"I don't think he did use powered speakers . It looks like they are very average bookshelf speakers stuck together one facing forward one facing back and the pre - amp has been added afterwards" - BAMRECORDINGS
The "Amplified Speaker" CE sticker on the bottom made me think the speakers came from the factory amplified?
Thanks so much for these photos and details! I searched through the emails between Fred and myself (we communicated maybe once a month on average over several years) but couldn't find anything referencing them, perhaps I'm remembering a discussion of them here at TW. IIRC the project was rushed and was a lot of work for him. During setup before the opening, he hit on using a star pattern for the grounding, which minimized interaction among them. Come the opening day, he found someone had changed that to a chain type grounding (perhaps seen in the cable coverings in the photo of Fred above), which wreaked havoc on things. In general, low impedance, quality grounding is essential for proper Theremin operation.