Time coherence - how important and what speakers?

I feel the need to try to set the record straight regarding our designs.

The Infinite Slope design we employ is absent of any ringing.
None. Nada. Don't believe me?
Go look at the review of the RM33si in Stereophile, see the waterfall plot of the RM33si. (it's online now)

Yet, the impedance curve is also well-behaved - not a "hard load" for an amplifier at all. Richard Modafferi is a stickler for excellent impedance curves, but then again he has the knowledge of filter theory necessary to properly implement this crossover.

The irony of all this is that initially, both Richard and I believed that phase linearity was an important factor in loudspeaker sound. Richard had concocted many experiments to examine loudspeaker phase. Richard's problem was that he had a stubborn professor who effectively debunked Richard's attempts to prove that it was significant. Richard finally had to come around to the viewpoint that it was not a serious problem. If phase is not such a big deal, then what is? Frequency response, and radiation patterns.

The off axis comb filtering of low order crossovers is a serious problem, which is why companies that employ that method often require the listener to tilt or "focus" the main lobe towards the firmly dictated listening position.

The broad overlap between the non-coincident drivers will create large peaks and dips in response if one moves from the optimium spot. This flaw in the radiation pattern of
slow slope crossover designs may be what certain listeners are accustomed to hearing from a stereo system.
That energy does not disappear into the sunset, but rather is bounced around the room, scrambling the magic "phase coherence" that the designer so carefully
struggled for.

Once I had lived with speakers that are free from this artifact, I found it impossible to go back. Whenever I listen to slow slope crossover designs, I find that I'm easily distracted by the large changes in tonality observed with small shifts in listening position. Which listening axis is correct? And if you can contort yourself into that position, can you stay there and refocus your energies on the music? And if you should stand up, the stark balance shift reminds you that what you're hearing is fake and unnatural.

While the idea of filtering bad recordings through such a speaker may have merit, it's more likely to be dynamic compression and radiation pattern that is taking the edge off the ol' Janis Joplin records, not superior phase response. Remember you're talking about a multi track phase scrambled recording played into a phase scrambled listening room. It's too bad that filter is not defeatable. Anyone who's visited us at shows knows that our speakers are equally at home with Louis Armstrong, Frankie Laine, Bill Evans, Nirvana, Norah Jones, Cassandra Wilson, Elvis Costello & the Soggy Bottom Boys.

Happy Tunes to you!
Jeff

Now we're getting somewhere. Designers sharing the merits and compromises they have to deal with in a decorous forum. As I have previously stated, I am consistently attracted to time coherent designs. How ever, the thought of lobing effects have caused me concern. Perhaps the experts would shed some light on the subject.

Every speaker design is a compromise. The perfect solution is not available and probably never will be. I'm sure that every speaker manufacturer feels "His" design is the best solution.
I prefer the 6db designs and I use Vandersteen 3A Signatures with a pair of matching 2wq subs. This has provided me with the best sound "I" have ever had in my dedicated listening room.
On the test bench, these speakers are about as good as any out there (testing wise using Stereophiles reviews and in Richard Hardesty's reports and comparisons in The Audioperfectionist) Obviously, there is more to speakers than what shows up on a test bench, eg:room acoustics.
I feel Jeff is trying to "Sell" his design. I'm sure his speakers are liked by some(most manufactures are) but I personally did not favor the sound. Is his solution the answer? I don't think so.
I do agree that 6db speaker designs are a little harder to set up and do have a limited "Sweet spot." But to be honest, in 40 years of being in this hobby, I have not heard a speaker that didn't take time to set up and was somewhat limited to a "Sweet spot." Vandersteen's have an area where the sound doesn't change and unless you are moving around listening to music, then, this is really a non issue. I haven't heard a speaker thats sound didn't change when moving around. I usually stay put.
I have owned probably in the neighborhood of 30 pair of different speakers over the expanded course of my trial and tribulations with this stuff. My final solution has been---If it sounds good then stick with it! I'm through spending my money chasing my tail for the "Perfect sound." And by the way, NOBODY KNOWS WHAT PERFECT SOUND IS!

Bigtee,

I agree that there are trade offs in every design, but for me the trade off's in low order crossover designs are too great to allow me to enjoy listening through them. I should mention one exception, however- the Quad ESL 63 with Crosby mod's was
within its limitations a very satisfying speaker. Just don't turn them up too loud, and place them very carefully.

One needs to be able to interpret the test data correctly, in order to identify what is significant and what is not. If you are willing to ignore peaks and dips of 10-14 dB off axis, I suppose that's your perogative.

I'm not laying claim to "PERFECT SOUND". Just "TRUER SOUND".
The problem with "if it sounds good, stick with it" is that
I couldn't find a speaker that I was completely satified with. Each system pointed out flaws in the others. That's why I went into the loudspeaker business to produce Richard Modafferi's Infinite Slope designs. These systems managed to
get more things right to my ears than any other system. And the measurements happen to bear that out.

Jeff

I don't have the means or ability to test my listening impressions. With that said, I have found the sweet spot of low impedance speakers to be wider in the horizontal plane and narrower in the veritcal plane. Despite the fact that my mother used to teach ballet, I'm not prone to dancing. I usually listen alone. As such it's an easy compromise to live with. Interestingly, the Dunlavy's seem to have overcome a bit of this vertical sweet spot compromise.