View Full Version : JBL 4612 OK, one of the two 8" woofers is restricted to "What" low-frequency region?

Mr Wizard
01-30-2012, 07:09 PM
Hello, According to the JBL 4612 OK spec sheet one of the two 2118J 8" woofers is restricted to the low-frequency region only ? What is the low-frequency region of the one woofer ? The 1st 2118J 8" woofer frequency range is from 60 hertz to the 3 kHz crossover point. The 2nd 2118J 8" woofer frequency range is from 60 hertz to ? Is the JBL 4612 OK crossover network a 3 way crossover network ? JBL Spec sheet states: The frequency dividing network shall have a crossover frequency of 3 kHz and shall be of the L-C high-pass type. An additional inductor shall restrict the response of one woofer to the low-frequency region only. Polypropylene and/or polystyrene bypass capacitors shall be wired in parallel with the network’s larger mylar or non-polarized electrolytic capacitors to reduce the hysteresis effects on the signal. JBL 4612 OK crossover schematic attached. Thanks. Mr Wizard

01-31-2012, 12:13 AM
The only real dividing network is on the tweeter.The slow (6dB/oct) rolloff on the one woofer, due to the inline 1.2mH inductor, will drop to ~-3dB (1/2 power) when the reactance of the inductor matches that of the woofer... If it really is ~16 ohms, then this would be at ~2KHz...reducing lobing effects due to the woofer spacing, and perhaps an emphasis that would have remained if both woofers were run "wide open"... The second woofer is not filtered and has a natural rolloff... probably around the specified crossover range.Someone has likely posted 2118J specs that would show this graphically.