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Old 20th July 2010, 11:33 PM   #6731
Pano is offline Pano  United States
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Old 21st July 2010, 12:25 AM   #6732
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Originally Posted by gedlee View Post
John

I don't follow this distinction. Are you saying that the "doublet" is two out of phase sources seperated by a distance and the "dipole" is two out of phase sources seperated by a baffle? Otherwise I don't see what you are getting at.
Actually after I posted I realized that I really didn't say what I wanted to say and it was to late to edit it. What I was trying to distinguish was the difference between the radiation pattern of an acoustic doublet (or acoustic dipole) which is a function of frequency and the classic dipole figure 8 pattern associated with things like magnetic and electric dipoles. See it even confused me. My thinking was that when the term dipole is read people generally think of the classic figure 8 patten which only applies at low frequency in an acoustic dipole or doublet.

So I was thinking that maybe using the term acoustic doublet would break the connection that dipole = figure 8 pattern.

And I am never sure when some one else talks about a dipole if they are talking about a figure 8 pattern or the frequency dependent characteristic that degrades from a figure 8 to a daisy peddle affair as the frequency rises above the first on axis peak.

All this talk about nulls and reducing nulls by damping the rear wave is a little disconcerting to me because once the frequency rises to the point where those nulls or dips are present the response no longer resembles any type of constant directivity and thus is useless from my (and your ) point of view. That is why I keep repeating the statement that an acoustic dipole (or doublet) has a useful frequency range to about 1 octave below the first on axis peak. Above that the polar response degenerates quickly form the figure 8 pattern. Below that the error is acceptable.
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Old 21st July 2010, 01:16 AM   #6733
gedlee is offline gedlee  United States
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John

A question for you, or anyone else.

When I looked at the Orion measurements it was obvious how well it controlled the directivity in the 200 - 500 Hz range, where I am not able to effect much control. Hopefully it is not a coincidence that this is precisely the region where I think the Orion shines. In my book I showed how a rear facing driver could be used to control the directivity in precisely this range while going away at LFs to yield a more efficient monopole. It turns out that this can be done passively, albeit not simply (passive attracts me for obvious reasons). I am going to try this and wondered if you, or anyone else, has actually done this as well and what your experience was (technically please!). This would not be too hard to impliment and may be an audible improvement. (There is no point in not disclosing this since its already public domain anyways.)
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Old 21st July 2010, 01:52 AM   #6734
CLS is offline CLS  Taiwan
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Originally Posted by gedlee View Post
....

When I looked at the Orion measurements it was obvious how well it controlled the directivity in the 200 - 500 Hz range, ....

I got an impression that you seem to be quite interested in dipole and brought it up several times. However you just haven't tried it yet, have you?

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Old 21st July 2010, 02:16 AM   #6735
soongsc is offline soongsc  Taiwan
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Originally Posted by gedlee View Post
John

A question for you, or anyone else.

When I looked at the Orion measurements it was obvious how well it controlled the directivity in the 200 - 500 Hz range, where I am not able to effect much control. Hopefully it is not a coincidence that this is precisely the region where I think the Orion shines. In my book I showed how a rear facing driver could be used to control the directivity in precisely this range while going away at LFs to yield a more efficient monopole. It turns out that this can be done passively, albeit not simply (passive attracts me for obvious reasons). I am going to try this and wondered if you, or anyone else, has actually done this as well and what your experience was (technically please!). This would not be too hard to impliment and may be an audible improvement. (There is no point in not disclosing this since its already public domain anyways.)
I have a design, while originally not designed for the purpose, but would be interesting how it effects directivity. However, 200~500Hz range is still a sensitive region where tradeoff between a simple wavefront and controlled directivity is VERY room dependent.
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Old 21st July 2010, 03:55 AM   #6736
gedlee is offline gedlee  United States
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Originally Posted by CLS View Post
I got an impression that you seem to be quite interested in dipole and brought it up several times. However you just haven't tried it yet, have you?

No, I haven't, and there is no guarantee that I will have the time to "try" it anytime soon either. It's not a major thing at all, it's a slight improvement in the 200 - 500 Hz region - not earth shattering, not a paradigm shift, nothing like that. And I have heard lots of dipoles before, so its not new from that perspective either. As I said, the technique is described in my book, which is almost ten years old now, so its nothing new.
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Old 21st July 2010, 03:56 AM   #6737
gedlee is offline gedlee  United States
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Originally Posted by soongsc View Post
200~500Hz range is still a sensitive region where tradeoff between a simple wavefront and controlled directivity is VERY room dependent.
Its above the Schroeder frequency and so it should not be room dependent at all.
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Old 21st July 2010, 04:11 AM   #6738
mige0 is offline mige0  Austria
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Originally Posted by dlr View Post
Why can't you do this on your own?

Dave
First steps have been undertaken – and already presented - no ?

There is some hard work to do in establishing a minimum of common ground on the subject of CMP first – and thats I'm even more interested in …

All the rest will come along by its own then.



Quote:
Originally Posted by john k... View Post
...See it even confused me.

I'd say you begin to see the power and implications of my concept.

As said – CMP is part and parcel to OB.
Its been you – IIRC - who stated that dipole can *always* be seen as two point sources separated by some distance.

In my understanding too this is not *exactly* the case – as I agree to your conclusion that we rather should keep dipole *directivety* at one hand and CMP (by OB) at the other hand clearly separated.

As said once in a pronounced manner – due to OB being a CMP system - we listen to a *monopole* for the first time interval and only after that time interval (given by the delay) we actually listen to a dipole.

and to repeat once more: with OB this is the case well below the dipole peak as well !


Coming back to "nude" speakers:
There we actually have dipole behaviour *and* we start out with (practically) no delay.
Sure – CMP is involved here too (later on) – but CMP is involved here in a very special form.


-------------

As a side note :
I'm deeply impressed by the lack of reaction to my statement that CMP *in genereal* flaws our most used tool in measurement - as clearly demonstrated.

for any uncorrected CMP system the frequency response becomes a matter of the time interval we look at!

Michael

Last edited by mige0; 21st July 2010 at 04:39 AM.
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Old 21st July 2010, 04:45 AM   #6739
mige0 is offline mige0  Austria
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Originally Posted by mige0 View Post
As a side note :
I'm deeply impressed by the lack of reaction to my statement that CMP *in genereal* flaws our most used tool in measurement - as clearly demonstrated.

for any uncorrected CMP system the frequency response becomes a matter of the time interval we look at!

Michael
Above becomes even more impact with looped reflections as seen with horns and compression drivers.

Michael
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Old 21st July 2010, 05:05 AM   #6740
mige0 is offline mige0  Austria
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Originally Posted by mige0 View Post
Coming back to "nude" speakers:
There we actually have dipole behaviour *and* we start out with (practically) no delay.
Sure – CMP is involved here too (later on) – but CMP is involved here in a very special form.
I possibly should be more precise here in stating that with nude speakers we start out (practically) with
"no delay - meaning: no delay that *sharply* separates two CMP intervals"

Michael

Last edited by mige0; 21st July 2010 at 05:07 AM.
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