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Line array steering ?
Line array steering ?
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Old 22nd February 2019, 08:44 PM   #21
Neil Davis is offline Neil Davis  United States
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Line array steering ?
I agree that the CBT approach, using a convex curvature, sounds more natural and does an amazing job of filling the room. However, the focused array has some interesting characteristics that are worth exploring if you are not interested in the constant directivity and coverage.

The speakers in the picture use 21 power amps per side, and the effective curvature can be adjusted from a cell phone app from concave to convex, with a delay range of over 50 inches per driver group. The power amps for the tweeter are only 2W each, and the amps for the woofers are about 15W. That's not enough to energize the neighborhood, but there is enough power to irritate the wife--I've proven that . Of course, the 250W amps on the 12" woofer help quite a bit.

The details are in this article: 10. Case study #3: A line array with DSP – Audiodevelopers Reborn

This was a prototype to evaluate a number of concepts, but I still haven't been able to do much testing. The DSP in each speaker is controlled by Bluetooth, and you need to connect to each speaker in turn to make changes. I've been trying to redo the interface using the MQTT protocol, which would allow publishing changes to both speakers at the same time. However, that effort is going very slowly.

Also, the effective curvature affects the high frequency response (see the line array analysis thread referenced in a prior post), and I don't have any algorithm implemented yet to change the frequency response as a function of curvature. So it's difficult to A/B the convex vs concave curvatures.

Someday I will probably update this design with better amplifiers and better drivers and take advantage of what I learned in building these. I've become a line array advocate, at least for large listening spaces.
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Old 23rd February 2019, 01:53 PM   #22
mark100 is online now mark100  United States
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Ongoing thanks again, to all,

Jim, your paper and your posts about your various projects are proving very helpful.
So are comments in the other currently running line-array threads.

My current 'testing room' is similarly sized to your living room, other than 3-4 ft narrower.
It is untreated acoustically for the most part and would be difficult to treat.
If a CBT design could make great sound in it...well, that's enticing !!

I know this is a bit of an aside, but I've found omni type radiators sound better in large reverberate spaces than i would expect.
It's like if you can't beat the room's reverberate nature, join it...with less focused, more diffused radiation.
I say this because my previous listening room was a little larger and i did treat it, getting an even, well damped RT-60 throughout the spectrum.
My omni-type speakers were OK before treatment, but sucked afterwards which was a surprise. Vice versa for the point source type of, which of course was as expected...

That experience, and the way the imaging and the sound-field of the CBT are depicted, are leading me to think maybe the CBT acts as a "direct-omni" so to speak

Neil, very cool project! I have seen it a few times in the past and always admired it....it's probably what planted the seed in my head to try this.
Then the seed got watered by the new beam steering RCF Lol.
Also, I recently got a QSC Q-Sys processor that would make all the DSP pretty easy for the needed channels. You just drag and drop whatever components you need into the processor design. And I could use matrix array presets to instantly switch between different curvatures/shadings/roll offs etc.

Wesayso, always helpful !

TNT, maybe to get started learning, it makes sense to use larger drivers like you did ....gonna keep reading through all the various thread builds
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Old 23rd February 2019, 02:15 PM   #23
TNT is offline TNT  Sweden
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I would have liked to use smaller drivers but I had set for a very limited budget so... thats what I found.

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Old 23rd February 2019, 10:53 PM   #24
Neil Davis is offline Neil Davis  United States
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Line array steering ?
As I said, I'm interested in updating the amplifier/DSP design, because it is a niche product that no is addressing and I think there might be enough interest in line arrays to make this a viable product. So I might look into working with Parts Express or finding some other collaborator to make a product or kit available. It's not on my short list right now, but it's something I'd like to get to some day.

Even if you could buy a 24-channel amplifier board and DSP software and control app, it would still be a formidable effort to build your own line array. There is a lot of woodworking and wiring involved, plus the cost of the drivers adds up quickly. But these things really sound good, and for a large living room they are ideal. And with built-in WiFi they have very high SAF, since they don't require any additional audio equipment.
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Old 25th February 2019, 12:31 AM   #25
mark100 is online now mark100  United States
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Quote:
Originally Posted by nc535 View Post
well I was hoping Mark would go curved CBT as that is where I seem to be heading. I would certainly choose CBT over floor to ceiling straight line for portability and I don't see a need for steering in a home setting, just have to pick a good arc angle initially.

I would advise modelling whatever line in Vituix. It can show vertical polar maps so you can evaluate weighting and steering schemes based initially on driver piston diameter and traced data sheet FR. Kimmosto claims it not accurate, at least not accurate enough to eliminate the need for measurements but its at least a good general idea of how array will perform. He suggested measuring single driver polars and using those in Vituix to predict array performance, ostensibly accurately.

Mark: I couldn't find much info about the Q-Sys system. I'm looking at Motu and a PC instead for 8 channels so far...
You know, CBT isn't dead !!! I've been thinkin...why not both ??
In Jim's CBT24 thread he says he built the front panel out of 1/2" MDF that bent sufficiently.....I'm saying to myself...hells bells...mount the drivers on the same such a panel, that can be screwed on to either a straight or curved mount.... Anybody see any issues?

I figure I can even make the CBT shading better than usual passive, since I'm already willing to go fully active with however many dsp/amp channels needed for straight line beam steering.

Seems i try both, not so hard...???

Q-Sys... it's awesome, and yes hard to find online info. The guts is a core processor..110f for anything short of a giant installation. There are online level 1 Q-Sys training vids that show the capability. Downer is price...but the 110f's do appear on ebay...i got mine from a bankrupt Toys-R-Us

Thx for the tip on Vituix !
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Old 25th February 2019, 01:09 AM   #26
nc535 is offline nc535
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why not both? too much work. I'll bet you stick with whatever you make first

I would do a straight, delay curved CBT iff I wanted on or in-wall mounting but out in the room a physically curved array conveys a degree of immunity from boundary nulls, although I was advised to absorb near reflections for best imaging.

Passive shading isn't hard with Vituix to verify it and show you how well it works. It doesn't seem to be especially critical either. BTW, I modelled both the curved line and its mirror image in Vituix, no other way to include the ground reflection.
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Old 25th February 2019, 08:06 AM   #27
wilbur-x is offline wilbur-x  Tibet
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I would like to add that for a physically curved focussed array you also take advantage of the drivers directivity at higher frequencies besides the absence of phase delay.
Please note that we do not sit located at the focussed points bullet eye, but move the chair/sofa a bit towards the speakers where the listening height is approx. 0,6m (24").
Here we do the measurements and adjustments by MiniDSP and Dirac Live. Deviations in delay is still minor, but realease the listener from being "nailed".
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Old 25th February 2019, 10:15 AM   #28
wonderfulaudio is offline wonderfulaudio
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Quote:
Originally Posted by mark100 View Post

My question is: with a normal 8ft or so ceiling, do you see beem steering such as in the RCF being an advantage?
Or does the non-steered, reflection extended line from the floor and ceiling totally suffice? Would the extended line be harmed be steering?
In Pro audio, the speaker height could differ and hence the need for beam steering, the distance to the listener could vary and hence the need for beamwidth control.

In case of home listening the speaker height is fixed, the listening distance is more or less fixed. Beam steering has no advantage here
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Old 25th February 2019, 10:24 AM   #29
wonderfulaudio is offline wonderfulaudio
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Default Concave CBT. CBT with a twist.

A concave focused array is always criticized for having a very small listening area (point) which is the center of the arc. Here is how to avoid it and make it better.

Make it a reverse CBT. Shade it like a CBT and it becomes a reverse CBT. Dont believe me, just see the polar balloon plots by Don Keeele. The CBT is a constant directivity device even at the rear. A concave array when shaded like CBT is also a CBT array just that it is being heard from the rear.

Now, widen the coverage by placing the focal point very very far (make CBT arc lets say 15 degrees or even less, 5 degrees??) and voila! you just avoided the floor/ceiling and still got constant directivity in the veritcal plane. It has a much wider listening window, vertically.

We now have an array whose vertical listening area (-6dB) keeps getting smaller and smaller with distance but note that its gradual. The focal point is beyond the room by a wide margin so the focal point does not matter.

CBT with a twist!

Last edited by wonderfulaudio; 25th February 2019 at 10:45 AM.
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Old 25th February 2019, 10:53 AM   #30
TBTL is offline TBTL  Germany
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CBT is not designed to be constant directivity at the rear. The idea is to generate an expanding wave front with a certain shape and a certain pressure distribution, by locating sources with amplitudes of that wavefront at spatial locations along that wave front. Strictly speaking the directivity of a curved, vertical array only follows the CBT ideas at zero horizontal angle.

Last edited by TBTL; 25th February 2019 at 10:57 AM.
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