Time coherence - how important and what speakers?

Well, Roy you share a quality with Jeff that I truly admire. You speak your mind. You also seem to share the same fault. You condemn those who take a different path. I do think that you seem to be a little overly critical of the "corporate entities". Jim Thiel and Richard Vandersteen both started their corporate entities out of their garages. Those who belittle success doesn't hold much promise for themselves. The designer who lacks 6th grade math skills (and we all know who you are referring to) seems to have fooled his university professors into giving him an engineering degree. This same designer seems to be aiming at the same target you are with his co-axial drivers (the mirror image of a microphone and it's pin point radiation pattern). You find fault with his approach. That's fine, your entitled to your opinion. It's also interesting that his success has allowed him to experiment with designing new drivers, a luxury many competitors don't enjoy. Attacking his education or intelligence doesn't seem like such a good marketing concept. I either don't remember learning this elementary math or never learned it in the first place. I'm sure I'm not alone. You may have just insulted a large percentage of potential customers. Don't worry I'm not that thin skinned. I can't help but feel that one can be opinonated and back up one's position with mathmatical evidence and still be diplomatic. See, I really do want you guys to succeed. I applaud both of you for sharing the evidence that brought about your design philosophies. I look forward to more from both of you and hope you lead others to be so frank.

I want to make an empirical observation about my Ohm Walsh 300's. They sound good to me no matter where I am in my apartment. I give their coherent sound credit for this. The only complaint that I have is that they won't play loud enough for some heavy tunes that I occasionally listen to. Roy's observations sure seem correct. I can't do this now but someday I would like to add a dedicated subwoofer to handle the lows. I think this will solve all problems.

I actually like some of my competitors! (even if I have differing ideas regarding design execution) I've met Roy many years ago at the Florida show and he struck me as a very nice fellow. Same for Pat McGinty.
David & Sheryl Lee Wilson came by and sat through my presentation during the last show, and David stayed and shook my hand afterward. Peter McGrath dropped by shortly thereafter. I've called upon guys like Ken Kantor and Michael Kelly for their advice, and they've always been gracious and accomodating. While the product is very important, a speaker company must be more than the product. The most sucessful companies know that you must take care of the customer after the sale. Ya gotta admire the people at Vandersteen, Thiel & B&W who take care of their consumers and do right by them. It's no small task, and they have set a standard of service that we try to emulate every day.

I'm surprised nobody has mentioned Von Schweikert speakers in this discussion of time and phase coherent speakers. Anybody have any opinion on Von Schweikert speakers as they fit into this discussion? BTW, I asked Albert Von Schweikert how he achieved time and phase coherence with a 4th order crossover. He gave me a very lengthy response to my e-mail, which was very interesting, but I am not sure he answered my question. Can anybody help ?

von Schweikert designs are not time coherent.

Yet, Albert makes very nice sound because:
1) He knows how to get the most out of the 4th-order approach (the only one that makes sense if you have to/choose to give up time coherency).

2) He makes a good cabinet- with proper placement of damping materials inside (it sounds like), and they are strong, fairly slim.

3) He chooses linear drivers, unlike most of what is out there.

4) Really a part of (1)- Albert is one of a few designers that knows mathematically and empirically most of the factors that influence the selection of the actual acoustic crossover points. Not too many do, as it takes years of homework in Physics, and then years of listening, measuring and designing to prove to your ears what is right or wrong with that Physics-based math. Electrical engineers are not taught this math (since the world went digital)- which is why there are so many non-musical speakers out there.

Recommended recording- Hugh Masekela's album "Hope" (CD). Stunning dynamics and excellent musicianship! The Burmeister sampler uses one of the cuts found on this.

Hugh M. is a horn artist, so this disc is not pretty at nightclub levels on non-time-coherent speakers that have a crossover point in the 2-3kHz range. We'll play it in `Vegas on our Continuum 3s, at the THE Show.

Remember, Mr. Bischoff, that there are many physical, electromagnetic and acoustic factors behind achieving time coherence. Those specific design factors are a checklist of well-known concepts, any one of which ignored means no coherence.

They include factors most of us have heard about:
uniform diaphragm motion,
small diaphragm/cone/dome size vs wavelength,
diffraction reduction,
crossover time delays,
time delays caused naturally by the enclosure tuning.

What a layman lacks is a rule of thumb, some numbers, for when "uniform" is "good enough" (as nothing's perfect), or a diaphragm size is "small enough", or diffraction low enough, or what the actual acoustic delay times are vs. frequency.

Those give enough information for a layman to choose music that will reveal a speaker's flaws immediately- some of which he probably can live with. This info will be on our website shortly, along with a "recommended recordings" list that makes sense to challenge a system with.

In the long run, Mr. Bischoff, you would find that phase error in speakers affects dispersion vs. frequency. It also affects dynamics vs. frequency, and imaging vs. frequency. It affects hearing the rhythmic pulse, the emotional inflections. That is, if one plays a wide variety of music. But if a listener sticks to tried and true recordings only, then he is not investigating very far into any problem with the system or speakers. Using a wide range of material with which you've become familiar speeds up speaker evaluation and system tuning.

Anyway, thanks to all for their kind comments, and Happy New Year to everyone at AudiogoN!
Wish for Peace in the new year.

Best regards,
Roy Johnson
Green Mountain Audio