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Old 8th October 2012, 11:44 PM   #11
tinitus is offline tinitus  Europe
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hmm, is it correct that cardioid is about changing the back polar pattern of a dipole by outphasing ?
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Old 8th October 2012, 11:51 PM   #12
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Quote:
Originally Posted by markus76 View Post
Did you also measure the in-room response around the listening position for both configurations?
Yes briefly. I consider LF measurement in room is too complex and single point measurement is much useless to post. I did move the mic around and observed peak dips, etc and paying attention to anything below 30hz.



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Originally Posted by john k... View Post
By sealing one woofer of the W frame you end up with a monopole and a dipole. This alone does not sum to yield a cardioid. The dipole and monopole must be individually equalized to have the same axial response. From you post it is not apparent when you talk about Eqing to meet your target is that is what you did.

But, as you know, I've been on the cardioid wagon since the infroduction of the NaO 10 teas ago.

[edit] Additionally, to get it "perfect" with that apporach the AC of the monopole must be at the axial center of the dipole.
Yeah, I really need to drag them outdoors for proper polar measurement. Obviously it's ideal to eq the drivers individually but then another xo channel is required and I don't want to get back to 3-way system. In any case if it does -30db at the back I'd be quite happy. The study shows that -20db is enough as in the case of ME Geithan. But -40db would be great.



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Originally Posted by RockLeeEV View Post
What's with the massive peaks at 600/1200/2400 hz? Cavity resonance? Mind showing the effect of stuffing the dipole section a bit with a thin layer of fibreglass?
Yes they are cavity resonance. The graph is taken without lowpass filter. When I low-pass at 120hz they are gone of course. No stuffing is needed.



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Originally Posted by DrDyna View Post
Sag percentage, it's like...3% or less? something like that.

Edit: It's 5%.
Yes, check this out for explanation:
Gainphile: Upside down / down-firing woofer



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Originally Posted by studiotech View Post
Thanks for the post Gain! At what distance was your measurement taken? Am I correct in assuming that the measurement was taken down low in front of the woofers and that's why the mids and highs look so off?

I am going to experiment with trying to get more of a cardioid response from my woofer too. I've been using the Bonded Logic behind the Neo10s , but want to try several layers behind and around the woofer now too. I think JohnK is going to redo his testing of the monopole, dipole and cardioid woofers and send the info to Elias to put through his wavelet app. Have you been reading that thread?

Greg
They are woofer only, nearfield, run full-range (no lowpass xo).

I have been following that thread (very quietly...!) it really inspired me to do this one.
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Old 8th October 2012, 11:58 PM   #13
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Quote:
Originally Posted by tinitus View Post
hmm, is it correct that cardioid is about changing the back polar pattern of a dipole by outphasing ?
Yes, that's one way to doit.

Using w-frame, For dipole both the front would be (simplified):

Front | Back

(+) | (-)
(+) | (-)


The cardioid setup:

(+)|(+)
(+)|(-)

Hence it cancels at the back.

The cabinet needs to be acoustically small.
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Last edited by gainphile; 9th October 2012 at 12:00 AM.
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Old 9th October 2012, 12:17 AM   #14
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Quote:
Originally Posted by tinitus View Post
hmm, is it correct that cardioid is about changing the back polar pattern of a dipole by outphasing ?
Yes, in an active set-up, one can play with the phase and delay of the rear woofer to tune the system to more of a cardioid response. Something like Meyer does with their PA subwoofers:

PSW-6 : High-Power Cardioid Subwoofer

Or in a passive U-frame style ala JohnK:

NaO U-frame

I'm hoping to add enough bonded logic around the lower backside of my baffle to get radiation somewhere less than a dipole and more like a cardioid. At least enough so that I get a smoother transition from full dipole to the omni of the subs that sit right next to them. Baffle to sub crossover is currently 60Hz.
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Old 9th October 2012, 12:25 AM   #15
tinitus is offline tinitus  Europe
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ok, thanks
so a back mounted passive radiator could have this function too ?
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Old 9th October 2012, 12:32 AM   #16
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Originally Posted by tinitus View Post
ok, thanks
so a back mounted passive radiator could have this function too ?
I am guessing because of that fact that the passive radiator is a tuned device, only really functioning across a narrow range of frequencies AND the fact that you have no electrical control over its delay, that it would not be workable as a good method to achieve a cardioid radiation pattern.
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Old 9th October 2012, 12:55 AM   #17
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Quote:
Originally Posted by gainphile View Post



Yeah, I really need to drag them outdoors for proper polar measurement. Obviously it's ideal to eq the drivers individually but then another xo channel is required and I don't want to get back to 3-way system. In any case if it does -30db at the back I'd be quite happy. The study shows that -20db is enough as in the case of ME Geithan. But -40db would be great.
If they aren't EQ separately you don't have a cardioid, period. If the same eq is applied to both woofers (rather than separate Eq) then the dipole will necessarily roll off at 6dB/octave relative to the monopole. Additionally, above the dipole = monopole frequency the dipole will have greater output and below it less output. The only frequency where you might achieve -30 dB is at the dipole = monopole frequency and I think that won't even happen because while the amplitude may be the same at that frequency the phase won't be exactly -180 degrees. Even with with well match eq getting better than -10 or -15dB over a wide frequency range is difficult. Remember, to get cancelation at the rear it is necessary to match amplitude and phase.
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Old 9th October 2012, 01:10 AM   #18
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The xo frequency is 120hz, so its below dipole peak.

Correct that there will be -6db/oct deviation monopole vs. dipole with single channel setup. I'll do a quick inroom measurement from the back later.
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Old 9th October 2012, 02:20 AM   #19
CLS is offline CLS  Taiwan
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Well done!

OTOH, sound quality is a big picture. I think many aspects are included - driver itself, loading, driving, in room response (acoustics)... etc.

I believe cardioid response can be very good at in room acoustics. However other factors also count. For example, properly loaded and driven, dipole bass can be very punchy, too.
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Old 9th October 2012, 07:41 AM   #20
Elias is offline Elias  Finland
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In theory I like cardioids too. They have the potential of allowing them placed very close to the room front wall.

I wish John K... manages to set up his mono-dipo-cardioid speaker and share some impulse responses.


- Elias
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