123A in L-65 Jubals

[oznob]

Looks like a decent pair of L-65's on ebay with 123A woofers. Are they a good replacement for the originals? Had a BIN of $500.

[GordonW]

My biggest qualm about using a 123A in a late-model L65 is that the 123A has a SIGNIFICANTLY lower DC resistance (and overall impedence curve values, as a result) than the 129H (average of about 4.5 ohms for the 123A, vs. about 5.75 ohms average for the 129H). This could reasonably cause a shift in the frequency response... probably making a "hole" between the woofer and the midrange.

This problem should be less prominent in earlier-model L65s... the 122A and 126A had lower DC resistance than the 129H. At a specified range of 4.5 to 5.5 ohms, it's much closer to the 123A.

However, in either case, there's still the issue that the 123A is quite a bit more efficient than any of the L65 woofers (to the tune of 2-3 dB). This may cause the system to be overly "bassy". It may be possible to "crank up" the L-pads for the midrange and the tweeter to compensate, but that's assuming there's enough "reserve gain" left there to make up the difference...

Also, the 123A has a much higher Q compared to the normal L65 woofers. This will cause a change to a less-damped bass response (ie, a "peak-up" of a couple dB, centered at around 60 Hz or so, compared to the normal L65 woofers in the L65 cabinet). However, since the L65 is larger than the L100, it should actually have better bass in that cabinet than in its normal L100 habitat... so it might be quite amenable to people who like the "fuller" bass sound...

Regards,
Gordon.

[edgewound]

The 123A(which version? A-1, A-3) is quite a bit different than the 126A, 122A,129H in the L65, L65A, and L65B. The resonant frequency is lower in the latter models with a foam surround and a straight sided cone, versus the curvilinear cone and pleated cloth goop covered surround of the 123A...all versions. All in all...the L-65 wasn't designed initially for the 123A...and you buy at your own peril....the ad probably said, "an improvement because the surrounds aren't foam that rot"....well that's that's not the only issue, here.

BTW....the 122A gets reconed with a 129H recone kit...per factory specs.

[GordonW]

Yeah, if I reconed a 122A with a 129H recone kit, I'd do one of two things:

a) add 10 grams cone mass (mass ring) to make the new kit behave more like the 122A kit (100 grams cone mass for a 122A, vs. 90 grams for the 129H/128H kits now)

or b) Redo the L65 crossover, to L65B specs. That'd take care of the DCR issue, as well as any efficiency/bass-curve-shape considerations.

Of the two , 'b)' is the more "comprehensively technically correct" option... but I've done 'a)' in practice, and it did give satisfactory results.

Regards,
Gordon.