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Infinite Line Source: analysis
Infinite Line Source: analysis
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Old 10th June 2019, 12:58 PM   #451
mayhem13 is offline mayhem13  United States
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I proposed in another thread using the Dayton PT Mini in a vertical line along with the TC9 specifically to address the off axis response.

https://www.parts-express.com/pedocs...ifications.pdf
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Old 10th June 2019, 01:26 PM   #452
mayhem13 is offline mayhem13  United States
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Quote:
Originally Posted by gedlee View Post
But the disadvantage is the large intensity of the first reflection which can be avoided altogether with a high DI point source. A high DI line array might alleviate that issue, but I have never seen anyone do that (except in large pro installations.)
Is the desire for Hi directivity or Constant directivity across the freq spectrum?

My listening experiences with Magnepan speakers is they do this very very well. A very recent listening of the 1.7i was a revealing experience and what’s possible with their new LRS is astonishing for the $$$.

Older posts, I know......but worth addressing attempts to combat horizontal directivity in nearfield arrays. Would an array of open baffle or dipole TC9s accomplish this?.....the TC already has a very high QTS making it somewhat suitable and the new SBAcoustics 3” has an even higher QTS.
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Old 10th June 2019, 01:35 PM   #453
BYRTT is offline BYRTT  Denmark
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Infinite Line Source: analysis
Tend to agree with nc535 that out of box its hard to get those nice smooth BMR factory curves, in red trace below is TEBM46C20N-4B factory curve verse my diy 192kHz rate session on a relative big dual cardboard baffle of size around 100-120 centimeter times 120-140 centimeter, green trace is 1/24 smoothing and black trace is FDW (6 width in cycles), zooming into DATS measurement we can see the two blib where response is worst. That said driver here was simply front mounted so who knows if one works with that weird frame figure to get it implemented smooth and flush into enclosure help with a smoother curve.

Infinite Line Source: analysis-1005-png
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File Type: png 1005.png (44.6 KB, 189 views)
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Old 11th June 2019, 11:30 AM   #454
onni is offline onni  Sweden
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Thanks for the kind words

I'm unsure whether the phase response off-axis is identical to ditto on-axis. Is it that simple? So that the only thing needed to know phase between two identical drivers is the difference in distance? I made a new version of the excel-sheet with this assumption to experiment with vertical directivity of each driver and to see how this affects the combined response.

Directivity modelling
Directivity is modeled by a frequency dependent response as function of off-axis angle. So on axis the frequency response is typically 0 dB from 100-20000 Hz. The at increasing angles the response decreases. You can either make your own curves in the Directivity tab (0-90 deg) or use the included assumption that the curves can be described using the formula:

on_axis_response-separation*(frequency/max_frequency)^slope*off_axis_angle

with this formula you can get
- constant directivity by setting slope = 0
- something resembling normal tweeter behavior by setting slope = ~1 and appropriate separation (0.5?)

Input it
- separation, which sets the separation between lines at 20 kHz multiplied by angle (so separation = 1 gives -45 dB at 45 deg).
- slope, which sets shape of curve

On-axis response
I also added a simple way to choose an on-axis response to counteract the downward slope with the formula
(frequency/max_frequency)^slope_0deg*elev_20
where
slope_0deg sets the shape of the curve and elev_20 sets hos much output is increased at 20 kHz.
Note that increasing on-axis output also increases off-axis output.

Examples
With FTC-array of 42 drivers at 4 m and parameters slope = 2 and separation = 0.5:
directivity 0.5db_deg, 4m, 42 drivers, dirplot.png

directivity 0.5db_deg, 4m, 42 drivers.png
No huge difference to monopole behavior.

What if we increase directivity (waveguide?) and set parameters slope = 1 and separation = 1:
directivity 1db_deg, 4m, 42 drivers, dirplot.png

directivity 1db_deg, 4m, 42 drivers.png
Looks a little better, more even response above 7 kHz (less to fix with DSP).

What if we add that output increases with frequency by setting slope_0deg =0.6 and elev_20 = 12 dB:
directivity 1db_deg, 4m, 42 drivers, sloped, dirplot.png
Note that all curves are modified.

directivity 1db_deg, 4m, 42 drivers, sloped.png
Not bad! (Note also that the "Without directivity"-curve is unaffected).

Let's take it to the extreme, what if we magically can make an array where the directivity only allows positive summing. So that when the off-axis angle causes negative summation (phase angle of more than 90 deg) the output drops to -100 dB:
only pos sum, 4m, 42 drivers, dirplot.png

only pos sum, 4m, 42 drivers.png
Increased output all the way and a lot more even frequency response Not possible to physically make though

File
The spread-sheet is attached, just rename to *.zip and unpack.

/Anton
Attached Files
File Type: mp4 line array calc v1-100dir.mp4 (5.46 MB, 4 views)
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Old 13th June 2019, 07:05 AM   #455
onni is offline onni  Sweden
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Default Error for "bottom driver" in last excel-sheet

I found an error in the excel-sheet in the previous post. It only affected the "bottom driver" so long array behavior was almost unaffected. But when I tried simulating a single driver the error became apparent. Attached is an updated version.

I was experimenting with constant directivity vs traditional speakers. A highly directional constant directivity speaker seems to behave well:
1 driver, 4 m, constant directivity, dirplot.png

1 driver, 4 m, constant directivity.png

Compared to a traditional (non-directional up to a few kHz and then narrowing):
1 driver, 4 m, traditional.png

Might be quite difficult to achieve that level of directivity though.

/Anton
Attached Files
File Type: mp4 line array calc v2-100dir.mp4 (2.72 MB, 10 views)
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Old 13th June 2019, 05:10 PM   #456
nc535 is offline nc535
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Hi Onni:
I love this spreadsheet. Its very timely as I'm building/experimenting with line arrays now. You might find it interesting to compare your results with those produced in Vituix, which can also model line arrays taking driver directivity into account, although with fewer maximum drivers.

A suggestion re' directivity: it would be "nice" to just enter a piston diameter and then have you compute the directivity roll off from that.

Thanks for doing this.
Jack
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Old 18th June 2019, 01:29 PM   #457
onni is offline onni  Sweden
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Quote:
Originally Posted by nc535 View Post
Hi Onni:
I love this spreadsheet. Its very timely as I'm building/experimenting with line arrays now. You might find it interesting to compare your results with those produced in Vituix, which can also model line arrays taking driver directivity into account, although with fewer maximum drivers.

A suggestion re' directivity: it would be "nice" to just enter a piston diameter and then have you compute the directivity roll off from that.

Thanks for doing this.
Jack
Great that it is appreciated

Good suggestion, not sure how to do it though... Is there an easy formula?

/Anton
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Old 18th June 2019, 04:49 PM   #458
nc535 is offline nc535
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Ha! turn about is fair play
a little more than a formula perhaps, but not that much more:
Infinite Line Source: analysis-piston-directivity-note-jpg
Attached Images
File Type: jpg piston directivity note.jpg (284.6 KB, 51 views)
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Last edited by nc535; 18th June 2019 at 05:12 PM.
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Old 18th June 2019, 06:37 PM   #459
BYRTT is offline BYRTT  Denmark
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Infinite Line Source: analysis
Quote:
Originally Posted by onni View Post
Great that it is appreciated

Good suggestion, not sure how to do it though... Is there an easy formula?

/Anton
member InOtIn share a spreadsheet here: Spreadsheet for calculating driver beaming / directivity / dispersion / beamwidth
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Old 18th June 2019, 07:42 PM   #460
bolserst is offline bolserst  United States
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Quote:
Originally Posted by onni View Post
... Is there an easy formula?
The directivity equation for a circular piston uses Bessel functions, which fortunately Excel has as a built in intrinsic function.
In the attached screen grab, you can see the required equation in the Excel formula bar.
Note that the polarity inverts at each off-axis lobe as you go up in frequency

The spreadsheet is also attached in *.zip file for those who happen to have Excel and want to play around.
The “ka” parameter is the ratio of the piston circumference to the wavelength.
ka = (2*pi*f/c) * (d/2) = (pi*d) / (c/f)
where:
f = frequency (hz)
c = speed of sound = 343 (m/s)
d = diameter of piston (m)
Attached Images
File Type: png Piston_Directivity_Spreadsheet.png (245.8 KB, 54 views)
Attached Files
File Type: zip Circular_Piston_Directivity.zip (252.3 KB, 4 views)
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