Cross over help for a newbe

KiwiDon

Member
2009-09-05 10:11 am
Hi All,
I have just found some Jbl MR25 speakers,one with a missing woofer.I had some Skytronic 130mm woofers sitting around.After fitting them found the not very loud and no bass.Me thinks with the Jbl woofers being 4.6 ohms and the new speakers 8 ohms ,something is out of balance.Can anyone give some help designing a new crossover? Thanks Don



New woofers
Surplustronics - Wide Range Kevlar 5.25" 100W RMS
 
In general, successful driver replacement requires a careful match of Fs, Qts, Re and efficiency. Anything else is a complete redesign, with a measuring mike, simulation software and all new crossover components.

I have 4 successful speakers designs and I would not attempt what you are doing.

HTH

Doug
 
Hey, Kiwi.
You can not compare the two mid/woofers (different SPL/different impedance/different specs), with out any more data/specs available (no specs).
Now, what you have is impedance of Re=7Ω on the new woofer (902402).
The JBL (76431) is Re=4,6Ω. There is an impedance mismatch that will bring your low frequencies down for a couple of dB's (1). Plus, your JBL speaker is 87 dB SPL... and your new woofer (902402) is 84,8 dB SPL (2). All together, less output from nº1 plus less output from nº2. You are engineering a nightmare. Good luck here