the sound in this room was uncolored and extended at both frequency extremes, revealed by a superb recording of a female singer accompanied by a double bass

I have never been a fan of transmission-line speakers. My experience has been that too often resonant problems in the line color the speaker's upper bass. But I didn't hear any such problems with the Acoustic Zen Crescendo speakers (US$16,000/pair), seen here with designer Robert Lee. The Crescendo combines two 5" midrange units with magnesium-impregnated paper cones placed either side of a horn-loaded tweeter with two 8" woofers that use ceramic-coated "non-pressed" paper cones, these loaded with a transmission line venting at the speaker's base. Driven by a Triode Corporation 20Wpc TRV-845SE integrated amplifier which uses two 845 output tubes running in class-A, and a Triode TRV-CD4SE CD player, the sound in this room was uncolored and extended at both frequency extremes, revealed by a superb recording of a female singer accompanied by a double bass.