Help with crossover design... for some JBLs

[Marvel]

I relaize I could probably get help on the Lansing-Heritage forums, but they might also want to string me up...

I have a pair of JBL 4311s from '73, that I WAS going to just replace the crossover caps. JBL did these simple, by only using a cap for the mid and tweeter, and no inductor on the woofer. My plan is to:

1. Replace the tweeter with a Beyma slot tweeter (similar to the JBL 2405), which will fit with only minor enlarging of the tweeter mounting hole.

2. Replace the mid, 5 inch cone, which has been a notoriously weak and distortion prone driver with another Beyma driver. I haven't totally spec'd out this yet, to see how close in size they are.

3. Replace the current crossover with something a little more fitting. There is a guy selling a crossover upgrade for these, but they are running $300. It might end up costing me as much, but I am interested in lowering the woofer to mid crossover point, which is currently at 1.5Khz. I would like to lower that to around 500Hz, which should be fine for the Beyma (5MP60/N). THe mid to tweeter can still cross over at the original freq., which is 6Khz.

THe crossovers contain pretty decent 8ohm l-pads, so I can use those to chop down the higher output level of the new mid and tweeter. So, my question is, are there any takers on the crossover design? The woofers are doing good, and have an Fs of 25Hz.

Thanks in advance.

Bruce

[Invidiosulus]

Oooh,

sounds fun.

Not terribly related but Troels Gravesen has a write up on his site of a mod he did to some L-26 decades where he made them a 3 way.

http://www.troelsgravesen.dk/JBL-L26-3way.htm

Sounds fun.

What should we make to put on top of the 4636?

smithhorns with some 902-16A ?

-Josh

[tigerwoodKhorns]

I'd give something like this a try:

http://www.ajdesigner.com/crossover/crossoverfirst.phphttp://www.pvconsultants.com/audio/crossover/xoversim.htm'>

Google crossover design software. If the original was just a one cap per driver it does not get much simpler than that, but I assume that you want to add inductors.

Getting the slot tweeter to come down to the output level of the mid and woofer may be a challenge with just L Pads btu I really do nto know. Something like 89 or 90 db vs 105 I assume between the tweeter and mid and woofer.

[Marvel]

Paul, the Beyma 5" is rated 91db, and should be a good match with the woofer. The original LE-5 2 is rated 95db. The tweeter will be the harder one, but the original 4311s were only rated 45-15Khz, 91db. Having a tweeter that can be almost flat to 20Khz will be a treat.

Bruce

[tigerwoodKhorns]

Bruce,

If the impedence of the new drivers is the same as the old ones, I'd hook it up with the original caps just to see what the output of the midrange and woofer sound like. I know that you want to change the crossover points, but this will give you an idea of whether or not he midrange needs to be attenuated at all. If you do not have to attenuate the midrange you may be able to design a network using a transformer for the tweeter only instead of an L Pad. Al posted recently about how L Pads drift after you get them all set up, so he prefers transformers.

Any your right, the original tweeter on the old JBL's is not very good, even if you are lucky enough to find one that does not have the dome pushed in.

Chris

[Marvel]

I bought these new for about $270 each, list was $329 each. One of the tweeters has the dome pushed in (Invidiosulus' sister did that if I remember correctly). You really couldn't tell the difference. The foam around the tweeters (to stop reflections) is crumbled and worthless. I just thought the slots would do wonders for the high end. The lpads on these are pretty good, but I could be tempted to get the levels I want and just make a fixed lpad instead.

I don't think there will need to be any attenuation on the mids at all.

Bruce