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Old 29th February 2012, 10:02 PM   #111
Remlab is offline Remlab  United States
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Quote:
Originally Posted by skorpion View Post
Seth,

To ascertain that we talk about the same phenomenon. What you call 'the lower cut off point' I suppose is what commonly is referenced as 'the dipole peak' which is dependent upon baffle size, and the effects of, also of baffle appearance and speaker placement.

/Erling
Erling
Using a 7" driver again as an example, the lower acoustic cut off point would start occurring when the frequency length exceeds the diameter of the drive unit. In this case, around 1,900 hz, right in the middle of the ear's most sensitive range. Below that point, on an open baffle, you get a smooth, even 6 db/octave roll off. What happens just above that point? The best analogy for this that you can actually see, is the zaph commentary on surface mounting tweeters with 4" diameter plates. Not exactly the same as an open baffle situation, but it is enough to illustrate the point..
Seth
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Old 29th February 2012, 10:08 PM   #112
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Seth,

We are talking about the same thing. I thought perhaps you meant something different with your term.
I would rather have called it 'upper cut off point' I think.

/Erling

Last edited by skorpion; 29th February 2012 at 10:11 PM.
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Old 29th February 2012, 11:31 PM   #113
Remlab is offline Remlab  United States
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Quote:
Originally Posted by skorpion View Post
Seth,

We are talking about the same thing. I thought perhaps you meant something different with your term.
I would rather have called it 'upper cut off point' I think.

/Erling
Erling
Do I have my phraseology screwed up? I see the upper cut off point as where you choose to "electrically" low pass the woofer. The lower cut off point(In this case) is when the 7" drive unit has an inevitable 6db/octave acoustic high pass roll off starting at 1,900 hz due to the driver's rear wave acoustically canceling out the front wave. The only way to compensate for this acoustic roll off is to use 6db/octave diametric equalization below 1,900 hz..Not a good thing.
Seth

Last edited by Remlab; 29th February 2012 at 11:41 PM.
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Old 1st March 2012, 12:17 AM   #114
Remlab is offline Remlab  United States
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Erling
Here is an excellent linkwitz article that illustrates exactly how a round open baffle shape effects the frequency response. Diffraction from baffle edges The key phrase regarding the "transition region" that I was referring to is in the last paragraph of the article..
Seth

Last edited by Remlab; 1st March 2012 at 12:45 AM.
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Old 1st March 2012, 09:37 AM   #115
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Seth,

Yes, Linkwitz is a good source of information for OB.
I'll give you another link to Rudolf Finkes's site, Dipolplus. He has some good dipole papers in German and English in the download section: Offene Schallwand (OB) . The German one is covering a little more ground than the English one. We are now just talking past each other with some different terminology.

/Erling
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Old 1st March 2012, 11:03 PM   #116
Remlab is offline Remlab  United States
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Erling
Finke's site is awsome! I really appreciate how he illustrates that listening to a circular baffle off axis ameliorates most of the problem..
Thanks!
Seth

Last edited by Remlab; 1st March 2012 at 11:15 PM.
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Old 2nd March 2012, 03:57 PM   #117
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On the topic of Neo10s and naked drivers: the three way nude swinging dipole thread
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Old 2nd March 2012, 10:30 PM   #118
Remlab is offline Remlab  United States
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Quote:
Originally Posted by natehansen66 View Post
On the topic of Neo10s and naked drivers: the three way nude swinging dipole thread
The Neo 10 and 3 are perfect for this type of "nude" speaker and I'm sure(maybe) it sounds as good as the measurements would indicate. The really difficult thing I have with this design though, is that the Neo 10 would begin (In real life) its inevitable acoustic high pass roll off at 2,700 hz due to its 5" width. That is, in my opinion, a very high price to pay for saving money on a router. To each his own...
Something about the measurements troubles me though. It appears that he is compensating for the acoustic roll off of each drive unit with some type of eq. Dsp perhaps? Anyway, there is no way that these drive units(especially the bass driver) could possibly go that low without a huge amount of low end compensation, which comes of course, at the expense of very high non linear distortion. Hmm..
Seth

Last edited by Remlab; 2nd March 2012 at 10:53 PM.
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Old 2nd March 2012, 11:50 PM   #119
Remlab is offline Remlab  United States
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As a perfect example of what I am talking about..
Jamo Reference R 907 loudspeaker Measurements | Stereophile.com . As you can see, the mid-range driver starts its 6db/octave acoustic high pass roll off at 600 hz (Its not a perfect 6db roll off, because the drive unit's resonant peak is pulling it up a bit..). This is with a 23" wide (Including thickness) baffle!
Seth

Last edited by Remlab; 3rd March 2012 at 12:08 AM.
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Old 3rd March 2012, 07:36 PM   #120
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Yeah, running drivers nude like that requires "dipole compensation" to get a linear response from the drivers.....it seems that the Neo10 in that app would be stressing at the low end, but I get the feeling that the designer in that thread is quite meticulous in his work.....

The real reason for doing this is not to save on the router, but to get the baffle as small as possible. The upshot is the driver can be used higher before it begins beaming, but the eq needed to get a flat response can be quite a bit, depending on the driver.

I've got 4-way dipoles set up this way, with the upper 3 way "nude" consisting of an 8" cone, a 3" cone (looking at a Neo8 to replace this), and a Neo3. To me, a 4-way is best here to keep each driver in its optimal passband and to reduce excursion and power demands at the lower end due to the dipole compensation.

Always tradeoffs!
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