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View Full Version : JBL LX-16 crossover and 2420 diaphragm impedence question



hatrack71
01-07-2011, 03:40 AM
I am not very familiar with what range a JBL diaphragm for a 2420 reads. I am not sure if the diaphragms have been replaced but the drivers are originally 16 ohms. My meter reads like 7.9 and 8 ohms for the diaphragms. Could these be 16 ohm? Secondly, what impedence driver is spec'd to run off the high pass of the LX-16 ( L-200 crossover)? If my diaphragms are truly 16 ohm and the crossover is set to work with 8 ohm driver, is there an autoformer in the crossover in which I have to change for a 16 ohm configuration- that is if mine are 16 ohm? Or is the LX-16 spec'd for a 16 ohm load on the compression driver? Just curious as the 2420/H91 combo has always sounded mis-matched and louder than any woofer I've used with my LX-16 crossovers in the Apollos. I've never thought about the impedence thing until now. I always just thought it was that huge gaping port on the Apollos giving the imbalance. Can anyone shed some light?

Earl K
01-07-2011, 04:26 AM
I am not very familiar with what range a JBL diaphragm for a 2420 reads. I am not sure if the diaphragms have been replaced but the drivers are originally 16 ohms. My meter reads like 7.9 and 8 ohms for the diaphragms. Could these be 16 ohm?

Your DCR readings are within the specified range for original 2420/le85 diaphragms ( labelled either 8 or 16 ohm / there was only one actual impedance / just different labelling protocals from JBL back when / AC impedance is a curve with high & low points ) .

The LX-16 was designed around the diaphragms that you presently have ( so you don't need to worry about changing out autoformers ) .

Your impression of level mismatches are not the result of your drivers having the wrong impedance diaphragms in them . You need to measure the Frequency Response ( FR ) of your setup to correlate "your impression" to others experience .
- FR plots are the common language for making comparisons .

Compression drivers do not somehow bleed any of their sound through "large gaping ports" ( unless the backcap is missing ) .

If you can't get into measuring your own stuff, then I recommend that you pay someone to do a house call to assess the problems your having with your le14 loaded Apollos ( or ask Zilch to design an updated crossover for your particular project / he's got all those parts on-hand ) .


<> cheers

hatrack71
01-07-2011, 05:19 AM
Your DCR readings are within the specified range for original 2420/le85 diaphragms ( labelled either 8 or 16 ohm / there was only one actual impedance / just different labelling protocals from JBL back when / AC impedance is a curve with high & low points ) .

The LX-16 was designed around the diaphragms that you presently have ( so you don't need to worry about changing out autoformers ) .

Your impression of level mismatches are not the result of your drivers having the wrong impedance diaphragms in them . You need to measure the Frequency Response ( FR ) of your setup to correlate "your impression" to others experience .
- FR plots are the common language for making comparisons .

Compression drivers do not somehow bleed any of their sound through "large gaping ports" ( unless the backcap is missing ) .

If you can't get into measuring your own stuff, then I recommend that you pay someone to do a house call to assess the problems your having with your le14 loaded Apollos ( or ask Zilch to design an updated crossover for your particular project / he's got all those parts on-hand ) .


<> cheers

OK, thanks Earl. Maybe you are right about the crossover. I always thought it was suitable but I'm sure Zilch could do better. It's not that I can't get into measuring my own stuff, I just don't have the instruments needed. Matter of fact I really don't know anyone around here who has that kind of test equipment or I'd borrow it. This project has been put aside a few times over the last year so I kind of have to slap myself in the face to get back on track. I am building the ports for the Apollos right now. I am using a 3" inner diameter and approximately 6.6875" long PVC port to tune to the cab. A fellow AK'er figured out the port. I assume it is correct? I may just recap the LX-16s next and see what happens before I venture into new crossovers. What do you think Earl?