"Point source" array

[H3nry]

New guy to speaker building here. I'm thinking of trying an array of small full range speakers shaped like a sphere or a section of one to approximate a wavefront coming from a point source. Surely somebody's tried this before, other than the guys at UC Berkeley and Meyer Sound. The references I find are electronic musicians building speakers for their instruments, like at SLORK. Anybody tried something along these lines for music reproduction? Suggestions for inexpensive drivers for a first cut at it? Maybe 9 of these PE 2 inchers per side?
http://www.parts-express.com/pe/show...number=289-124

Would a sphere or hemisphere eliminate the arrival time effects of a line array, especially if it's relatively small, while keeping the dynamics of spreading the work over several drivers? Am I nutz?

[chris661]

Welcome to the forums!

I like the idea of making a sphere, as it would make the sound very omni-directional. However, you could run into phase issues, which could result in cancelling various frequencies and highlighting others, which wouldn't sound brilliant.

You could try something more like a guitar stack (drivers arranged in a square) which a more conventional box. This would take away the phase issues.

Chris

[mightym]

This gent has done something along the lines of your inquiry. Reading about his experience may be of some assistance.


See Here:www.dmitrynizh.com/labaffles.htm

I hope this is some useful information.

John

[H3nry]

Thanks for the pointer. It looks well worth reading in depth. What I'm envisioning is something like a soccer ball, maybe a bit bigger, with small drivers tightly clustered on it to minimize phase cancellations, or at least push them way up in frequency. I've seen concave arrays to combat phasing, but that puts listeners at a focal point. What I'm wondering about is bending the array the other direction, simulating a wave expanding from a point source. Haven't seen many designs like that, perhaps like the Quad ESL57 curves in an attempt to broaden the sweet spot. I'm wondering if it's been tried and found to be just awful for some reason...

A guitar stack in miniature is also an intriguing idea.

[GM]

You mean something like the Bozak B200XA tweeter array designed to mimic a large multi-cell theater horn in a relatively small/inexpensive package as shown in the Concert Grand (B310 series)?
http://www.hifilit.com/hifilit/Bozak/1960-7.jpg
http://www.hifilit.com/hifilit/Bozak/1968-5.jpg
http://www.hifilit.com/hifilit/Bozak/1968-4.jpg

If so, it works fairly well with the caveat that just like the big horns it has increasingly audible phasing issues as it collapses from a point source to a bunch of increasingly beaming 'cells' with increasing frequency. Mono ruled when it was introduced, so was actually an acceptable compromise to ameliorate off axis HF roll off (beaming), but stereo...........??? Yeck!

So, Rudy (Bozak) then adapted the early RCA theater line array concept for his stereo variants, the Symphony No.1 (B4000). Much better, but still somewhat lacking and not a commercial success AFAIK. http://www.hifilit.com/hifilit/Bozak/1968-5.jpg

Later, McIntosh would expand on the line array concept till it became a sonic tour de force with the XR290 'infinite' array. It takes a very high level of performance to impress me and these do it like few other systems have over the decades: http://www.roger-russell.com/columns/xr290prod.jpg

GM

[H3nry]

I'd forgotten the Bozak tweeter array. Never heard one, and never was all that fond of Bozak tonal balance. Best Bozak system I ran across back in the day was a friend's tri-amped (with McIntosh) Concert Grands with a JBL Paragon sitting between them. Impressive sound, if a bit vague on imaging, if memory serves, and memory serves less & less after all these years. The big cabinet with all the MC225s, MC240s and MC275s was also impressive as heck.

Another example I've heard of but never heard was Dr. Amar Bose's first speaker system, which was a corner-resident 1/8 sphere made with something like 32 small 4" drivers. Not practical in many rooms, and he abandoned it for the original 901.

I see your point about becoming less a point radiator and more a "sonic disco ball" at high frequencies, so the drivers have to be small to avoid beaming and close together to avoid phasing. I figure if it turns out badly, I can build a line array with the drivers.

[Don Hills]

Search on the Web for a file called "aes102.pdf". It describes the modelling, construction and measurement of a spherical array made from multiple small drivers.

[FredT]

If I understand your concept correctly this speaker does what you're trying to accomplish: http://www.raal-requisite.com/

[GM]

Originally Posted by H3nry

I see your point about becoming less a point radiator and more a "sonic disco ball" at high frequencies, so the drivers have to be small to avoid beaming and close together to avoid phasing. I figure if it turns out badly, I can build a line array with the drivers.

Well, ideally you'll need at most, ~3/8" o.d. wide BW drivers which don't exist AFAIK, so unless all your HF hearing is gone, having a 'plan B' is a good plan.

Good luck with it, looking forward to your findings.

GM

[H3nry]

The main object of my curiosity is the constant refrain "ideal point source". Is a point the ideal source? And what does it sound like with which recordings? Would it image well with recordings made with a spaced pair of mics? Seems quite possible. What about coincident pair mics? Multitrack recordings?

The best reproduction in my experience sounds like there is a pair of windows from my listening room into the concert hall. With good speakers, the windows can be fairly large and lots of music comes through. Sometimes the illusion is that my room is in the front row balcony, sometimes that it's onstage, especially with pop and jazz close-mic'd. Some speakers sound like there are drapes covering the windows, some sound like there are pipes between my room and the performance. Occasionally a system sounds like "the performance is in the room with me", and in fact it is - there is sufficient distortion & resonance that the source becomes the speaker, not the original performer. These systems are limited in the kind of material they play well, and become tiring to listen to.

I've been surprised the last few years by several "computer" speakers which sound much better than their very modest parts would suggest. They have common attributes: small full-range drivers (usually with a separate woofer), modest amplifiers, etc. Think H-K Soundsticks or Henry Kloss' original Cambridge Soundworks. This has me thinking about scaling up to a larger system with no crossover, small drivers which are less prone to cone flex, and so on.