High Performance Home Theater Calibration - page 3

Configuring the System
Much of this part of the lecture started as you might guess with the settings inside your typical surround processor receiver. Tony then expanded on the nuts and bolts that anyone can read in the owner's manual and gave us a sense of configuring the speakers as a separate and distinct entity - when to use, for instance, a point-source speaker (always for left-center-rights) versus a dipole or bipole design or another point-source (monopole) for the surrounds.

The goal of the left-center-right for instance is to be able to hear pans as they were heard in the mixing studio. So in the case of Mix Studio D at Skywalker Ranch that meant front left channel and right channel positioned at -22.5° and +22.5° from the 0° center speaker. (Editor's note; Those last bits of info were gleaned from a talk Tom Holman gave a few years back.) The goal of the surrounds is to find a balance between spaciousness and localization.

The subwoofer(s) are last to be set up in a calibration because they operate and interact in a modal manner within the room. So they are treated and set up separately.

Tony, by the way, says that you must absolutely positively operate from a "to-do" checklist every step of the way throughout this calibration process. Much like a pilot goes through his checklist before takeoff, the proper diagnosing and calibration of a home theater system requires one step built upon another in a predetermined sequence if you want to keep that set-up and calibration time down to one and one-half days and avoid frustrating reworks.

System Verification

Now the test gear comes into play. You need to verify signal presence, then level, on both the satellites and sub(s). You need a system diagram to help you stay on track as you methodically go through your checklist of setting input voltages at the speaker terminals using your AC voltmeter and pink noise from your test discs. (BTW- Tony had a checklist available to the CEDIA students who took the class.)

You need to verify that your amp is not oscillating at frequencies between 1 MHz and 2MHz from some tough speaker loads or some “Voodoo Logic” speaker cable that has way too much capacitance. (Here’s where that ‘scope comes in handy.) The point here though is that Tony is teaching us to stay with known good cables that are cost effective.

Did you remember to check that the speakers are functioning properly and that the in-wall’s speaker frame didn’t somehow get too tweaked when you bolted it into the wall? Buy the inexpensive no-name speakers from your local lumber emporium and you’ll likely end up with a flexy plastic frame which can cause the speaker to rub and buzz when bolted to a less-then-flat wall OR, if it actually does play okay, it won’t sound very good.

Have you verified speaker polarity at all locations? Do you know how to use the 5.1 Audio Tool Kit’s test discs to verify that left and center and right are all properly in phase with each other? The list goes on…

How about what was probably a real shocker to many of the installers; the configuration of the center channel speaker... 

     
 

 That’s right. Tony contends that the most common two-way center channel speaker layout, that of a D’Apollito on its side is incorrect. I absolutely agree. Remember your significant other sitting right beside you on the couch? See how the green lobe in the illustration which carries all that dialog information is pointed right toward you and that seat cushion beside you is hearing the signal from a null (the white space to either side of the main green finger)?

How about a trick that can at least partially take nasty room reflections out of the equation; aiming with door stops! Don’t laugh. This works big time. For me this one trick alone was worth its weight in gold record sound. Here’s what my Infinity Modulus left-center-right set-up looks like from the rear with the addition of two large door stops under the center channel and a small doorstop under the left and right corners of the Modulus custom TV bracket.

The addition of the soft rubber doorstops performed three sound-improvement functions at once:

• All three speakers were now pointed to exact ear level from our listening position on the sofa 8 feet away. (Note: These speakers and bracket sit atop a 40” Mitsubishi tube TV. Note also that this system is mounted into a corner at a 45° angle so first order axial reflections had not been a concern beforehand.)
• The second problem alleviated by the tilt was that of moving the delayed ceiling bounce reflection I was getting at the listening position from all three speakers. What became immediately apparent is that I was now receiving a slightly louder more articulated direct sound while the sound from the ceiling bounce was seriously attenuated.
• Lastly, I shimmed the outboard bracket holding each of the left and right speakers so that the speakers are now aimed more inward directly across the width of the couch listening area. There’s now a much more cohesive soundstage across the five foot couch with more of a sense of balanced sound from, for instance the left speaker when you’re sitting on the right side of the couch.