Room Dimension Goals for having a builder create the home theater

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...

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

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.

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

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.

btw;

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