DEMYSTIFYING LINE ARRAYS
Thank you for the excellent article on line arrays [March 2001]. We would like to further clarify the issues surrounding sharply curved “line arrays.”
Real-world line array loudspeakers use “classical” line array theory only in the low and mid frequencies, where it is practical to control driver size and spacing so that constructive and destructive interference can provide directional control. At high frequencies, all use some form of waveguide (or horn). To prevent multiple arrivals and match the directional characteristics of the low and mid frequencies, this horn must have a very narrow vertical pattern and a wide horizontal pattern.
Because of this requirement, radically splaying cabinets in a line array system will necessarily result in hot spots and areas of poor high-frequency coverage. Indeed, every different degree of curvature would require a different horn design if smooth coverage is to be assured.
The accompanying plots illustrate this point. The left column shows the vertical coverage of a curved line array and the right of a straight array. In each case, the high-frequency horn has a 45° (±22.5°) vertical pattern, chosen in an attempt to make the curved array work.
For the curved array, the relatively wide vertical pattern of the horn aids in spreading the high frequencies, though at the cost of significant lobing. Furthermore, the array remains very directional at frequencies below 1 kHz, because the curvature is trivial relative to the wavelength. This behavior will result in very inconsistent coverage, with a large proportion of the coverage area “seeing” very little low-frequency energy.
The right-hand column shows that the wide high-frequency horn is unsuitable for a straight line array. While the lows are well-behaved, the pattern at 1 kHz and above features strong vertical lobes due to interference. These can be expected to excite the reverberant field excessively and thus destroy intelligibility.
Luckily, there is nothing special or different about the soundwaves that line arrays propagate. It is, therefore, entirely possible for skilled professionals, working with the right tools, to integrate other types of loudspeakers seamlessly for downfill coverage, as long as their phase response matches that of the line array elements. This practice eliminates the need for radical curvature and its attendant problems and properly uses the line array for what it handles best: long throws.
I'd like to express how much I enjoy reading your magazine, and I want to say thanks, in particular, for the New Media Special in the February issue. The “File Transfer Technologies” article was quite well done, but I do want to comment on an item in the “Jargon Guide” that, in my opinion, only told half of the story.
You define Virtual Private Network as “… virtual private connections over an unsecure public network,” but I know of at least one exception: The WAM!NET fiber network, marketed to the fields of entertainment media production/post-production by MasterMind company Broadness (where I just happen to be VP of marketing) is among the world's largest and most secure privately owned and managed fiber backbones. It offers password-protected private connections over a managed global network that utilizes multiple firewalls, security checkpoints and SSL password protection, and that monitors and reports any security breach attempts.
The media production community can securely store, catalog, view, retrieve and distribute digital assets (such as video or audio masters) via a “library” within WAM!BASE, a near-line digital archive housed in two mirrored, redundant, super-computing storage centers that are geographically distant from each other. I hope you'll provide clarification of the VPN category by including this letter in your “Feedback” section.
THE PRICE OF ART
As one who happily looks forward to my quarterly BMI checks, Stephen St.Croix's sermon regarding the proliferation of Internet music piracy had me initially saying, “amen.”
And then, as the column segued into the writer's vision of a bleak artistic future, my mind began to wander, and I began to imagine an altogether different road we may take. As one who appreciates the positive power of music — and laments the sad state of the modern mega-corporate entertainment biz — there's something appealing about crippling the market-driven system that has loosed the likes of Britney Spears and the Backstreet Boys upon an unwitting world. Take away the profit motive, and the only people making and distributing music will be artists with something to say. The new stars will not be the fresh, sexy faces that the marketing department has decided to sell to teens, but songwriters and bands making art for art's sake. For that kind of future, I would gladly give up my royalties.
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