Here's a little perspective on my personal history with speaker break in and with the Performance Series in particular.
When I got my first "real" speakers in 1970, they were L100s. Before that I'd purchased some discount stuff like Electrophonic and Audiovox, but the JBLs were worlds apart from them.
Even though I had aspirations of being a knowledgeable audio enthusiast, I had the sophistication of a hard rockin' college musician.
So if there were such a thing as break in with new speakers, it was unknown to me and I played them loud and hard from day one. I did not anticipate or listen for any change.
In subsequent years, I've had a lot more speakers, but given the realities of life, most of them were used, remanufactured, or floor demos, so if break in were a reality, it had already been done for better or for worse by others before I got them.
With the SVA 1800s and the L7s, I didn't do anythying special other than be a little more respectful during the first day or two of operation. And I listened more carefully to them. Honestly, it's impossible to say if the sound improved a tad after a few days or, more likely, that my ears adjusted to the new sound. However, any improvement after a so-called break in period was slight and just as likely caused by my subjective response as by any technical cause.
Now we come to the Performance Series. The two sets I heard before purchase were not new. They had been played a lot, and loudly as well. At the Chicago trade show, the environment was challenging. At the JBL showroom in Northridge, the environment was quite good.
My home environment is somehwere between the two; hopefully, closer to the JBL listening room than to the trade hall. However, its one advantage is that I'm intimately familiar with it. When the Performance Series came, I kept the L7/L5 set up in the room for a week to see what subjective comparisons I could make.
Before listening to the Performance Series for the first time, I gave myself a good 15 minutes of L Series listening to be sure I had a fix on the sound. Then in a few minutes I switched the connections, fired up the Performances, and...
Tight, nondynamic, strained--what have I done? Did I just waste thousands of dollars?
Well, thank heaven for J. Gordon Holt, whose review I found online as I searched for an explanation. To quote: "The Performance system sounded unpromising when I fired it up—pinched, tizzy, almost shrill—but these shortcomings rapidly diminished with use."
So over the next week I alternated between the Performance Series and the L Series in a number of listening sessions, and darned if the Performances didn't sound much, much better by day two and outstanding (as I remembered them) by day three, until it just wasn't fair to the L Series to keep asking them to compete.
So this post serves as a suggestion/warning to anyone who buys the Performance Series or any of its Ti drivers to give them a little time before judging them. Either the drivers, or your ears, or both might require a little time to adjust.
FWIW.