View Full Version : How to Upgrade your JBL 4343 to a 4344

Ian Mackenzie
07-21-2005, 12:49 AM
This thread will be dedicated to a How to guide for those interested in upgrading their JBL 4343 monitors to a more recent specification.

We will discuss several upgrade options in some posts ahead that will suit both the desires of those wishing to maintain the original vintage character and driver upgrades to more recent specifications.

Perhaps as a matter of protocol it would be preferred if a seperate discussion thread is opened for opinions, feedback and questions / answers so that the design and description does not get lost in the thread.

More to follow soon.

Ian Mackenzie
08-16-2005, 07:50 AM
Well everyone,

There has a been a short pause while l have been verifying and making final measurements of the reference system...I do believe after listening to the system tonight we are ready to proceed.

As a prelude to the introduction of the project one of our fellow members wrote me late last year asking if I would be interested in preparing an upgraded crossover to compliment the drivers that had been recently upgraded in his JBL 4343 to the JBL 4344 spec.

There have been quite a few posts on the forums on crossover upgrades for the 4343 and while we consider this an important element we have taken a more holistic view of improving and refining the 4343 concept to the 4344 specifications.

From my own perspective this has meant applying liberal amounts of lateral thinking to ensure we have left no stone unturned in our quest for the ultimate performance from the 4344.

So what will follow over the next few months is a practical no nonsense guide to upgrading your 4343 to the 4344 that can be taken in several logical steps.

Just as a reminder we have posted a sister discussion thread for opinions, feedback and questions / answers



Ian Mackenzie
09-08-2005, 09:58 PM
Upgrade Modifications to the JBL 4343/4343B Studio Monitors:

This thread will describe several different upgrades available to owners of 4343 and 4343B Studio Monitors. Although we are focusing primarily on upgrades to the 4343 series monitors, owners of other Studio Monitors, 4344, 4350, 4333, etc, will find that many of these upgrades could apply to them also. The upgrades will be broken down into various upgrades starting with relatively simple upgrades up through a full upgrade of the drivers and crossovers. The basic framework here is to offer modifications that improve the performance of the 4343/4343B monitors while preserving their vintage appearance. A requirement here is that the speakers continue to look original. Therefore we will avoid any modifications to the cabinets or grilles. In addition, it is not within the scope of this thread to discuss how to restore the cabinet or grills. There are numerous other threads on the LH Forum that cover these aspects in great detail.

Setup and placement

Amplifier power recommendations


Room acoustics and monitor placement

Slot Tweeter placement- inner vs outer

Removing the top baffle

Measuring performance.

Upgrade 1 System Maintenance:

Clean L-Pads, replace if necessary

Clean/improve terminations.

Testing condition of drivers and crossovers

Recones, refoams and new diaphragms.

Upgrade 2 Upgrade 4343 drivers to 4343B spec.

Replace 2231A with 2231H

Replace 2121 with 2121H

Upgrade 3 Bypassing the bi-amp switch.

Upgrade 4 Upgrade the stock crossovers.

Replacing capacitors.

Bypass Capacitors

Charge coupling

Upgrade crossover to 3145 spec.

Upgrade 5 Discussion on Bi-amping.

Pros and cons.

Active crossovers available on the market

Upgrade 6 Upgrade drivers to 4344 spec.

Replace or recone LF drivers to 2235H

Replace or recone MF drivers to 2122H

Replace or rediaphragm HF compression driver to 2425J.

Upgrade 7 Converting to Hi End Crossovers.

Internal vs External placement



Upgrade 8 Cabinet Upgrades

Improve internal bracing.

Modifying the top 4343 baffle

Modifying the bottom 4343 baffle

Cabinet and grille repairs

Upgrade 9 Discussion on modern drivers.

Modern driver choices available today

Use of a subwoofer.

Upgrade 10 Other Upgrades.

External Horns


Other upgrades

Ian Mackenzie
09-08-2005, 10:33 PM
Upgrade 1 System Maintenance:

Clean L-Pads, replace if necessary

Clean/improve terminations.

Testing condition of drivers and crossovers

Recones, refoams and new diaphragms.

Okay lets get on with project..its dragging on a bit....

Cleaning L Pads

Remember we are following a total system philosophy here, so there is no point just focusing on say cleaning the L Pads without addressing all the issues in each topic.

Before proceeding to embark on the above consider if you want to do upgrade No 6 and 7 as these upgrades will require change out of the Mid and HF L Pads in the original 4343.

If however you are like me and prefer to build an external outboard crossover with audiophile parts the original L pads can be bypassed and left in place by using external L Pads contained within the outboard crossover. This approach will allow you to preserve the 4343 in vintage state should you decide to sell your 4343's a some stage. (we will discuss details of external crossover implementation shortly)

At any rate give the L Pads a turn and listen if they crackle. If they do then you will need to either replace or clean them. I would tend to replace them if they are stock due to age..they are not expensive. They are a 50 watt 16 ohm version for the mid and HF Levels and 8 ohm version = for the Uhf Level. These parts can be found on the Parts Express on line catalogue.

I personally am not familiar with the proceedure for removal of the L pads in the 43xx monitors but you will need a hot air gun or hair dryer to carefully remove the Foil Cal.

Perhap someone can come in with the fine detail here......



Now the terminations.

Unfortunately, teminations tend to oxidize over time and should be cleaned with a contact clean..ProGold or similar.

The stock terminations as I recall were not the best by todays standards so you might also want to consider replacing them with a set of quality binding posts.... I highly recommend the Cardas and the Eichmann range.



Do Not use cheap brass binding posts, they have poor conductivity and tend to be of poor quality construction.

The speaker wire should be stripped and the conductors cleaned with a sharp knife until you see bright copper. The bare wire can either to secured firmly to the binding post or you can use a spade.

Again, Do Not use cheap Brass Spades, use only pure Copper Spades.

You can see in the picture below how someone has replaced the binding posts to the rear terminal panel of the 4343.(C/ - Jean)

Testing condition of drivers and crossovers.

Have a look at the crossover for signs of heat stress or burns. If any of the resisters are blackened they should be replaced. Consult a qulaified technician unless you have the tools and skills to perform the repairs. Some experienced members may also be willing to assist.

Now the drivers, as per the hundreds of posts on the forums check if the woofer and mid cone have damage to cones or foam rot. I do not recommend attempting to refoam a driver. Again there are threads on the forums that explain the reasons for this.

Send your drivers to an authorised JBL Service Agent, they will come back as good as new.

The same applies to the compression horn driver and slot radiator for diaphragm replacement, its just not worth screwing around with at home.

However if you must look inside the compression driver go here: