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Multi-Way Conventional loudspeakers with crossovers

Line array prototype (with waveguide and CBT shading)
Line array prototype (with waveguide and CBT shading)
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Old 16th December 2014, 09:55 AM   #1
FoLLgoTT is offline FoLLgoTT  Germany
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Default Line array prototype (with waveguide and CBT shading)

I built a prototype of a line array segment. I developed a waveguide to avoid the bad horizontal directivity of Keele's CBT line arrays.

I used 1" fullrange drivers (Aurasound NSW1-205-8A) which should be used above 300 Hz. The woofer section was not part of the study. The concept I have in mind consists of a 1m long line with woofers beneath and above. This should expand the narrow vertical directivity. CBT-like shading (amplitude and delay) works quite well even with only 7 drivers and symmetry around the driver in the middle.

The paper is in german only. But I think the measurements speak for themselves.


Line array prototype with waveguide and shading (german)


Prototype with 8 drivers (36 cm high):
Line array prototype (with waveguide and CBT shading)-line-array-1-png

Horizontal directivity:
Line array prototype (with waveguide and CBT shading)-line-array-2-png

Vertical directivity (with truncated CBT9 shading):
Line array prototype (with waveguide and CBT shading)-line-array-3-png

The vertical horns dramatically reduce lobing above 9 kHz as you can see in the paper. In professional designs like the Seeburg GL 16 this is a standard feature.

When there is further progress I will let you know.
Attached Images
File Type: png Line array 1.png (391.9 KB, 4545 views)
File Type: png Line array 2.png (30.4 KB, 2692 views)
File Type: png Line array 3.png (54.3 KB, 1412 views)
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Old 16th December 2014, 10:48 AM   #2
keyser is offline keyser  Netherlands
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Quite impressive! You show a vertical directivity plot, but do you have the frequency response measurements also (I mean the vertical version of Abbildung 3)?
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Old 16th December 2014, 10:52 AM   #3
FoLLgoTT is offline FoLLgoTT  Germany
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Thanks! I'll create the frequency response plot later when I'm at home.
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Old 16th December 2014, 03:43 PM   #4
FoLLgoTT is offline FoLLgoTT  Germany
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Here comes the requested diagram. The frequency response at 0° was equalized roughly.
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Old 16th December 2014, 03:58 PM   #5
Juhazi is offline Juhazi  Finland
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Those polars are not-normalized.
Do you use dsp or similar for EQ and xo?
How is low end distortion - where to cross to subwoofer?
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Old 16th December 2014, 04:34 PM   #6
FoLLgoTT is offline FoLLgoTT  Germany
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Quote:
Originally Posted by Juhazi View Post
Those polars are not-normalized.
This is not correct. They are normalized to 0°.

Quote:
Do you use dsp or similar for EQ and xo?
Yes, I use a digital 3-way crossover from ALTO Pro Audio to apply the shading, delays, equalizing etc.

Quote:
How is low end distortion - where to cross to subwoofer?
There are distortion measurements in the PDF file at 90 dB and 100 dB. THD is pretty low above about 300 Hz. So I would not set the crossover point below that. In this case calling the second way a "subwoofer" is not quite applicable.
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Old 16th December 2014, 05:01 PM   #7
Rick Craig is offline Rick Craig  United States
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Interesting project! Your assumption is wrong though in claiming the CBT designs proposed by Don Keele are "bad" in controlling horizontal directivity. This is usually assumed because it doesn't follow the common model.

In real use though (and I have heard and also designed / built several CBT arrays) I have found the horizontal coverage to work very well. In both home and pro audio I have not noticed any issues; in fact, the intelligibility of the pro audio systems has been excellent. If the horizontal directivity was an issue that area would be heavily affected. The ground plane CBT speakers also have greater control into the lower frequencies; as a result, the room interface is very good and they certainly outperform conventional designs in this respect.
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Old 16th December 2014, 05:17 PM   #8
adason is offline adason  United States
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"I developed a waveguide to avoid the bad horizontal directivity of Keele's CBT line arrays."

Can you explain what is bad about CBT horizontal directivity?
Please see this and scroll down for CBT...

Constant directivity loudspeaker designs
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Old 16th December 2014, 05:20 PM   #9
adason is offline adason  United States
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Quote:
Originally Posted by FoLLgoTT View Post
Here comes the requested diagram. The frequency response at 0° was equalized roughly.
This looks to me lot worse than original CBT...
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Old 16th December 2014, 05:26 PM   #10
FoLLgoTT is offline FoLLgoTT  Germany
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Quote:
Originally Posted by Rick Craig View Post
Interesting project! Your assumption is wrong though in claiming the CBT designs proposed by Don Keele are "bad" in controlling horizontal directivity. This is usually assumed because it doesn't follow the common model.
What do you mean with "common model"?

The horizontal directivity can be considered independantly from the vertical. Aligning the drivers horizontally like Keele does leads to interferences, because the steepness of the crossover slope is not infinitely high.

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In real use though (and I have heard and also designed / built several CBT arrays) I have found the horizontal coverage to work very well.
Do you have measurements of the horizontal directivity of Keele's designs?

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The ground plane CBT speakers also have greater control into the lower frequencies; as a result, the room interface is very good and they certainly outperform conventional designs in this respect.
Yes, I believe this.
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