I've just sketched out a scale drawing of a typical dipole scenario with a 60 degree triangle and speakers toed in the full 30 degrees. This will vary slightly with assumptions about back wall distances, but I got a back wall reflection from about 45 to 50 degrees off the speaker's axis. I also got a path length that is a ratio of 5.9 to 3.8 vs. the direct path.
From Linkwitz and others you can see that the generic dipole directivity is -1dB at 30 degrees, -3dB at 45 degrees, -6dB at 60 degrees and no output at 90 degrees.
The distance ratio results in -3.8dB distance loss for the reflection level. We'll call the off-axis (dipole radiation) response level -3.2dB for an even 7 dB drop for the estimated reflection level.
The back wall image reflection is only 10 degrees separated from the real source, so binaural hearing will not help seperate the two. If you have other than drywall then you may have significant additional attenuation.
Note that you can toe in the dipoles a considerable amount (about 70 degrees) and have the back wall reflection coincide with the null angle of the system, giving no reflection at all. At the same time I suspect that a lot of "Maggie" (or other dipole) owners don't toe in their speakers the full 30 degrees, so their conditions will be worse.
In all the cases I've looked at the side wall reflections are virtually non-existent. I know that some feel that killing all reflections "must be a good thing". They should read the Toole section in his book about dipole imaging, specifically about in-head effects caused by inadequate reflections.
I don't for a minute believe that dipole owners hear an effect as bad as the simulations. I agree that the multiplicity of live room reflections will to some degree mask the single reflection. That said, if a single reflection stands out from the rest, studies show it will audibly color the sound. Bech specifically singled out the floor bounce and the back wall reflection in that regard.
I repeat what I said initially, that dipole speakers have an unfortunate polar pattern in that they encourage a stronger back wall bounce and provide little in the way of lateral reflections.
Most Cordially,
David S.
If I remember correctly 54° has been found to be most effective for added spaciousness.
Why not? A 10° positional change is easy to hear.
That's good . . . because in almost all cases it's not audible at all.
That's good . . . because in almost all cases the masking is total.
That's true . . . fortunately they almost never do.
But that's wrong . . . in the great majority of listening rooms the advantages of the dipole speaker's polar pattern substantially outweighs the (mostly imaginary) disadvantages. Their front polar pattern, for example, is typically wider than many ostensably "CD" speakers, giving as great or greater "lateral reflections". The same applies to the back wave, where there are also front-wall-to-side-wall-to-listener reflections . . . and that, according to your theory, should give dipoles an advantage.
...unless one starts using speakers with narrow directivity like dipoles 😉
I think a design like the AR MGC-1 is a better idea. But first add a real center speaker.
This is not an arrival angle but the radiation angle of the speaker, hence setting level of the reflection.
I'll leave it to you to show a reference that 10 degree separated reflections can be issolated.
Is this opinion masquerading as fact or have you actually surveyed a vast number of situations?
"......Why not? A 10° positional change is easy to hear.
__________________
Markus "
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You need to think this one through. This a refelction with a relatively short delay from the primary. It is a not separate, distinct signal.
There is some literature on this topic (analagous, and I won't bother trying to summarize it). But the short answer is: No. It would not be a "positional change that is easy to hear"
Next thought:
For what it is worth, I have also been a fan of dipoles. They do some things very nicely, but not all things.
Sadly, I am afraid that Speaker Dave and his expertise are being dismissed, because his analysis conflicts with some deep-seated religious values of those who like dipoles. Guys, his comments are worth considering.
__________________
Markus "
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You need to think this one through. This a refelction with a relatively short delay from the primary. It is a not separate, distinct signal.
There is some literature on this topic (analagous, and I won't bother trying to summarize it). But the short answer is: No. It would not be a "positional change that is easy to hear"
Next thought:
For what it is worth, I have also been a fan of dipoles. They do some things very nicely, but not all things.
Sadly, I am afraid that Speaker Dave and his expertise are being dismissed, because his analysis conflicts with some deep-seated religious values of those who like dipoles. Guys, his comments are worth considering.
I have informally surveyed a large number of situations - many audio shows, private listening, showrooms, contests, etc. Hundreds of speakers. I have not found the dipoles to be any worse than the monopoles in these situations. Often a bit better.
ah, the old religion card played for the umpteen millionth time on an internet forum.
I very much respect Dave's POV and look forward to all of posts, but when reality clashes with theory, arguments such as this come up. Leave the religion out of it.
"....
I very much respect Dave's POV and look forward to all of posts,
..."
Good, we agree on something.
I very much respect Dave's POV and look forward to all of posts,
..."
Good, we agree on something.
I've got some absorption added to the front as well as having my stereo equipment stand in between, so I suspect I've got a fair amount of diffuseness/absorption included. This helps whether using monopoles or dipoles, though I have never tried to quantify it.
I accept your position on this, I'm trying to square the theory with what I get in practice. Floor bounce, that's without doubt the most difficult and the most prominent. That's why I've preferred a 3-way with a woofer slightly raised above the floor (19" for a single worked well as a compromise with mid separation integration) and about a 300-350 Hz crossover. My current quasi-cardioid (as I call it) dual 10" woofers seem to be better suited as well for the floor bounce since it's more distributed vertically. The rear wall just does not seem to be as big a problem, but again I haven't got measurements to show.
Agreed in principle, but either I'm too accustomed to this or it's not as prominent due to the front wall damping/dispersion applied as far as the front wall. I do usually have a lot more distance to the side wall as I prefer the improved image it provides.
Let me add one other point. I no longer have the ribbon dipoles. My current system is actually only a dipole to the middle midrange where it crosses to the tweeter. I have not yet tested a rear-firing tweeter nor a small dipole tweeter, though that will be part of my next system. The rear wall was a bigger issue when I had my near full-range ribbons. But then the long ribbon was a bigger problem due to the seat really being to close.
Dave
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Something that hasn't been mentioned in the discussion, so far, is that it's likely that the effect of front wall reflections is likely to be level dependent. That is, the higher the overall SPL level, the less likely their effect will be masked as our hearing seems more sensitive to higher levels of reflected sound.
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In a nutshell: No.
The presence of masking will mostly be a function of the ratio of the reflected sound (think of this as the "signal being masked") and the direct sound (think of this as a "possible masker").
So as the direct sound increases in level, so will the reflected sound. Please, let's not bother with 3rd order effects that won't essentially change things.
Yes, that was floor to center, 10" woofer. I was going for a compromise between woofer-to-floor and woofer/mid c-t-c. This was the best compromise.
Dave
At low SPLs reflected sounds are masked to our hearing. At increasing SPLs they become unmasked. Our hearing in this domain is not linear - so at low SPLs coloration caused by reflections is not noticeable but at higher SPLs it is.
Well, you can say it twice but it does not make it true.
As I said before, it "mostly a function of the ratio of the reflected sound to direct sound". There are some deviations from this; however, they are really not pertinent here.
I am trying to figure out why you are saying this. Are you thinking of "upward spread of masking"?
Reflections can be viewed as a form of linear distortion. Our hearing is non-linear in its response to linear distortion; that is, we are more sensitive to reflections as SPLs increase. Our sensitivity to linear distortion increases with both level and delay.
There is a paper by Geddes and Lee on the topic demonstrating this. If I've taken a mistaken liberty in my interpretation and thoughts about the applicability of their conclusions to the topic of these frontal reflections, I'm sure I'll hear about it.
Paper by Geddes and Lee can be found here:
http://www.gedlee.com/downloads/AES06Gedlee_ll.pdf
It's really an interesting topic and unfortunately, there's not been a lot of work done that's directly applicable to small audio listening rooms although I suspect acousticians working on concert halls have lots to say about it in their domain.
What is a 'dipole' ?
What is a 'monopole' ?
As long as we compare the textbook defintion of
the above mentioned ideal radiation patterns,
we will wonder about listening expriences due
to real implementations will not match theroretical
expectations very often.
Examples:
A (concrete) 'dipole speaker' (implemantation) may be:
A small fullranger on a wide baffle ...
A tall and narrow baffled 'dipole' line array or a
'nude dipole'...
A large panel ESL (curved or not) with no
(additional ) means of directivity control ...
A large Panel ESL having segments, patially rolled
off at higher freqencies ...
A planar megnetic woofer with 'line source' ribbon,
having different baffle designs ...
A panel form bending wave wave speaker ...
Many of that implementations do not exhibit dipole
radiation patterns 1-2 octaves above schroeder
frequency.
E.g. a small fullranger on a wide baffle, will have
noticeable side lobing and cause more side reflections
than below 2Khz than a conventional 2-way 'monopole'
speaker implementation ...
For 'monopole speaker' implemantations, also the polar
pattern in the midrange will depend on baffle size and
the driver size(s) and configuration.
Most interesting for me in this thread is currently
having the effects mentioned and discussed which
play a role in room acoustics and psychoachoustics.
A certain aspect of interest for me currently is
perceived depth of imageing.
In a post before there was mentioned that side reflections
<3Khz contribute to perceived 'depth' and dide reflections
above that range contribute more to 'spaceousness'.
That finding was ascribed to Blauert, but i have no
reference found currently.
My own experiences correlate with that, when comparing
different speakers i listened to, each causing noticeably
different amount of side reflections below 3Khz.
But i would not go so far to say this is the only property
contributing to 'depth' of imageing.
My suspect is that also diffusivity of the first reflections
contribute to that.
Does that mean a "large amount of diffuse side reflections"
will largely increase the perceived depth ?
There is an observable effect in the perceptive domain,
and there may often be multiple physical correlates which
contribute.
To sort each contributing physical effect out, is not
possible without listening tests under controled conditions,
simulating such things as 'single reflection', 'interaural
time delay', level decrease due to distance and
listening angle relative to some idealized radiation
pattern.
In real world, with our concrete 'speaker implementations'
and the 'real listening rooms', there are no such things.
I do not mean psychoacoustic research is useless, don't
get me wrong. But direct comparison of scientific results
to listening experience with implemantations in real
listening rooms will always be 'fuzzy'.
Sometimes a list of "physical effects possibly contributing"
to a perceived property in reprpodutcion seems more
valuable to me, that trying to estimate each effects
contribution in an exact percent ratio, which seems
fairly impossible in here given the great variety of
settings in each members home and also the
different backgrounds and admissions to individual
listening.
What is a 'monopole' ?
As long as we compare the textbook defintion of
the above mentioned ideal radiation patterns,
we will wonder about listening expriences due
to real implementations will not match theroretical
expectations very often.
Examples:
A (concrete) 'dipole speaker' (implemantation) may be:
A small fullranger on a wide baffle ...
A tall and narrow baffled 'dipole' line array or a
'nude dipole'...
A large panel ESL (curved or not) with no
(additional ) means of directivity control ...
A large Panel ESL having segments, patially rolled
off at higher freqencies ...
A planar megnetic woofer with 'line source' ribbon,
having different baffle designs ...
A panel form bending wave wave speaker ...
Many of that implementations do not exhibit dipole
radiation patterns 1-2 octaves above schroeder
frequency.
E.g. a small fullranger on a wide baffle, will have
noticeable side lobing and cause more side reflections
than below 2Khz than a conventional 2-way 'monopole'
speaker implementation ...
For 'monopole speaker' implemantations, also the polar
pattern in the midrange will depend on baffle size and
the driver size(s) and configuration.
Most interesting for me in this thread is currently
having the effects mentioned and discussed which
play a role in room acoustics and psychoachoustics.
A certain aspect of interest for me currently is
perceived depth of imageing.
In a post before there was mentioned that side reflections
<3Khz contribute to perceived 'depth' and dide reflections
above that range contribute more to 'spaceousness'.
That finding was ascribed to Blauert, but i have no
reference found currently.
My own experiences correlate with that, when comparing
different speakers i listened to, each causing noticeably
different amount of side reflections below 3Khz.
But i would not go so far to say this is the only property
contributing to 'depth' of imageing.
My suspect is that also diffusivity of the first reflections
contribute to that.
Does that mean a "large amount of diffuse side reflections"
will largely increase the perceived depth ?
There is an observable effect in the perceptive domain,
and there may often be multiple physical correlates which
contribute.
To sort each contributing physical effect out, is not
possible without listening tests under controled conditions,
simulating such things as 'single reflection', 'interaural
time delay', level decrease due to distance and
listening angle relative to some idealized radiation
pattern.
In real world, with our concrete 'speaker implementations'
and the 'real listening rooms', there are no such things.
I do not mean psychoacoustic research is useless, don't
get me wrong. But direct comparison of scientific results
to listening experience with implemantations in real
listening rooms will always be 'fuzzy'.
Sometimes a list of "physical effects possibly contributing"
to a perceived property in reprpodutcion seems more
valuable to me, that trying to estimate each effects
contribution in an exact percent ratio, which seems
fairly impossible in here given the great variety of
settings in each members home and also the
different backgrounds and admissions to individual
listening.
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