What was the last number 1 US album that was released exclusively in mono?
I thought your post was going to be about an album called Last Number that just got released in mono.
The title be edited to say:
Last Number 1 Album released in Mono
According to Wikipedia, mono records were officially phased out in 1968. It doesn’t list one definitive “last” mono record, but in 1968, several albums were released in both mono and stereo, and the mono releases were considered superior to the stereo ones. These include
Jimi Hendrix - Axis: Bold As Love
Pink Floyd - The Piper at the Gates of Dawn and A Saucer Full of Secrets
The Monkees - The Birds, The Bees, and The Monkees
There were a lot of albums released in both mono and stereo long before 1968. You might have to go back to the 1950s to find a #1 exclusively in mono.
What would be the advantage of mono over stereo? What made them better?
Here’s a good explanation of stereo mixing in the early days, in regards to what happened with the Capitol versions of the original British albums.
One paragraph gives the flavor:
Today these are usually called “rechanneled stereo.” Dave Marsh used to go apeshit over this.
This brings up a good question. Does rechanneled stereo count, or only albums released in true stereo as the originals?
The main difference is that if you are going for a mono mix, you balance it to sound good mono. If you then try to convert that to stereo - to take advantage of stereo separation - you compromise the original tracks and can’t really exploit the stereo features (you can’t isolate and pan left or right as easily). Bottom line, a clusterfuck.
The Beatles recorded mostly in mono - and their mono stuff sounds better by a longshot. Not because mono is better objectively - but because the mixes where intended for mono.