Three Common Home Theater Layout Mistakes Even the Pros Make
Even the “pros” make basic home theater layout mistakes. As an enthusiast you’d think that someone who works day in, day out in the industry should know better but the sad truth is that many are not well versed in the intricacies of home theater layout and design, even if their retail store sells high end equipment. Here are three we come across with all too frequently…
1) Too many seats
If you are aiming for a “Individual Cinema Experience” then each seat should be as good as all the others in terms of audio and video performance. That is extremely hard to achieve. Even “No Bad Seats” is difficult to achieve.
Why? Because you need to put seats away from walls and surround speakers. Seats too close to walls end up with boomy bass. Seats too close to speakers will result in incorrect localization and the infamous “screen door effect”.
To do things right you need 4′ minimum from any seat to any speaker or wall. If you are using proper home theater recliners that means a two row theater will end up about 23′ long. A 12′ room will have a three seat row across the room, and add 3′ for each additional seat across.
For more see home theater seating layout article!
2) Image too small
This is one area where we see enthusiasts and pro installers making mistakes. Enthusiasts tend to want a screen that are too big, and installers seem to specify screens that are too small.
If you follow the CEDIA standard CEB-23: Home Theater Video Design then you’ll end up with a 43 degree viewing angle from the prime seats for a 2.35:1 Cinemascope image. If you look, however, at the viewing angles in commercial theaters (and don’t we all basically want a commercial cinema in our home at the end of the day?) then you’ll see that 43 degrees is actually on the low side relative to the angle you’ll get when you are out at the movies.
I think most home theater dealers are using screens that are too small because they are afraid (wrongly) of using acoustically transparent screens. Really when you look at your layout, once you get over a certain size screen (about 90″ wide) using a non-acoustically transparent screen puts the center speaker in completely the wrong place in a multi-row theater. Most end up below the screen, resulting in the heads and seat backs of the first row being in the “line of fire” from the center speaker to the second row. And, to top it all off, the installer usually ends up using a horizontal format center speaker, of all travesties! (see here for more).
3) Subwoofers in the wrong places
Picture this: a modest two row dedicated theater with 6 seats total. How many subwoofers does the typical home theater installer / dealer / enthusiast specify? One, or two if you are lucky. How many do you need? Actually four.
As per recommended practice CEDIA CEB-22: Home Theater Audio Design the following rules apply:
- One listening position – one sub
- One row – two subs
- Multiple rows – four or more subs
The science behind this “subwoofer number rule of thumb” is called room mode cancellation. See this guide to subwoofers to learn more.
Furthermore, even if you have enough subs (which hardly anyone does), then you also need to put them in specific places for room mode cancellation to work. The most well known work on this topic was done by Todd Welti at Harman Group , who analyzed many different subwoofer placement strategies.
For a square or rectangular room it pretty much comes down to some simple rules of thumb: wall mid points are best, 25/75% of width are good, corners are ok.
For non-rectangular rooms (or even rectangular rooms with large soffits, baffle walls or risers) all bets are off (as Floyd Toole likes to say).
The only way to know is to do some boundary element modeling (BEM). To our knowledge very few home theater designers do this. Acoustic Frontiers uses BEM to predict frequency response at individual seats for different subwoofer numbers and placements. JBL Synthesis also have a service called FLO which does a similar thing.
Here’s a nice video which shows the folks at Martin Logan teaching you how to use their “Perfect Bass Kit” to optimize a multi-seat home theater with only one sub. If you’ve read the above paragraph you’ll be laughing with me. What are they thinking? You need multiple subs, not one. No amount of single sub DSP trickery is going to provide even, consistent and smooth bass across all the seats in that theater!