S23 - 4 way Active Cardioid Loudspeakers - diyAudio
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Old 31st August 2014, 10:57 AM   #1
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Default S23 - 4 way Active Cardioid Loudspeakers

This design utilise my last dipole speakers as a platform.

I'm surprised at how much configurable it is.

Click the image to open in full size.

The idea is to make two alternating channels as monopole, hence the acoustic sum renders a cardioid polar response.

I need to fine tune and take outdoor polar response measurements (spring is coming yay!! ) but pleasantly hearing very solid renditions already especially of vocals and mid bass.

I can foresee the challenge where the wavelength is not acoustically small between woofer and mid-woofer. An asymmetrical crossover might be needed.

Click the image to open in full size.

First/very early impressions:
- Great vocals. Even some recording which I thought did not sound right on dipoles
- Great lower bass.
- Sharper imaging than dipole. Not too diffused. But also not laser-sharp like waveguide
- More LFE power/feel compared to dipoles

The bad (??)
- Lost that dipole transparency "magic"
- When I move off center the sound follows ??
- LFE slams still not as great as simple sealed subs
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Old 31st August 2014, 01:02 PM   #2
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Interesting evolution, but you should not make a closed box, two much problem with internal reflection. I think if you replace the hard back side by damping material should give a more open sound. It looks like an aperiodic box (see variovent). And another problem is your upper mid is not very at ease in a small closed space (SEAS recommends 9L).
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Old 31st August 2014, 10:28 PM   #3
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Thanks. I've been a patient follower of MBK's work here regarding damped midrange cardioid:
www.diyaudio.com/forums/multi-way/142691-adventures-cardioid.html?highlight=cardioid+singapore

It is very hard. The 'problem' is they become more dipole lower in the frequency. While I need dipole+monopole combination to create the Cardioid response.

The smaller enclosure of W15 should not be an issue, I think, as they are operated only from 100hz-1.5khz.
In fact I need this enclosure small to push the cavity modes higher in the frequency. They measured flat for the desired range.

... only measurements will tell. Hoping for a clear, windless weekend now
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Old 1st September 2014, 12:58 AM   #4
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This should get interesting.
I find cardioids to sound excellent, but a bit surprised that more people aren't doing them.

Considering your previous projects, I think you have the background to make a great cardioid.
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Old 6th September 2014, 11:00 AM   #5
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It was a great today for measurement. Unfortunately it was also a great day for the neighbours to do lawnmowing, etc. Patience was really tested!

Click the image to open in full size.

So I have the data. I think for this endeavour it's best to use Full Polar polot instead of my favourite sonograms. 360 was quite a painstaking process!


1) From 20khz down to 1.6khz (Tweeters)

Seas DXT showing great control. Mostly forward directional with a hint of hyper-cardioid at the lower end of it where it crosses with W15 at 1.5khz

Click the image to open in full size.


2) From 1.6khz down to 800hz

Instead of turning into Omni, W15 radiation is somewhat hyper-cardioid. At the lower end (800hz) a hint of transitioning to dipole.

Click the image to open in full size.


3) From 800hz down to 400hz

More influence from W22, and it formed a weak dipole. Not a full null at the sides. At 600hz, rear radiation is still -6db less.

Click the image to open in full size.

4) From 400hz down to 20hz

From then on it gradually transition to Omni and below. This is because I changed the sub configuration to simple monopole. Audibly more slam and power. At this range the measurement accuracy is very poor.

Click the image to open in full size.



In summary
- The perfect Cardioid was never formed fully
- Forward directivity is maintain from 20khz down to 600hz. -6db less rear radiation or better.
- Then it transtition to a weak dipole to Omni. The transition is smooth and not abrupt.
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Last edited by gainphile; 6th September 2014 at 11:29 AM.
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Old 8th September 2014, 01:03 PM   #6
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An earlier work by Natehansen66 on Cardioid speakers. His method is the classical opposing monopoles with DSP delay. I had been thinking about this and glad to have found this thread.

www.diyaudio.com/forums/multi-way/259724-dsp-midrange-directivity-control-aka-kinda-cardioid.html

The Cardioid also did not form perfectly. This points to the opposing monopoles needs to be acoustically small. The challenge become somewhat similiar with dipoles at certain frequency range.

Nevertheless rear radiation is much reduced.
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Old 8th September 2014, 09:27 PM   #7
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Actually, I tested quite a few different configurations. The opposing monopoles (which I take it you're talking front and back) was actually the worst result due to the greater front to rear distance. I found that using either active drive units on the side, or a large vent on each side gave the widest band of useable directivity. It works best when the out of phase radiation is a 1/4 wl or so (of the highest freq of interest) behind the front baffle plane. The baffle and forward piston size dictate how high you can take it as usual.

Cool project, gain. Your website has been an inspiration since I started building speakers. I had gotten away from dipoles but it seems I'm kinda finding my way back.
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Old 9th September 2014, 11:18 AM   #8
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I am very interested in this project, I was also looking at cardioid response for an adaptation of the Econowave mini or JBL AC16 which uses a 6.5" woofer and 90x90 6" waveguide and compression driver.

I was hoping to achieve a response that transitions into cardioid rather than omni as these speakers would be used for voice reinforcement and wanted to improve system gain by reducing the feedback level through he microphone.

Would it be possible to achieve this by adding another driver to the rear of the cabinet and using MiniDSP for the eq and delay or as natehansen66 has experimented with, using two smaller drivers on the sides of the cabinet?

What would I expect to see on such a small cabinet with small drivers?

Last edited by rich31td; 9th September 2014 at 11:45 AM.
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Old 9th September 2014, 11:23 AM   #9
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Most of your recent projects have moved away from waveguide designs. I'm curious if you prefer the sound of conventional domes to waveguide/CD combinations? The reason I ask is my next project will be a hybrid cardoid design and I'm contemplating the high freq section.
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Old 9th September 2014, 05:55 PM   #10
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Very interesting project as always . Do you have measurements of the dipole and monopole mid amplitude and phase response?
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