Time coherence - how important and what speakers?

Gmood1-
I am glad to know you do not generalize based upon the design of the speakers. Ears should lead the way- So play an extremely wide variety of music and recordings (old/new/audiophile/distorted) until you hear what the speaker cannot do, as if you don't find those faults in the store, you will find them in the home at some point.

And when you find a flaw- such as "too peaky sounding on bluegrass", that means not only can you not play bluegrass, you'll find you cannot stand the sound of the massed, slightly dissonant strings that a 20th-century composer such as Samuel Barber or Morton Gould used to great effect, or soprano voices, or a Vienna Boys Choir disc, or realize the effect which comes over you hearing a Rachmaninoff piano concerto at full tilt, or appreciate more fully the genius of Hendrix, or the delicacy of touch required for ragtime piano, or Dixieland, or the inflections of Billie Holiday, or Janis Joplin, or Creedence Clearwater, or Chris Whitley, or King Crimson, or No Doubt, or Massive Attack, or Metallica, or Screamin' Jay Hawkins, or appreciate the real differences between...

So you play only the 'approved' audiophile recordings, of rather bland music.

You are wrong however, when you say there is no "best way to design a speaker" I could assume you are talking about basic decisions like woofer size, port or transmission line, six tweeters or one, but actually I really don't know what you mean with that statement.

There is a best WAY to design a speaker, which I'm sure you hadn't known, nor would I expect anyone to. It's the scientific methodology used to think through and then test and build and test and... And that method is for the designer to always start with the listener's location and the room around him and the SPL required and the bandwidth desired and the coverage angles. Those are exactly the parameters any professional concert-sound designer starts with. Then he's paid to work backwards to the drivers which will deliver that desired sound. Time coherence is only part of the equation, an important part.

And this approach to design is contrary to the way most all home speakers are designed- most of their designers got a wild hair and said something like, "the d'Appolito configuration is the way to go!" and never went beyond that, into understanding what happens because of that decision out at the listener's location. They began their designs at the cabinets instead of at your ears. This explains why so many high-end speakers are bought and then sold- the dissatisfaction.

So again, I'm not sure what you meant- maybe it was "don't trust any designer". Fine- in fact an excellent idea! But as you use your ears, don't do yourself a major disservice by listening to only audiophile recordings to find the best speakers. Happy listening!

Karls, thanks for the links- I've had a look, but will not respond here, as this is not the thread for that, and I probably have not the time to say anything useful. I do see, at first glance, what appear to be some wrong assumptions about what the impedance curve peaks mean vs. the 1/4-wave line lengths. But I'm likely wrong- their measurements do not go low enough below 20Hz to reveal the errors.

Phasecorrect- you make some good points about design execution, and bear in mind most speaker designers are nowhere near fully trained. Fortunately, no permanent harm comes from bad speakers, so those designers can "get away with it". You just wouldn't want them to engineer your car or medicines or food-handling machinery or house.

If I seem mean-spirited or overly critical- I am sorry, but what I've said about poor design methods is true- I have spoken to `way too many designers, while great guys, well-intentioned, smart and hard-working, simply never slogged through the graduate calculus and fluid dynamics, thermodynamics and the mechanical engineering it takes to make a speaker that performs well on most all music, in most rooms, with most amplifiers. And reviewers support those halfway design decisions saying, "These speakers really need tubes." or "They really can't play a distorted recording." While those are accurate statements, they put the blame on something else in the chain, and not the speaker. What a disservice to you, the listener! But then reviewers are usually not technically trained, so it's only natural. I would hope that anyone reading these submissions of mine here and on that European link I gave will see how basic physics applies to speakers and how that explains what we hear and also the discrepencies between measurement and hearing.

Best regards,
Roy

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