First, thanks for the jostle of other phase coherent brands. It also seems that some ultra-expensive European brands are honoring the time domain. (Reminder: engage brain before responding) Cheers.
Regarding grille and grille frames - they, like other design elements, offer opportunities to address problems. Thiel did so from early-on.
Thiel's O1 had a reticulated foam grille. For the O1a, we formulated and sculpted the foam to be ultra thin on-axis and 1" thick off-axis, which attenuated the bounce wave along the baffle to reduce edge diffraction. The O1b sported an ALD (Acoustic Loading Device) - a sandwiched filter, attached to the grille which was nearly invisible on-axis, but further reduced baffle waves. The grilles were nearly universally derided, disregarded or discarded, even though they improved performance considerably.
The O2 had an "ordinary frame" for a fabric grille, since we learned that audiophiles would remove it anyhow.
The O3 and O3a grilles just covered up felt blocks, etc. on the baffle.
The O4's grille was pretty sophisticated, incorporating a tweeter wave guide, woofer edge-softening profile and port impedance-matching flair. We attached it with serious goo which made it evident it belonged on and ugly when taken off.
The CS2 in the mid 80s got more serious as we increased our precision of acoustic measurement and understanding. The tweeter wave guide became more sophisticated; the wave launch profiles of all 3 drivers were supported by the grille frame, the fabric was engineered for transparency on axis and absorption off axis, and the outside edge was engineered to minimizetweeter diffraction. It was successful EXCEPT that Larry Archibald of Stereophile printed multiple critiques of the "harshness" of the CS2. When we all figured out that he used and measured them without grilles, he re-visited their performance, but never admitted his mis-use as causing his problems. He stated that Thiel had upgraded and mitigated the problems he had heard and reported. Hmmm.
The CS1 series incorporated an even more sophisticated grille for wave launch and baffle vibration damping.
Similar issues prevailed through the years, with the common thread being that users' preconceptions about the harm of grilles persisted. In the case of Thiel products, the grille was always an integral design element. They were in place during development, voicing and testing. Removing them may provide a more immediate on-axis connection, but problems are always introduced which degrade musicality. More recent models incorporate the wave guides into the baffle, and the grille frames are farther aft, minimizing harm when not used, or non-existent. Newest models use perforated or woven metal, which is more transparent.
One of my intended experiments employs wool felt on baffles. We tried that early-on to good effect, but opted for grille fabric and frame solutions as more cost- effective and good-looking. I'll try some soft baffle ideas on my CS2 2s.
