I just acquired a pair of Advanced Acoustics 440 Bi-Phonic Coupler Speakers from the late 50's - early 60's. My son says they're in great shape as he picked them up for me in Toronto. 22"X19"X4". Apparently the entire wooden face/board is made to resonate from behind via some sort of conventional dynamic motor for bass with a tweeter inset at the top corner. Weird.