(Editor's Note: Click here to read Tom's ProSoundWeb article on alignment and delay.)

Moderator: Welcome to tonight's PSW live chat session with Tom Young, who will be addressing questions regarding system alignment (and misalignment), and delay techniques. Also feel free to ask Tom other system/audio-related questions.

Bink: Say Tom, in your PSW article, you mention the empty spaces between cabinets in an array. You say that a flat panel between cabinets can help reduce those spaces, creating problems with out-of-phase and delayed sounds interfering with the direct sound. What if that same space is filled with a wedge that sticks out from the array some few inches? Wouldn't that help more that a flat panel? I saw McCune Sound out of San Francisco putting these between cabs some ten years ago.

Tom Young: I don't see how it would be better. Perhaps it reduces higher frequency reflections (?).When I do the panels, I ensure that the front surfaces are covered with fiberglass and cloth to reduce these reflections. These are also measurable with Smaart.

Bink: Interesting.

Tom: What was most interesting to me is that you don't need to fill the gap, just cover the opening.

Bink: What I saw were hardwood wedges that could possibly have added some smearing.

Moderator: Yes, it seems to me that anything extending out, especially hardwood, would have, perhaps, a detrimental effect.

Tom: Another interesting/puzzling aspect to this is that two boxes don't appear to create a problem. Every time I check it out, it takes three or more boxes (or two or more cavities) to result in a serious notch in the combined response.

Bink: Why do you think that is?

Tom: I think that the notch comes from diffracted sound that wraps around into the cavity and is re-emitted. I "think" that one cavity and its re-emitted energy does not have enough level, but two or more do. Remember that anything having to do with time-based anomalies has a level component as well as a time component.

Bink: I'd like to see various manufacturers offer panels and mounting holes to get your idea into an easier form.

Tom: I'm not sure that any manufacturer would find it cost effective to provide panels. They will be used mostly by installers, and perhaps a few enlightened temporary system providers who have the time to do this. And the cavity openings vary from gig to gig, as you vary the cluster rigging for specific coverage.

Moderator: What do you see as the single most common mistake and/or misconception with regard to proper system alignment?

Tom: The biggest misconception is that system alignment is not relevant or "perfect" because you align at certain mic positions, and as soon as you are in a different listening spot, things are misaligned (again). The reality is that aligning to one (or several) mic positions significantly improves alignment for all seating, assuming you chose correct mic positions.

Too Tall: How far off can a single speaker be in time alignment (say between the highs and mids) before your ears can tell IF the response has been EQ'd flat on axis?

Tom: The common wisdom is that folks hear delay beginning at about 30mS. But this is in general, and not frequency related. Alignment of drivers within an enclosure can be beneficial down to the microsecond level. My experience is that what you hear is less than perfect response, and when you measure, you discover there is misalignment. In other words, if a speaker is lousy, it probably has poor alignment (plus lousy drivers). I do recall hearing a coaxial loudspeaker where I knew it was out of alignment when I moved on-off axis. Measurement verified this.

Tom (continued): But the real value of Smaart (and SIM and TEF) is being able to evaluate response of not just individual boxes, but how they array and how their acoustics or architecture affect them. Once you try a correction, you can verify whether anything was accomplished.

Moderator: Are there certain loudspeakers that are especially poor with respect to alignment between drivers?

Tom: Sure. One can get very discouraged when you weigh in with all of the problems that can exist in loudspeakers. But (again) it is demonstrable that making small yet significant corrections has an audible and beneficial effect.

Bink: If Too Tall's speaker is a two-way, and it is misaligned by a few microseconds, then won't there be a place of perfect alignment above or below the aiming point of the horn?