I just moved some Celestion V30s from the cab I was using to another and then replaced them with brand new ones. I was ready to hear if the need to break them in was a real issue. As soon as I played through the new speakers it was confirmed immediately.
Day 1. First I played at low volume at night and only for 20 minutes after installing. The sound was unbearable. The first few minutes were really fizzy and shrill. For the first few moments I heard them changing at a rate that was perceivable. There was a strange fizz that just slowly slipped away and disappeared. I was questioning if they were defective because they sounded so bad and began visually inspecting them for flaws. I stayed with it and realized the the break in could be more drastic that I had anticipated, and I ended up being right. I could picture playing at bedroom volume never getting the speakers broken in and leaving a bedroom warrior with an unusually bad bedroom volume sound.
Day 2. I had a full volume band practice with a loud drummer. The band is the one where I play a bass into a high gain guitar amp, so it was pretty intense compared to a guitar in standard tuning. I was pumping some serious power into the cab. The speakers began sounding a lot better, but still a good distance from normal. The highs were a bit boring and unpleasant and the lows were non present enough. There wasn't much punch either.
Day 3. I started getting in a big hurry to get the speakers sounding right and plugged in my bass, selected the clean channel, cranked up the volume to the point where the speakers were on the edge of breakup and played the top string (.135 tuned to A) a lot. The speaker was flapping in the wind and I could tell I was getting somewhere. I then played my 8 string guitar a bit and then my JP6 for a bit both at extreme volume. The speakers were getting a lot more sensitive rather than stiff.
Day 4. This is the day where the speakers started sounding the way they should. High volume JP6 followed by distorted bass at an insane level. The highs are now smoothed right out and the low end is now as present as it should be. Everything I like about the V30s have finally come out. The speakers sound a lot more pleasant at quiet practice/bedroom volume too thanks to being more responsive overall. I believe the frequency response actually extends after break in. I don't expect any more drastic or noticeable changes after today since they match the sound I have experienced for years.
I think that most likely the popular cab manufacturers break in speakers before shipping cabs.
The reason speakers need the break in is because the suspension(the surround around the cone) and spider(the part that flexes around the voice coil) both need to lose initial stiffness before they start pumping out the goodies.
I can't picture anyone breaking in speakers in just a few days with a guitar tuned to standard. Some bedroom warriors may never get to hear what it's supposed to sound like if they don't ever get to crank it. Maybe that's where the baffling and rare V30 hate comes from.
Hmm, nice to see a breakdown of what it takes to break one in!