Time coherence - how important and what speakers?

Roy great response...I was just thinking about this the other day...the real challenge in a time/phase design is not the crossover...its building the entire darn thing in a proper manner to use a first order network...in short...all your ducks must be in a row...and this can be applied to any "minimal" crossover network as well...a good design isnt enough...it has to be well executed with quality componets,etc...which is why I assume so many DIY speakers sound like crap...it is much more than simply throwing off the shelf drivers in a box and hoping for the best...I am constantly surprised at how many think they can outsmart engineers...even those with hi quality gear that like to perform their own mods....

Also..Roy...could you shed some light on the correlation between a wide dispersion pattern and time/phase integrity?
Secondly...I believe it was Joseph from JA who brought up a valid point in what I assume was in defensive to his designs(which I dont own)...that is...if time/phase accuracy is indeed retained...why do all time/phase coherent speakers sound different? I know you are a busy man...and this is not intended as a set-up question...I am just curious...thanks for all your informative replies...

The original OHM with full range Walsh driver could reproduce an almost perfect square wave... as evidenced by oscilloscope pictures. It delivered an omnidirectional cylindrical wavefront, and the imaging that I heard was superb, as you would expect. To my knowledge no other speaker has ever attempted this test, or perhaps,no one has published the (rotten) results. Unfortunately, the speaker wasn't so great in other ways. Ain't that a shame.

Yeah, the original Ohm had a lot going for it. Magazines replaced square-wave tests with the computerized MLS test, which can interpolate the phase response and any ringing from the MLS psuedo-noise (but not in great detail- as most of what you see are the averages of 20Hz-wide frequency bins).

Some of the first-order speakers currently marketed do well on square waves, but manufacturers see no reason to publish the test, for marketing reasons, so the competition cannot find out easily, and because this test is not the only one to be passed for good sound, as I'm sure you suspect.

What you heard, good or bad, in the Ohm lays far deeper than what the square wave can reveal- for two reasons:
--the square wave is composed of only odd-order harmonics plus the fundamental (any even-order content seen on the `scope is distortion). Thus it only tests certain tones, not all tones.
--the square wave's dynamic range is far different than music- it does not stress the drivers enough, nor last long enough to excite the woofer.

A square wave is a guide- if you can find out where the little departures from a flat-topped characteristic come from, and then fix them, great! However, there are better tests for the problems behind those squiggles, ones which a smart manufacturer is not going to reveal, nor a poor one reveal that they don't perform!

You raise valid points- not a very professional industry is it? Becoming a better listener and gaining some technological understanding seems to be the only way to find something decent!

Best,
Roy

Phasecorrect-
If you use pink noise or MLS or swept sine waves (common for testing dispersion), most of what we see on the printout does not explain what we hear. Dispersion, as heard on music, depends on some very definite factors:
--the diameter of the driver (not so much its shape) vs. the wavelength.
--does that driver remain a rigid piston in its operating band? Most do not.
--how the reflections from the enclosure's front and sides, and reflections off the other drivers' surfaces smear transients.
--how the crossover disturbs those transients.

The real problem is that we listen to music. Look at a musical waveform on a `scope- what do you see? Do you see any sine waves, or square waves, or sharp, stand-alone impulses? No. You see an ever-changing wave "form" that has more dynamic range than the face of the scope can reveal. It REPRESENTS how the mic diaphragm moved in and out, and how our ear drum is supposed to.

The music we hear- all its tones, rhythmic interplays, harmonies, imaging- our minds interpret from that complex "wave envelope". It is this unpredictable envelope's shape that counts. When a designer focuses on the theoretical "sine wave" components only, then the shape of the envelope has become immaterial to him.

Except to the ear. Which is why time coherence, and lack of cabinet problems, and linear drivers, and fewer crappy crossover parts, and proper crossover points are all important. Those all affect dispersion AS HEARD ON MUSIC.

Phasecorrect- you asked, "if time/phase accuracy is indeed retained...why do all time/phase coherent speakers sound different?" Because they are basing their claims of accuracy upon flawed measurements. The measurements don't pick up on all that we hear.

Ever wonder why we can't often play poor recordings? Everyone blames the studios, but it's the speaker's time-domain problems that are further distorting that distortion, contributing to unlistenabilty. Test: play a poor recording on phase-coherent headphones (Grado, Stax, others) then play it on a high-order crossover speaker just as loud.

Music is about time as much as tone and loudness. If you only test for two out of three, you won't be designing- only shoving parts into a box.

Best,
Roy