OK you have been to Burning Man fer sure
Bob K3DJC
On Thu, 02 Sep 2010 02:01:14 +0000 Steve Dove <[email protected]>
writes:
> Hi Mal, Warren,
>
> You both have points, and misapprehensions, in about even measure.
>
> In still, homogeneous air, the results are as Warren states.
> They did after all measure all this stuff once upon a time.
> On doing system design for Very Big rock shows we used those
> figures as a basis for what went on low in the stacks for
> close in to the stage, and in the upper levels for further out
> in the crowd; very different configurations. The delay
> towers a couple of hundred meters out had similar upper/lower
> constraints. And all these were adjusted on-the-fly with
> respect to temperature and humidity which both and in
> combination radically affect air attenuation vs. frequency.
>
> But the response from communities miles and miles away (as per
> Jim) belied the theory totally! The complaints - often with
> cassettes! - showed that given pretty average summer-evening
> temperature inversion ducting the shows could be 'enjoyed'
> widely. No real highs, but the vocals were understandable and
> the tunes recognizable.
>
> Most interesting on the tapes, though, was occasional
> frequency-dependent dispersion or perhaps different paths /
> modes; the bass and kick drum often seemed 'out-of-sync' with
> the rest. I put this down to the bass-bins being effectively
> omnidirectional, whilst everything else had the advantage of
> stacking gain, directional cabinets, or horns; they could well
> excite different modes. Alternatively the LF was arriving
> through normal 'ground wave', and the rest through ducting.
>
> Amplifier power ran typically 100-200kW overall over four
> frequency bands, but speaker efficiencies meant that it
> probably wasn't ever much more than a handful of acoustic kW,
> and certainly not from a point source.
>
> Sirens ARE very close to point source and save the frictional
> losses are very mechanical-to-acoustically efficient; the
> SPLs they can generate are fabulous and which easily rival or
> excel those of a mondo festival PA. Albeit at one note.
>
> High audio frequencies ARE difficult to make travel - I
> remember having 15dB of gain at 15kHz on an already
> small-horn-heavy upstairs array to hit the back of a stadium
> still sounding decent. And the 'next-town-over' tapes
> certainly had little above 2kHz on them.
>
> The parallels with RF are striking in that DX is possible
> beyond the dogmatically theoretical but only by odd
> 'propagation' modes. But, like high audio frequencies, all
> this really isn't going very far, is it?
>
> 73
>
> Steve
>
>
>
>
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