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Multi-Way Conventional loudspeakers with crossovers

Pseudo-coaxial with narrow directivity (and Horbach-Keele filters)
Pseudo-coaxial with narrow directivity (and Horbach-Keele filters)
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Old 21st December 2015, 09:12 AM   #1
FoLLgoTT is offline FoLLgoTT  Germany
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Default Pseudo-coaxial with narrow directivity (and Horbach-Keele filters)

*UPDATE*: Here is now my final build.


I want to show you my prototype of a pseudo-coaxial design. It is the 10th of its kind. It is not easy to achieve a constant directivity that is narrow at the same time.

Click the image to open in full size.

It took me months to get the directivity like it is. And it still could be better under high angles. But since the overall amplitude is so low under these angles I doubt that it counts much in a medium damped room.

The cabinet dimensions are 50 x 50 x 20 cm. The final version will be a bit more shallow. This is the reason why a synergy horn was not an option. Depth is what I don't have in my room.
The horn is my own design and was 3D printed. The final version of this speaker will have a CNC-milled baffle which is made of one piece. But for the prototype this was not important.

The crossover is linear phase and is based on a Linux PC with BruteFIR. It uses optimized Horbach-Keele filters to achieve the directivity. First I tried minimum phase filters, but without phase correction the result was never as good as with linear phase filters.

Horbach-Keele filters:
Click the image to open in full size.

The whole speaker was designed to be used with a subwoofer system and should be crossed at about 100 Hz. I also evaluated several possibilities to integrate a 4th way (the woofers). But the cabinet would be much larger and I don't see any benefit for a narrow dispersion in the low frequencies inside a room. So I decided to install a subwoofer system later.

If more maximum SPL is desired the number of low-mid-drivers can be doubled without influence on directivity.


Measurements

Directivity normalized to 0°:
Click the image to open in full size.

Directivity normalized amplitude (10° steps, 0 - 90°):
Click the image to open in full size.

Directivity index:
Click the image to open in full size.

The whole story of the prototypes can be read here (in German).

Sound
I can not tell too much about sound, since I have only one prototype and never listened to stereo with it. But the perception of distance is impressive. Even at 2.5 m in a small underdamped room it sounds like a nearfield monitor. And you can go very close to the baffle and the image never collapses to multiple point sources. This is truly an advantage of the pseudo-coaxial design.

I think this speaker works very well with larger distances and underdamped room. And it can play loud (low distortion), because there are many drivers and a high crossed horn in the middle.

When I build the final version I will post pictures. It will be looking a bit better.
Attached Images
File Type: jpg _MG_2018_klein.jpg (210.1 KB, 2976 views)
File Type: png Abstrahlung.png (47.4 KB, 1305 views)
File Type: png Abstrahlung Amplitude.png (16.6 KB, 1298 views)
File Type: png Bündelungsmaß.png (9.1 KB, 1282 views)
File Type: png Filter.png (9.8 KB, 1291 views)

Last edited by FoLLgoTT; 29th July 2018 at 08:18 AM.
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Old 21st December 2015, 09:53 AM   #2
Flaesh is offline Flaesh  Russian Federation
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I wanted to ask you about 3way H-K pseudo-coax for a long time.
Like this tread.

Can you share step responce?..
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Old 21st December 2015, 10:10 AM   #3
FoLLgoTT is offline FoLLgoTT  Germany
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Quote:
Originally Posted by Flaesh View Post
Can you share step responce?..
Of course.

Step response:
Pseudo-coaxial with narrow directivity (and Horbach-Keele filters)-sprungantwort-png
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File Type: png Sprungantwort.png (18.1 KB, 1243 views)
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Old 21st December 2015, 10:14 AM   #4
S4m is offline S4m  Germany
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Hi FollGott and hello neighbor
I'm working in Hanover and went there studying some years ago.
You've created a very interesting design. Are the small mids Aurasounds NS-2?
From my point of view: well done!

On this forum the guys are more experimenting with the Synergy-Horn.
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Old 21st December 2015, 10:18 AM   #5
FoLLgoTT is offline FoLLgoTT  Germany
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Quote:
Originally Posted by S4m View Post
Hi FollGott and hello neighbor
I'm working in Hanover and went there studying some years ago.
Hi neighbour. I studied here in Hanover, too. Maybe we met some day and didn't know it.

Quote:
You've created a very interesting design. Are the small mids Aurasounds NS-2?
These are Aurasound NSW2-326-8A. The lower midranges are Tang Band W4-1320 and the horn is loaded by a Celestion CDX1-1425.

Quote:
On this forum the guys are more experimenting with the Synergy-Horn.
Yes, I noticed that. But maybe an alternative with smaller depth could be interesting for some.
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Old 21st December 2015, 10:34 AM   #6
natehansen66 is offline natehansen66  United States
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Wow........that's really cool! I've thought it would be fun to try an array like that but I had no idea that the pattern could get that narrow. Very attractive if you don't have much depth for sure. You said the woofers are what limits the spl....what is the array of mids capable of? I'd imagine they do ok working over 1khz.
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Old 21st December 2015, 10:48 AM   #7
Flaesh is offline Flaesh  Russian Federation
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Quote:
Originally Posted by natehansen66 View Post
the woofers are what limits the spl..
Add 4 woofers more?.. ))
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Old 21st December 2015, 11:05 AM   #8
ewollowe is offline ewollowe  Australia
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Very interesting, reminds me of the DNA Sequence Speakers.
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Old 21st December 2015, 02:29 PM   #9
bbutterfield is online now bbutterfield  United States
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I really like the concept... sort of an expanding Mills Cross array. What are your intentions as far as toe-in, and covering multiple listeners?
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Old 21st December 2015, 02:34 PM   #10
FoLLgoTT is offline FoLLgoTT  Germany
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Quote:
Originally Posted by natehansen66 View Post
You said the woofers are what limits the spl....what is the array of mids capable of? I'd imagine they do ok working over 1khz.
I don't know exactly. I have to do THD measurements. But I need to put the speaker in the garden for that. Maybe I'll can do it in spring.

I don't think the Aurasounds are limiting in its frequency range.

Quote:
Originally Posted by bbutterfield View Post
What are your intentions as far as toe-in, and covering multiple listeners?
The sweet spot is not large. Since directivity gets much wider under about 800 Hz the sound changes under angles. The lower frequencies stay nearly constant in the whole room (because of reflections), but the higher doesn't. So this speakers must point directly to the listener. And it is clearly a one-man-speaker.
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