My old (early 70s) JBLs are big box 3 ways – 15″ woofer, 1″ horn midrange, and a slot tweeter. I’m currently running them with my aging JVC AV receiver – its a nice unit, but it doesn’t provide much headroom for the woofers. JBLs are very efficient speakers – it doesn’t take a lot of power to run tweeters or mid-range horns, but woofers are power eaters in a decent system, and big woofers are worse. You see, speakers make music by moving air, and it takes lots of power to move a big speaker cone.
Another reason for more power is dynamic range – thats the difference in volume (sound level) between a quiet sound and a louder sound. Your speaker may play fine in normal use, but you need more power to play cleanly with a dramatic change in volume like the cannons in the 1812 Overture, (or “bullet time” in The Matrix).
The best audiophile technique is to give each driver in the speaker its own amp, but that can get real pricey. Second best is to feed the woofers with a more powerful amp, and use a medium powered amp for the midrange (MF) and tweeters (UHF). Thats the approach I’ve decided to take.
Through ebay and some other sources, I’ve started collecting the parts that will allow me to biAmp my speakers. From one of the Lansing Heritage folks in Australia, I got a JBL/UREI active crossover. I’ll feed that from my receiver’s preamp out, and divide the audio band into Low Frequency and mid/hi range.
I got an old Crown D75 amp (75w/ch) to feed the left and right mid/hi drivers, then found an old Harman Kardon Citation 22 to feed the woofers. This is a heavy monster, over 60 lbs (!), and its still on the way here, but it puts out 200w/channel. Not that I need to run the system that loud, but with nearly double the power to the woofers, it means nice crisp signal shapes for things like drum beats and other sounds with a sharp attack.
I’ll post more when I’m further along …