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Old 5th May 2014, 12:41 PM   #1
Jag768 is offline Jag768  Netherlands
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Default Full range cardioid, need advice on next prototype

Currently i'm working on a new speaker build, aiming for a cardioid radiation pattern from 50Hz on up. I have made a prototype consisting of a top cabinet which has a A&D R1030 10" woofer in a damped Uframe, and a Hypex PSC 2 400 plate amp (2 ch amp + dsp). I experimented with the opening of the Uframe, adding slots and especially the placement and quantity of damping material. See attached files for the optimal polar pattern. For high frequencies, I have a B&C DE250 on a Dayton 10 waveguide. I modified the waveguide slightly to accept the bolt on compression driver and remove any irregularities in the transition to the waveguide.

For the sub cabinet, I have 2 Peerless XLS10 woofers and a Hypex PSC 2 400. In order to achieve cardioid radiation, I have combined a sealed and dipole enclosure. The dipole is high passed at 50Hz using a 4th order filter in order to limit cone excursion and to have the advantages of a pressure source <50Hz. Free field measurements showed a polar resembling cardioid from 63Hz on up.


However, there are some points for improvement for which I would like your advice!
1. In order to achieve maximum suppression of LF at rear, I had to delay the monopole sub by 1,9ms. This resulted in less than optimal summation of the two drivers at the front. The dipole woofer is actually positioned 20cm behind the woofer in the sealed enclosure.
2. The polar has a maximum which is about 20degrees of center, caused by asymmetric construction of the dipole. I think I will make a new version using a regular H frame.
3. Im considering adding passive radiators to increase output of the monopole <50Hz for LFE use. Im a bit concerned this will complicate achieving cardioid radiation in the 50-150Hz region.
Attached Images
File Type: jpg Cardioid sub.jpg (813.9 KB, 653 views)
File Type: jpg B&C_DE250.jpg (399.9 KB, 611 views)
File Type: png Gesloten_dipool_cardoid_respons.png (9.3 KB, 582 views)
File Type: png Prototype_Cardiod_sub_80Hz_polar.png (38.9 KB, 572 views)
File Type: png Sonogram_B&C DE250.png (152.7 KB, 574 views)
File Type: jpg Topkast.jpg (718.4 KB, 229 views)
File Type: png Sonogram_woofer.png (116.6 KB, 220 views)

Last edited by Jag768; 5th May 2014 at 02:01 PM.
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Old 5th May 2014, 06:35 PM   #2
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Quote:
Originally Posted by Jag768 View Post
For the sub cabinet, I have 2 Peerless XLS10 woofers and a Hypex PSC 2 400. In order to achieve cardioid radiation, I have combined a sealed and dipole enclosure. The dipole is high passed at 50Hz using a 4th order filter in order to limit cone excursion and to have the advantages of a pressure source <50Hz. Free field measurements showed a polar resembling cardioid from 63Hz on up.
1. In order to achieve maximum suppression of LF at rear, I had to delay the monopole sub by 1,9ms. This resulted in less than optimal summation of the two drivers at the front. The dipole woofer is actually positioned 20cm behind the woofer in the sealed enclosure.
The cardioid arrangement you describe will always have less than optimal summation of the two drivers at the front, and can only have maximal attenuation at the rear at one frequency determined by placement and delay.

At low bass frequencies, the cardioid arrangement won't be very effective in small rooms, as the reflected waves off the boundaries changes the phase relationship of the two drivers compared to outdoors or large rooms where boundaries are wavelength distances away.
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Old 5th May 2014, 07:43 PM   #3
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Quote:
Originally Posted by weltersys View Post

At low bass frequencies, the cardioid arrangement won't be very effective in small rooms, as the reflected waves off the boundaries changes the phase relationship of the two drivers compared to outdoors or large rooms where boundaries are wavelength distances away.
I'm not sure I understand this. I don't think there is any connection between room size, boundary proximity and effectiveness.

I was doing some simulations a couple of weeks ago in the context of killing a wall bounce for a typical wall mounted (but with some finite spacing) system.

In free space we would want to make a cardioid with some range of operation. As long as there is a rear firing null then there is no bounce off of the wall behind (at least on the system axis, not necessarily if you moved to oblique angles).

In the case I was working on I had a small element, say, 6" off the wall and a cancelling unit flush on the wall. As long as I compensated for their respective boundary conditions (one in free space the other boundary mounted) I could achieve full cancelation of the wall reflection.

Everything was tied to the distance of the system from the wall, could be adjusted for any wall spacing, and had nothing to do with an overall room size.

Regards,
David
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Old 6th May 2014, 12:58 PM   #4
Jag768 is offline Jag768  Netherlands
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Quote:
Originally Posted by weltersys View Post
The cardioid arrangement you describe will always have less than optimal summation of the two drivers at the front, and can only have maximal attenuation at the rear at one frequency determined by placement and delay.

At low bass frequencies, the cardioid arrangement won't be very effective in small rooms, as the reflected waves off the boundaries changes the phase relationship of the two drivers compared to outdoors or large rooms where boundaries are wavelength distances away.
Thank you for your reply! Im trying to understand why it would only work at one frequency. Measurements indeed show attenuation around a maximum at 100Hz. See attached off axis repons measured outdoors without gating, at 2meter distance, at 0,45,90,135,180 degrees. Attenuation shows a maximum of over 25dB, which was probably more since the respons was "dancing" on the wind at 180degrees.

Im also having a hard time understanding why the monopole needed around 1,9ms of delay to get max attunuation at the rear, while the monopole is actually positioned more to the front.

Quote:
In free space we would want to make a cardioid with some range of operation. As long as there is a rear firing null then there is no bounce off of the wall behind
Interesting point. Only, im not sure how close the null would be to the speaker, since the respons of a dipole is different in the nearfield. Tailoring the filter for the dipole to the specific distance to the wall, might eliviate this problem wouldn't it?
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File Type: png Prototype Cardiod sub off axis respons.png (32.3 KB, 79 views)
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Old 6th May 2014, 05:51 PM   #5
Jag768 is offline Jag768  Netherlands
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Ok, just realised that polarity was wrong for the dipole woofer. I will post new measurements with correct polarity. Hopefully, that will give easier to understand results!
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Old 6th May 2014, 05:58 PM   #6
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Quote:
Originally Posted by speaker dave View Post
I'm not sure I understand this. I don't think there is any connection between room size, boundary proximity and effectiveness.

In the case I was working on I had a small element, say, 6" off the wall and a cancelling unit flush on the wall. As long as I compensated for their respective boundary conditions (one in free space the other boundary mounted) I could achieve full cancelation of the wall reflection.

Everything was tied to the distance of the system from the wall, could be adjusted for any wall spacing, and had nothing to do with an overall room size.
David,

Room size will often determine boundary distance to some extent. You adjusted your simulation to account for the boundary distance where the cancelling unit was located, requiring a different set up than what would be effective outdoors or with boundaries at a different distance.

Sounds like you are developing some cool new stuff, how are you liking the new job?

Art
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Old 6th May 2014, 06:38 PM   #7
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Originally Posted by Jag768 View Post
Im also having a hard time understanding why the monopole needed around 1,9ms of delay to get max attunuation at the rear, while the monopole is actually positioned more to the front.
These sources will do a lot better at helping you visualize what is going on with your tests than my explanations:

Phase Wavelengths: The End Fire Cardioid Array made visible | Bob McCarthy's Blog

New website Merlijn van Veen, home of the Subwoofer Array Designer calculator

Merlijn really did a nice job with the calculator.
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Old 6th May 2014, 09:28 PM   #8
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Originally Posted by weltersys View Post
David,

Room size will often determine boundary distance to some extent. You adjusted your simulation to account for the boundary distance where the cancelling unit was located, requiring a different set up than what would be effective outdoors or with boundaries at a different distance.
I adjusted to account for boundary distance just because I was modeling a speaker with a given depth and a canceling drive on the wall (a bit like the "pitcher/catcher" bass arrays that have been discussed occasionally). In reality if you create a free standing cardioid pattern then there is a rearward aiming null and the wall can be any distance behind. It is in the null so no rear wall bounce will occur.

Of course this only applies for the listener directly in front of the speaker. As you move to the side you are on a line back to the speaker that is not at the angle with greatest depth of null. Still, for that new angle you could create a hyper cardioid polar from the speaker (with 2 nulls) such that you are once again on the null of the system (actually, relative to the reflected virtual speaker) and the wall will once again disappear.

Quote:
Sounds like you are developing some cool new stuff, how are you liking the new job?

Art
I'm enjoying it a lot. Thanks for asking.

There are great facilities here and a lot of brilliant people. The environment is very academic and they have me taking an intense DSP class.

The products are very sophisticated in their technology (takes a lot of DSP to get acceptable sound out of a tiny plastic box with 1 1/2" drivers!)

David S.
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Old 6th May 2014, 09:45 PM   #9
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Quote:
Originally Posted by Jag768 View Post

"In free space we would want to make a cardioid with some range of operation. As long as there is a rear firing null then there is no bounce off of the wall behind."

Interesting point. Only, im not sure how close the null would be to the speaker, since the response of a dipole is different in the nearfield. Tailoring the filter for the dipole to the specific distance to the wall, might eliviate this problem wouldn't it?
If anything varies with distance then the distance to the wall is not the issue, but the distance from speaker to listener.

In fact it is the distance from the virtual reflection speaker to the listener.

Remember, what you are setting up is a speaker in front of a boundary. If the boundary is a mirror (for the sound) then you will see both the real speaker and a backwards facing virtual speaker just beyond the mirror (wall). You want to configure that virtual speaker such that at your distance and angle it has created a wide band null that kills its output. By doing so the wall bounce and hence the wall cease to exist.

I don't know how much the dipole varies with distance but I would think that with most realistic scenarios you would close enough to far field conditions.

As to your somewhat narrow null, you need to look at the phase response of your two elements in the rearwards direction. Cancelation requires 2 things: equal strength and opposite phase. I'm guessing the phase curves swing at different angles, so they are only 180 degrees apart for a fairly narrow range.

The easiest way to do this over a wider range is with electronic delay for one of the elements.

David
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Old 6th May 2014, 10:17 PM   #10
puppet is offline puppet  United States
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David ... I'm under the impression that neither equal strength or opposite phase is a requirement. I'll site an EV pamphlet which states that the "control" driver (rear) can be 6db lower in output. Drivers (front and rear) are wired "in phase" and require delay applied to the control driver along with appropriate spacing. Since the enclosures are separate, adjusting the position of the rear drivers should shape the null.

Last edited by puppet; 6th May 2014 at 10:20 PM.
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