HT construction query

Discussion in 'Home Theater Projects' started by JayD, Jul 30, 2004.

  1. JayD

    JayD Auditioning

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    OK people newbie here, first post. Found the site through HT Builder Mag. My wife and I are designing our dream house. The basement will be the audio/HT room. The house will be insulated concrete form construction with radiant floor heating (zoned) under a Permacrete surface. Now we can make this room virtually any size or shape since we are in the design phase. Browsing the forums gives a lot of advice especially the section where people post the things they would do if they had it to do over. My first question is, how do we determine what the best size and shape of the room is? For example, our first drawings have the room at 37'X60'. Should it be more square or more rectangle? We can also use almost any ceiling or wall covering. Anything over the Permacrete will kill the radiant heat save for a few area rugs so we don't have much choice there. I am more into music than movies, but love concert DVD's so the audio portion is extremely important. After the room design, what is the next step? FYI we are planning an underground basement (no windows)sound proofed from the rest of the house. Thanks! JD
     
  2. SethH

    SethH Cinematographer

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    Rectangle is better for audio. Generally speaking you want about 1:1.5, so you could go 30'x45' for instance. There are some more exact numbers out there, but I can't recall where they are. Sqaure is bad as is 1:2 (ie 30x60). You'll definitely want to put rugs down, but since you can't cover the entire floor you may want to condsider putting some sound absorbing material in the ceiling to make up for the floor a little. The next step after the room size would be planning out equipment. After you figure out speaker placement you can work on sound absorbtion throughout the room. Many people do this by using a laser pointer and mirror to find reflection points.
     
  3. JayD

    JayD Auditioning

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    Thanks for the reply Seth, would I want the HT at the end of the length (30') of the width (40')? I can have any wall surface I want and I was thinking of using heavy curtains for sound deadening. I don't really understand how to do the reflection point thing. Am I trying to knock down all sound reflection? JD
     
  4. SethH

    SethH Cinematographer

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    The following method is used by a lot of people: get a friend, a mirror, and a laser pointer. You sit in the main listening position (or centered listening position) with the laser pointer. Get the friend to hold the mirror against the wall. You point the laser pointer at the mirror. Move the mirror and laser pointer beam along the wall until the beam bounces off the mirror and hits a speaker. This point is a reflection point. If you knock out the first reflection points for the speakers then you'll be well on your way to having a pretty good sounding room. About the HT at the end of the length or width, I don't think it should matter, but perhaps someone else could clear that up for you.
     
  5. Wayne A. Pflughaupt

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    Jay,

    First, welcome to the Forum!

    A big problem with rectangular rooms is that it can be hard to get uniform bass response across the entire seating area. Bass will tend to have a “dead spot” in the center of the room and increase in intensity as you move closer to a boundary, being the most powerful against the walls and (especially) at corners. Fortunately, your room will be very large, so the problem will not be as severe as it would be in a small room.

    Still, since you’re building from scratch you might take a cue from recording studio construction. To help minimize bass issues they will often build out all 90-degree angles (i.e., wall/ceiling, wall/wall junctions) at 45-degrees. You might want to leave one front corner intact for subwoofer placement. Even with the 45 build outs, you may need additional low frequency absorption such as bass traps. These can be added after-the-fact.

    Of course absorption at higher frequencies is even more important. In a typical living room setting normal household furnishings – things like overstuffed furniture, draperies and wall-to-wall carpet - do a good job of doubling as acoustical treatment. However, a dedicated room is often devoid of some of these things so specific treatment is needed. This will especially be the case in a large room like this one.

    Personally I’m not fond of the laser approach to treating a room. IMO the problem with it is that sound from the speakers does not travel like a laser beam. Sound waves widely disperse from the point source, like waves from a pebble dropped in a pond. I suggest instead taking a cue here from actual theaters – you will notice that they treat entire walls with pleated fabrics, and floors with carpet. The former might be a little drastic for a home theater, since there will not be listeners distributed over virtually every square foot of the room, but the idea is to reduce reflections over the entire large listening area, not just for a single seat.

    You certainly have a disadvantage not being able to carpet the floor. Certainly you don’t want an entire surface, especially one that large, left untreated. I second Seth’s recommendation to apply liberal treatment to the ceiling to make up for it, perhaps something like the carpet they use in office buildings with virtually no knap.

    You mentioned soundproofing, but it’s not clear from your post if that’s going to be accomplished by the concrete construction or by special build-out of the room. If it’s the latter, you might want to once again take a cue from recording studios and utilize double-walled construction. Basically we’re talking about a “room within a room” where the interior walls and ceilings are completely and physically decoupled, as this picture shows:


    [​IMG]


    This kind of build-out would require two heavy solid-core doors for each entry and special AC ventilation requirements, since the room would be air-tight.

    You didn’t mention it, but hopefully your research has brought back information on the electric requirements you’ll need – dedicated circuits for the equipment on a separate phase from the other room circuits, etc.

    Regards,
    Wayne A. Pflughaupt
     
  6. JayD

    JayD Auditioning

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    Wow, excellent information guys! What I'm gathering is that I want uniform frequency response in the primary seating area without reflection from the room acoustics i.e. walls, floor, etc. I can do area rugs which I may be able to manipulate into covering a good portion of the floor between the HT and the speakers. Is there a ceiling tile out there that will accomplish the desired level of sound reduction? My local radiator repair shop is also a bluegrass recording studio (remember this is Nashville) and they have the foam egg crate material on their sound deadened surfaces. I could easily do that on my ceiling, and walls for that matter. The sound proofing will be accomplished by the concrete construction of the house. This is actually my introduction into HT construction so I haven't broached the electrical area yet. I think I should take this one step at a time and make sure my contractor is understanding every thing I need to be included in the room which is why I started in this forum. JD
     
  7. Wayne A. Pflughaupt

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    Radiator shop-cum-recording studio, huh? Only in Nashville, I suppose! Well, brass is brass, so I imagine this is one studio where it’s easy to get an emergency repair on a saxophone! [​IMG]

    The egg crate foam won’t absorb as well as something like draperies or carpet, because it is a harder surface. Carpet and draperies should absorb down to 1kHz or so; the foam wouldn’t absorb that low.

    However it will offer excellent diffusion properties – it will break up and “scatter” the sound waves. This is excellent for minimizing reflections, and it’s a good idea to combine both absorption and diffusion. Diffusion helps with acoustical properties yet keeps a room from sounding clinically “dead” – i.e., it helps retain a certain amount of “liveness” (although a really good diffuser would be a harder surface than the foam).

    You wouldn’t have to treat the entire ceiling, but you would probably at least want to treat everything above the listening area, and in front between the speakers and seating.

    Another great place to apply the egg crate material would be any wall that has a speaker pointing directly at it - like the rear wall.

    Regards,
    Wayne A. Pflughaupt
     

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