I currently have (2)JBL PRX6-15m & (2) JBL PRX618S-XLF speakers as part of my DJ System.
I had the grey JBL EONS G1s for 8 years which led to buy the new PRX6 series. I bought my new speakers on 1/12/2011 so after reading the forums I think I have the first generation speakers for the series.
My first overheating experience was at a small bar/club and my console, two tops and one 18in subs were in the corner. After 3 hours my sub turn off 2 times due to amp getting hot. The next day I called JBL about my problem and they said the speakers needed more air circulation or else it will shutdown otherwise you need to get a small 5in house fan. I then hung up. Wow, If they only spent $5 on a installing an internal fan like QSC I would have this problem! DOH!
My second experience with overheating was at a wedding. I had my two 15in top and after 3 hours in to the dance I notice the speakers sounding weird. They did not shutdown but I was pushing them enough for the red limiter to come with every bass note. The amp was hot and it sounded like the circuitry was toning down the bass for me which kept me pushing up the volume on the mixer. Soon it started sounding like a large old school boom box. After that the mid range got crappy from all the distortion and I finally brought the volume half way down.
The speakers sound awesome for the first couple hours when the amp is not super hot, after that it all goes to pot. The amps seem to live on the edge of meltdown due to it having no fan or any type of circulation, not even holes to let air pass through the inside of the amp where are the components live. An almost flat heat sink is just not enough to cool the amp sufficiently. I wish they did some real world testing before they mass produce it. Imagine if this was an outdoor party during a hot day; overheat in 30 minutes = Epic Fail.
Here is what I had to do to resolve my PRX6-15m & PRX618S-XLF overheating issue.
Click link for solution:
Bay Area DJ