Thiel Owners

While I commend Stereophile for actually measuring some of the gear they review.

The discussion is not really about Stereophile measurements but more about the underlying meaning of "time coherent" or "phase coincidence" (Tom terminology). My argument is a perfect "phase coincidence" is not physically realizable in real world environment irrespective of measurements. I think you can have a speaker that is "phase coincident" but only within a certain frequency range, NOT from 0 - 20KHz.

Even with a speaker that only has one driver, it will have different phase at different frequency, and yes it will have a proper step response, but based on Tom strict definition then it is not "phase coincident" at least not at all frequencies.

I am not criticizing Thiel products in anyway, it just seems that Tom was using an argument that is a bit unreasonable.

Tom,

If you look at Stereophile measurement of the Thiel CS3.7 here:
https://www.stereophile.com/content/thiel-cs37-loudspeaker-measurements

You can see there is a rather pronounce peak on top of the step response which means the tweeter phase is not well aligned with the rest of the frequency range, otherwise there would not be such pronounced peak.  Again I don't mean to criticize here but more like trying to understand your definition of the term "phase coincidence".  You definitely threw a curve ball into the conversation :-)  It looks to me the tweeter phase is deviating from the frequency cross over point between the mid and the tweeter.  John Atkinson would call this "phase coherent" and I would too.  But then it appears that from your above post, you would disagree.  If that is the case then it would imply the CS3.7 does not meet your criteria as "time coherent".

Unsound - right on. Dunlavy took them to task and Vandersteen chided in an interview. Thiel chose to not respond as a policy, but discussed it with John. The biggest problem with them is their (usually) 50" mic distance, which does not allow the wavefront to integrate, and then JA reading in to the ragged scan, which was caused by the technique, not the speaker. They published excess phase charts on older models, which are near zero, and even at 20kHz, they drift less than 10°. In our development measurements, all models (in my time, and probably later) fell within that 10° from minimum, except the CS5, which was <5° (plus Jim published a time delay spec which I remember being in the microseconds.)

Andy - I don't remember using "phase coincidence" or "time coherent", since I find both terms confusing.

The separate drivers are placed in 3-D space to sum properly when listening at 35"±~4" and greater than 8', optimized for 3M / 10'. That is a stated constraint, which we believed to be reasonable for real people in real listening situations. A lot of the confusion revolves around magazines/reviewers not being able to measure in those real-world situations.  

Here's the Stereophile measurements of the CS1.5: https://www.stereophile.com/content/thiel-cs15-measurements
Regarding Vandersteen, I plead ignorance of any particulars. Richard didn't go places that were unfriendly. He knew the pitfalls of those measurements and had plenty of sales to side-step that playing field, although he and JA were on the best of terms. From everything I have read, he was pursuing the same expression of minimum phase as Thiel.

Andy - regarding your last paragraph on the 3.7 charts. Those charts would indeed FAIL my definitions of both "time coincidence" and "phase coherence". BUT I don't buy the charts. Note they are taken at 50" and on the tweeter axis, both of which meet Stereophile's MO, but are illegitimate for the system under test. At 100" and 35" ear height, those measurements actually yield clean triangles without those false anomalies.

I am really not the guy to try to explain this stuff. It's pretty deep and complicated by real and imagined factors, and my knowledge is real, but not fluent. Here is what I can say: Jim was an engineer's engineer, and an honest mathematician and physicist. He pursued the problems to their root causes and engineered thorough solutions. I have only conversational knowledge of what he knew to his bones. That said, I was in the lab every day for 20 years and helped devise and implement the test set-ups and cross-checks. For frequencies lower than our chamber could reliably measure (100 Hz±) we had a roof system (100'x 500' flat roof) which we correlated with both straight and ground-plane techniques. It is germane that our test system included impulses for step responses at 1/3 octave intervals from 10Hz to 30kHz. Thiel speakers pass those pulses from bottom to top, including through the crossover regions. I don't know of a more stringent test for coherence, and to my knowledge, all speakers from the 03 in 1977 meet that requirement.

Hi Tom,

Actually I appreciate your timely feedback and I have said many times I have a lot of admiration for Thiel’s products.

I’ve looked at a lot of Stereophile measurements it seems like there are speaker manufacturers that pursued "time phase coherence" but at too much expenses at other parameters that I think are just important. And some are using the term "time phase coherence" too loosely as a marketing gimmick than from actual engineering.

Thanks again for your feedback. I was going to ask you if you would care for another theoretical discussion but my guess is you probably have had enough for one day :-)


PS: As for measuring step response at 8ft, my guess is although the step response will show valid result, but the frequency response may suffer because the tweeter at 8ft distant may exhibit dips or bumps at some frequencies because the phase will not be at same say at 4ft for example.  Anyway, just my 2cents.

I'm off to a dinner meeting. I agree that the terms are used pretty loosely.BTW: Thiel considered in-room power response to be the number one parameter.

T