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Old 26th November 2012, 07:35 AM   #111
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I've meaning to ask this question for some time: why does none of the dipole projects by either JohnK or SL make use of asymmetrical driver placement within the baffle or even an asymmetrical baffle, such as one straight and one slanted side?

This would serve to smear the transitions somewhat. FR-wise, it would probably be just as easy to equalize, and it might also serve to smear some things in the temporal response.
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Old 30th November 2012, 06:12 PM   #112
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Quote:
Originally Posted by capslock View Post
I've meaning to ask this question for some time: why does none of the dipole projects by either JohnK or SL make use of asymmetrical driver placement within the baffle or even an asymmetrical baffle, such as one straight and one slanted side?

This would serve to smear the transitions somewhat. FR-wise, it would probably be just as easy to equalize, and it might also serve to smear some things in the temporal response.
It results in asymmetric horizontal response.

By the way, the Note II Rs will be at DIY New England this weekend (tomorrow) in case you missed mention of it on other boards. Hope to release the design by the Dec 7th.
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Old 30th November 2012, 07:52 PM   #113
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Yes, but is that necessarily a bad thing? Specifically, you would try to point the side with the better high end dispersion towards the listener rather than the side walls. Also, wouldn't the advantages in terms of time domain behavior offset any disadvantages from non-symmetrical horizontal profiles?

Too bad, my last trip to the US for this year ended about a week ago...
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Old 30th November 2012, 10:54 PM   #114
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I though I might post this just for the record. I have packed up the Note for DIY NE tomorrow, 12/1/12. After that I set up my NaO II RS system. As a result I am reconsidering the switch from U-frame woofer system to the dipole. The Note II RS may ultimately be released with a U-frame woofer. I will discuss the reasons for this when the final decision is made. Let me just say that I was overwhelmed by my exuberance over presenting a full range dipole system, thus abandon my usual pensive approach and my past experience that the u-frame is the better way to go.
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Old 30th November 2012, 11:14 PM   #115
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Capslock: My understanding is the best possible time domain behavior for a dipole is to have the smallest possible baffle, at least at higher frequencies where baffles tend to become acoustically large. Smallest possible will be left-right symmetric, basically shrink-wrapped around the drivers.

EDGE models suggest that a shrink-wrapped round baffle is better than a larger baffle of irregular shape, i.e. the polar contours are more consistently parallel. An irregular baffle will give flatter response for some listening angles but the polar contours will cross, so it's not possible to equalize the response effectively.

Last edited by thomasjefferson; 30th November 2012 at 11:16 PM.
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Old 1st December 2012, 01:11 AM   #116
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Quote:
Originally Posted by thomasjefferson View Post
Capslock: My understanding is the best possible time domain behavior for a dipole is to have the smallest possible baffle, at least at higher frequencies where baffles tend to become acoustically large. Smallest possible will be left-right symmetric, basically shrink-wrapped around the drivers.

EDGE models suggest that a shrink-wrapped round baffle is better than a larger baffle of irregular shape, i.e. the polar contours are more consistently parallel. An irregular baffle will give flatter response for some listening angles but the polar contours will cross, so it's not possible to equalize the response effectively.
Not sure what you are referring to when you say polar contours will cross. But as far as time domain behavior, once a dipole source is equalized to some target band pass response, like a midrange with 100 Hz high pass and 2k Hz low pass, it with have the same time domain behavior as a a box speaker with the same response.
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Old 1st December 2012, 02:45 AM   #117
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Default Crossing polar contours

I made two sims with EDGE, both using a 15cm driver (10cm piston diameter). One version has a minimal hexagonal baffle and the other baffle is larger. Polar contours cross with the larger baffle at 2.5 kHz. A larger baffle than this will have contours crossing repeatedly. These are 5 increments out to 45.

Baffle - Minimal.PNG

Baffle - Larger.PNG

Edge Mid 15cm_Minimal.PNG

Edge Mid 15cm_Irregular.PNG
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Old 1st December 2012, 02:27 PM   #118
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Finally found a European seller for that tweeter (the Tymphany).
Speaker & Co

Neo3PDR is near 100Euros these days!!!

Last edited by SAC; 1st December 2012 at 02:33 PM.
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Old 2nd December 2012, 12:45 PM   #119
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DIY NE has come and gone. The Note II RS was very well received. The bass problem I alluded to was still present and I will have to correct it. But there was not problem with deep authoritative bass using the SLS woofer. There was also a pair of Orion 4's present. My impression was that the shelving down of the tweeter in the Orion 4 takes a lot of the air and space out of the speaker sound. It would say that to shelf or not to shelf is really dependent on the source material. On large orchestral works it may sound OK but on my CD of Chopin piano concertos it sounded like some one threw a blanket over the sound board. The impact of the hammers hitting the strings was lost. In any event, with the miniDSP in the loop such a shelf can be inserted or removed in the Note with a mouse click and you have your choice.

This week I will be working of the woofer system. I will try to determine the problem with the dipole woofer (could be a simply enclosure resonance). I will also look at the SLS woofer in a U-frame as I have a feeling that over all the U-frames do perform better in an arbitrary room.
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Old 2nd December 2012, 01:39 PM   #120
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I'm afraid I don't agree with the Edge simulations. They show the dipole peak becoming lower in frequency as the off axis angle increases when it should rise. Source directionality will have some effect on this, but when I run the edge for a point source it does not show the dipole peak rising as it should (and does). Here are some measured data for a dipole with symmetric front and rear sources. You can see the shift of the dipole peak higher. Additionally, I have mathematically shown that at low frequency any shaped baffle is equivalent to a circular baffle of some effective radius, and it has been shown by others (in text books on acoustics) that at low frequency a circular baffle will behave as a doublet (two sources of equal strength but opposite phase separated by some distance, d). So I am a bit confused when you say that "contours will cross. That will not happen in the 6dB roll off region.

Click the image to open in full size.
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