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Old Yesterday, 01:09 PM   #1
RyanC is online now RyanC  United States
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Default Promising loaded cardioid woofer test

Hello all-

After considering a lot of options to match directivity to some SEOS24's I decided to follow Face's lead and experiment with some cardioid loaded woofers.

Grabbed a pair of dayton pa255-8 10" to experiment with...I figure if the directivity is coming from the cardioid loading, why not minimize C2C. So I made up the test boxes you see here, roughly following the layout used by gradient (seems like as good of a place to start as any).

One thing I noticed in cardioid woofer tests is that often not a lot of info/thought/data is going into what kind of material is used for the acoustic impedance. I know from the acoustics side (bass traps etc) and using the porous absorber calculator that gas flow resistivity vs thickness of material is not always intuitive. But after playing with PAC for a bit my thought was that GFR needs to be VERY high for an even absorbtion coefficient over the pass band, especially where mine is <500hz. Somewhere around 100k Rayls/m at 3-4 inches.

So time to test it! At first I put only two layers of denim carpet padding and the results were not good. Additionally with a 50hz sine you could hear audible chuffing noise at the ports. So with 4 layers of tightly packed pad, and fiberfill additionally packed in tightly here are the results. Also no port noise (I will cut roundovers on all of them anyway)...Also the waterfall is very clean for as good of a test as I can get there.

All the measurements were done inside, but the room there has a very clean ETC as there are essentially no specular reflections (diffusers) and there are many bass traps behind the eps diffusers. The measurements may not be perfect but IMO good enough to show that the cardioid loading is working...Also the waterfall looks very clean, it's difficult to draw too much from that measured inside but at least it shows no major stored energy. Walking around the box you can clearly hear the directivity of it.

The next step will be to finish and paint and pair them up with the SEOS24's Radian951Be's, if all goes well eventually I'll probably do new boxes for AE TD12's or something.
Attached Images
File Type: png card off axis.png (199.1 KB, 100 views)
File Type: jpg 2014-04-15 14.10.59.jpg (279.6 KB, 99 views)
File Type: jpg 2014-04-15 13.54.08.jpg (370.2 KB, 98 views)
File Type: png 0 axis waterfall.png (668.5 KB, 97 views)

Last edited by RyanC; Yesterday at 01:52 PM.
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Old Yesterday, 01:18 PM   #2
RyanC is online now RyanC  United States
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Here is a better pic of the ports-

"Loaded cardioid", Should have been "cardioid loaded" Lol, I know when I get loaded I can only go in one direction..
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Old Yesterday, 01:34 PM   #3
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Great results.
Can you make a measurement in sealed box for comparison ?
Also I'd be nice to see some detailed pictures of layers of stuffing.
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Old Yesterday, 02:14 PM   #4
Juhazi is offline Juhazi  Finland
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Nice! What is impulse gating, 500ms? This long gating indoors does mask real directivity due to reflections and frequencies below Schroeder. I am sure that in reality directivity is stronger at >45¤ han these measurements show. How far did you measure? Looks like 10¤ steps. Please take the gear outdoors soon! Then measure also 90-180¤!

Low end directivity and response looks like dipole and there might be dipole null at 280Hz. The null is not as sharp as true dipoles, this looks very good for cardioid bass and mid up to xo around 1000 - 1500Hz
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Old Yesterday, 11:13 PM   #5
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Nice start Ryan!
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Old Today, 10:13 AM   #6
RyanC is online now RyanC  United States
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Quote:
Originally Posted by fakamada View Post
Great results.
Can you make a measurement in sealed box for comparison ?
Also I'd be nice to see some detailed pictures of layers of stuffing.
Oh man I wish I had time to make up a sealed box just for test purposes right now...

Not for the dayton drivers at least. I'm going to eventually try to replace all my guitar cabs with card boxes as well, so when I get to the JBL d120's I can compare them to the sealed boxes they are currently in. Paint is drying now, but I'll get some close ups of the stuffing as soon as I can.

Last edited by RyanC; Today at 10:22 AM.
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Old Today, 10:27 AM   #7
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Yeah. Such comparison could be VERY informative. Maybe you could just seal the holes with some tape or bitumen pads or smth else just for measurement?
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Old Today, 10:48 AM   #8
RyanC is online now RyanC  United States
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Quote:
Originally Posted by fakamada View Post
Yeah. Such comparison could be VERY informative. Maybe you could just seal the holes with some tape or bitumen pads or smth else just for measurement?
Hmmm-

I think the whole test shows that GFR has to be very high in the first place. I don't think tape would have much effect at all. I do hear you, it's certainly not scientific without a control. I might be able to tape some MDF sheets over the ports...I'll give it a shot when I have a min to do more tests.
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Old Today, 10:49 AM   #9
RyanC is online now RyanC  United States
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Quote:
Originally Posted by Juhazi View Post
Nice! What is impulse gating, 500ms? This long gating indoors does mask real directivity due to reflections and frequencies below Schroeder. I am sure that in reality directivity is stronger at >45¤ han these measurements show. How far did you measure? Looks like 10¤ steps. Please take the gear outdoors soon! Then measure also 90-180¤!

Low end directivity and response looks like dipole and there might be dipole null at 280Hz. The null is not as sharp as true dipoles, this looks very good for cardioid bass and mid up to xo around 1000 - 1500Hz
Thanks. REW default- turkey L125 R500, and yes 90 degrees in 10 degree increments. I know these aren't perfect, but I live in the city so it's hard to get outside to measure...This particular room is a bit of an odd ball as well. It's (intentionally) very leaky, no drywall on the ceiling (just vapor barrier and loosely stuffed fiberglass in the attic), and literally a ton of 703 for bass traps. But yeah eventually I'll take the SEOS24's and these or a later iteration outside for further testing.

I was looking for ~12dB separation @90 degrees @500hz to match the SEOS24's. Everything will be with DSP (dlcp).
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Old Today, 11:02 AM   #10
Juhazi is offline Juhazi  Finland
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RyanC, for xo area investigation you can use eg. 9ms gating indoors with good results. I get lots of reflections at 12ms gating. Below 500Hz is most difficult to "see" clearly indoors. If you have saved those measurements, use IR button to change gating for each measurement. For quick check and to get in the ballpark you can use just 0¤ 30¤ and 60¤ measurements.
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