Enabling JBL LSR308 filters on LSR305

[roci_big_ear]

Since my trusted LSR305 have been sitting in the closet for 5 years, I decided to have fun. The LSR305 and LSR308 share the same PCB and are using a DSP for the per-driver EQs. Sure enough, there are strap resistors that tell the control MCU which speaker it is driving. So, I switched the LSR305 to think it is LSR308.

The results are interesting. Other than bumping up the bass (as expected), I feel it flattened the response a bit, as it made the tweeter 2 dB louder relative to the woofer.

I use a calibrated UMIK-1 mic, 60 cm in front of the center of the speaker, in the middle of a room.

The port tuning frequency of LSR305 is 52 Hz, so more bass under that region will result in over-excursion of the woofer. Certainly, a bit of a concern with this mod.

Thoughts? Should I revert it or leave as is?

Btw, I tried the same trick on my 306P mkii and after switching them to 308p mkii, it made absolutely no difference. So either the two models use the same exact EQ, or JBL has changed and have per speaker MCU firmware, instead of straps.

 

[jEDGEc0m]

Interesting.

According to specs, the 305PII and 308PII have pretty similar crossover frequencies, but the 306PII is quite a bit lower. Might have expected more difference if the entire DSP/crossover profile were switched between models (If I understand what your change might have been expected to do)...

If it were me, I don't see enough measured difference for the mod to be worthwhile, and could easily enough eq to preference/match anyway (assuming one has access to eq in the signal chain).

https://jblpro.com/en/site_elements/3-series-mkii-owner-s-manual-english

 

[roci_big_ear]

Your post made me realize that it indeed took effect. Because the measurements are identical outside of 300 Hz - 2 kHz, but in that region there's a small difference. So it must have done something to the crossover.

In either case, it seems like the 306p vs 308p difference is almost entirely in the woofer and box, and not so much in the DSP. The power rail voltages are also the same, unlike the 305 which has lower amp voltage.