Thiel Owners

@thoft, those are pretty big speakers for a room that size.

thoft - any answer to your question of amp / speaker / room adequacy is by nature incomplete, often in danger of mucking things up more than clarifying them. The equation is very complex. Many combinations work OK, and the pursuit of "better" performance is fraught with trade-offs including cost. I know it sounds trite, but if it works for you, that’s the goal.

Now for my personal take. I have outlined my amps and rooms here before, and my MO of playing the next-album-up for my evaluations. That album often works all day, and I hear cuts in the background, in intensive listening, standing and sitting, in measurements, and with different amps, cables, circuits, treatments, etc. I say that significant, recognizable aspects of each amp are audible - and they may be important to you, or not.

Your Adcom 5800 is a big brother to my little Adcom 5300 (at 250 vs 80W/C). They use MOSFETs in the signal path which lean toward tube sensibilities. I have no direct experience with your amp and can’t judge anything about your setup. But Nelson Pass either designed it, or was part of its design development path. Nelson is a world-beater, and his amps deliver high current, which Thiel's demand.
If you enjoy the game, you might find a way to borrow or audition another contender for direct comparison. The game takes time and costs money. At some point we might consider letting musical enjoyment guide us.

Prof - your information is correct. As a company we aimed our products at living-room listeners. Thus the relatively high cost of our enclosures. We assumed grilles would be in place for listening. Over the years, our fabrics became more sheer and less audible, culminating in perforated metal grilles, which are very transparent.
To various degrees, fabric reduces amplitude in the 1.5 to 8kHz range by as much as 1dB. That’s pretty huge, considering that sophisticated listeners can register 1/10th dB differences when sustained over a broad sonic range. The bare speaker will sound more aggressive, especially in less-treated rooms.
To another point. Thiel’s grille frames were used as a significant mitigation to cabinet edge diffraction, and sometimes as wave guides to shape off-axis dispersion. In the case of a very dead room and a listener preference for the additional brightness content, we highly encourage taking the fabric off the frame and using the frame for its engineered purposes. I have also noted wave propagation effects directly on the baffle surface which are tamed by the fabric itself (on models with fabric touching baffle.) Generally speaking the grille is a significant engineering element and removing it undoes significant design effort. I’ll add that many of the long-standing criticisms of the Thiel sound (up-front, in-your-face, tizzy, harsh, etc.), directly result from removing the grille.

Let’s side-step to your model 02s. That model preceded our knowledge and attention to most of these diffraction and wave-guide considerations, but the frequency response is more accurate with grilles on (and overall performance is probably a toss-up. The Renaissance 02 reworks the grille for considerably higher performance while retaining the general aesthetic of the original 1976 design.

Thoft - to augment unsound’s point - an aspect to consider is voltage sensitivity of a speaker in a room. I like that you can listen at 3/4 volume setting. Many preamp designs lose performance as the volume setting decreases. Often the criticism that a speaker doesn’t perform well at low volume is less a characteristic of the speaker than it is of the amplification driving it. Of course our ears roll off in the bass and treble at lower volume, so speakers with a bloated bass will sound "better" at lower volume. But the preamp considerations are a significant determinant factor. PS Audio’s ’Gain Cell’ solution side-steps the issue and sound "the same" at any volume setting. Such a puzzle. Nice solution. PS's moderately priced Gain Cell DAC-Pre is my go-to preamp for this reason among others.

Thanks very much for the info Tom.  That's what I figured.  I don't have
much urge to take the grills off my 2.7s.

I do find my Joseph speakers benefit somewhat with grills off in terms of opening up the high end and delivering all they are capable of.  At the same time, though, they are actually a bit more coherent with the grills on (high frequencies more seamlessly integrated).   In fact I find many speakers sound a bit more coherent in the top frequencies with the grills on.