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Old 17th May 2012, 10:13 PM   #41
boris81 is offline boris81  United States
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Quote:
Originally Posted by njoak View Post
What I see in those figures is exactly what I am trying to argue: If you have no delay, you get a dipole. Add delay, get cardioid. In my mind it is all about how the radiation sources (the point where the waves exit the box, if we put it that way) interfere. To have two monopole sources sum to a cardioid pattern, they must be phase-inverted, and the rear one delayed by T=D/c, where D is the separation. A different delay gives a different pattern (0 gives dipole, D/(2c), roughly, gives supercardioid).

Edit: By the way, the relation between the separation and the caridoid-izable wavelengths is seen in the right figure as well. You need to keep the separation such that you are in the roughly linear region in the response plot.
Right. I'm going a step further to say that a cardioid might also be described by a 3rd model - no delay, 2 polar opposite sources one of which is attenuated. I'm suggesting that the difference of the sources' powers and the delay in this abstraction might be interchangeable. The practical implication of this would be that the phase distance of the 2 sources will remain the same in the 3rd model.

If I am wrong and it can be shown that leaky boxes and U-Frames act the same then I will abandon the original idea. As far as I'm concerned U-Frames are easier to build and will allow me to better tune the low end.
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Old 18th May 2012, 07:01 AM   #42
njoak is online now njoak  Sweden
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Quote:
Originally Posted by boris81 View Post
Right. I'm going a step further to say that a cardioid might also be described by a 3rd model - no delay, 2 polar opposite sources one of which is attenuated. I'm suggesting that the difference of the sources' powers and the delay in this abstraction might be interchangeable. The practical implication of this would be that the phase distance of the 2 sources will remain the same in the 3rd model.

If I am wrong and it can be shown that leaky boxes and U-Frames act the same then I will abandon the original idea. As far as I'm concerned U-Frames are easier to build and will allow me to better tune the low end.
Got it, thank's for the patient explanation.
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Old 18th May 2012, 08:09 PM   #43
keyser is offline keyser  Netherlands
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Interesting project! I'll be following this one!
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Old 21st May 2012, 03:28 PM   #44
Tytte71 is offline Tytte71  Norway
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Very interesting project that in many ways are similar to mine (Build Thread: OBEOS). Although nothing has been written on my thread for a long time, the project is far from dead. Also we have a Norwegian forum project ongoing utilizing cardioid midrange.

I would like to discuss if it is feasible to apply a damped U-baffle for the midrange. The idea is to combine the dispersion of the damped U-baffle with the natural dispersion of the driver. Simplified maths says yes, but I encounter some problems when measuring it indoor. I have to add that I haven't been able to measure outdoor, which is the next thing on the menu when the weather allows for it.
In basic we want to make the U-baffle with the dipole peak entering the frequency band above the point where the baffle/driver itself starts beaming. Adding the selected damping material should attenuate the rear energy and consequently the dipole peak will be supressed. This way "high efficiency" cardioid dispersion may be achieved over a wider bandwidth, letting the driver control the dispersion in high frequencies and the U-baffle in the lower.

Could it work?

By the way, it would be very nice if JohnK could share his experience and opinions in this thread.
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Old 21st May 2012, 04:59 PM   #45
njoak is online now njoak  Sweden
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Originally Posted by Tytte71 View Post
Very interesting project that in many ways are similar to mine (Build Thread: OBEOS). Although nothing has been written on my thread for a long time, the project is far from dead. Also we have a Norwegian forum project ongoing utilizing cardioid midrange.

I would like to discuss if it is feasible to apply a damped U-baffle for the midrange. The idea is to combine the dispersion of the damped U-baffle with the natural dispersion of the driver. Simplified maths says yes, but I encounter some problems when measuring it indoor. I have to add that I haven't been able to measure outdoor, which is the next thing on the menu when the weather allows for it.
In basic we want to make the U-baffle with the dipole peak entering the frequency band above the point where the baffle/driver itself starts beaming. Adding the selected damping material should attenuate the rear energy and consequently the dipole peak will be supressed. This way "high efficiency" cardioid dispersion may be achieved over a wider bandwidth, letting the driver control the dispersion in high frequencies and the U-baffle in the lower.

Could it work?

By the way, it would be very nice if JohnK could share his experience and opinions in this thread.
Could you link to the thread on the norwegian forum? I might be interested to check it out since I want to do the same thing.

Personally I think the difficult part is to find a material/port combination which has the correct resistivity, and is such that the resistivity does not change over the relevant frequency range and SPL. Linkwitz explains it here: Frontiers
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Old 21st May 2012, 08:36 PM   #46
Tytte71 is offline Tytte71  Norway
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The forum thread in question: AVforum.no - Dynamiker's forslag til Forumprosjektet 2012. Your contribution will be highly appreciated

Thanks, I'll read the Linkwitz articles thoroughly to see if there is a solution to be found between the lines.
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Old 22nd May 2012, 06:54 PM   #47
boris81 is offline boris81  United States
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Quote:
Originally Posted by Tytte71 View Post
I would like to discuss if it is feasible to apply a damped U-baffle for the midrange. The idea is to combine the dispersion of the damped U-baffle with the natural dispersion of the driver. Simplified maths says yes, but I encounter some problems when measuring it indoor. I have to add that I haven't been able to measure outdoor, which is the next thing on the menu when the weather allows for it.
In basic we want to make the U-baffle with the dipole peak entering the frequency band above the point where the baffle/driver itself starts beaming. Adding the selected damping material should attenuate the rear energy and consequently the dipole peak will be supressed. This way "high efficiency" cardioid dispersion may be achieved over a wider bandwidth, letting the driver control the dispersion in high frequencies and the U-baffle in the lower.

Could it work?

By the way, it would be very nice if JohnK could share his experience and opinions in this thread.
From your description it sounds like you are trying to do what JohnK was experimenting with. When using a U-Frame I believe the front wave can be made to transition smoothly from beaming into cardioid but the rear wave will be a problem. If you are interested in a good rear wave I might be wrong I don't believe it's doable with a U-Frame regardless of damping.
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Old 22nd May 2012, 08:09 PM   #48
Tytte71 is offline Tytte71  Norway
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Thanks Boris. Do you know if there's an article to read about JohnK's attempt?
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Old 22nd May 2012, 09:11 PM   #49
boris81 is offline boris81  United States
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Originally Posted by Tytte71 View Post
Thanks Boris. Do you know if there's an article to read about JohnK's attempt?
NaO U-frame

This is the article I'm referring to. Although the damped response ends up looking OK, JohnK chooses to use the U-Frame only below the dipole peak. I do hope that he joins this thread and help us understand this better.
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Old 25th May 2012, 04:06 AM   #50
boris81 is offline boris81  United States
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Default some progress

I became inpatient and put together a crude structure. I had some promising results and many setbacks. I finally have a prototype and can begin testing but it's become obvious that I need to rethink many of my original ideas for the enclosure.
2011-12-boris-bday-speaker 108.jpg 2011-12-boris-bday-speaker 106.jpg

Stability is a major concern with such a tall, slim and heavy structure, especially when it's placed on carpet. I have to construct wide feet with spikes and I worry that they might have to spread more than I anticipated.

I realised the way I was planning to support the woofers at the rear was flawed and I need to come up with a different strategy. I was going to use tension bolts that pull the basket but supporting the magnet itself will be more effective. Interestingly, vibration doesn't seem to be an issue at moderate listening levels although I haven't really investigated that area.

I had a problem with the bass equalization that took me a few days to figure out. It was caused by the kx-Project - my DSP platform. The WaveIn stream had no headroom and applying bass boost filters sounded horrible. That was a strange issue because the ASIO stream, which I usually use is attenuated by 12dB.

When that was finally solved I took some indoor measurements. They are mostly to figure out the crossover for the tweeter and the midwoofer. There is also some very crude off-axis data from the midwoofer. I couldn't get good measurements between 90-160 degrees but it looks like the response is forming a supercardioid.

Tweeter and Midwoofer with a quick crossover. These are very crude indoor measurements, I will try to get something better. 0degrees - red, 60 - Blue, 90 - Green, 160 - Gray, 180 - Black.
c402-tm-2xo-0-60-90-160-180.jpg


I focused most of my attention on the TM crossover. This is showing a Le Cleac'h at 1400Hz.
c401-tm-eq-lecleach.png
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