Question about JBL PSW1000 Speaker
I hav double ciol sub woofer & i made a box accoding to its measurements.i connected two coil serially.its 4ohom 500 max watt per coil.since searially connected it soud be 8ohom & 1000 max watt for the bffle.is it ok connecting serially?
I pulled this up for you to review , its a quickie on the subwoofer and why how where they function, I suggest you contact JBL Customer service and ask for Tech Support on this if all else failed, they may have a quick fix kit to install (Servo) to suppress the feed back.
Background on Subwoofers
Subwoofers are designed to produce only the very low end of the music spectrum. Most subs perform between 20 and 80 Hz only. Though the exact range varies depending on preference. In order to filter the frequencies above 80 Hz, you need a high-order low-pass filter. We chose to build a 24 dB/octave filter at 90 Hz by cascading two 2-pole Sallen-Key filters together. This filter can be bypassed if an external crossover is to be used. There are also many types of subwoofer enclosures ranging from 2nd order IB, to 6th order bandpass that we could choose from. Each design is more complicated than the first and much more difficult to achieve predicted results. In our case we chose to go with a 2nd order sealed (or acoustic suspension) because of simplicity and accuracy in achieving predicted results. Also sealed enclosures have a more linear phase response with relationship to frequency. They have a naturally more shallow roll-off rate of 12 dB/octave. So it can be argued that in a sense they yield the most low frequency response. Also a sealed enclosure has more control over the motion of the cone. Since we are actively monitoring the motion of the cone, we wanted to make sure that it was tightly under control to begin with. The driver has less of a tendency to bottom out in sealed enclosures. Overall it was a much better design approach to go with that any of the others.
A subwoofer must also have a really good flat response curve. Below you will see the response curve of our subwoofer as it was after we built the enclosure and mounted the subwoofer. An air tight seal is essential. This can be checked by pressing in the cone and then watching how fast the cone moves back up to its rest position. Our cone sure enough took about 3 seconds to return so we were definite we had a good sealed box. [It was pointed out to me recently that this is actually an indication of a small leak in the enclosure. With a truly air-tight enclosure pushing in the cone will actually compress the air inside that when released will result in the cone springing back rapidly, not slowly, to its rest position.]
Posted on Aug 16, 2010
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