Time coherence - how important and what speakers?

Roy,
Whats up with the Green Mountain Audio website???

There's been no spare time to finish the last few pages (for the new speakers), as we take care of orders/existing customers. However, it shouldn't be too much longer `till we can get back to it and get it published. Thanks for checking!
Best,
Roy

New Speakers?

Are you designing or upgrading any new bookshelfs?........

The Europa was upgraded many months ago, and I have been working on other designs, both smaller and larger. However, I feel uncomfortable using this forum for promotion, but I do appreciate your asking. Such info will be on the website, and anyone may email me or call and I'd be happy to give them an idea what is to come, prior to the site's publication.

But the first shipments of the new Continuum 3 (replaces the C-2) must come before finishing the site's last pages. The increased sales of existing models had slowed the C-3 production down, but we are almost there. I will post a notice here, if the moderator feels that is appropriate, when the website gets up and running.

For a couple of months, I had wanted to offer my summary of this "time coherence" debate, because while I had made some points about the effect on sound quality and the physical limits to "perfect" time-coherence in any design, it still seemed to be hard for some to visualize what a time coherent speaker did for the sound, for the "waveform".

I believe part of that comes from the way the electronic age has let us visualize sound- still struggling to somehow see it directly, like we can with a water wave.

We have filmed the movement of the ear drum- we know it moves in and out with local changes in air pressure. Is that a linear response- air pressure to mental response? No. But on what we each hear from a given stimulation, we will generally agree. We don't call that stimulation a "wave"- we call it a sound. Maybe that's mom, or Mozart, a large bus passing by, or something we've never heard before.

We know a mic diaphragm also moves in and out- we can see the corresponding voltage rise and fall on the `scope. The `scope face freezes for us a 10th of a second of the diaphragm's motion- and we see there's a wave pattern going up and down.!

But to the mind- all we know is the pressure on the body went up and down.

Time-coherent speaker design means preserving that sequence of pressure changes- the same sequence of pressure variations the mic turned into voltage variations.

Non-time coherent design means the "wave pattern" we see on the scope does not matter- we can present the eardrum with a new sequence of pressure variations, and expect somehow that this will sound the same, or nearly so.

Why do some think that pattern can be changed? When they claim, "Mathematically, and audibly, that is just a collection of particular tones. The ear doesn't care EXACTLY when they arrive- just as long as they do, sort of near their original sequence- say, within a couple of wavelengths or so (~720 degrees of phase shift)."

And there is the mistake. We know in our heads those are a bunch of individual tones- we can hear them, and point to their source. We know that mathematically as well, and can now see this via a computer's FFT.

They are heard as tones, seen as tones... they are NOT tones when impinging on the body- they are a series of apparently random pressure fluctuations imposed upon it.

For me there is no choice; a speaker must be capable of making that original sequence of pressure variations traverse your body. This is an event, a series of events- described by the frozen-in-time "envelope" or "wave packet" seen on a `scope. Our minds decode the tones out of that sequence. And when they occur. And how loud they are.

Most speaker designers throw out the "When" and use tests that ignore any distortions of "When".
A sinewave frequecy response test doesn't care "when".
An FFT throws out the "when".
A pink noise test ignores the "when".

I think keeping track of distortions in the time domain, the "when" of every moment-by-moment variation in pressure, is as important as preserving the pressure (loudness or amplitude) of any particular variation.

Speaker design is easy when you ignore the time domain, but once you hear the difference, you cannot ignore the importance of reproducing the "when". Perhaps one of the non-time-coherent speaker designers could tell us why they believe the "when" is unimportant.

But to do so, they will somehow ignore the most fundamental concept- that Sound is air pressure changing in time. That is all it is. Pressure vs. time, a particular pressure change at a particular moment.

I believe reproduction approaches "hi-fi" when any change in the air pressure next to our bodies as time flows is dictated more by the sound/by the music, than the loudspeaker.

Best regards,
Roy Johnson
Green Mountain Audio

NSM, Role Audio, and maybe Jordan single driver speakers are time and phase coherent.
NSM states "Time coherent" at their website here:
NSM

Any comments Roy?