View Full Version : 4343 References Thread

05-30-2007, 05:01 PM
This thread is an index to various other threads and references on the early JBL 4-way monitors.

From the L250 profile on this site:
The four-way concept allows for very wide dynamic range since the individual drivers are called on to reproduce a relatively narrow range of frequencies and therefore the overall system can handle more power. Within their narrow range, each driver can be fine tuned in the network design to result in an inordinately flat response ...a 4-way concept that Greg Timbers pioneered in the 4315 monitor of 1974. (http://www.audioheritage.org/html/profiles/jbl/l250.htm)

The 4343 is a second vision of the "big" 4-way Studio Monitors - it was preceded by the 4340/4341 series and used the same drivers, but in a somewhat larger cabinet:
the 4343 cabinet is 41 3/8 x 25 in x 17 1/8 with a net weight of 175 lbs
the 4341 cabinet is 37 3/4 x 23 3/4 x 19 3/4 and weighs "just" 160 lbs!

The difference is actually in the midrange chamber for the 10" driver - the 4341 chamber is 0.3 cu ft., the 4343 chamber is 0.5 cu. ft.

One notable feature - the baffleboard is split into two panels - the lower panel contains the LF 15 woofer, the upper panel can be rotated 90 for horizontal placement. It also has both a left and a right mounting hole for the 2405 slot tweeter (the unused hole to be capped) thus allowing mirrored Right-left speaker imaging.

The top image with 4 JBL monitors is from a 2003 photo Tom Loizeaux (http://audioheritage.org/vbulletin/member.php?u=30) had posted ( I edited the image slightly just to add the model numbers). Tom was a big fan of the JBL Monitors (http://audioheritage.org/vbulletin/showthread.php?t=280) and always had a helpful tip or friendly comment to share. He passed unexpectedly in early 2007 and we miss him.

The next picture is from a thread from John Reissen, master restoration whiz -
the image is great because it shows a 4343 in the back, with a smaller 4341 in front

The lower image is from another Reissen project (http://audioheritage.org/vbulletin/showthread.php?t=5605&highlight=4343)showing a restored 4343 sans grill ...
I highly recommend you click the link to go see what they looked like BEFORE restoration - the man is amazing!

The bottom image (http://audioheritage.org/vbulletin/showpost.php?p=134457&postcount=1)is from the JBL fan site http://jbl43.com/ (http://jbl43.com/)

05-30-2007, 05:02 PM
There were 3 versions of the series, the original 4343, the 4343A, and then later the 4343B.

In a previous thread, Giskard posted this pricing information -

"The oldest Pro price list I have only goes back to April of 1977 -
(http://www.jblpro.com/pages/pub/components/2012h.pdf)http://audioheritage.csdco.com/vbulletin/showthread.php?t=349&highlight=studio+monitor+pric e+list" (http://audioheritage.csdco.com/vbulletin/showthread.php?t=349&highlight=studio+monitor+price+list)

Thanks, Giskard!
(HJ - Note the prices for the 4343 show $1179 in April 1977 and went to $1770 for the 4343BWX in April 1981)

Here is a Link to 1977 4343 brochure (http://www.lansingheritage.org/html/jbl/specs/pro-speakers/1977-4343.htm)in the Library section of this website.

Link to 4343B brochure at JBL Pro http://www.jblpro.com/pub/obsolete/4343b.pdf

Another must read thread - Costs of bringing 4343 drivers to factory spec (http://audioheritage.org/vbulletin/showthread.php?t=2369) (note - prices circa 2004)

Thinking about buy a set of 4343s? Link to 4343 Buyer's Guide thread (http://audioheritage.org/vbulletin/showthread.php?t=3464)

Here's a driver chart from JBL Pro Division - I modified it slightly to display the major 4-way Monitor systems all on the same page

05-30-2007, 05:06 PM
One of the magical things about the 4340/41, 4343 and 4345 Monitors is the 10 inch Midbass driver. This driver helps the big woofer (15 or 18") handle just the really low notes, and keeps the horn/compression driver from having to go below its optimal range.

Here's a thread showing how Infredible redid the surrounds on a pair of those ultra-rare 2121s - http://audioheritage.org/vbulletin/showthread.php?t=3527 (http://audioheritage.org/vbulletin/showthread.php?t=3527)

In an older thread, (http://audioheritage.org/vbulletin/showpost.php?p=2177&postcount=11)Giskard said

The 4343 uses the alnico 2121 and the 4343B uses the SFG ferrite 2121H. Both have the 4" inverted paper dust cover.

The 4344 and 4345 use the newer 2122H which has a harder 3" dust cap. It is less susceptible to break-up.

All of them use a 3-inch edgewound copper ribbon voice coil.
"Isn't this inconsistent with what we would normally use above 300Hz? I would assume aluminum would be desired due to the lightness and quick response at the higher frequencies."

Sure, it just wasn't in the cards way back then. The newer 2123H uses an aluminum voice coil.

Thanks for that info, G!

One thing thats a problem for modern fans is that the original model 2121 driver is unavailable. It was replaced by the model 2122 - which is rapidly getting near impossible to find as well. You can occasionally find a replacement cone (as of May 2007) for a rebuild, but even they are in quite short supply.
Some folks have substituted the model 2123 driver - but its not equivalent, its more efficient (higher output levels), and has a different response curve that the earlier 2 drivers. You'd need to re-design the crossover and, frankly, its just not the same driver.
But some folks do like it.

For those who can read the design specs - here's a chart Giskard has posted numerous time showing the different parameters.

05-30-2007, 06:35 PM
Link to the standard crossover network for Model 4343 (3143 network):

The recommended upgrade for the model 4343 monitor is the 3145 network from the Model 4345 - http://www.jblproservice.com/pdf/Network%20Schematics/3145%20Network.pdf

Giskard has engineered a Charge-Coupled replacement crossover design for the 4343 series

Guido and friends spoke more about CC networks here (http://audioheritage.org/vbulletin/showthread.php?t=5391)

Ian and friends talk about Charge Coupling on the Cheap (http://audioheritage.org/vbulletin/showthread.php?t=8111)

This thread talks more (http://audioheritage.org/vbulletin/showthread.php?t=3555) about JBLs work in Charge-Coupled crossover design - aka Bypassed and Biased Capacitors.

Here's another discussion on upgrading the crossover networks (http://audioheritage.org/vbulletin/showthread.php?t=975)

Of course, there is always the question of where to set the LPads on the speakers!
Here's a tip from Tom

Starting with the attitude that I knew more about how these JBL monitors should be balanced than the guys at JBL, I've tried a variety of settings over many months, working to meet my mood of that day, but have found that after enough time and variety of settings, I seemed to get the level controls for the mids and highs very near mid (12 o'clock) position on my passive monitor speakers!
When I run my monitors in bi-amp mode I turn all the mid and high pots up full because their's no reason to burn off power coming rom the high frequency amp. I then balance the mids and highs by setting the power amp levels.
I've read that these level controls were included to adjust these speakers to variations in the type of rooms...and I believe that is correct. The adjustments from mid position should probably be subtle.


05-30-2007, 06:36 PM
Here's a link to the 4343 rebuild and Configuration project (http://audioheritage.org/vbulletin/showthread.php?t=8919)

Ian's 20 page threadon JBL 4343 to 4344 upgrade (http://audioheritage.org/vbulletin/showthread.php?t=6633&)

Ian posted this information on inproving the 4343 (http://audioheritage.org/vbulletin/showthread.php?t=8026)

There are a number of low cost improvements that can be done. Some of the links are below.

There are many other threads with valuable information on getting the best out of your 4343's so enjoy browsing the forums.





Here is a link to the JBL 5235 manual which thoroughly describes bi amping.




05-31-2007, 09:32 AM
One of the first recommendations to improve the sound of the 4343 (or any of the big 4-way pro monitors) is to biamp the system. This means to use an external crossover circuit to separate the audio from your preamp into low frequency and high frequency ranges and feed those signals to a dedicated pair of amplifiers. The low split output feeds just the woofers, and is will be a much higher powered amp (200-300w/ch) than the high split side - the high split should be very low noise as the 2405 slot tweeters will tend to accentuate any hiss in the circuits.

Porschepm posted this link (http://audioheritage.org/vbulletin/showpost.php?p=78120&postcount=4) to a generic article on the basics of biamping: http://sound.westhost.com/bi-amp.htm#elect_xovers

Biamp image below courtesy of Ian

05-31-2007, 09:33 AM
Please note - I have just begun this thread and have a LOT left to add ...

This is designed to be a longer term references to other resources here and outside on the web. We are trying to keep the signal to noise ratio high.

To keep the thread "on topic", please give me the next few days before posting ANY replies or comments here.

Your on-topic images, information, insights and links are most welcome and I'll give you credit for your contributions.

Your PMs are most welcome.

Thanks for your help!

Heather James

Need a set of 4343 Grill badges? Checkout this thread - http://audioheritage.org/vbulletin/showthread.php?t=1899

06-02-2007, 12:47 PM
Just wanted to post a copy here -
(link takes you to the original post)

John Eargle from High Fidelity 1979 (http://audioheritage.org/vbulletin/showpost.php?p=169153&postcount=28)

08-25-2007, 12:05 PM
Hi Fangio,

... At the moment the new foam is setting on the mid range units and the next step will be to strip the speakers down. The trouble is that I am not sure whether the back removes. Also, if I take off the front panel do I have to remove the speakers first, and what stops the units falling in if I do. Any ideas on this ?

Recommend you have some masking tape and a pen handy so you can label the various wires as you disconnect them from the drivers.
Lay a 2x4 or chunk of styrofoam or something on the floor (a book at the two top corners?) so once you lay the speaker on its back there is room around the edge to get your hands in and lift the cabinet back up later.
Put a towel on the baffleboard (so you can rest the woofer magnet there in a bit and not scratch anything up. If you have a lens on the horn remove that and put it aside. I have found the plastic snap on cap from a 1 lb can of Yuban (coffee) will slip on the open end of the horn and prevent the risk of something falling into the horn. (If you have to, masking tape will cover the opening just as well).

Lay the cabinet on its back. Remove the screws holding the woofer in place and gently slip a putty knife under the edge to give you room to lift it. If it doesn't come free recheck all the screws and then careful run the putty knife under the edge of the woofer frame to be sure its not stuck to the face (careful - don't want to nick the cone or anything). set the speaker on the towel and label the wires (LF red and LF blk - for the red and Black clips on the woofer) remove the two wires from the spring clips and move the woofer to somewhere safe.

Now, remove the screws holding the 10" midBass driver and lift it up, put it on the towel. Label the wires MB red and MB blk (as needed), unclip the wires and put the 10" somewhere safe.

Update - the following ONLY APPLIES to the 4343
To access the horn and slot tweeter in a 4343, you'll need to remove the upper baffleboard.
Fangio says there are two different -length screws screws used to hold that upper front panel on -
so I'd recommend making a drawing of the panel and noting which screws go into each hole.

Update - the following ONLY APPLIES to the 4341 -
To access the horn and slot tweeter in a 4341, stand the cabinet back up and you can remove the access plate on the upper back. I use a piece of styrofoam or similar to wedge it under the horn against the "dogbox" (the 10"s internal box) and support the compression driver. Now is as good a time as any to label the wires for the horn (HF red & HF blk), and for the slot tweeter (UH red & UH blk).

Go around to the front and you can remove the 4 big screws that hold the horn and compression driver in place. Do them in opposing pairs and reach your hand into the cabinet to support the driver as you undo the screws.
Lower the compression driver and attached horn into the cabinet, release the wires, and lift the whole assembly out through the access hole. You can do the same for the slot tweeter (2405)

Thanks to George and Florian for the info to update this procedure,

09-01-2007, 08:12 PM
Thought I'll just chip in on the L Pad adjustment for the 4343B. Having lived with the 4343B for a few months now, I must agree with Tom L that the speakers sound best with all L Pads at 12 o'clock position.

07-02-2012, 08:37 AM
Here is a clean schematic of the 3143 crossover but in biwiring ......


07-02-2012, 09:16 AM
Here is what inside the box of the crossover


07-02-2012, 10:48 AM
Wiring the 52 uF so that it isn't inline with the 4 uF and 1 uF capacitors.

10-29-2012, 01:28 AM
After scouring all the above and most else that I can find, not much has been said about the different driver impedance loads.
We are able to work out from our table above that the 'H' = 8 ohms. ok. We take a look at the schematic by andychris, &, nothing alludes to what the
"driver" impedance is? You can't exactly follow the 'L-Pads' to give you a clue either, as the 2121 was 8 ohms until given its H designation.
The Low Freq. were always 'A' or 'H', so that ones easy. MF is 8 ohms but using a 16 ohm L-Pad.. The HF, however, DOES mention the 'B' or 'J' and also HAS got the 16 ohm L-Pad.. !?? ...the UHF as we have managed to come to know is happy with a 8 ohm load, no matter what the badge says.
The schematic is drawn so that all is done in parallel and the masters that produced what came to become the 3143 network knew what they were doing.
Just doesn't seem to follow most of the crossover "rules" we have come to know... Anyone able to help here?



10-29-2012, 07:20 AM
JBL used "12 ohms" for the compression drivers and "10 ohms" for the ring radiators.

Since JBL did pretty much everything empirically their networks might not make alot of sense if you try and plug them into standard formulas.

The key to the intended nominal impedance value for the given network load is to measure the impedance of the driver and L-Pad (along with a shunt resistor or conjugate across the driver if there is one) with the L-Pad set to the 0 dB reference. I specifically asked Mark Gander back in '79 why the 16-ohm L-Pad on the 8-ohm driver and he said "we used it to increase power handling", so there you have it.

10-30-2012, 11:35 PM
.... so there you have it.

Hi 4313B,

Thankyou for clearing away the migrane I got trying to figure out the "why-for's"! I'm just going to replicate the circuit and put 0.01uf film & foil
bypass caps accross each capacitor and start from there.

Still weird to have only 'one' 16 ohm driver [HF] and the rest 8, but, i'll get the hang of it if I stop trying to figure it all out and just listen to the results... Thanks again 4313B!