Re: Driver Break In In Procedure?
I think Art Welter recommended 20Hz overnight...be careful, as they loosen up they will start to bottom out! Supervise them carefully.
Silas ,
I may have made that recommendation, though that long of a time is not needed if the speaker is run in at around Xmax. Filtered pink noise works well for break in, but VLF sine waves “git er done” faster.
You may recall my recommendation from around January 2009, when you were designing your cabinets for the Eminence 4015LF, which was first released in 2006.
With a rated 9 mm Xmax, Xlim 15.5 and 700 watt power handling, it was a pretty potent speaker for the time.
That said, Eminence really messed me up with that speaker.
In January of 2008, I bought one for evaluation, while doing the run in process, found it distorted badly at 11 mm peak to peak , and clacked at 16 mm P to P, which should mean the Xmax if rated one way should be around 4.5 and Xlim 7.75 mm, half of the actual rating.
It was not clacking when I started the break in, it had loosened up a bit and started clacking after a while.
Having never actually measured excursion carefully before that point, I mistakenly concluded that Eminence Xmax rating was P to P, but Xmax is one way, a 9 mm rated Xmax speaker should go 18 mm P to P before distortion at Fs (cone resonance).
The 4015LF sounded fine below 11 mm P to P.
I had owned Eminence Lab 12s speakers since 2003, running them in FLH (front loaded horn) cabinets, I was not satisfied with the low frequency output unless used in multiples.
That led to the design of the dual BR Lab 12 cabinets which reused the old FLH cabinet shells:
http://soundforums.net/diy-audio/134-free-sub-plan-dual-lab12-front-loaded-welter-systems.html
I tried different tunings in the actual box until I got the best combination of low frequency without too much excursion above Fb, laboring under the assumption that the speakers Xmax and Xlim were half of what they actually were.
Because the 4015LF distorted at a much lower volume and needed a larger box compared to the Labs 12s, I did not pursue cabinet design with it too far, put it in a small drum fill.
As it turned out, there was something in the gap of the 4015LF (probably some glue from the magnet structure) which was eliminated by plenty of kick drum.
After realizing that I was wrong in my Xmax assumption, I retested the 4015LF, it measured within factory specifications, very little distortion until exceeding Xmax, a full 18 mm P to P, far less distortion than it originally had at only 11 mm P to P.
On 2/15/11 purchased a pair of B&C18SW115-4 from Pro Sound Service (thanks Charlie !), broke them in with a 50 volt, 11 Hz sine wave to a series pair for two hours to loosen up the suspension.
Open air, they still did not exceed the 15 mm Xmax , they started at about 25 mm P to P, loosened up to 27 mm two hours later.
As has been noted before, break in of woofer does not cause much change, and most of that occurs within the first few hours.
Also did a test at about 55 V sine wave into a single B&C18SW115-4, about 750 watts.
Didn’t get an accurate excursion measurement as I swept down from 60 Hz, the speaker walked around quite a bit at certain frequencies.
It hopped off the speaker cords it was sitting on, which had kept the vent open during the 2 hour break in.
As a rough guess the cone was moving 30 mm P to P down at 10 Hz, still hardly exceeding Xmax, and only half of it’s 60 mm P to P (30) Xlim.
Been using them in my Keystone subs, which are six dB more efficient than bass reflex cabinets for the last year. The pair have replaced eight Lab 12s, giving more bass output, and around twice as much (10 dB more) upper bass.
The pair of 18”, driven with about 2000 watts each, are used under twenty eight 8” mid drivers, and ten EVDH1AMT 3” diaphragm HF drivers.
No FOH engineers have asked for more bottom so far.
Silas, if you decide to upgrade from JBL 2268, the BC18SW115 or the new lower cost ceramic magnet BC18SW115 would be a good choice.
Art
