View Full Version : Feedback loop in N200B ?

01-17-2005, 10:00 PM
I am going to try a bit of a tweak on my quasi L-300 system. I have LE15H, LE85/HL91 and 2405. Xovers are LX5 and N7000. I think the 500hz xover point is too low for the LE85 and I would like to raise it. How high can I safely go considering the upper limits of the LE15H ? The N200B has an xover of 1200 hz.
Is this too high for the woofer ? I think I am over stressing my LE85 when I really light them up.

Also, the point of my thread : What is that cct (5 ohm, .16mH and 1uf cap) in the high side of the HF section ? Almost looks feedback from the L-pad. Also, I noticed the phase is reversed. Why ?http://audioheritage.org/vbulletin/images/smilies/scratchchin.gif

01-17-2005, 10:16 PM
L200B Xover is 800 Hz. L200 and L200A are 1200 Hz.

500 Hz was used with the LE85 and LE15A in the S7 systems. With the short horn, it was a stretch, but fine with the longer horn used in L300.

I don't know the usable upper limits of LE15H, alas.

The "loop" is actually a bypass. The VHF is fed around the attenuation to augment the high end response. The idea was later exploited in the 4425, 30, and 35 monitors to make those two-way systems viable. They're "quasi-three-way," more like.

Phase is reversed to compensate for phase delay created by differential location of the sources, front to rear. It pushes the nulls off-axis....

01-18-2005, 08:01 AM
Unless your listening habits border on the "abusive" (ie, very high listening levels for long periods), I'd say that 800 Hz should be fine. Given that the L200B was built this way, obviously JBL thought so...


Alex Lancaster
01-18-2005, 08:21 AM
:) JBL recommended a max xover of 800Hz for the LE15H, but with 2KHz operating band which is of course contradictory, anyway, if You could get at least 800 Hz xovers (3110's), try them, but because of the short horn, try 1,200 (3120īs) also, these are always cheaper on eBay than 3110's.

500Hz is too low IMO, specially with the short horn.

01-18-2005, 08:37 AM
With the short horn, it was a stretch, but fine with the longer horn used in L300

Was the horn in the L300 the longer HL92 ? Short horn you are refering to is the HL91 ?

Mr. Widget
01-18-2005, 10:04 AM
What does JBL recommend and when did the recommend it?

The LE15A (essentially the same as the ferrite LE15H) and LE85 were paired in the S7 and S7R system back in the 60s through mid 70's. They used the shorter exponential horn the H91 and crossed over at 500Hz.

Later they recommended that this same pair of drivers be crossed over at 800Hz in the 4320 and still used the H91.

Later still they determined that the LE15A should not be crossed over above 500Hz and the H91 should not be used below 1200Hz. This shows the compromises of the earlier systems. JBL did not come to this conclusion until they conveniently had a better horn down to 800Hz the H92 and had a better woofer for getting up to 800Hz the 136A (2231A). These components were used in the 4330 and subsequent 4331, 4333, and in the L300.


01-18-2005, 10:10 AM
Was the horn in the L300 the longer HL92 ? Short horn you are refering to is the HL91 ?Yes. But you can't fit H92 in L200 without blowin' out the back, I don't believe.

As Mr. Widget says, the designs evolved as technology for quantifying actual response capabilities and characteristics developed. Many owners love the vintage character of the sound of those vintage systems: S7, S8, L200, etc. By contemporary standards, though, there were significant compromises in their designs.

Stay tuned. Mr. Widget and I are working on ways to "sweeten" L200's.

For your immediate choices, I'd be looking at 2231 or 2235 in lieu of LE15H, and moving the crossover frequency up to 800 Hz with 3110's. Buy 3110A's if you can find them, so you have the extra HF boost to play with in the future....

Here's a pair of 136H: http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&rd=1&item=5744573721

A pair of 3110A's just sold for $100: http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=3776152929

Alex Lancaster
01-18-2005, 10:17 AM
:) Widget: JBL recommended the max xover in (al least) cat # PC-1/80.

Zilch: I think You would have to open up the rear of the cabinets to acommodate the H92/2312 horn.

I have 4 mint L200 Studio Masters in my brotherīs drunk-o-drome, and running external tweeters, I don't want to mess around with their originality.