Lynn Olson
Active Member
- Joined
- Aug 29, 2010
- Messages
- 98
The Shadow Vector experience, with all its ups and downs, provided a good experience for loudspeaker design, although without the daylong discussion at KEF with Laurie Fincham in 1975, it would have been a lot harder when Charlie at Audionics threw me into the deep end of the pool with the order to finish the TL-M200 loudspeaker.
One result was to make me much more aware of the phase angles between pairs of drivers; a lot of speaker designers get kind of sloppy, and let phase angles between midbass and tweeters be 90 degrees or more (at crossover). It looks harmless enough on the frequency-response plot, but sounds very disjointed in practice. Even though you might be sitting 10 feet/3 meters away, it is plainly audible if you know what's wrong with the sound. I try and aim for 5 degrees or less of phase difference - this makes the pair of drivers sound like a single large driver, regardless of listening distance.
When two loudspeakers spaced 10 feet or more apart also have 90-degree phase difference, it helps if the phase difference is the result of a well-constructed phase-shifter, and the pairs have identical drivers, crossover, and polar pattern. Thanks to THX, this is NOT true of HT systems, where the surround speakers are intentionally dissimilar, which guarantees that a dynamic matrix will not provide a uniform soundfield with music.
Even a good discrete mix will sound somewhat disjointed and separated from the front array if the surrounds are dissimilar. Of course, a cohesive soundfield was never a design goal with THX; it was always about replicating the theater experience, not creating a realistic or even plausible soundfield.
It's kind of weird seeing THX using 9 speakers to do what we did with 4 - and we had better results, too, since the soundfield was designed from the get-go to be smooth and uniform, while THX speakers are a weird catchall of at least four different types - Center, the LR pair, dipole or monopole surrounds, and the little guys intended for height or extra-width applications. All different from each other, all with different crossovers, and all with different polar patterns. A circular pan is going to have noticeable timbre shifts - which Audyssey EQ will not be able to correct - while reverb information will fall into several different pools (or trapped in the loudspeaker), instead of joining into a single cohesive soundfield.
My biggest gripe with Audyssey is that is plainly aimed at lo-fi speakers - the frequency response correction in the mids and treble might smooth out the overall room sound, but the first-arrival wave coming from the speaker is then wrong - and it's the first-arrival that determines timbre, not the overall sum from the room. I might use the EQ gizmos if they limited the correction to 300 Hz and below - that's the range where a decently designed speaker is inherently flat, and the room is starting to really go up and down (also, first-arrival and room sounds start merge at those frequencies).
But room correction should not be applied to a flat loudspeaker at frequencies above 500 Hz. The ear works like a cross-correlator, and can easily distinguish between the first-arrival spectra and the first 10 or 20 reflections. It uses the first arrival as a reference, and compares the reflections against it, to try and determine the acoustical properties of the space. If you gum up these 10 or 20 reflections, then the spatial information is degraded, and listening fatigue is increased.
One result was to make me much more aware of the phase angles between pairs of drivers; a lot of speaker designers get kind of sloppy, and let phase angles between midbass and tweeters be 90 degrees or more (at crossover). It looks harmless enough on the frequency-response plot, but sounds very disjointed in practice. Even though you might be sitting 10 feet/3 meters away, it is plainly audible if you know what's wrong with the sound. I try and aim for 5 degrees or less of phase difference - this makes the pair of drivers sound like a single large driver, regardless of listening distance.
When two loudspeakers spaced 10 feet or more apart also have 90-degree phase difference, it helps if the phase difference is the result of a well-constructed phase-shifter, and the pairs have identical drivers, crossover, and polar pattern. Thanks to THX, this is NOT true of HT systems, where the surround speakers are intentionally dissimilar, which guarantees that a dynamic matrix will not provide a uniform soundfield with music.
Even a good discrete mix will sound somewhat disjointed and separated from the front array if the surrounds are dissimilar. Of course, a cohesive soundfield was never a design goal with THX; it was always about replicating the theater experience, not creating a realistic or even plausible soundfield.
It's kind of weird seeing THX using 9 speakers to do what we did with 4 - and we had better results, too, since the soundfield was designed from the get-go to be smooth and uniform, while THX speakers are a weird catchall of at least four different types - Center, the LR pair, dipole or monopole surrounds, and the little guys intended for height or extra-width applications. All different from each other, all with different crossovers, and all with different polar patterns. A circular pan is going to have noticeable timbre shifts - which Audyssey EQ will not be able to correct - while reverb information will fall into several different pools (or trapped in the loudspeaker), instead of joining into a single cohesive soundfield.
My biggest gripe with Audyssey is that is plainly aimed at lo-fi speakers - the frequency response correction in the mids and treble might smooth out the overall room sound, but the first-arrival wave coming from the speaker is then wrong - and it's the first-arrival that determines timbre, not the overall sum from the room. I might use the EQ gizmos if they limited the correction to 300 Hz and below - that's the range where a decently designed speaker is inherently flat, and the room is starting to really go up and down (also, first-arrival and room sounds start merge at those frequencies).
But room correction should not be applied to a flat loudspeaker at frequencies above 500 Hz. The ear works like a cross-correlator, and can easily distinguish between the first-arrival spectra and the first 10 or 20 reflections. It uses the first arrival as a reference, and compares the reflections against it, to try and determine the acoustical properties of the space. If you gum up these 10 or 20 reflections, then the spatial information is degraded, and listening fatigue is increased.