Thiel Owners

As I’ve alluded to previously the sensitivity ratings can be confusing. In practice they’re really not as sensitive as they might appear at first glance.

unsound - Indeed the matter is not simple; it requires some study to understand. One good article from Benchmark is available on the web.
https://benchmarkmedia.com/blogs/application_notes/speaker-efficiency-and-amplifier-power There are other good articles and texts to study.

The relationship between voltage and power sensitivities produces a large array of interrelated results in the speaker and power amp. The common way to specify the sensitivity of a speaker is to state both aspects: voltage and current ie, 88dB @2.83volts @ 4 ohms. As was said previously, that voltage sensitivity would be (-3dB) or 85dB IF it were at 8 ohms, but it is not. And those two speakers ( 4 and 8 ohms) will act differently from each other in many regards and require amplifiers with different characteristics than each other.

Jim Thiel didn't make low-impedance speakers to torture amplifiers or listeners; there are practical limitations of physics. He chose underhung motors which require a 2-layer coil to remain short enough to get the significant low-distortion advantages of the topology. That coil requires a wider magnetic gap. Even with huge magnets, the maximum efficiency of that driver is lower (half) than a normal overhung motor. Given the point of diminishing returns of that topology, the maximum impedance of that driver is established. More wire turns (higher impedance) yields lower linear excursion and higher mass for lower efficiency. And so forth. So the driver parameters settle where they settle. Then, Jim chose to balance, compensate and correct many anomalies of driver response over a very wide operating range necessitated by the 1st order slopes. Each correction element lowers impedance further. And in the end, the impedance is maddeningly low. Jim's rationale was that amplifiers can be found to drive low impedance loads whereas the speaker constraints (described above) are immutable. Focused gaps and rare-earth magnet geometries were all applied to raise base efficiency as much as possible. Thiel drivers are far more sophisticated than the vast majority of drivers in the marketplace, and their distortion performance is an order of magnitude better. I guess the low impedance is a price we pay.

I direct you to the Benchmark or other articles to explicate the relationship between voltage and power. Once the relationship is understood, the rating scheme becomes more clear.

tomthiel
Thank You for the detailed explanation and more insight into Jim's design, philosophy.  Hope you are well and getting ready for Fall.

Happy Listening!

@tomthiel, thank you for the valuable link.
Um, what I was really inquiring about was your thoughts on my 09-17-2018 post.

unsound - Oh. Let's try again.
I have no experience with Roon, although I am using 24x192 digital downloads through my Metric Halo D-A to lovely effect. The model 3 up to the 3.5 was designed for equalization, which does some things well, but runs out of air-moving capacity sooner than the passive radiators. Regarding room placement, we must be careful. Room correction modifies the output into the entire room to optimize at the sole listening spot, which messes with the power response and ambient energy of the room. I can often sound somehow wrong.

Regarding placement near the back wall, yes it boosts the bass and requires less woofer output. But the downside is that wall placement couples strongly to some room modes creating associated sonic problems. Also, a potentially destructive reflection pattern occurs. The ear-brain tries to resolve-combine any sound sooner than about 5 milliseconds from the original sound, resulting in time smear. After 5mS±, the reflection is heard as a reflection and cognitively integrates as such, causing little to no distress. In round numbers, about 3' from the wall gives ample time for the back-bounce to trail the direct sound for good listening. All in all, I am not a fan of placing speakers close to a wall.

As an aside, the PowerPoint gets the wall reinforcement advantage with no bounce via its 45 degree launch plane from the ceiling (etc.) It works.

If I were trying to use 3.5s in a large room or loud levels or bass-heavy material, I would try for a subwoofer, crossed over without the equalizer, with appropriate matching 2nd order slopes and physical placement-alignment. That would really give it new life. BTW, the 3.5 was the last product to have 1% double bypass caps around the 1mF tin foil / styrene film caps and 6-9s super coils. If the 3.5 sand cast resistors were replaced with Mills MRA-12s, the result would be very sweet indeed.