Using TAD TD-2001 in place of 2426J in JBL 4344 monitors - proper polarity, etc.

[mattking52]

Apologies in advance for the long post...

There are several great threads on this forum from various users who had upgraded the compression drivers in their 4344/4345 to TAD TD-2001 and TD-2002 with great results. I believe boputnam, Chas, and Ian McKenzie are the names that come to mind -- there were probably others as well. I know Guido posted a great thread using the same driver in his 4435 monitors, and took some good measurements of the drivers, etc. All of these posts are 10-12 years old at this point, though!


I recently got my hands on a nice pair of TD-2001, and have installed them in my JBL 4344 speakers. The timbre, spaciousness, etc. of the high frequency range is much improved with the Beryllium diaphragms compared to the stock Ti diaphragms... I am loving these so far!

I do, however, worry about the correct phasing/polarity of these drivers. Initially, I operated under two assumptions:

1. that the TADs are conventional, positive polarity drivers (red = positive; black = negative) -- the opposite of the stock JBL drivers, which are black = positive
2. [this is a known fact, rather than an assumption] that JBL takes care of the polarity in their crossover wiring such that black-striped wire goes to the black terminal on the JBL drivers, and the solid colored wire goes to the red terminal on the JBL drivers.

Therefore, when I first hooked them up, I reversed the polarity on both drivers, assuming that this would maintain the same phasing/time-alignment with the rest of the drivers.

As I was listening to this configuration, and reviewing the old threads, I noticed that no else seemed to be accounting for a difference in polarity between the TAD and JBL drivers. In fact, I saw at least one picture in which someone was hooking up a TAD in a 4345 with the same polarity that they would a JBL.

I tried it that way, also, and I'll be damned if it doesn't sound a little better to my ears... but I'd love to know which way is "correct." In the first configuration, I had to turn UP the level on the L-pad to get the drivers blending correctly; in the latter configuration, I had to turn them down, as they were a bit "hotter" than normal.

I'm sure measurements would tell me the full story, but I haven't quite gotten there yet. I do have a calibrated microphone I could use for this purpose.

Any advice would be appreciated!

[Ian Mackenzie]

Have you proceeded with any measurements.

A couple of points.

The measurements that Guido did were a diy acquaplas dusted Jbl diaphragm.
Dusting the diaphragm changes the frequency response and the driver impedance.
So bare that in mind if you are looking at that thread as a point of reference.

The 2001 has response variations in comparison to the 2425. If you can try measurements of the native drivers with and without the crossover network that will give you insights on where the differences are. Be careful if you do this and use a protection capacitor on the compression driver and limit your measurements to 500 hertz and above.

The compression drive horn assembly in the 4344 has a high pass 3rd order filter. Those types of filters generally have a 270 degree phase shift and 90 degree phase shift with the electrical phase reversed. A 180 degree phase shift is a lot more obvious subjectively.

These variations and the acoustic phase of the driver impact on the summation of the midrange drive and the horn in the crossover region. The horn - slot radiator crossover region may also be effected.