[Theater_Yeti]

Planning to build from new construction, an infinite baffle type theater. I'm using a room-within-a-room design to decouple and reduce sound transmission between rooms. I would like some feedback on the location of the indoor unit of a mini-split system. I have two possible locations. Location #1 is mounting to the exterior wall. This location allows the weight of the roof to reduce vibrations to the mini split caused by bass pressurization of the room.

Location #2 (see attached file) is mounting to the interior isolation wall. This location would allow the mini-split to shake with the wall during pressurization.

 

[nathan_h]

Nice looking plan.

I would put it on the internal wall. That way the penetration is jsut the size of the "hose".

But the real answer is that i would try to do a ducted minisplit, so the blower is not in the room introducing noise. They have some quiet ones these days, but nothing is as quiet as it not being there in the first place. Of course, that might double the cost so that may not make sense.

 

[Da Wiz]

The best design practice is to first choose dimensions for the room that avoid "stacking" of room modes. A room with dimensions of 15x15x15 would be TERRIBLE for sound quality because all 3 dimensions would support the same room modes. 15 x 15 x 9 would be better, but there would still be two reinforcements of the same room modes. The best room would be 17 x 19 x 21 since all 3 dimensions have DIFFERENT room modes that do not "stack up" and double or triple peaks or valleys in response. You can Google "calculating room modes" to find the formula to plug-in to a spreadsheet that will lead you to the best combination of room dimensions. I did this for a room in an architect-designed home we built in NY. It was so successful, that even before the home was finished, you could walk into the theater room and notice the resonance-free, reflection-free, and lack of boominess in that room even before drywall was installed. For a modicum of isolation, install "soft" homasote first with conventional drywall on top of the homasote. This helps reduce resonance transfer into the structure. If you are doing room within a room, the homasote can be applied to almost any surface in the the walls, ceiling and floor for increased isolation. The other thing we did was to put 45 degree flat surfaces about 12-inches wide in each corner (vertical corners and ceiling corners) to inhibit formation of standing waves. It all worked surprisingly well... making that room "sound" like no other room I've experienced since we moved from that home in 2006. Do not overlook room dimensions. Also... SYMMETRY of the room is critical for the best sound. If there is a window on the left wall, there should be a window of the same dimensions on the right wall with the same window coverings as the window on the left wall. If there is a door feature on the back wall of the room, the front wall should have the same feature. The left and right sides of the ceiling should be the same. Symmetry and dimensions are important. Also... stiffness of the room is important. Use 2x6 lumber for walls instead of 2x4 (2x8 is even better). Use 2 layers of 3/4 inch plywood for the floor. Put homasote on joists and studs to reduce noise transmission. Floor and ceiling joists should be closer than 16 inches and at least one size larger than building code. If you really want to go for noise transmission reductions, there is a drywall product called Quiet-rock that has alternating layers of differing materials. It is a drywall substitute that reduces noise transmission significantly. Use ducts with fiberglass lining for HVAC outlets in the theater room... you will be SO GLAD THOSE DUCTS WERE USED. If the fiberglass part is long enough before your room, the air coming out of the outlets will be silent. This was one of the best things I specified in the build-out of that room in our home.

Room modes will happen in positive and negative values with a frequency. For example, if a room has modes at 40, 80, and 160, when you alter something to shift the mode, all the frequencies of the mode will shift. The spreadsheet you create will reveal the frequencies of the modes. What you want is for the modes to be spread out as much as possible and that they are not allowed to "build up" where 2 or 3 dimensions have modes at the same frequencies. This is a fairly basic means of dealing with room modes that does not fully address axial, tangential, and oblique modes at the same time. I found breaking the room modes spreadsheet down into axial, tangential, and oblique modes so that ALL modes can be reduced turned out to be too complex for this project. I only concerned myself with the primary modes.

 

[Theater_Yeti]

The best design practice is to first choose dimensions for the room that avoid "stacking" of room modes. A room with dimensions of 15x15x15 would be TERRIBLE for sound quality because all 3 dimensions would support the same room modes. 15 x 15 x 9 would be better, but there would still be two reinforcements of the same room modes. The best room would be 17 x 19 x 21 since all 3 dimensions have DIFFERENT room modes that do not "stack up" and double or triple peaks or valleys in response. You can Google "calculating room modes" to find the formula to plug-in to a spreadsheet that will lead you to the best combination of room dimensions. I did this for a room in an architect-designed home we built in NY. It was so successful, that even before the home was finished, you could walk into the theater room and notice the resonance-free, reflection-free, and lack of boominess in that room even before drywall was installed. For a modicum of isolation, install "soft" homasote first with conventional drywall on top of the homasote. This helps reduce resonance transfer into the structure. If you are doing room within a room, the homasote can be applied to almost any surface in the the walls, ceiling and floor for increased isolation. The other thing we did was to put 45 degree flat surfaces about 12-inches wide in each corner (vertical corners and ceiling corners) to inhibit formation of standing waves. It all worked surprisingly well... making that room "sound" like no other room I've experienced since we moved from that home in 2006. Do not overlook room dimensions. Also... SYMMETRY of the room is critical for the best sound. If there is a window on the left wall, there should be a window of the same dimensions on the right wall with the same window coverings as the window on the left wall. If there is a door feature on the back wall of the room, the front wall should have the same feature. The left and right sides of the ceiling should be the same. Symmetry and dimensions are important. Also... stiffness of the room is important. Use 2x6 lumber for walls instead of 2x4 (2x8 is even better). Use 2 layers of 3/4 inch plywood for the floor. Put homasote on joists and studs to reduce noise transmission. Floor and ceiling joists should be closer than 16 inches and at least one size larger than building code. If you really want to go for noise transmission reductions, there is a drywall product called Quiet-rock that has alternating layers of differing materials. It is a drywall substitute that reduces noise transmission significantly. Use ducts with fiberglass lining for HVAC outlets in the theater room... you will be SO GLAD THOSE DUCTS WERE USED. If the fiberglass part is long enough before your room, the air coming out of the outlets will be silent. This was one of the best things I specified in the build-out of that room in our home.

Room modes will happen in positive and negative values with a frequency. For example, if a room has modes at 40, 80, and 160, when you alter something to shift the mode, all the frequencies of the mode will shift. The spreadsheet you create will reveal the frequencies of the modes. What you want is for the modes to be spread out as much as possible and that they are not allowed to "build up" where 2 or 3 dimensions have modes at the same frequencies. This is a fairly basic means of dealing with room modes that does not fully address axial, tangential, and oblique modes at the same time. I found breaking the room modes spreadsheet down into axial, tangential, and oblique modes so that ALL modes can be reduced turned out to be too complex for this project. I only concerned myself with the primary modes.

View attachment 175975

Never heard of homasote. What type of material is it? I have calculated the room modes. Finished room dimensions 21.3'L x16'W x 10'H. My question is should allow the mini-split to vibrate with the inner wall system or attach it to the outer wall system and attempt to dampen the vibration with the mass of the second wall.

 

[Da Wiz]

Homasote comes in 4-foot x 8-foot gray panels that look like what you'd expect from newspaper with ink turned into a secondary product. It's soft, solid, good for vibration/sound isolation. It can be used different ways depending on budget and design goals. You could put on a layer of 5/8" drywall, a layer of homasote, and another layer of 5/8" drywall for even MORE sound/vibration isolation (compared to just a layer of homasote covered with a layer of drywall). The photo shows 2 kinds of homasote... the "chunky" version and another version with finer particles. The best way to reduce sound transmission is to have the sound encounter materials with different densities layered on each other. A serious soundproof wall could have both kinds of homasote sandwiched between 3 layers of different thicknesses of dry wall, for example. Homasote is made from cellulose... so fiber from wood/recycled paper or fiber from suitable other types of vegetation. They even have a product called 440 Sound Barrier. Homasote is the company name and the product name. Fiberboard is a more generic name for Homasote. Homasote can even be a "foundation" layer for room acoustic treatments... cut a piece of homasote the size you need, add a layer of acoustic foam, then staple-on acoustic cloth, and hang it on a wall where you need to stop reflected sound. For larger size panels, use 3/8" plywood as the first layer, then a layer of homasote, then acoustic foam, then cover with acoustic fabric. You may not find this product at Home Depot or Lowes, but places that cater more specifically to construction materials will have it or possibly some other brand of a similar fiberboard product. You can see in the photo how much the homasote panels look like recycled paper.