Sonic Enhancements Juneau AK

HOW TO CONFIGURE SYSTEMS FOR EXCELLENT PHANTOM IMAGING

Last month I talked about phantom imaging— what it is, what makes it happen, and why it’s an important part of the sonic experience you should deliver to your clients.

Assuming the speakers’ response curves matched when you equalized them, you shouldn’t need to make changes to fix imaging problems.

That discussion, however, begged the question, “How do I make sure my systems are producing good phantom images?”

THE ESSENTIALS
First, you need to assemble some tools. I doubt that you would be stoked about buying multithousand- dollar test equipment given the current economy, so I’ll just stick to the essentials: (A) your ears, (B) this column, (C) some familiar program material, and (D) a disc with the appropriate test noise signals. These signals are:

• 500Hz-2kHz gated bursts at equal amplitude in all channels
• 200Hz-10kHz one-third-octave filtered noise at equal amplitude in all channels
• 200Hz -10kHz single-octave filtered noise at equal amplitude in all channels
  

All channels” obviously depends on how many channels there are in your system. For our purposes here, “all channels” will be Left (L), Center (C), Right (R), Side left (Sl), Side right (Sr), and Back (with either one or two Back speakers). The test disc that I would suggest you use, the Gold Line/PMI 5.1 Audio Toolkit, includes test noise for these channels.

It’s also important to note that I’m assuming the room already has been calibrated: speakers arrayed according to industry standards (discussed last month), acoustic treatments installed and tweaked, speaker distances set with a measuring tape, levels calibrated to within 0.5dB using an SPL meter, and EQ applied by employing an analyzer.

THE MOST IMPORTANT IMAGE
By far the most important phantom image is phantom center, so that’s where you start. Play 500Hz- 2kHz gated noise bursts through just the L/R speakers, sit at the main seat (which must be equidistant from them), and listen closely. The noise should appear to come from a point precisely midway between the L/R. (If the C speaker occupies that location, your ears should tell you the noise is coming from it.) Depending on the directivity of your speakers, the noise burst may be small and sharp or large and fuzzy. The former is usually better, but they’re both OK as long as they’re centered. None of the noise—not even a little pop or hiss—should sound like it’s coming from only one of the speakers. If it does, you have a problem somewhere: a broken speaker, a poorly matched speaker pair, incorrect calibration, or poor room acoustics.

So, let’s assume you hear a phantom image, but it’s not exactly in the center—maybe it’s shifted left or right. The temptation is to think one speaker is louder than the other, which can’t be true because they’ve been level-matched! In reality, one speaker is probably a bit closer to you than the other, thereby distorting the image.

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