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In Reply to: Does a loudspeaker's time coherence matter ? posted by bunni on February 22, 2007 at 17:36:31:
The human ear has a difficult time distinguishing phase of multiple components of a complex but continuous tone. So, a non-coherent loudspeaker can sound virtually identical to a single-driver coherent source when producing continuous tones even though component partials have been phase shifted. For example, a violin string playing a whole tone A will sound similar when produced by coherent and non-coherent loudpeakers, on axis that is. However, a coherent source is required for the accurate reproduction of assymmetric wave forms and anharmonic sounds. For example, the strike of a piano hammer and the subsequent decay require a coherent source for accurate reproduction. The strike speaks to the superiority of coherent sources in reproduction of image localization, which is dependent on relative amplitude and phase. The decay speaks to the superiority of coherent loudspeakers in capturing the hall acoustic. Virtually all percussive instruments, bells, cymbals, triangles, tympani, etc., are assymmetric wave form generators. Finally, there are the anharmonic fine details of the recording, the page turning sounds, coughing, clanging of stands, squeaking of chairs, etc., that coherent sources excel at reproducing. The Thiel and Vandersteens are superb coherent sources, on axis. Off axis, they are plagued by lobing due to phase shifts from the non-coincident point sources the individual drivers represent. The best example of the coherent point-line source is the single driver Ohm F. The newer ohms, such as the Ohm Walsh 5 make some design compromises in the pursuit of superior efficiency, range and dynamics, and resort to a single bending-wave "Walsh" driver line source (a truncated Ohm F if you will) to reproduce the full bandwidth [except for 8 khz and above] and thus is perfectly coherent both on and off axis. As the bulk of the music we hear in fact occurs below 8 khz, and as the supertweeter is crossed over in a first order high pass filter at 8 khz so as to be phase correct, the Ohms produce an exceptional uncolored and phase-time coherent sound that is detailed, uncolored and most present and realistic.So, the short answer is, if you want good sound, there are many fine loudpspeakers to choose from; but if you want the last word in realism and hall presence, a coherent point-line source loudspeaker is what you seek.
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- Re: Does a loudspeaker's time coherence matter ? - mamboni 18:55:44 02/22/07 (0)
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