N1200 Crossover Upgrade - ??

[alcerritelli]

I have a pair of JBL Signature C34 cabinets with original parts – 130A, 175DLH & N1200. They are working fine and sound great except at high volume, I believe I am experiencing distortion at about an octave below the crossover point (600hz).

Just wondering, is this a characteristic of this system? Is it the woofer being taxed at it's upper limit, or the horn at it's lower limit? Is there an upgrade or replacement to this crossover? Is it possible to get this crossover to have less distortion? Does the crossover even have a distortion spec?

I have always used clean McIntosh power of various vintages. My Mac C34 (coincidence?) preamp has an equalizer, and by rolling off the 500hz band, I can minimize the problem.

Your thoughts please...

Thanks!

[Mannermusic]

A few thoughts: I've been messing with the old Signature gear for about 40 years and I think the one thing I hear consistently from fellow users is that eventually they become disenchanted with the octave from 600 to 1200 Hz. Seems a bit muddy, lack of definition. The physics of the big 15" driver is just not in favor of optimum performance in that range! A lot of us end up adding a "mid bass" driver (300 - 1200 Hz) of one sort or another, 2122/23, 2118. I assume you have checked the woofers for the usual surround issues, tired suspension, etc. All that gear is 40+ years old and needs TLC to keep everything up to snuff. The crossover would be the second thing I would consider . . . and is the distortion on both left and right or just one side? You could swap parts to see if it follows the suspected hardware. Check the threads here re crossover mods. Many possibilities. I don't think there are any distortion specs on those old Signature crossovers. They are relatively simple inside. There should be a schematic at the bottom of the "Table of Contents" threads under JBL Pro links, network schematics. A JBL pro shop could give you the low-down on those woofers in short order. I'm not the resident expert here by a long shot but perhaps this is a useful starter! Mike

[alcerritelli]

Thanks for your insight Mike. It makes a lot of sense.
Al

[Beowulf57]

A few thoughts from my post in the DIY forum on adding the 2405Hs to my D130/131/LE85 custom system:

N1200S versus LX5
Well, after some preliminary listening I think the LX5 crossovers may win out over the N1200Ss. I'll do more auditioning with high quality LPs and SACDs, however, the midrange is over-emphasized with the N1200S to the detriment of warmth and the bass region. The deepest bass is fine, but the mid/upper bass balance is not as good as with the LX5.

After studying the response curves of the D130/131 and the LE85 (2420), I think this may be due to the rising response of the D130/131 which shows a peak between 1KHz and 3-4KHz. The 1200Hz crossover point brings this peak into play as the response is down 4dB at 1KHz and 13.5dB at 2KHz for the LF section; with the LX5, it is down 20 dB at 900Hz. Further down at 500Hz, the N1200 is 0dB, whereas the LX5 is -9dB. Good clarity with the N1200 (and good for dialogue on films), but not as well balanced for music, which is after all is said and done my primary concern.

The LX5 seems to have been designed to compensate for the drop off in response and power handling of the LE85 with the HL91 horn below 500Hz. So far, to my ears this is a better combination than using the 1200Hz crossover with the D130/131."

[toddalin]

N1200S versus LX5
Well, after some preliminary listening I think the LX5 crossovers may win out over the N1200Ss. I'll do more auditioning with high quality LPs and SACDs, however, the midrange is over-emphasized with the N1200S to the detriment of warmth and the bass region. The deepest bass is fine, but the mid/upper bass balance is not as good as with the LX5.


I used N1200s for many years and agree that the N1200 puts too much to the horn even at its lowest setting. However, if you place an L-pad on the horn and dial it in, it is much more pleasing.

[Beowulf57]

I used N1200s for many years and agree that the N1200 puts too much to the horn even at its lowest setting. However, if you place an L-pad on the horn and dial it in, it is much more pleasing.

So, you think it is the crossover signal fed to the LE85, not the peak in the D130 response which I suspected came into play with the higher crossover point? Please check my post and let me know if you are in disagreement with my hypothesis.

P.S. I don't want to hijack this thread...so if you wish, you could respond in my thread in the DIY forum.

Thanks,

Beowulf57

[toddalin]

So, you think it is the crossover signal fed to the LE85, not the peak in the D130 response which I suspected came into play with the higher crossover point? Please check my post and let me know if you are in disagreement with my hypothesis.

P.S. I don't want to hijack this thread...so if you wish, you could respond in my thread in the DIY forum.

Thanks,

Beowulf57

Probably the interaction of the two.

Like I said, try it with an L-pad, you may like it better..., I know I did.

You may also want to try putting a 20 ohm, 10 watt resistor across the horn driver terminals as is done in the later crossovers. Again, try it, you may just like it.

[Beowulf57]

Probably the interaction of the two.

Like I said, try it with an L-pad, you may like it better..., I know I did.

You may also want to try putting a 20 ohm, 10 watt resistor across the horn driver terminals as is done in the later crossovers. Again, try it, you may just like it.

Thanks...I'll give it a try.

[Beowulf57]

Probably the interaction of the two.

Like I said, try it with an L-pad, you may like it better..., I know I did.

You may also want to try putting a 20 ohm, 10 watt resistor across the horn driver terminals as is done in the later crossovers. Again, try it, you may just like it.

P.S. That 20 ohm, 10 watt resistor is already there in my N8000 (3106) crossover.