Sloped baffle

Thanks Roy. For those of us time and phase dummies who have already invested in expensive gear, and who are confounded by the difficulties associated with meaningfully auditioning speakers, what are your thoughts about using the DEQX unit to unscramble the time coherence egg?

As an fyi, which I may have mentioned in this thread or elsewhere, I auditioned a pair of Vandies and another speaker (Brand X). All conditions were held constant. Notably, the amp was the same model as my former amp. I struggled to get happy with the Vandy Treos. Spent close to 90 minutes with them. Played all kinds of music. Moved my listening chair forward, backwards, sideways. Even listened backwards. :)

I was getting ready to walkout and the dealer offered to compare another speaker that is similar to mine. Same set up, amp, etc. Brand X ate the Vandy's lunch. It wasn't even close.

Maybe I like sonic swill??? Dunno

Back to my Q: Any thoughts or comments about the DEQX??

Thanks Roy. Again, you beeped. I'll counter with pop, bang, whack, pow, and all the other 60's Batman fight words that seem to have something else in common. Not arguing you're goal of recreating as accurately as possible but the words describe multiple, changing tones that appear to define our hearing ability more than the actual sound. So, my rhetorical question becomes: Is the b and p really in beep or is that our imagination?

Hi Roy, thanks for coming back. Your contributions are most welcome.
I have few questions for you.
Could you explain the pros and cons of making a speaker time coherent either by analog/digital/active/passive means?
If one were to use digital eq that only deals with room considerations and not speaker refinement, would there be a chance (and if so how much) of altering the time coherence of speakers such as yours?
The late John Dunlavy seemed to be somewhat unique (there might be another but for the life of me I can't remember the name of the manufacturer that was once a regular contributor here) in that he used W M T M W driver, as well as down firing woofer configurations. He told me that because of his previous experience in military antenna array technology he had more experience than most in wave propagation technology. Others who tout their speakers as time coherent seem to stick with more traditional W M T arrays. Is this due to size and marketing considerations, or something else?
Though most manufactures of speakers designed for time coherence seem to make fairly similar placement suggestions, they do vary a bit, from equi-T, to equilateral triangle, to wider than near, etc.. Why would that be?
It would seem to me that ideally a speaker designed for time coherence would have a sealed box, yet none of your current offerings seem to be designed that way. Am I wrong? If not, why aren't they?

Again, I look forward to people coming to understand the concepts behind my waveform illustrations. This understanding is necessary to our discussion here, because we then have agreed on the nature of these concepts at hand and also on some vocabulary.

And I wish my answers could be shorter, but that would leave out necessary details- the same ones glossed over/ignored by the press.

Bifwynne,
DEQX seems fine in theory, and certainly makes a positive difference. For me, it has serious limitations because it cannot measure exactly what needs to be corrected. This leads to results that depend on the music being played and sometimes a limitation in one's seating position.

In particular, DEQX cannot see the immediate reflections from the cabinet surface surrounding the tweeter. It cannot correct properly for anything happening below middle C because of floor-bounce effects on the microphone are not the same as they are to our ears on music.
There are other issues, but to me, those are the two largest ones. I find that a much higher level of coherence is achievable passively.

Regarding Treos-- I've not heard them and it's never good for me to comment on the sound of other speakers. I say to trust your ears above all. And you are right to listen backwards and from another room if possible! I can point out Treo, like other Vandersteens and most speakers for that matter, has a terribly complex crossover circuit, made of what I know are not the most transparent parts.


Ngjockey, thank you for your comments. Our experiences with everyday sounds and noises allows us to use them to imagine the SHAPE of a sound, which means its starting and stopping, and what happens in between. The next step up the chain is to imagine the combination of that sound with another, or literally just hear it via programming a synthesizer.

Remember, in the word 'beep', the opening 'b' has its own shape, since the lips are opening. That 'b' is is a CHANGE that happens along a certain TIMELINE, and we recognize its waveform's CHANGING SHAPE as unique to the letter 'b'. The same happens at the end when the lips close, but like 'p' instead. When you imagine hearing only the the middle 'eee', that is exactly what comes out of a sinewave test tone being switched on and then off. Which is exactly what I illustrate in my drawing.


Unsound, I am glad you find my comments useful. Thanks! Using digital EQ to treat room problems seems like a good idea, but again, just know that what you will measure is not what you are hearing-- not to say there will not be some or even a good amount of improvement. If it is used just for subwoofer correction, there are issues in most every sub's design that look exactly like room problems to the measurement microphone.

I think it best to first measure and correct a sub up close with the mic, then use that correction as your basis for further corrections YOU HEAR out in the room, listening to string bass run the scale and to kick drum (the first for tone balance; the second for transient alignment with the main speakers).

Mr. Dunlavy decided early on that driver symmetry about the ear was important, since it was important to his microphone and to his antenna-derived math. Turns out that when you are seated, the MTM arrangement is not important to the ear. In particular, you hear the tweeter's sound come from the mid when just one tweeter and one mid operate time-coherently without cabinet-surface reflections.

An MTM arrangement, including the infamous D'Appolito arrangement, always places one mid above our heads. This causes the image to be unstable with small head movements, and just plain poor for anyone off center. Why would this be? Because we have a head between our ears and a chest below them. Thus, with a small head movement to the left, much more middle-range sound literally leaks over the TOP of the head to the right ear than it does from the mid placed below the head, so the image jumps to the left speaker. This is also true for any large sound-source, such as a panel speaker or a so-called 'line-array', for the same reason.

When only one mid is used time-coherently with one tweeter, and then placed right in front of us, that single source of sound then leaks over the top of the head by the same amount no matter how much we rotate, move sideways or even stand backwards! So the image remains stable, even when far off-center, if and only if the speaker baffle is also narrow and reflections are not allowed from around the tweeter and mid.

MTM also leads to room placement issues, since sidewall reflections throughout the voice range are more complicated than when only one time-coherent tweeter and mid are used.

Time-coherent Coax operation ala Thiel would be best, except there's no way to avoid the intense tweeter reflections off the mid's cone. Also, a terribly complex crossover is required to get the tweeter's timing right. There are other limitations.

Finally, with two woofers placed high and low, for a WMTMW alignment, the bass response in any room becomes unpredictable, since you are driving bass near TWO boundaries, with your ears trapped in between.

Since everything is a compromise, a one-woofer arrangement works best when the woofer is a certain distance from the floor, in medium-size rooms, with a certain crossover frequency. But in those rooms, the bass output will then be predictable, which helps me. Nothing wrong with having the extra 'slam' from two large woofers- it just requires a very large room to make them perform as one. Then again, a very large room I find uncommon.

Speaker placement/spread is similar for very many speakers using slender front baffles, regardless of their crossover design, when these speakers are placed in 'good' rooms. This is because we need to hear a certain amount of crosstalk for the image to be continuous.

Sidewall reflections and reflections off all the fancy gear piled up between the speakers affects the final spread and the toe-in. Speakers having a large amount of reflections off their fronts are sometimes used with less toe-in, so those reflections are not shot as directly into one's ears. When there are many center-reflections (from that gear or off a video screen), toe-in is reduced. When a speaker is not time-coherent, its particular phase shift may mean those speakers sound best placed close together, pointed nearly straight ahead.

Sealed box is the best for woofers, but the market prefers more efficiency and compact enclosures, so our woofers are smaller, requiring a port. Our new three-way coming out uses twin 6.5-inch woofers, each ported at 40Hz in its own enclosure, for a sensitivity of 91dB with the same cone area as one 11-inch woofer. A single ten-inch sealed-box woofer would be in a cabinet half again larger, with only an 88dB sensitivity (requiring twice the power). The mid and tweeter would also need to be turned down by 3dB -not a great solution.

Again, I hope this helps! I realize other questions still remain, posed earlier in this tread, but I thought it best to get these out of the way right now, so I can look forward to folks' thoughts on my waveform illustrations. I will endeavor to cover the other questions soon.

Best,
Roy

Hi Roy,
good to note that you are back on this thread & have been kind enough to give us your time on this subject. Thanks!

yes, I personally have looked at the waveforms (on the photobucket.com website) you pointed us to. I understand it much better now thanks to your recent post where you explained the diff between time-coherency & phase-coherency. I was looking at the waveforms but did not draw that conclusion; now I have! Also, the 2 cars & 2 cyclists analogy was very helpful.
I have no particular question for you but I'm hoping that many other members who are on the fence re. time-coherence & others you are determined nay-sayers of time-coherence will take this opportunity of your being on this thread to ask their questions....

Bifwynne had a question re. the electrical properties of a driver & how that translated into distortion. Almarg enunciated the issue quite well & I've cut & paste his text below:

"Consider a simple two-way speaker having a first order crossover consisting of a capacitor in series with the tweeter, and an inductor in series with the woofer. For each driver that will result in well behaved 6 db/octave rolloff characteristics, which will result in time and phase coherence if other aspects of the design are also supportive, **IF** the impedances of the woofer and tweeter are purely resistive.

However I believe Bruce has been alluding to the fact that the impedances of the drivers are not purely resistive. And it would be more accurate (if still somewhat oversimplified) to electrically model them as consisting of a resistor and an inductor in series.

So the question then becomes: Doesn't the presence of that inductive component of the driver impedance (especially in the case of the tweeter) cause a deviation from first order 6 db/octave behavior? And if so, to a degree that may audibly compromise phase and time coherence? And if so, is that or can that be compensated for in other aspects of the speaker's design?"

Can you please address this question for us? thank you.
(My understanding of this question was that the driver is resistive in its pass-band frequency range where its response is flat. I understood that it could be flat response in its pass-band only if it was linear i.e. resistive over that range of frequencies but I could be totally wrong).