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The Impact Of Breaking The Line

What's actually happening with a line of loudspeakers when it's broken or tapered...

By Bob McCarthy July 20, 2018

A friend of mine who’s not an audio engineer went to a show and later told me it sounded too loud and unintelligible. Plausible? Sure.

Now try this: another friend said it sounded like the line of the loudspeakers had been broken. Still seem plausible? No?

I figure everyone knows what a broken line sounds like since it’s such a big issue for discussion in the audio community. Every time I tune a system or hold a seminar, someone tells me all the things I can’t do because I’ll break the line: “Whatever you do don’t break the line because it will sound like…” Help me out here – sound like what?

Deaf & Blind Test

I invite you to blindfold me and roll me around the venue. We can listen to pink noise or music and I’ll use my trained ears to tell you when it gets louder or softer, more reverberant or less, and brighter or duller as we move around the venue. I can tell you specific peaks and comb filter areas, and even identify transitions between elements of the sound system or the timing and strength of echoes. This is not because I’m special – any audio engineer with a trained pair of ears can do this.

Conversely, remove the blindfold, cover my ears, and put me in a remote room in front of an FFT analyzer. I can still identify these same features as a measurement microphone is moved around a room. Again, I’m not special – any audio engineer with a trained pair of eyes can do this, as long as they know how to read the analyzer and recognize the relationship of the traces to what they hear.

It’s admittedly an advanced skill, but one required of anyone tuning systems. The reason is these are objective, verifiable, audible characteristics of a sound system in a space. A 6 dB level difference between two locations is not a theory – it’s true or not true. It can be directly experienced and measured.

The Sound Of Breaking The Line

Here’s what I cannot tell you by either of the above methods: whether or not the line array theory has been violated and the line is broken. When the line breaks, do we hear a snap? Does the frequency response show tear marks? These are absurd questions but please tell me, what are the tell-tale signs? Why is there such widespread fear of breaking the line? My theory is that there’s as much or more fear of breaking the party line as the acoustical one.

There are two principal manifestations of the “don’t break the line” strategy. The first is the prohibition of level tapering within a multi-element array. So if it’s 6 dB too loud in the front area (a verifiable fact we can hear and measure) we should not solve this with level tapering because we’ll break the line (a theoretical construct we cannot characterize sonically or measure).

The second is the prohibition of spatial separation between sections of an array. Balconies are the prime movers in this discussion. Should we cover the upper and lower levels with one array or split it into two? The answer should be whichever of these can achieve the highest uniformity (something we can measure). Line length absolutists will vote to keep the array together even when this results in reduced uniformity in order to preserve the line.


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About Bob

Bob McCarthy
Bob McCarthy

Director of System Optimization, Meyer Sound
 
Bob has been designing and tuning sound systems for over 30 years. The third edition of his book Sound Systems: Design and Optimization is available from Focal Press. He lives in NYC and is the director of system optimization for Meyer Sound.

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Scott Mullane says

Very informative. Thank you Bob.

Ben Stiegler says

Thank you, Bob! Just came off a 2 day Meyer training with Magu, and its great both to hear the tuning thinking presented in a slightly different vocabulary, and to stand on the base of what we learned from Magu to better understand the nuances you present. Hope I can take a class with you someday as well.

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