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Infinite Line Source: analysis
Infinite Line Source: analysis
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Old 18th November 2017, 08:40 PM   #21
werewolf is offline werewolf  United States
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Originally Posted by gedlee View Post
Sorry, I missed where you had defined the source strength that way. Normally in acoustics we use volume velocity.
No worries!

I think it works for my presentation to start with a point-source 'monopole' of constant volume acceleration, because such a source "offers" a flat (constant-with-frequency) frequency response at any point in space. Shortly, we will be building an infinite line source with a continual line of such 'monopoles', and the frequency response of the infinite line can then be readily compared to the "ideal" (flat) response of the single monopole.

It's hard to 'cross' disciplines, sometimes. My background is engineering, and that gives me a certain "perspective" on the world. I try to "fit" things into my background ... in this case, signal processing ... but if i try too hard, and force-fit something that doesn't belong (or, is flat-out 'wrong') ... please don't hesitate to correct me!

It really is my intention to learn, as well as teach ...
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Old 18th November 2017, 09:28 PM   #22
Dr1v3n is offline Dr1v3n  United States
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Will anyone be getting into Constant Beamwidth Tech or any other kind of curved line arrays?
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Old 18th November 2017, 09:34 PM   #23
gedlee is offline gedlee  United States
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I could certainly do that, but I don't want to hijack werewolf's thread. Maybe just comments on specific points if required.

The curved line like Keele does requires some fairly high level math - may not be suitable here.
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Old 18th November 2017, 10:00 PM   #24
turk 182 is online now turk 182  Canada
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hot air popper on high,melting butter...best part the virtual company, down in the front please!
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Old 18th November 2017, 10:23 PM   #25
werewolf is offline werewolf  United States
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"truncating the infinite" ....

It always poses some difficult challenges, and clever solutions, in any field that involves Fourier math:

- in signal processing, we deal with the consequences of "truncating the infinite" in the sub-field of "spectral estimation", the field of estimating the power spectrum (and statistics) of an infinitely long signal from a finite sample of that signal. Hann Windows, Blackman Windows ... all designed to provide some degree of "tapering" or "shading" to modify the frequency-domain "sinc" function of the rectangular window.

- in optics, various forms of lens/mirror shading have been studied to modify the Airy disc ... which is a sinc-like function that results from the lens/mirror only observing a finite section of an (essentially) infinitely-wide star beam (yes, lenses take Fourier Transforms too!).

- in audio, various forms of "tapering" or "shading" a finite line array have been studied, to address the effects of truncating an infinite line source. The infinite line source is not "ideal", all by itself (although it does have some wonderful merits, as we will see), but truncating the infinite line introduces even further challenges. Keele's work is very compelling in this regard, but probably best left for another thread ... perhaps, the Finite Line Source thread as Earl said, the math gets a bit complex ... but the goals and results are well-worth discussing!

By the way guys, Earl Geddes, Don Keele ... these guys are GIANTS in acoustics. My background is more on the electronics and signal processing side of audio ... so i'm honored, and humbled, to be in their company as well
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Old 18th November 2017, 10:45 PM   #26
Dr1v3n is offline Dr1v3n  United States
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...down in the front please!
OK, sorry m8!
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Old 18th November 2017, 10:53 PM   #27
Markw4 is offline Markw4
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So far, it looks like the discussion might be framed as having been about point sources and line sources, and about how areas of wavefronts emanating therefrom expand over distance, thereby spreading out acoustic energy.

A possibly interesting way of thinking about other types of curved arrays, etc., from a very basic perspective might be to think about the wavefronts they produce, and how similar wavefronts might be produced by an array of point sources, perhaps in a planar array or other basic configuration. Also related, how physical dimensions of a finite sized phased array would be expected to affect wavefront evolution over distance as a function of frequency.
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Old 18th November 2017, 11:18 PM   #28
Overkill Audio is offline Overkill Audio  United Kingdom
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Default Free from commercial bias.

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Originally Posted by werewolf View Post
By the way guys, Earl Geddes, Don Keele ... these guys are GIANTS in acoustics. My background is more on the electronics and signal processing side of audio ... so i'm honored, and humbled, to be in their company as well
The fact that you are not "in acoustics" makes your opinion so valuable and is why I am so interested in your findings and research.
You clearly have a powerful mind well focused on audio electronics and a willingness to share valuable information without any commercial bias.

All of the "giants" you mention had / have major commercial interests and advocated products / solutions to benefit their employers or their own product range / type.... Thats way of the world, nothing wrong with that but well worth noting!

The one exception I have found to the commercial interest bias on this site is Tom Danley.
He has posted a huge amount of valuable speaker design information and is a genius....Proven by building a multi million $ audio business based on his own ideas and hard work... Not writing a book or becoming a consultant to a multinational... Not saying there bad either, just noting the difference!

Anyway, back over to you Werewolf!
Cheers
Derek.
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Old 18th November 2017, 11:54 PM   #29
turk 182 is online now turk 182  Canada
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Danley's work is not entirely his own... down in front...please!
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Old 19th November 2017, 12:05 AM   #30
gedlee is offline gedlee  United States
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Originally Posted by werewolf View Post
- in optics, various forms of lens/mirror shading have been studied to modify the Airy disc ... which is a sinc-like function that results from the lens/mirror only observing a finite section of an (essentially) infinitely-wide star beam (yes, lenses take Fourier Transforms too!).
Having taken a class in Fourier Optics (its very close to acoustics!) let me just correct you a bit here. If the lens is circular then the transforms are Bessel Transforms which result in a circ function that is like a rotated sinc function (but Bessel instead of cosine). If the lens is rectangular then a 2d Fourier transform would apply (but those are rare). It's called Fourier optics even though for real lenses its really Bessel optics!

PS: I don't sell speakers anymore so does that mean that I can be trusted now? What does someone have to do to get their credibility back?
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Last edited by gedlee; 19th November 2017 at 12:07 AM.
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