http://forum.soundillusions.net/showthread.php?t=38445

The data they posted is fine, they explain the 'bad science' behind
line arrays. It's good data. But the data seemed more useful to
dissuade the DIY'er from making an attempt to build. I was expecting
some positive reinforcement on how to combat some of the issues.

It's no big deal. I view this as an example where science clashes
with a subjective topic. The human perception of sound quality
may not be measured variable, everyone has their own tastes in audio.

analogy,

You like Loudspeaker 'A', I don't like Loudspeaker 'A'.

Speaker design is a game of compromise and even though a design
may have 'bad science', that is no indicator that the gremlins
will be audible.

Even if there is mixed opinion on the sound quality of a design,
that is no reason to discard the design either. But if a 100 out
of a 100 people vote 'no' on design due to audition, then you
may have to come to the conclusion that you need a redesign of your
sound system.

The specific part that I'm interested in is wondering how something
with bad science can be interpreted as sounding good. The only
thing that comes to mind is the 'human equation'.

No one claimed that the science behind nearfield line arrays is terrible like you suggest. Wiggins and Co. claimed that arrays used nearfield are sporadic. Rybaudio showed that and explained some of the difficulties. What they say is that it is bad engineering and decision making to use arrays nearfield because there are other options with less obstacles to overcome. It is not the science that is bad, it is the decision to use an array in that application.

I encourage those of you who have an interest in line arrays to first read about them. Also make an effort to actually hear some of the recent line arrays--DIY and commercial should be available--before jumping to conclusions as to whether they are bad or good. It is like a lot of things in life--you may or may not like how line arrays sound--while others may have a different impression. Remember bad science or not a well executed line array design may float your boat.

If you wish to read more informative recent reasearch on the line arrays, start with the papers written by L-Acoustics reseachers which are available on their site:

http://www.l-acoustics.com/anglais/accueilgb.htm

Click on the R&D tab and you will see a list of "Wavefront Sculpture Technology" papers published in AES journals. The most recent one is the October 2003 AES Journal paper which summarizes their earlier work which can be downloaded once you click on it. These papers cover more that 14 years of study and work to develop L-Acoustics arrays.

The www.JBLpro.com references the JBL line array work but much of it is from the far field analysis viewpoint. Far field analysis is more amenable to pro sound applications than home applications. You can click the Technical Library tab and proceed to the VERTEC series papers to get downloads of the JBL work. Most of these are AES Journal and Convention papers but should be read to understand their research.

I used much of this material in my writing of my Near Field Line Array white paper.

Jim

• Near Field Line Array White Paper

Some of my more used references include:

- Fundamentals of Acoustics by Kinsler, Frey, Coppens, and Sanders
- Audio Engineering Handbook by K. Blair Brown
- Underwater Acoustics by Acker

Meyersound has a great little white paper describing the issues with line arrays: http://www.meyersound.com/support/papers/line_array_theory.htm . It's pretty complete in its treatment of the subject. One should note that Meyersound sells speakers specifically designed for use as line arrays - they are a VERY strong proponent of line arrays, but also caution against use in the near-field situation, and explicitly state that line arrays do NOT create cylindrical wavefronts.

I also see that Art Ludwig has some good descriptors of the near-field and field calculation on his website. It can be found at http://www.silcom.com/~aludwig/Physics/Exact_piston/Exact_piston.htm . Note that he shows the chaotic nature of the near-field of a piston radiator at http://www.silcom.com/~aludwig/Physics/Exact_piston/Cone_near_field.gif - it is, IMHO, quite instructive of the nature of the beast being dealt with.

One can use this equation to superimpose the output of multiple sources on an arbitary point; I wrote a small Windows program back in 1992 or so that did just that. Iterating the point through a surface (sphere or plane) allowed a visual graph of the pressure of the array over the surface. Iterating across a bandwidth and flipping images (after considerable processing time) allowed an animated image of the nature of the acoustic power on that plane. It quickly became apparent to me that working within the near-field of a radiator is loaded with problems, and that simply staying out of the near-field was, IMHO, the best solution. In SONAR or audio.

Does this mean that no one should like line arrays? Of course not! I don't like 2W SET tube amps either, but I know many who do, and more power to them. The whole issue arose over a request for help on line arrays, and some general feedback about some of the issues that I feel should be considered when working with them. It's not preference - it's about understanding the definite tradeoffs one makes when working in the near-field of ANY radiator. Arrays tend to be more problematic simply because the near-field extends out so much further.

Anyway, IF you had to do a near-field line array, I think Dr. Griffin's paper is a good starting point, and said so up-front. He has a good treatise on the issues at hand, and the use of a Bessel array definitely solves many of the associated problems. It does mean reducing much of the acoustic gain one gets from the line, but again that is not because of a bad implementation, it is because of the underlying physics. Rybaudio's posts confirmed that where bandwidth and power output was adjusted across the elements of the line to make an IMHO very bad situation less bad.

I hope this clarifies the whole issue. Anyone is free to enjoy what they want; however, there are definite advantages and disadvantages to any particular implementation. My experience and knowledge has led me to a different set of problems (and solutions) than line arrays used near-field. Is that bad? No, it's different.

There was no slight or put-down intended of line-array proponents; just a caution about some of the issues that should be considered when dealing with these complex build-ups.

Dan Wiggins

Dan Wiggins

**********
Dan said;
"I've read Dr. Griffin's paper, and while it is generally good, it does overlook much of the near-field issues that a good strong reference (Steven's recommendation of Fundamentals of Acoustics by Kinsler et al is excellent) cover."

Then he said;
"The paper linked is Jim Griffin's paper, and it's not accurate at all."

http://forum.soundillusions.net/showthread.php?t=38445&page=1&pp=15

Then he said here days later;
"Anyway, IF you had to do a near-field line array, I think Dr. Griffin's paper is a good starting point, and said so up-front."
**********

It's not a big deal really, but it's easy to misjudge when the
poster is sending mixed signals or changing their minds midstream :)