Room Dimension Goals for having a builder create the home theater - AVS Forum
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post #1 of 7 Old 07-30-2012, 12:08 PM - Thread Starter
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Hi,

I have been searching for homes in order to set up a home theater. I have not had much like finding what meets my needs, so I am considering having someone build a home with a dedicated great sounding room. This will be utilized 100% for watching movies at reference level with subs running hot.

I have previously told one builder that I wanted to create a room that was 30 ft x 50 ft, with 14 foot ceilings. They didn't seem too thrilled with these dimensions, which I can understand, because rooms like that don't seem to be around.

Below you will find a quote from an article that I found in Home Theater magazine about ideal room sizes. The link to the article may be found here:

http://www.hometheater.com/content/home-theater-builder-part-2-selecting-your-room
Quote:
There isn't really any such thing as the perfect dimensions for a theater—at least, that anyone can agree on. What I've done here is list sample ratios (height : width : length) from each of the four acoustics experts cited in figure 13-2 on page 277 of Alton Everest's Master Handbook of Acoustics (which, if you are planning to build a theater yourself, is one of a few books you will want to have next to you at all times).

Sepmeyer: 1.0 : 1.28 : 1.54
Louden: 1.0 : 1.4 : 1.9
Volkmann: 1.0 : 1.5 : 2.5
Boner: 1.0 : 1.26 : 1.5


As you can see from the above, it appears that the ceiling height acts as the limiting factor to the best room sizes discussed in the article. Under the Volkmann theory, a room with a 14 foot ceiling would yield room dimensions of 21 x 35 ft. With a 10 foot ceiling, the room size would decrease to 15 x 25 feet.

Does anyone care to share their thoughts about the best ceiling height and room size for listening to movies at reference? Do these ratios seem accurate, or would you recommend something else if you were to utilize a 9 or 10 foot ceiling?

In case people are wondering, here is a list of the equipment that I would plan to run in the set-up:

Mains: Seaton Catalyst 12C's (Active)
Surrounds: ? (Active)
Subs: Dual JTR Orbit Shifters or Dual Seaton Terraform XL's
Processor: Denon 4811 or Integra 80.3

Thanks everyone!
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post #2 of 7 Old 07-30-2012, 12:58 PM
 
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Don't obsess over the ratios. There are no 'perfect' ratios - rather a range of ratios that avoid reinforcing 'each other' (in other words, NO common denominators, so the reference to 15 x 25 feet is OUT!).

Even with a 'perfect' ratio you will STILL have modes! They will simply each be distributed 'separately' avoiding co-location and reinforcement of each other.

Unfortunately many have the mistaken notion that one can avoid modes in a bounded space, and that is simply erroneous.

In building a room you simply have a little additional latitude in attempting to distribute the modes in a manner where they do not reinforce each other and create a larger issue.

Note also what the ratios assume (as well as ALL of the calculators). they assume perfectly reflective walls. And they assume a perfectly rectangular shape, allowing for no real world variation in the acoustical impedance of the surfaces - meaning no doors (as they exhibit a varying acoustical impedance), windows, or cutouts/alcoves/ or deviations of ANY kind. it is an IDEAL rectangle. Obviously this will not agree with the real world space, and one can reasonably expect deviation in the real world behavior. Thus measurements become the go to method of choice in order to determine the ACTUAL behavior in the room, as the real world variables are simply too complex to calculate with precision.

So...you start with a goal, and then shift to the measure of the real world performance and proceed with a combination of pressure (tuned) or velocity based traps, location, location, location of the speakers and listening position in order to place the listening position in a location 'between modal nodes and antinodes, and lastly, one can try a bit of EQ as a last resort.




I will also mention a topic that is far beyond the scope of this discussion, and it is a technique that has been used quite successfully over the years in the most sophisticated rooms, and that is a technique whereby a massive outer shell is designed for modal distribution, and then an interior 'specularly reflective' shell which allows the low frequency energy to pass is designed and placed offset asymmetrically within the massive outer shell such that the modal distribution is offset avoiding the location of the nulls and peaks in the center of the room where the primary listening positions are normally located, thus reducing the extent of the problem at the primary seating locations.

This involves a design of an inner shell whose acoustical impedance is such that it allows both the modal energies to pass while also remaining reflective to the specular energies - a low pass filter, if you will.
This is mentioned not to get into the specific design of such a shell, but merely to mention other more advanced techniques that are possible, simply to make those whom may not be familiar with this option aware of additional (more advanced) possibilities in the area...
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post #3 of 7 Old 07-30-2012, 01:54 PM
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Quote:
Originally Posted by pennynike1 View Post

Hi,
I have been searching for homes in order to set up a home theater. I have not had much like finding what meets my needs, so I am considering having someone build a home with a dedicated great sounding room. This will be utilized 100% for watching movies at reference level with subs running hot.
I have previously told one builder that I wanted to create a room that was 30 ft x 50 ft, with 14 foot ceilings.

These references have some information on this topic:

http://www.gedlee.com/downloads/Philosophy.pdf

http://seriousaudioblog.blogspot.com/2012/05/two-great-articles-on-multiple.html
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post #4 of 7 Old 07-30-2012, 03:54 PM
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For a project the size your preliminary dimensions suggest and with the kind of budget your equipment list suggests, perhaps the services of a Home Theater professional would be in order, rather than making it an expensive DIY project.
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post #5 of 7 Old 07-30-2012, 04:07 PM
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Are you going to seat 50 people, or is it going to be a drive-in?
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post #6 of 7 Old 07-31-2012, 08:52 AM
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Quote:
Originally Posted by commsysman View Post

Are you going to seat 50 people, or is it going to be a drive-in?

smile.gif

Actually, if one pursues what dragon mentioned, which has been a dream of mine upon first discovering it (an off-set specular shell within a modal distribution/mega trapped structure), as much room as possible is needed for the entirety.

Perhaps a HT pro would be in order, maybe not, .. all depends on the level of savvy of the DIYer. I say it's doable. Expense? I see way too much money mis-appropriated in so many builds, brute force acoustics such as this isn't necessarily that expensive. Space, is exactly what the Dr ordered wrt addressing the physics involved.


Best of luck, go for it.

------------------------------------
Flat, Deep, Clean, Linear, and Loud
------------------------------------
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post #7 of 7 Old 07-31-2012, 08:59 AM
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btw;

Reminds me of a paper Keele did, wrt anechoic chambers, and LF dissipating walls.

------------------------------------
Flat, Deep, Clean, Linear, and Loud
------------------------------------
Active 16.8kw, 7.3 system
(3)Seaton Cat12C up front, (4)QSC K8 sides/rears
(2)Seaton SubM-HP, (4)18" IB
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