View Full Version : 4331 monitors

Mike C
05-02-2003, 02:27 AM
Hi guys, I received my 4331's this week ( ebay $950 au ). They are a little rough in the cabinets though. The drivers all work fine, and I removed the bass drivers for a peek inside and was happy to see these 2231-a's were reconed to 2235's. I think the horn drivers have seen better days but I will fit new diaphrams in them and see how they go. What I did do was desconnect the wires to the horns and ran the wires out through the vents and hooked them up to my Altec 511-B's with 909 drivers. WOW what a difference, the 909's are a great match to the 2235's, it made the vocals and mids sound very natural and life like. I would like to have the crossovers looked at and update any components that may be needed. Is there any notes availible to help me in this direction?.

05-02-2003, 06:42 AM
The addition of polystyrene and foil or polypropylene and foil bypass capacitors should be the first order of business.

You can go the much more expensive route and simply replace all the original capacitors with Theta Caps or Hovland Caps.

Biamping in also an excellent alternative.

Earl K
05-02-2003, 08:59 AM
Hi Mike

Go to JBL Pro Network Schematics (http://www.jblproservice.com/navigation/Network%20Schematics.html) and download the 3131 & 3131a schematics. Depending on the vintage of your 4331, you'll use one or the other to identify the caps that most benifit the sonics by being changing out . As Rob G just said swapping out the existing caps for the mentioned better types is a good way to go . If you want to do this in stages ( based on economics ) then start with any caps that are in series with the horn driver. Replace with types as mentioned by Rob and add the "transcap" ( .01 mfd foil type ) in parallel with each newly replaced cap . ( That's parallel with the new "cap" not the + & - of the circuit itself ) . To see examples of "transcap or bypass caps" in the circuit, also download the schematic for the 3134 crossover (http://www.jblproservice.com/pdf/Network%20Schematics/3134%20Network.pdf) . C7, C9, & C11 show "bypass" caps in the 3134 circuit .

Does your model 4331 have a large toggle switch on the back for biamping ? If it's present with an extra set of inputs, then that indicates the crossover you have should be a 3131a type ( if it's not stated on the bcak ) .

If the original JBL driver diaphragms are working well , I'm not sure they are worth replacing/retrofitting . I think you've already discovered a great mod. for this box by using a different horn with your Altec driver. In a way , what you've discovered is a juiced-up hybrid between the Altec Model 19 and JBLs best HiFi woofer from that era . Maybe you've got some balance issues using the stock crossover, but maybe not. If so , biamping helps address that quite easily . I'd experiment with turning the box on its end or side to see if you can get a better blending of that horn/woofer combination . You can always build a handsome wood grain "cowling" for the 511 horn to shroud it some. That could make it appear to be part of the 4331 ( a la the look of the integrated 811 horn in the Altec model 19 ) .

regards <> Earl K

Mike C
05-03-2003, 01:03 AM
Hi Earl and Rob thanks for the replys. Earl I went and purchased a s/h Behringer RTA today, model DSP 8000. I know its probably not the best one to have, but wow what a tuning tool. In auto mode it showed up some interesting curves and once set made the whole system a bunch nicer in my room!. The curves seemed to be suprisingly flat across the crossover point, though it did add about 6 db rising gradually from about 1k up to 10k then flattened out again. It took at least 10db out of the bottom end from 100hz down. The bottom end is much more defined now, its great. The 4331's I have the drivers vertically aligned and are not bi ampable. ( I will fix that soon enough ) I will purchase a pair of 2405's soon and see how they go. The 4331's are crossed into a pair of my 18" 2241-h's ( in 6.5 cuft bins you did the tunings for ).
As said before the 4331 bins are a little ratty so I will probably make some new ones and incorperate the 511/909 combo. I was really pleased to see the bass drivers had been re-coned to 2235's, if I do build new bins I will source two more of them and make them into 2234's. I need more money!!! I'm using the Crown DC-150-11 to drive the 4331's and can't belive how clean the sound is. Anyway back to playing!!!!!!!!!

Earl K
05-03-2003, 04:31 PM
Hi Mike

I figured it was you Mike. I thought it better if you spoke first.
What happened to your purchase of 904 duplexes and 2245h 18"ers with Crown 300 amps ? I figured the next time you surfaced you'd have that system working in some test boxes . Took a change in direction I guess. I have those Behringers 8000 & 8024. You're right, really useful . I use mine to help quantify or identify the EQ quirks that I prefer to live with . ie; I don't let the autoEQ tell me what listening curve I like. After years in the biz, I realize my own builtin "Loudness" curve is the only one I want. :p Drop me a private mail sometime .

regards <> Earl K :)