In 2003, shortly after legendary soul singer Reverend Al Green reunited with record producer Willie Mitchell for the album "I Can't Stop", Seth Mnookin spoke with them about their favorite microphone:

No. 9 is the microphone that Mitchell first used to record Green, more than three decades ago. He hasn’t allowed anyone to sing into it since. “Willie loves that mike, man, he does,” Green said. “It sounds full and it sounds wholesome. Every time I come down there, he takes No. 9 down off the shelf and out of that same box and polishes it just like a baby."

“When I first got Al to come into the studio,” Mitchell said, “I knew he was special and I knew I had to be perfect to capture it. So I tried to use all kinds of mikes for his voice. And when I heard him on No. 9 I said, ‘Oh my God, this is the real thing.’ I put numbers on the mikes we used that day so I could keep track of them. At least I think that’s why I put numbers on them—I was drinking vodka. But when I got to this one I put a nine on it. It has a real romantic sound, a soft, warm sound. Like on ‘How Can You Mend a Broken Heart?’ when he breathes on the mike, you hear that.”

No. 9 is an RCA 77DX ribbon microphone, one of those iconic capsule-shaped mikes similar to the ones that Larry King and David Letterman keep on their desks. Ribbon microphones are extremely delicate and can pick up the subtlest variations in volume, which is why Green’s recorded murmurings and half whispers sound as emotional and intense as his shouts and yell.

Seth Mnookin. "No. 9." The New Yorker. December 8th, 2003.