7.1 set-up of dipole surrounds (ADP-390) phase question

Originally Posted by dragonfyr

Thanks, but I am WELL aware of what is happening with the superposed sources!! And symmetry of the drivers/speakers has nothing to do with this!

Superposed spaced sources reproducing the same passband NECESSARILY result in frequency related polar lobing that appears as comb filtering in the frequency domain.

In fact, thus far the only two techniques that avoid this (in terms of the combination of drivers) are the Bessel array in the far field and the Constant Beamwidth Tranducer (CBT) technology. But even two Bessels or 2 CBTs will interact in the same destructive manner! (well, unless each of the spaces sources are similarly arranged in a large scale Bessel or CBT configuration!)

{And considering the fundamental difficulty 'surround' technology has with the confusion of the surround sources as sources of localization and the support for accurate later arriving semi-diffuse soundfields considered optimal in a bounded small acoustical space. The surround formats do not adequately provide for both the time domain development of later arriving semi-diffuse soundfields simultaneously with the supplying of simple decorrelated ambient noise components.

In other words, the surrounds provide direction cues based primarily upon what is included and excluded and gain. But they do not adequately provide an exponentially decaying semi-diffuse soundfield (derivative of the source that is properly generated in an optimally designed small acoustical space. Instead of an accurate later arriving exponentially decaying laterally arriving semi-diffuse sound field, the interaction of additional spaced surround sources intentionally reproducing the same passband simply creates an anything but diffuse pattern of polar lobing and comb filleting. How's that for trying to summarize two complex psycho-acoustical models down to a few run-on sentences?}

But those shortcomings aside, Whatever signal is subsequently provided from the surround sources is necessarily subject to destructive polar lobing and resultant comb filtering due to the interaction of the spaced sources over the same passband. And such destructive interference, due to the fundamental variance from an accurate psycho-acoustical localization model to begin with, does not add to accurate localization but simply creates non-diffuse localized response aberrations dependent upon where one sits relative to the phase(time) relationships of the interacting spaced sources.

In other words, a sense of envelopment complete with additional localized aberrant polar lobing and comb filtering due to multiple sources replaces any hope of a more accurate reproduction of the source material.

Basic physics trumps fancy marketing brochures...not to mention the quite humorous response quoted above from Paradigm!

Originally Posted by dragonfyr

No! Driver symmetry, mirror imaging, or polarity don't ultimately matter with regards to the resulting interference patterns of spaced sources reproducing the same passband. By that I mean that driver spacing - the resulting time relationship will modify the interactive results, but none save co-location will necessity eliminate or avoid them.

In-phase alignment is possible at, at most, one precise plane if we strictly limit the sources, or spot in a more general case, relative to the two sources. Add more spaced sources and there effectively is no common spot. Hence the efforts expended in the last 40 years to develop quality co-axially aligned sources.

The examination of signal superposition in the time domain makes all of this easily understandable observable.

All of this speaks to the fundamental schizoid issue inherent in the current surround sound formats.

On the one hand, the rear surround speakers can be used to literally replace the (properly tuned) room supported response of an exponentially decaying laterally arriving semi-diffuse sound field that creates a sense of spaciousness in an otherwise small bounded space

Or, they can, by providing de-correlated varying content based upon simple direction and gain, add a sense of immersion and ambience by adding additional non critical content.

But they don't do both with the current standards. And thus you have a choice:To make the room essentially dead and to let the surround speakers function as the source of the latter arriving soundfield. Or one can create a room tuning that supports the mechanical generation of a proper psycho-acoustically accurate later arriving exponentially decaying laterally arriving semi-diffuse soundfield as one might do for a hybrid music/HT use room while accepting the surrounds simply as sources of additional ambient cues providing immersive elements.

But in either case, spaced surround signals that simply add additional spaced drivers that are oriented to intentionally cover the same spatial regions with the same passband create destructive local polar lobing interference patterns.

That part is simply basic physics that is necessary to be understood in order to understand the acoustical propagation of sound. And i will also add that it is critical to understand this in a 3space volumetric environment and NOT simply in the all too common erroneous 2D wave diagram such as is displayed on an oscilloscope!

The fact is, currently employed surround topology is not sufficiently sophisticated to address the complexity of the psycho-acoustic models necessary for truly accurate surround localization (as if such was even desirable - as film producers do NOT want acoustic cues to be accurate enough to prompt someone to turn their attention away from the front screen to look to the side or behind them in a theater! Now, I am not proposing one run about as Chicken Little and stand outside Best Buy scaring would be buyers away! But it SHOULD help to raise an awareness of what we can reasonably expect and what the real limitations are so that we can address the choices reasonably and to the best of our abilities and preferences.

The irony is that dipoles were originally posited by THX in the mid 70's in an attempt to provide for a less directional lateral soundfield. Unfortunately, simply adding more low Q localized sources result not in a more sufficiently complex semi-diffuse soundfield, but instead result in increased local polar lobing that appears as comb filtering in the frequency domain. This polar lobing consists of a spatial distribution that is literally regions where the sound is present interlaced with regions where the sonic material is literally absent - canceled. And these regions vary with one's location due to the time (phase) relationships of the various arriving signals that add NOTHING to an accurate localized reproduction of the source material. But I'm sorry folks, that in no way correlates to an increase in acoustical accuracy.

That said, the fact is that some MAY like it. As this is exactly the premise employed that so many like to complain about in the early Bose direct reflecting systems, where accuracy of reproduction was substituted by an apparently wider sweet spot comprised of a less accurate but more homogenized' soundfield. Homogenized in the sense that one cannot tell a hard distinction between distinctly good and bad response regions and instead settles for a larger mediocre' response region that seemed OK primarily due to a lack of the ability to compare it with a region of better' or more accurate reception. In large measure this is the same response championed by Floyd Toole with his application of averaged EQ.

So, I'm not saying that someone cannot or should not like or do it. That is a matter for each to make themselves. Instead I would suggest a better understanding of the tradeoffs involved and; and then I would suggest that it's a matter of being aware of what one is actually achieving with the various topologies involved and the various response models that are achieved; and based upon one's desires, making choices and more optimally achieving the response that they truly prefer.

Originally Posted by dragonfyr

.....Much like most do in querying this forum.

Originally Posted by sivadselim

And you helped, how?

Originally Posted by dragonfyr

By all means rush to dial the customer service number and talk to some 22 year old part time CSR who having no clues as to the actual subject matter, queries a canned data base. ...Much like most do in querying this forum.