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Cardioid construction with coax and woofers

Digital_Thor

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Have a new idea.... or at least, I think it's new :)

Been playing with a KEF coax driver in my DIY active system for a while now. It sits on top of 2 x 8" SB NRX woofers and is integrated with 4 subwoofers scattered around the room.

Not pretty, and I need to design the finished cabinet for either a 2 box or a combined box for the Coax and the woofers.

First question is. Is there a real world benefit to place the woofers top/bottom of the coax - like WCW - instead of leaving them together under the coax like most designs. Floor bounce smoothing?

Second question. Would it be possible to make both woofers cardioid? Benefits seems cool - but I understand the challenges are not easy as a DIY project.

I was thinking of using the new Dayton signature 225, because they look cool and seem to be a lot of value for the price. Also, data suggest that they play in small volumes, reaching 65Hz at -3dB, matching my multi subwoofer system nicely.

Any help is highly appreciated.
 

Slick Minkus

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First question is. Is there a real world benefit to place the woofers top/bottom of the coax - like WCW - instead of leaving them together under the coax like most designs.
Better vertical lobing, and less floor and ceiling interaction in a limited frequency range (subject to distance between drivers).
à la D'Appolito.

Would it be possible to make both woofers cardioid? Benefits seems cool - but I understand the challenges are not easy as a DIY project.

Active cardioid, using one of the two drivers to cancel the other?
 
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Digital_Thor

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Better vertical lobing, and less floor and ceiling interaction in a limited frequency range (subject to distance between drivers).
à la D'Appolito.



Active cardioid, using one of the two drivers to cancel the other?
Oh...sorry I forgot to mention. I plan on doing it "passive" with slots on the side of the cabinet. Hope to build a quick test cab tomorrow, with sliding covers over the open slots on the sides, to see if I can measure the effect in my room.

I could add an extra DSP and make my system 14 channel, and have enough to be make an active DIY cardioid.... would require an extra stereo amplifier though.....
 
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Digital_Thor

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Coax in the center -> better vertical radiation

Woofers on top of each other -> more controlled horizontal directivity.
Hmmm... wonder if it's worth it, then. Could be that I would have a few less issues with my rear wall then, since it's slanted 45 degrees 60 cm from the floor.
I find it tricky to choose, but isn't horizon directivity slightly more important than vertical?
 

Timcognito

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Go to dyiaudio.com and type cardioid into the search box (titles only) and get some advice like this. Too many threads to repost. FYI
 

ernestcarl

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Coax in the center -> better vertical radiation

Woofers on top of each other -> more controlled horizontal directivity.

An example from the discontinued Presonus studiolive AI series:

1698519009547.png



1698518970126.png 1698518959728.png 1698518978467.png
 

abdo123

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Hmmm... wonder if it's worth it, then. Could be that I would have a few less issues with my rear wall then, since it's slanted 45 degrees 60 cm from the floor.
I find it tricky to choose, but isn't horizon directivity slightly more important than vertical?

Not slightly, but massively.
 
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Digital_Thor

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Ok.... I should have searched more. I basically want to copy the KEF R900, a model I have overlooked, since everyone talks about all the smaller versions.
But would I need to do the cardioid with both midrange and woofers, to take full advantage of the concept?
 

D!sco

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That depends on what band you want to be cardioid. The cancellations work on a particular resonance band and cancel each other out. How this is applied and which frequencies it applies to is complicated. Passive cardioid requires measurement tools only Fluid or ctrl have demonstrated on this forum so far, measuring a simulated cone's airflow against a box. Active is easy to simulate! Unless you don't know how. The Directiva R2 posts may help, but not as much as you'd expect. Cutting holes in your boxes is the new black magic. It works, so people do it. I'm sure there's a port calculation that can be applied somehow, but it's not something that's been published for the end user. When people figure it out, they go into business and hide what they can, like with the D&D 8C.
 
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Digital_Thor

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That depends on what band you want to be cardioid. The cancellations work on a particular resonance band and cancel each other out. How this is applied and which frequencies it applies to is complicated. Passive cardioid requires measurement tools only Fluid or ctrl have demonstrated on this forum so far, measuring a simulated cone's airflow against a box. Active is easy to simulate! Unless you don't know how. The Directiva R2 posts may help, but not as much as you'd expect. Cutting holes in your boxes is the new black magic. It works, so people do it. I'm sure there's a port calculation that can be applied somehow, but it's not something that's been published for the end user. When people figure it out, they go into business and hide what they can, like with the D&D 8C.
Make sense - thanks for the links :)
My point is, that I see that by copying the R900, I can get a smooth frequency curve like most other well-built speakers, even like the DIY I have right now. But I won't get the power response of the Directiva R2. So today - for learning - I will simply cut some holes on my DIY box and see what happens to the KEF coax in my room. Jumping into it, might be the best learning experience :D
 

D!sco

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The hardest part is consistently the loss of sensitivity across the cancellation band. If you want a little context, this was a three driver coaxial arrangement I simulated ages ago, and this is approximately what it takes in driver surface to have cardioid bass. I didn't even bother simulating the midrange, because like you, I planned to do it acoustically. But you'll still have losses and increased distortion from the leaky enclosure.

1698596449264.png
1698596463762.png

Screen Shot 2023-10-29 at 09.21.50.png

^How to flip a driver and separate it from the forward facing drivers in VCAD^

And the woofers are all overkill SEAS ER18RNX woofers. I imagine there will be similar difficulty in providing enough surface area for adequate midrange, but I could be totally wrong. I just look at the 8C and it's massive 8" midrange and dual 10's with proprietary OEM everything and can recognize the challenge involved.
 
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Digital_Thor

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The hardest part is consistently the loss of sensitivity across the cancellation band. If you want a little context, this was a three driver coaxial arrangement I simulated ages ago, and this is approximately what it takes in driver surface to have cardioid bass. I didn't even bother simulating the midrange, because like you, I planned to do it acoustically. But you'll still have losses and increased distortion from the leaky enclosure.

View attachment 322234View attachment 322235
View attachment 322236
^How to flip a driver and separate it from the forward facing drivers in VCAD^

And the woofers are all overkill SEAS ER18RNX woofers. I imagine there will be similar difficulty in providing enough surface area for adequate midrange, but I could be totally wrong. I just look at the 8C and it's massive 8" midrange and dual 10's with proprietary OEM everything and can recognize the challenge involved.
Wow... that's a lot! I just tried with 3 slots per side in my coax cabinet.... it's no miracle, that's for sure. Need to measure some more, to really see what the difference is. Listening to the one with slots and then the one without, seems like little difference... maybe less "boxy" sound... if there even is any noticeable difference.
I have made the slots big enough to also fit an 8" to see what happens further down i frequency.
 

D!sco

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The 8C patent also includes notes about rear vents. Anyways, if you have a mic and a lazy susan it should be easy to do horizontal polars. But it should be obvious when you walk around the speaker that the sound output suddenly drops.
 

Momomo67890

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Momomo67890

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BTW you can test this for your self but pretty much any size slot within reason anywhere from .5-8x sd per side plus 2-3 inchs of melamine foam thickness and depth = cardoid secret sauce. Done this on 3 different drivers all worked without any real tweaking so it could
Probably be dialed in even better if I cared.
 

ernestcarl

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