POS, Ivica and other good members,

Can you please explain to me how the M2 combination of passive electric -6db/oct, DSP electric -6db/oct and acoustic filters -24db/oct (horn/mouth and driver/back cap) interact to protect the D2 driver and get to a 36db/oct LR filter slope.

The JBL 2430K seem to be 20 ohms impedance and the resistor attenuator in the M2 cabinet reduces sensitivity -9db. The values match exactly (13ohms/11ohms) and also seem to match the system sensitivity taking the DSP settings into account. Also the designation “K” indicates that it should be higher than “J” = 16 ohms following the old JBL nomenclature.

If that is a correct assumption, the 38mf (33,3+4,7) capacitor in line with 20ohms corresponds to a first order 6db/oct slope with -3db at approximately 209Hz. I addition there is a DSP filter of first order 6db/oct Butterworth with -3db at 782Hz.

The DSP PEQ settings of -4,3 db @ 760Hz and -5,6db @ 3,3kHz seem to have too narrow Q to help much. And the system input EQ at +1.1db at 500 does not help either…

Is the horn loading the driver harder below a certain frequency or is it the back cap reducing the diaphragms movement. For the mechanical amplitude of the driver diaphragm to be reduced below a certain frequency, given fixed voltage across the range, the electric impedance in the driver below a certain level would have to increase to reduce current trough it?? -And when the impedance falls again further down in frequency the idea is that the electric filters shall have reduced the voltage level to un-harmful levels??

From the available JBL impedance curves for the 244X/245X drivers it appears that the impedance peak at about the double on nominal impedance, dependant on horn. Is that alone enough to save a D2 when receiving several hundreds of system watts and only 12db/oct electric protection?? -Or will it indeed give large dome/ring movements but that they are not fatal to the D2 driver??

The combination of Butterworth and LR is interesting and I assume that the combination of passive XO -6db/oct Butterworth, DSP XO -6db/oct Butterworth and acoustic XO –24 db/oct sums up to a 36db LR slope to give a perfect summation.

Still learning.

Kind regards

//RoB