A few favourites to start:
Mahavishnu Orchestra 'Between Nothingness & Eternity Live' (1973) The mix is pretty straightforward, but effective - guitars, bass and drums across the front in stereo, with violin in one rear speaker and keyboards in the other, and the crowd in both. The effect makes you feel like you're onstage with the band and the effect is great when the lead instruments are trading solos or playing unison lines. I actually like this mix better than the quad mix of Birds Of Fire. The performance is top-notch as well, MO were a live juggernaut.
Aretha Franklin 'Live At Fillmore West' (1971) What I really like about this quad mix is it makes use of all 4 of the stereo soundfields available in a quad mix, ie stuff in stereo across the front and back, but also stuff in stereo across the side walls too. Aretha's in the front (along with drums and bass), horns are along the left wall, backing vocalists along the right wall, and keyboards, guitars etc are dotted around the room, and the crowd is all around you. It's a really immersive mix and King Curtis' band that's backing Aretha is Hot with a capital H, including the great Bernard Purdie on drums, one of my favourite drummers of all time. Because Aretha was playing the Fillmore she was playing a lot of 'crossover' material including Eleanor Rigby, Love The One You're With, Bridge Over Troubled Waters and I Wanna Make It With You in addition to her usual repertoire and she owns it all, but that isn't even the best part - there's a true 'hairs stand up on the back of the neck' moment toward the end where she pulls Ray Charles out of the audience to duet with her on Spirit In The Dark. I guess Rhino didn't have much success with the Quadio disc of Aretha's Greatest Hits, but I'd love to see AF do a SACD of this one - it's a remarkable performance and listening to it in stereo is like watching it on TV while the quad mix makes you feel like you're actually in the crowd.
Isaac Hayes 'Live At Sahara Tahoe' (1973) A really active, discrete mix - drums, bass, guitars and vocals in front, with the string and horn sections, piano and crowd in the rears. The sound quality is so good I wouldn't be surprised if a lot of the strings and horns were re-recorded in the studio later. Features Hayes and his really tight band performing his hits and a bunch of extended reworked covers (Light My Fire, The Look Of Love, Use Me, It's Too Late, and more) and for most of this early stuff (aside from the Shaft soundtrack songs) it's the only way to hear it in quad. Such a shame these Stax quad mixes are still languishing in the vault after all these years.
Honourable mention to
Focus 'Live At The Rainbow' (1973) It's not the the most imaginative live mix as I recall - guitar/bass/drums in front, and Thijs Van Leer himself (ie keyboards, flute and yodelling) and the crowd in the rears, but Focus earned their reputation as a live band and you can hear why on this album. They play Hocus Pocus at such a ferocious pace on this live album that it makes the studio version seem like a ballad by comparison. Interestingly, this gig was filmed too (you can watch some of it on
YouTube) so they could conceivably sync the quad mix with the video and release it as a BluRay or DVD.