[What happened to Plant's voice in 1972 ?]

Plant's vocal problems started earlier - in March 1971. Damage from his new singing style, courtesy of the songs on the 4th album. I really don't think lack of warmups, or cigarette use had anything to do with it. He simply strained himself too much with songs that required him to scream out at the top of his vocal range. Notice that during the 1970 Aug/Sept tour, he was nailing his vocals every single night. That was his vocal peak, and laid the foundation for his vocals on the 4th album, recorded a few months later in January 1971.

The very first show of 1971, at Belfast, and Plant was hitting all of the notes in the new songs Stairway, Rock and Roll, and Black Dog. But it only lasted that one night, and the very next night in Dublin he had stopped singing some of those key high notes, because it was too much to keep up. He obviously kept trying though, because over the 3 weeks of shows on that Clubs tour he ended up losing his voice, which he mentions on the BBC sessions performance from April 1971, at the end of that tour. He kept singing through 1971, and after the short periods of time off, he had some great moments at Copenhagen, Montreux, and the first LA Forum show, but he never regained the ability to hit those really really high notes, even at those shows where he had rest. Most shows in 1971 had some kind of voice crack that wasn't there before - something that never happened in September 1970, which had just as rigorous of a touring schedule.

From there, starting in August/September 1971, it was a gradual loss, over many months. But the beginning of the end definitely started with that clubs tour. Into 1972, Plant's voice had even more ups and downs, and imo his last "true" voice was the June 14 show at Uniondale. His singing during the cover of "Weekend" in the encore is kind of the swan song to his original voice - and Plant nails every high note. That show was the last time they ever covered that song. For the rest of the 1972 summer tour, Plant started using that falsetto voice to mimic the highs for his singing, which you can hear all over HTWWW.

I agree to some degree, IMO his last true voice was the Australian tour, although I see what you mean with the 06/14 show, it really is one of the better shows for Plant on this tour. To see what I mean search for 'Rock and Roll live Australia'' on youtube. When I think of Robert Plant, I think of that clip.

That does make more sense regarding the reason for his vocal problems, I remember listening to a bootleg for the BBC concert in April and hearing him explain why his voice was so hoarse, wasn't it during the acoustic set ?

This was exactly the answer I was looking for, you can't lose your voice like Plant did by smoking cigarettes and doing cocaine, it's impossible.

And sorry for the poor writing structure, English isn't my native language and my sentences can sometimes be hard to read.

[What happened to Plant's voice in 1972 ?]

After thinking a bit more about this I have concluded that he must have gotten early symptoms of laryngitis around august 1971, then he gets some rest between December and February and gets his range back but is still suffering from Laryngitis that gets worse during the HOTH sessions. I mean that must be the cause, usually when he got a break from touring his voice seemed to be in somewhat better shape but when he gets Laryngitis it just gets worse.

According to Wikipedia Laryngitis can also be caused by infection, they were traveling in Japan and Australia so maybe he got it there although I think it's more likely that he got it due to overuse of his vocal cords.

[What happened to Plant's voice in 1972 ?]

I am curious to know what happened to his voice between March 1972 and May 1972/the HOTH sessions. To me it seems like he lost his iconic raspiness that you hear so clearly when they do Hello Mary Lou in Sidney 1972, then when you listen to HTWWW his voice is a lot more clear.

Does anyone know what happened ?

[Best Stairway]

Percy's voice in '71 was just perfect

So true, his voice had been damaged/aged to a perfect point in those first shows of '71, then it just spiraled out of control and became what we hear in HTWWW.

[Best Stairway]

In my opinion this is the best version. Just because of 4:20.