractor construction notes
Building a Drywall sound isolation shell
High Performance Home Theaters
Four principles of sound Isolation are utilized:
MASS - ISOLATION-ABSORPTION-DAMPENING
Electrical- Theater Room
- Loose fill insulation in walls and ceiling
- two layers of 5/8 heavy drywall
- Green Glue dampening compound between layers
- Drywall installed on a clip and hat channel isolation system with 1 1/4 and 2 inch long screws for first and second layers respectively
- Clips and channel spaced per vendor specifications, no more and no less. Clips staggered on all available studs and joists, additional studs will be required in all inside corners for adjacent clip clearance.
- Channel is 25 ga 7/8 inch tall furring channel (Hat channel) do not use 22 ga
- Install drywall in sequence that results in a cascading joints and overlapping seams. First layer ceiling, then first layer walls, second layer ceiling, second layer walls.
- Every hole cut in the drywall shell needs to addressed with a backer box, a putty pad, acoustical caulk or by other means. This includes items such as outlets, switches recessed light fixtures, in-wall speakers. Where possible these items will be installed inside the theater shell by passing wires through small holes which caulking around the holes.
- Items such as seating risers, stages, soffits will be built after the drywall shell is constructed unless they are required to hide piping or ducts. In those cases the covering of the soffit will be the same construction as the sound isolation walls and ceiling.
- If walls are non load bearing frame the walls one inch short to the ceiling joists and securing the top plate with IB3 clips spaced at the end of the walls and every 48 inches. Add additional clips above the hinge side of door framing. This will improve vibration isolation
- Consider double wall framing or staggered studs for critical walls where sound isolation is critical, bedrooms, stairways etc.
- Minimum of 1 1/2 inch diameter electrical conduit to projector location from equipment stack location - for future cable swaps as HDMI standards change.
- No wall penetrations for speaker wire wall plates just caulked holes.
- Consider wiring for convenience connections, Cat6 for network, game connections at front of riser. Run in conduit and down to riser inside speaker column. Inside riser run to the front face.
- Thermostat wiring through hole in wall, caulked
- Wiring for temperature sensor inside hush box (if any) to utility room and future exhaust fan, based on selected fan.
- Projector outlet connected to power inlet in equipment stack location , not breaker box
- Recommend all other outlets mounted inside theater shell. Outlets at sides of columns furthest from the door, surface mounted behind screen, front face of riser in center, top of riser for back of second row of seating. If holes are cut for electrical boxes they must be dressed with putty pads. Leave extra service loops at each location with wires hanging inside of room passing through small caulked holes.
- Zone lighting circuits in room, recessed lights over screen, sconces, ceiling recessed fixtures front of room separate from rear of room, step lights for safety All lights on dimmers. Consider connected controller with simple key pad in room. Any holes cut other than soffit and riser lights need to be in backer boxes or covered with putty pads.
- Several dedicated 20 amp circuits (4-5) at equipment stack location. Install whole house surge protection.
Overall goals: sufficient quantity of air to maintain 72 degrees routinely, the room will be an air tight sealed room with a seating capacity of _____ adults and maybe kids sitting on the floor. The air flow should be sufficient and quiet. Noise criterion goal of NC20
room connected with oversized ducts to maintain quiet slow flow
velocity at face of ducts 250 ft/min or less
bar diffuser vents on bottom of soffit/ceiling. two supplies in front, two returns in bottom of rear soffit. (Dayus from HVACquick.com) probably 4x48 inches
Use soffit as a sound break with partitioned chase-way zones, air coming in from ceiling and traveling horizontally inside soffit before exiting. Line chase-ways with JM Linacoustic.
Connect theater with either insulated flex duct or Linacoustic lined metal ductwork.
Separate zone with thermostat control with thermostat inside theater.
4 inch duct run from ceiling inside hush box (if included in design) location to utility room.
Build after the room is drywalled
Build with at least 1/2 gap to wall
decking is three layers of 5/8 OSB with Green Glue between layers
Line each cavity with plastic and fill with play sand.
interior is one large connected air space filled with insulation
Vents will be cut on top surface at back per final plans so that the riser functions as a pressure relief bass trap.
add step lights and outlets
decking is three layers of 5/8 OSB with Green Glue
Floor (Best practice)
- 1 3/4 inch thick solid core with Zero International perimeter door seals automatic door bottom. Install hard surface door threshold to mate with door bottom, order/make custom width jamb
- Best practice is communicating doors, one swinging in one swinging out creating an airlock.
- 1/2 inch rubber mat (Serenity Mat) secured to floor with DA5 adhesive 3/16 v notch trowel
- 3/4 T&G OSB glued with DA5 to mat. OSB floated with no mechanical fasteners.
- Stage and Riser built on top of sub-floor.
- Locally sourced Horse Stall mats can be substituted if available cheaper (Tractor Supply)