Crossover Mod. When Replacing 2231H With 2235H?

[johnlcnm]

Has anyone modified a 3133A crossover after replacing the 2231H with the 2235H? It appears the inductance compensation circuit is different in the 4333B verses the compensation circuit in the 4430. A 20uFd + 10 Ohm for the 4333B verses a 14uFd + 7.5 Ohm for the 4430. This difference would likely affect the frequency response in the midrange? I am in the process of rebuilding a pair of 4333Bs. I am tempted to modify the crossover as the LF drivers have been replaced with 2235Hs.

John

[ivica]

Has anyone modified a 3133A crossover after replacing the 2231H with the 2235H? It appears the inductance compensation circuit is different in the 4333B verses the compensation circuit in the 4430. A 20uFd + 10 Ohm for the 4333B verses a 14uFd + 7.5 Ohm for the 4430. This difference would likely affect the frequency response in the midrange? I am in the process of rebuilding a pair of 4333Bs. I am tempted to modify the crossover as the LF drivers have been replaced with 2235Hs.

John

I would not expect large differences

regards
ivica

[johnlcnm]

Ivica, thank you for the reply. I had seen an old post by SpeakerDave:

"Not in that speaker, but I did try some 2235H's in my 4333a's when I had them just to see what would happen. The improvement in bass was not subtle and was immediately apparent. However, in that speaker my opinion was that the 2235 did not tie in well with the crossover(at 800 Hz) and midrange horn and because of that was a no go. Since the 4350 is biamp only and crossed over at 300 I would not see any problem at all, and you will be the beneficiary of the improved bass. Note, though, I was using the actual 2235H,
not a 2235-loaded Alnico frame."

This got my attention.

Regards,

John

[speakerdave]

Hi,

I posted on the subject a couple of times back when I had my 4333a's. The 2235H kit is the JBL-specified replacement for the 2231 and is on the "goes into" list as such, but they do not say it is an exact match. Despite that I thought at the time I was writing that on this forum and other forums people were being encouraged to "upgrade" the 2231's in their L300's and 4333's by reconing with 2235 kits REGARDLESS OF THE CONDITION of the original woofers. My 4333A's were purchased from the son of the original owner, a very refined gentleman; both he and his father were MD's and the speakers were pristine, having lived a very easy life. While I was in the process of refoaming my 2231A's I experimented with 2225H's and 2235H's in their place (both without retuning the cabinets). The 2225's played better into the midrange and had significantly more slam but lost the bottom octave. You have quoted my take on the 2235's. I thought it worthwhile to share my experience with other owners of those models so they would have that information when deciding whether to recone their woofers with 2235 kits.

I would like to have had the improvement in the bass that came with the 2235 and could easily have had it by using an active crossover, but I was not set up for that at that time. Today that is what I would do.

Your proposed solution may work, I don't know. I would think it might, if you can get the values right, since the zobel stays in play while in biamp mode. The sophistication of JBL's crossover designs since the late seventies is such that I could not assume the impedance compensation circuit across the woofer coil plays no other role in the overall design. Therefore since I did not feel capable of re-engineering the network I didn't even consider getting into it.

If I still had the 4333A's I would biamp. In that case the zobel and the network for the upper two elements both remain in the circuit, and the woofer should be rolled off at 12 dB octave at 800 Hz with an external line level crossover. Given the differences in response of the 2231 and 2235 I would also experiment with an 18 dB rolloff.

Or, your ears may not agree with mine, and you may feel the 2235H's play perfectly well with the original crossover.

Congratulations on a very fine set of speakers. I wish you success with your restoration.



Ivica, thank you for the reply. I had seen an old post by SpeakerDave:

"Not in that speaker, but I did try some 2235H's in my 4333a's when I had them just to see what would happen. The improvement in bass was not subtle and was immediately apparent. However, in that speaker my opinion was that the 2235 did not tie in well with the crossover(at 800 Hz) and midrange horn and because of that was a no go. Since the 4350 is biamp only and crossed over at 300 I would not see any problem at all, and you will be the beneficiary of the improved bass. Note, though, I was using the actual 2235H,
not a 2235-loaded Alnico frame."

This got my attention.

Regards,

John

[ivica]

Ivica, thank you for the reply. I had seen an old post by SpeakerDave:

"Not in that speaker, but I did try some 2235H's in my 4333a's when I had them just to see what would happen. The improvement in bass was not subtle and was immediately apparent. However, in that speaker my opinion was that the 2235 did not tie in well with the crossover(at 800 Hz) and midrange horn and because of that was a no go. Since the 4350 is biamp only and crossed over at 300 I would not see any problem at all, and you will be the beneficiary of the improved bass. Note, though, I was using the actual 2235H,
not a 2235-loaded Alnico frame."
This got my attention.
Regards,
John

Hi johnlcnm,

We I said that Zobel elements change is not necessary , I did not say that 2231A and 2235H have the same acoustic "feeling". If Your 2231A have ONLY suspension degradation, I will only change the foam suspension, not the whole cone. On my experience 2231A has much more pleasant LF reproduction then 2231A re-coned with 2235 kit. May be You can experiment by adding another 20uF capacitor in-paralleled to the driver if 2235 would be Your option, so cross-over frequency would be reduced for some amount on the bass driver side.

regards
ivica

[johnlcnm]

Dave. I value your ears. At this point my comments are strictly speculation, as I have not listened to the 4333s since the 1970s. When I purchased the 4333Bs I did not realize one of the LF drivers was a 2231H and the other a 2235H. When disassembling the boxes I found the 2231H was coned as a 2235. So I guess both are technically a 2235H. Searched and found an impedance plot, on this site, of the 2231H, but not the 2235H. My thinking is to modify the crossover networks while I have them removed from the cabinets to compensate.

A fifteen inch is definitely pushed into breakup at one kilohertz. It looks like the second breakup mode is at 1.2kHz. So a sharp rolloff is probably a good plan. An impedance rise there won't allow the crossover to do it's job. Probably preaching to the choir here.

Regards,

John

[4313B]

Searched and found an impedance plot, on this site, of the 2231H, but not the 2235H.A typical 2235H impedance curve:


http://www.audioheritage.org/vbulletin/showthread.php?10651-2235H

[johnlcnm]

4313B, and Ivica, SpeakerDave. Thank you folks for your expert advice. You convinced me not to monkey with the crossover. I am going to go the bi-amp route and leave the 4333B internals intact. The Internal Crossover/Bi-Amp switches appear to never have been switched. They also look to be gold plated.

4313B, I did see your conjugate simulation plots. Looks like adjustments at 1kHz up to 3dB or better can be made. That certainly is audible in that frequency range. I think that Nelson Pass had a go at re-designing the L300 crossover. He commented that it would be very hard to improve on the original JBL design. He wound up with a very similar "final" in the end.

Regards,

John