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In Reply to: RE: POLL: How many of you use(or would prefer to use) "time-coincident" speakers? posted by genungo on September 04, 2014 at 08:36:45
To be clear, acoustic phase as described by Heyser is the bottom line so far as “time”, that measurement describes the acoustic output relative to the input signal.
VERY few multi-way hifi speakers radiate as if they were a single driver in time and space. While DSP can correct time, it can only do so for one set of path lengths to the listener as having drivers that are too far apart to combine coherently, means they radiate independently as seen by a pattern of lobes and nulls in their vertical and/or horizontal polar patterns. While two or more sources can add coherently, the distance between them has to be a quarter wavelength or less at the highest frequency of interest.
The larger a loudspeaker system becomes, the more audible this problem becomes and is why large scale sound generally is very dismal especially with large arrays which radiate from many locations in space and so also in time. The interference pattern they create is complex and so if the wind blows, that becomes very audible as well.
In the small scale like home hifi, the advantage to a simple single point of radiation is that the location of the loudspeaker in depth is not obvious. In stereo, that means that when playing a mono signal (same signal to both speakers) that one hears a solid phantom image in the center and you DO NOT hear the right and left source.
Speakers that radiate from different locations produce an interference pattern produce a mono phantom image but also have an obvious right and left source as well.
Arrays of many drivers often produce a much less solid mono phantom image but produce more like a ‘wall of sound” as what arrives at ones ears is comprised of many individual arrivals in time according to the path lengths differences from each source.
As a result of the electrical signal representing “one point” in time and space, speakers which radiate that way tend to have the best reproduction of the recorded stereo image, speakers which have directivity and the latter property, tend to have the largest near field and most faithful stereo image.
Follow Ups:
How about these:- Tannoy Dual Concentric
- Dunlavy
- Quad
- Vandersteen
- Thiel
- Martin Logan fullrange models
- Sound labs fullrange models
- Single-driver systems
- Ryan
- Danley
If these brands or types do not qualify as "time/phase coherent", what can we say about those who claim to hear "THE DIFFERENCE"?
Edits: 09/04/14 09/04/14 09/04/14
Full range electrostatics like Martin logan, Sound labs do radiate from a single point in time although may produce somewhat of an interference pattern due to their physical size, the Quad esl63 radiates like a single point in space and time, most full range multiway loudspeakers do not radiate from one point in space because the drivers (where they interact) are too far apart to add coherently (into one new source).
A first order crossover is the only passive crossover of the ”named variety” that sums without an overall “all pass” phase shift.
A single small full range driver mounted to a large flat baffle can be VERY good in this regard. There is no “all pass” phase shift crossovers above first order crossovers produce, no significant secondary radiation from cabinet edges but they do have other limitations.
The spherical segment radiation of a quad ESL-63 was part of the inspiration for the Synergy horn (Danley) and many of these do act / measure / sound like a single crossover-less driver with constant directivity and the earlier Unity horns radiated like a single driver with some degree of crossover phase shift.
Best,
Tom Danley
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