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Line array steering ?
Line array steering ?
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Old 14th April 2019, 06:32 PM   #161
nc535 is offline nc535
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The reason I wanted to use the auto-eq/mirror filter because in looking at polar charts, it appeared that normalize might be emphasizing the vertical sidelobes in the HF. Looking at them now, I don't see much difference in the sidelobes but I do see a more intense and uniform mainlobe, compared to the manually equed mainlobe.

Line array steering ?-sb65_asca_directivity_-ver-png

Yes, normalize is equivalent but learning how to create mirror filter was worth the time. I'm not sure what my workflow will be when I have a real array to tune but that might be part of it, at least for a quick start.
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Old 14th April 2019, 07:23 PM   #162
mark100 is online now mark100  United States
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Quote:
Originally Posted by wesayso View Post



DRC-FIR should be able to improve the top you get.
Shading might be another way and I keep forgetting that you guys don't need the bottom end to go low. I would have only used shading on the top end, to keep the bottom end go as low as possible.

I've often thought/dreamed about a synergy like horn in the middle of a line array of woofers. I think you can appreciate the why of that idea .
Good stuff, Ron

I see what you mean about the FDW options in DRC-FIR.
Probably the biggest tuning decision in FirD centers on the same issue...how much correction to apply, and when in the process. It's all done with usual partial octave smoothing choices...works well...but i can see DRC offers more to play with.

Yes, freq shading for HF/VHF only...no need lower down where line theory is holding together.

It could be that simple amplitude shading might help too (as opposed to the freq shading just mentioned) .
One thing that was stressed several times in the 3-day Smaart class i recently took, is how much it helps to vary the amplitude of speakers that have lobing issues when coupling.
A little bit of difference in amplitude goes further than i would have expected in reducing the depth of combing, without costing that much in beneficial coupling.


And a big yes to the idea of a synergy in the middle of a line !!

Don't laugh at me, but I'm already wondering if I could put my coax cd and horn into a line of six 12" drivers.
I'd need the 12" line drivers to cover up to about 700Hz, and of course as low as possible. Been looking at cheap 12"s this morning
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Old 14th April 2019, 10:48 PM   #163
wesayso is online now wesayso  Netherlands
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I'll hook you up with parameters to use in DRC-FIR. That is, if you want to try it.
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Old 17th April 2019, 01:06 AM   #164
RHosch is offline RHosch  United States
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Would appreciate thoughts on shading implementation for a 16 driver CBT array. I would prefer not to use 8 or 16 channels of amplification, even 4 channels would not be ideal as this will actually be a 2 way array similar to the CBT36. And the ultimate goal is for a multichannel system... so 8 or 16 or 32 channels per speaker times 7+ speakers...

Well, hoping there is a more practical way. Would be willing to dedicated 2 channels for the 16 woofer column. Using a mix of otherwise identical 4 and 8 ohm drivers I can work out shading to follow the Legendre curve pretty closely with as many as 8 steps sparingly using a power resistor here or there. But maybe that isn't needed.

How would you guys approach passive shading of a 16 driver column? I have debated whether to treat it as a 16 driver arc (top driver down 40dB) or an 18 driver arc with top two dropped. Is there a straightforward wiring scheme for groups that I am overlooking?

The tweeter column will use 48 drivers, 3 for each woofer, and i assume that once I solve the woofer column scheme I can duplicate it fairly closely using 3 tweeter groups.

Thanks.
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Old 17th April 2019, 03:14 AM   #165
nc535 is offline nc535
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I posted a spreadsheet earlier in this thread showing several options for 24 driver shadings. The methodology can certainly be adapted for fewer drivers. Chances are you already have your own.

Typically the first two groups can be done w/o resistors; just by series paralleling differently per Keele papers and Griffin thread, then resistor dividers for remaining groups.
I would do 16 drivers as 8,4,2,2.
I would start from a larger array - 18 or 19 - and truncate down to 16 where the weights get small.

With reasonably efficient drivers the R's are no big deal except for the inconvenience of having to put them somewhere, which is less inconvenient and costly than the multiple amplifier alternative. Yes there is a slight frequency dependence of weight due to driver Z variation but its small if you use both a series R plus another R across the drivers to swamp their Z.

How many groups do you need? Jim Griffin was satisfied with 3. Keele has done 5. I doubt you need to do more. Vituix can model the weights and show you the resulting vertical directivity, allowing you to optimize/compromise sensibly.
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Old 17th April 2019, 04:17 AM   #166
RHosch is offline RHosch  United States
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I read the thread and saw the spreadsheet mentioned but didn't actually see it. Will go back and look for it. Thanks.

Downloading vituix now to start learning.

I may use two amp channels for the woofer column simply for power requirements but not certain of that.

I think I will truncate the array. -40dB seems a waste. Even the next driver at -24dB is doubtful whether it contributes substantially to the steering. 18 truncated to 16 seems most reasonable.

Although my current xsim 8 segment curves do look pretty.

Thanks again.
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Old 17th April 2019, 01:29 PM   #167
nc535 is offline nc535
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Here is an update on my spreadsheet modified for 16 drivers.
I added the refinement of scaling the first group to exactly 0 db.
Truncating from 17 instead of 18 worked out better in that the second group came out to -3.57 db which is what you get using the Keele/Griffin series/parallel connections of two groups with 2n and n drivers respectively.

Line array steering ?-cbt16-shading-screenshot-jpg
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Old 21st April 2019, 02:04 AM   #168
RHosch is offline RHosch  United States
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Thanks... I had started a very similar spreadsheet, glad to know I am on track. Played with a lot of variations, think I will settle on something a little different... 4, 2, 4, 2, 2, 2.

That is because I plan to split the column into two amp channels vertically to ease wiring complexity and minimize power burned through resistors. Also because I happen to have amplifier channels to spare but they are only modest power (~200w/4r). This split balances power between the two channels reasonably well and gives a pretty easy schematic when dropping gain on upper half -3dB.
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Old 22nd April 2019, 07:34 PM   #169
mark100 is online now mark100  United States
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Hi all, Here's a few straight line vs cbt observations.....
Please take them as purely preliminary as it's surely too early to have any hard conclusions...

I've spent most of my time measuring/tuning/then listening to the straight arrays. This has been freestanding outdoors, and in room corners as well as freestanding out in the room a bit. Different rooms too.

I keep coming back to EQ correction that takes the speaker flat outdoors, and then uses different degrees of low shelving depending on whether in a corner, and or which room. I little parametric help can be needed in the corners, but other wise that's it for now. Sounds good.

Any attempt to tune to a narrow area indoors hasn't yet been as good as just doing the above.

For simple listening comparisons to the cbt, I use the same EQ settings that were made for the straight line. (This has been in mono, as I only have two driver baffles.)

First, comparing the cbt freestanding out in the room to the straight in a corner.....
As expected the corner straight has significantly stronger lower end. I could almost live with its bottom end, when I'm listening at low to moderate levels.
But I couldn't live with bottom end of the cbt. Without the corner loading the little TC9's just don't have the displacement imo. That's just not solvable with EQ.

The table kinda reverses comparing from mid range up. I've found the cbt easier to keep open sounding. It's cool how easy it adopts to different room positions. I should stop and say the only tuning variable in these comparisons is the amount of low shelving and it's freq point/Q.
(I'm also guessing the corner interaction with the straight isn't fully sorted out, which helps make the cbt comparatively easier....

One thing that's really cool imo is the difference in where the image comes from.
On the straight line, as many have said, it follows ear-level height, moving up and down the line.
With the cbt, it stays in the center of the arc, even when I stand right in front of it looking down on the arc.
It has a focal point! Jim, if you or any other cbt owners read this, do you experience the same imaging phenom?

I do wish the focal center was a little higher though...feels a little weird to have something so tall image only 3 ft off the ground.

Today, I've converted the cbt to a second straight unit, and have begun some stereo listening. Happy to say the baffle moved over easier than hoped for. I was sweating it a little, because now matter how careful I tried to be, getting the 16 baffle mounting bolts to line up with t-nuts and inserts in both boxes was tricky. Well, at least one side interchanges well

Gonna listen for a while, and integrate some subs.
Then will try two cbt's in stereo and with subs...

After taking a break to just listen for a while, I'll get back on the measurement trail...
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Old 23rd April 2019, 02:59 AM   #170
RHosch is offline RHosch  United States
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Interesting observations. I'm interested in CBT for a mixed home theater/music room application. Some of the attributes seem a home run for theater... output/dynamics, smooth vertical response over a range of heights to cover multiple rows, -3dB per doubling distance to maintain better balance over multiple rows etc. ie many of the good characteristics of line arrays.

Other attributes are good for theater and music... smooth horizontal polar response, imaging.

But that perceived imaging height worries me. Ideally for theater the front stage speakers match screen center or close to it. Having audio center too far below screen center may be an issue. And for surrounds generally these are elevated a bit above listener level to reduce attenuation by seats/people behind. A CBT isn't designed to be elevated. I had hoped that the good vertical coverage would mitigate that somewhat.

I'm building a pair to experiment with. Will just have to see/hear for myself.
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