High Performance Home Theater Calibration - page 4

Subwoofer Placement and Tuning
The subject of subwoofers, how many are required and their proper placement and tuning ended up being a topic taught just slightly differently by Tony, John Dahl of THX whose seminar I’ll cover in round three and Dr. Floyd Toole of Harman International who taught the last seminar I attended. This is not surprising when you consider that Tony has performed over 150 installations in the last five years using products available at the time. John Dahl teaches subwoofers in a more cursory manner because his level 300 course is a bit more global in scope. And Dr. Toole is teaching multiple-subwoofer calibration from the prospective of a research scientist.

What I would like to point out to attendees of these three courses are the slight perceived differences in how these three men teach this confounding subject. If you heard each of these men speak for the first time it is probably not obvious that they are talking about the same basic difficulties frequencies below 100Hz bring to the home theater. Rather, my take is that new information is coming to the forefront on a relatively continuous basis. So what we are learning is how to do bass correctly from the perspective of THX (John Dahl) who has put their sound into thousands of theaters, from Tony who performs his bass magic on a day-by-day basis for an ever expanding base of satisfied home theater owners and from Dr. Floyd Toole who continues with his research staff to unravel more deeply, wavelengths that measure anywhere from 11.3 feet to 56.5 feet, and how they react into rooms that are considered “small spaces”.

Here then are a few “constants” that always exist when we speak a bass reproduction in small listening spaces-

• If you have a rectangular room you’re in luck. A room-mode modeling program is available for free at www.harman.com
• If your room isn’t a rectangle, all modeling programs go out the window. You’ve got to be able to diagnose proper room placement for the sub or subs in real time.
• Keep a single sub in the front area of the room and close to the center channel to avoid sat/sub blending problems  at the crossover frequencies caused by asymmetry.

    

• Multiple subs are better

• If you don’t have at least a 1/12 octave single band equalizer which will allow you to place a subwoofer pretty much at any floor-wall junction you please, you’re going to have to figure out the best bass performance location by moving it (use a dolly for the big subs!) and charting the response from the listening position.
• Bass traps are a slight misnomer as their purpose is more to smooth the bass response across the 2 ¼ octaves (20Hz – 100Hz) so that you hear multiple tuneful bass notes, from real sounding instruments such as a kick drum and a bass guitar playing together.
• Forget foam for a bass trap. Even 4”-thick, solid, flat, open-cell foam will cause absorption down to only about 125 Hz.
• More info on subwoofers and rooms to follow in John Dahl’s and Dr. Floyd Toole’s seminar reviews.

Front and Surround Speaker Placement
Most of the speaker placement is done during the design phase. Here are a couple of slides which show the basics for the front left-center-right speakers.

For surround speaker placement we were given the following slide:

   

We were also advised that “placement details would be covered in other courses”. (Which we’re getting to also.)