JBL LX300 - Upgrading woofers vs. used JBL 406G-1

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I am repairing a pair of JBL LX300 made in Denmark (first 5 pictures). There are two main versions Mk1 and Mk2 and maybe a third also made in Europe. The version in the LAST picture and crossover are made in USA.
My speakers are 4 ohms versions but I believe them being of similar system impedance as the US 8 ohms nominal version (measured 4.3 vs. 5.8 ohm MK1). I ONLY have one damaged midwoofer THE OTHER IS MISSING.

Calculated alignments are Vb=14.6L/0.52ft3(+/-16L)/Fb=50Hz with port size (D-L) 6cm/2.36"-14.8cm/5.82".

Physical and Mounting Info:
Outside Diameter (external diam. of driver) = 184mm
Bolt Circle Diameter = 167.5mm
Number of Bolts & Size = 4 @5mm
Front Mount Cutout (internal diam. of driver) = 142mm

A serious candidate to the MK1 6.5 in. (165mm) JBL 406G-1 mid-woofer (5.8 Ohm, 90dB) is the SB Acoustics SB16PFC25-08 with the basket made of composite material.

Edit: Now I know Mk1 and Mk2 don't have the same crossover and drivers. Midwoofers are different. Alternative drivers to JBL A606 don't exist but very close with similar parameters like Davis Acoustics 17MP6GR (-2dB) and Audax HM170X2 (-1.5dB, discontinued) both 8 ohms.


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The crossovers in the speakers are not the same from the crossover layout published here (fig.6). Resistors and cap found in the speakers Xovers read (fig.2):
10W 3R3 ohms,+- 5%, Bennic
10W 6R8 ohms,+- 5%, Bennic
C=16uF, 100 Volts


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JBL LX300/JBL LX300 MKII (european)

The speakers are not JBL LX300 (System Impedance 8 Ohms, Made in USA).

They are a later(?) LX300 or novel danish version "Made in Denmark, 4 ohms" similar to the model JBL LX300 MKII (european) with drivers "Made in France" and DCR values ~4.4/4.5 ohms.

Crossover is similar to the JBL LX300 MKII with the same layout but with different component values LF. parallel cap/HF. series resistor. The two versions are presented here, the #1 "diyaudio.pl_25256-JBL-LX300-MKII-jakie-głośniki" crossover and mine (#2).

As I understand at the moment the loudspeaker is designated as JBL LX300 but they are probably an earlier /or later:tongue: year JBL LX300 MKII version/type (with similar crossover and) with drivers models:
Low Freq - JBL A606
Tweeter - JBL A026TS


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Refoamed JBL A606 pair for JBL LX300 (Denmark model)

The JBL A606 drivers arrived from Poland. They are almost a matched pair with DCR values ~4.3/4.4 ohms, very similar between them and in a very good looking shape almost like NOS. They are probably a good professional refoam and repair work with same materials and unnoticeable details/glue. Kudos for the seller Audio-Zen @Allegro.Pl, type of "ePay" in that country.:D
I payed 62 euros, 44 euros for drivers + 18 euros for the transport for both with DHL/TNT mail across Europe and plus other small taxes, bank transfer and PayPal for mail extra costs outside Poland (~10%). Note: Transport or customs wasn't very much affected by coronavirus crisis.
The most difficult part is that you have to translate everything from polish because there isn't a second language.:eek:
The expenses of building a second crossover and choosing and buying different drivers instead of the originals would not pay the cost of the time consuming work involved.


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Here I got the T/S parameters for the JBL A606 (pair) and nominal specs values.
We can now simulate the original alignment Vb=14.6L/Fb=50Hz and test different alignments including speaker JBL LX 300.:)


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