# Reflections on reflections - live vs dead



## sandbag (Aug 2, 2009)

I can get adequate 1,000 Hz and above detailing from my 7.1 electronics with minor tweaks and adjustments in my dedicated room with windows and doors shut. But I cannot experience gut punching cheek flapping collisions, explosions, and other massive sounds of heroic strife and tragic calamity that enable the armchair adventurer to engage the airlock, secure the blast doors, grip the controls and firewall the accelerators to phase shift into the parallel universe in which all things are possible, and the spouse does not awake in panic that the "big one" has started and that you are no longer welcome in her house.

So, the easiest and cheapest approach is to drastically reduce expectations, go to headhones and a butt-kicker chair in a dark closet. Or, sparing no expense, to build an isolated structure having two foot thick rammed earth walls and a reinforced concrete ceiling.

Is there a compromise? Sure. It is the home theater or dedicated listening "room" part of the house. 
Much has been written about nodes, reflections, absorbers -- much of which was derived by conventional two channel stereo during the early days of "hifi" -- that may not be so relevant to today's multichannel listening environment.

In rethinking my theater design since selling my best theater to date with the house it was born in, I have been pondering the constraints of the defined sound box on the listener's perception of five or more discrete point source signal transducers surrounding the listener's head.

The most thrilling "live performance" sound I've been able to achieve is by using two Magnepan mains reflecting off a hard rear wall to create a defined, broad sound stage with the sound decaying into a large space having large irregular openings into even larger space. This means the "action" is clearly front and center, with just enough reflected sound to remind the listener that he is subject to gravity. Pleasing sound circulates around the living area without intruding painfully on other's more quiet enjoyment.

In contrast, my home theater needs to dramatically isolate its immersive sound from the rest of the house. In theory, I can "tune" the room to achieve the sound ambience I want, provided I am not leaking sound or mechanically transmitting it to other structure. The acid test is whether one can sleep in the adjacent bedrooms while the viewer is enjoying full immersive sound in the theater.

Much has been written about nodes, reflections, absorbers -- much of which was derived by conventional two channel stereo during the early days of "hifi" -- that may not be so relevant to today's multichannel listening environment.

Maybe "dead" walls have more to offer when the drivers are arrayed and timed to hit the listener directly. Dead walls (and ceilings) more closely approximate the outdoors in that reflections are minimized.

What say you all?


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## bpape (Sep 14, 2006)

Keeping sound from getting out and having proper sounds inside (absorbtive panels, etc.) are 2 completely different things and require different approaches. If the bedroom is truly adjacent with a shared wall, the isolation is going to be almost impossible without a large expenditure. It can be done. They do it in studios all the time. It's just expensive.

Bryan


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## ScruffyHT (Sep 23, 2008)

To keep sound from "escaping" to the rest of the house you can use a few different approaches, but one picture to keep in mind is that the theatre is a "Aquarium" and you want as few "leaks" in the aquarium as possible 

So in order to keep the sound in you have to isolate it as best you can from the rest of the structure

Resilient clips are designed to decouple and add resilience. This approach is used mostly for ceilings. Staggered studs can be used to decouple walls that are not already adjacent to outside concrete walls.
You could also build a "room within a room" and achieve decoupling that way for all walls and the ceiling.

Double drywall adds mass - the more mass the better

Green Glue damps. see www.greengluecompany.com for specs - bottom line is that this product will help tame the bass from those subs

Insulation absorbs. - prvents the walls/ceiling from acting like a drum

These are all related, but different functions. So doing one or two doesn't mean they replace the function of the other components.

You also need to consider the electrical boxes as holes in the aquarium so building backer boxes around them will help contain the sound ... obviously the least number of holes the better

you also should consider HVAC as another flanking path to the rest of the house ... there are ways to build mufflers and dead vents but the best way is to have a seperate heating/cooling for that room so that it is not connected to the rest of the house ... this is not always possible so you make the compromises where you see fit

lastly is the door to the theatre ... this should be a solid core door with weatherstripping and a door threshold

Sooo ... once you decide what approach you want to take from a sound isloation point of view then you can tackle the room acoustics 

REW is a free program that you can use to calibrate your room and is available for download here at the Shack. This will help you decide where to put acoustic treatments and how much. Basically you cant go wrong with as much bass trapping as possible. 

or ... you could just contact bpape and have him do all the calibrating for you


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