Having sat in on more than two dozen recording sessions during the mid-60s at the old Capitol Records' studios at 151 West 46th Street in New York City, a frequent destination back then for Manhattan's jazz musicians after their late night club gigs, I am probably among the few still around to have seen and recall, albeit vaguely, their echo chamber. I don't have a photographic memory of it, probably because the setup was shown to me in passing by recording engineer John Chiuchiolo (credited with the famous "doo-lang" opening chorus in "He's So Fine" from The Chiffons' early 60s rock 'n roll hit). But I remember its lasting impact on me when it came to respecting acoustical/mechanical versus all-electronics designs and, in line with that, my reverence for simple analog versus digital designs in general.
The echo chamber appeared to be a simple rectangular closet space and not much more. And perhaps not even half the distance from home plate to the pitcher's mound. Nor do I remember seeing any kind of special sound-reflecting materials in it, or tunnels leading anywhere. So it didn't appear near as long or large or complicated as the subterranean concrete bunkers built 30 feet underground that I envisioned at Capitol's Los Angeles, Calif., studios. The echo chamber I saw in NYC butted up against the head of the audio-mixer console in the control room (in which studio I just can't recall) and looked as if it was fitted with several pickups to capture the reverberation effect.
The discussion that day wasn't so much about echo chamber designs. It was more generally about the quality of sound in acoustic-based versus electronics-based sound processing, notwithstanding musicians who used various fuzzbox systems to intentionally create distortion. John's opinion was that the echo effect was cleaner and truer coming from a system that had its roots in the instruments' own space-acoustics.
I respected John as a first-class audio and RF technician and as a musician. John demonstrated the acoustics-versus-electronics difference. For the particular example he chose that day (a playback of one of his own guitar instrumentals), he proved his point to me. I'm sure it wasn't the first time I recognized the link between analog and mechanical, and how such systems could do the job as well as pure electrical networks. But it might have been the first time that I could also see acoustic and analog solutions might be less messy. And this was before digital techniques transformed into much more than "a special case of analog." It's rather taught the other way around today.
Not only could the analog solutions be less messy, sometimes they could be better. I inherently recognized the link between digital and unwanted switching transients, and what you had to do to get rid of those. Sure, we all saw the future of digital computing and super-speed operations in a world of future shock. I just didn't see, and still don't see, a need for high technology everywhere.
A few early examples based in amateur radio set that tone for me. At or near the top of the heap in their day, Collins Radio Company established one early standard for tight IF-stage filtering at 455 kHz using a mechanical-electrical transducer design in their communications receivers. These so-called mechanical filters could provide a bandpass from a few hundred hertz to a few kilohertz.
Somewhat related were the crystal filters. They were considered more of an electrical solution, but if you examine the filtering mechanism of one you'll see that they have a mechanical basis with similar filter characteristics. Either filter is superior to traditional transformer-coupled electric filters.
The transformer-based filters have only so much capability (at both large bandwidths and small) and, pound-for-pound, probably wouldn't be able to provide anywhere near the same bandwidth characteristics as either the mechanical-electrical or crystal filters mentioned above -- unless you're considering an IF stage at an impracticably low frequency. In any case, DSP-based systems are in vogue today and touted for providing much tighter bandwidths with much less in the way of side effects when properly designed.