4320 Project

[hjames]

I worked in campus radio at USC (So. Carolina) in the early 70s and got spoiled by the sound of the JBL 4310 Studio Monitors. After school, in 1976 I bought my first JBLs - a set of L36 Decades (still have them and love 'em).
After finding the heritage site last year I decided to upgrade my system and started looking for a set of L300s (or even L200s) I could upgrade, but the eBay prices quickly went beyond what I could justify for a set of speakers.

Mid February I saw a set of "JBL 4505" speakers on eBay. I checked the site and with some helpful folks here I found they were actually 4320 Control Monitors - a 2 way system for recording studios from the early 70s. http://www.lansingheritage.org/html/.../1972-4320.htm
They were big boxes and required local pickup ... so after a brief delay for a snowy weekend, we drove to Philly and brought them back to Virginia.

I found a pair of 2405 drivers with diaphrams to install, again, on ebay, so they were bought and delivered a week later. I'm not a sound engineer, but I do have a technical background and know how to solder. I'm sure they weren't JBL diaphrams, but I could install the furnished diaphrams and if they didn't work right, I could have JBL techs put factory diaphrams in later.

I did a search here and found detailed directions on replacing diaphrams -
http://audioheritage.org/vbulletin/showthread.php?t=700&highlight=2405+diaphram

Anyway - here are a few pictures showing the stages of rebuilding the drivers, cleaning the gap with a piece of clear plastic (cut from the diaphram packaging)
and the final image with dated stickers on the back.

Once they were done I mounted them in the predrilled holes to the left of the horn outlet on the baffleboard, but I once I have the crossover sorted out I'd like to mount them above the horn.

I followed a tip from Zilch and built a pair of 3106 crossovers to tie to the high output of the exisiting crossovers in the box, but I had almost no output on the 2405 slots - tho they worked fine when substituted for some tweeters in another speaker system in the guest room.
I have minimal test gear these days - so I checked some crossovers for sale on ebay and found a pair for JBL L166 - the low cross was at 1000hz - the high cross at 6500 is lower than the 10k I'd like to use, but it allowed me to have all the drivers working until I can redo or replace the MF and HF legs of the crossover.

[grumpy]

Nice project. Thanks for sharing the in-progress pics! -grumpy

[Zilch]

Hi, Heather, and thanks for posting pics of your project!

If you haven't come across it yet, there's a chain of threads over in DIY for a potential crossover incorporating the 3106, still a work in progress, beginning here:

http://audioheritage.org/vbulletin/s...ead.php?t=8507

For the bottom line, you can also jump to the latest thread here:

http://audioheritage.org/vbulletin/s...ead.php?t=9221

Once work on the basic crossover is complete, a 10 kHz version for 077/2405 seems a logical next step....

[MORE pics, please. Yup, yup!]

I followed a tip from Zilch and built a pair of 3106 crossovers to tie to the high output of the exisiting crossovers in the box, but I had almost no output on the 2405 slots....

I have minimal test gear these days....

If you'd like me to check out your DIY 3106's with 2405's, PM me for the address to send 'em.

[hjames]

I took my 2405's downstairs and substituted them for the tweeters in a pair of Optimus 3 ways and they worked fine - so I know the slot-tweeters work fine. The 2420 horns and 2215 woofs had worked fine when I used the systems in their original 2 way config for the first weeks, so I figure thats all fine.

The 3106 crossovers I built I had connect to the hi output of the original 3110 crossovers that came with the system didn't seem to work, and it was consistant no matter which one I put on either speaker - so I tried something new. I'm running the speakers in conventional mode with a standard 110w/ch JVC receiver, no bi or tri-amping at the moment ...

I bought a pair of L166 (3way) crossovers off ebay ... the low cross is at 1k, the high cross at 6k (lower than I want, but its a test), and dropped them as the only network in the boxes. The speakers worked fine using them, but now I know what folks mean about harshness using the slots at the lower end of their range - I think I prefer feeding more of the mids through the horns.
I dropped the 3110s back into the box, and fed the high output of those into the L166 networks. I dropped the lowpass (woofer leg) off the L166, and just used the mid and high output of them ... its closer, but I think I need to rework them and get the high cross up near 10k.

I can gut them and use the precision resisters and the 4 JBL style Lpads to build better networks - once I learn what caps and chokes to use for the mid and high legs of the new 3way ... but I have to find time for that ...

I got the JBL cloth from Zilch and bought a pile of pine lumber to build the griills - fortunately our cats don't seem to have cone destroyer tendencies - but we spent this weekend clearing the garden for spring plantings - and hoping we don't get a final snow before winter formally ends. Of course anything is possible in the DC area ... sigh ...
Hopefully I'll get back to the crossover work soon ...

[jbl4ever]

Hello hjames, can you post a picture of the 2405 diaphrams front and back. They look like aftermarket by the one picture. Hard to tell. If they
are aftermarket ones the impedance will most likely be different than stock. A impedance curve would be needed to properly design the new circuit for this.

[hjames]

Hello hjames, can you post a picture of the 2405 diaphrams front and back. They look like aftermarket by the one picture. Hard to tell. If they are aftermarket ones the impedance will most likely be different than stock. A impedance curve would be needed to properly design the new circuit for this.

Not easily - I'd have to pull the woofers to gain access to the drivers, unmount the 2405s, then tear down a working driver.

In truth, I'd rather build the crossovers as if they were the right (JBL) diaphrams - once money is a bit less dear I may send the 2405s out for JBL pro rebuilds anyway, and if I build networks specifically for the aftermarket parts, I'd just have to redo the networks when I change.

I got the 2405s on ebay - the deal was they needed diaphrams installed and a new pair of diaphrams were provided to install. Knowing that any set I bought on eBay have worn or tired diaphrams anyway, they were cheaper than most others pairs offered. From the price of JBL diaphrams, (provided free with the 2405s) I'll assume they are aftermarket.
The diaphrams were sealed in clear plastic trays numbered DWT044S-8.


3110 Crossover LF out to 2215 woof, MF out to L166 Crossover
L166 Crossover LF leg (choke) removed - MF & HF only used
2215 15" woofer
2420 MF driver
2405 HF driver