L200 - Should I cut some holes in these things?

[hjames]

Do understand I've had 2 pair of cabinets over the years (You can see 3 cabinets in the lowest picture).
The first pair had been oversanded (by a flipper, I think) at one point, along one edge he had sanded clean through the veneer!
But once I had the original 3 ways (quasi-L300 style) config working, and realized they were keepers, I found a 2nd pair of boxes in much nicer condition -
tho I had to haul them back from nearly 2 states away (Aberdeen MD to Northern VA).

Also realize that I had a really good offer for them almost 2 years ago and sold them
(mostly intact - I did sell the walnut wooden lenses and the extra pair of pristine 066 slot tweeters).

Good luck on your project! Have great fun!

[toddalin]

I had no qualms about the mods I did. My components were previously in University cabinets. I paid $50 for the two L200 cabinets with the "window screens" (no grills) and they needed lots of serious work.

On one, the lower front portion was completely broken away and I made a new piece and glued it into place. These were kept outside and none of the veneer was any good and the front trim was quite "dented" in many places. I saved them from being scrap.

[badman]

It's no surprise that the active was way better than with a series resistor. Series resistors on 4 ohm drivers do not equal 8 ohm comparable. The efficiency of 4/8 ohm drivers is the same, the sensitivity is different. Add a resistor to the 4 ohm driver and the driver is now 3dB less sensitive than the 8 ohm driver, so not surprising that would perform suboptimally. I'd probably sell and do a custom system as some others have mentioned.

[nikster22]

It's no surprise that the active was way better than with a series resistor. Series resistors on 4 ohm drivers do not equal 8 ohm comparable. The efficiency of 4/8 ohm drivers is the same, the sensitivity is different. Add a resistor to the 4 ohm driver and the driver is now 3dB less sensitive than the 8 ohm driver, so not surprising that would perform suboptimally. I'd probably sell and do a custom system as some others have mentioned.

It was not sub-optimal. The impedance of that LE15B was affecting the crossover point and the driver is more sensitive than the 136A which the network was designed for. Padding it down reeled in the the output level and put the crossover point where it should be. I did a frequency sweep to confirm that the resistor had the desired effect. The 3dB drop was known and intended for the application.

Having said that, in my opinion, active crossovers with drivers connected directly to amplifiers will always be superior. I believe this explains the prevalence of multi-amp, active crossover studio monitors today. It is now cost-effective to build everything into one box and the performance is hard to beat with a single amp and passive components.

[nikster22]

I had no qualms about the mods I did. My components were previously in University cabinets. I paid $50 for the two L200 cabinets with the "window screens" (no grills) and they needed lots of serious work.

On one, the lower front portion was completely broken away and I made a new piece and glued it into place. These were kept outside and none of the veneer was any good and the front trim was quite "dented" in many places. I saved them from being scrap.

Good to know. 50 bucks is a steal even for beat ones! I'm amazed that press board survived at all being left outside. Any sheet of it I've ever seen subjected to moisture has severely warped or turned to mush.

[nikster22]

Do understand I've had 2 pair of cabinets over the years (You can see 3 cabinets in the lowest picture).
The first pair had been oversanded (by a flipper, I think) at one point, along one edge he had sanded clean through the veneer!
But once I had the original 3 ways (quasi-L300 style) config working, and realized they were keepers, I found a 2nd pair of boxes in much nicer condition -
tho I had to haul them back from nearly 2 states away (Aberdeen MD to Northern VA).

Also realize that I had a really good offer for them almost 2 years ago and sold them
(mostly intact - I did sell the walnut wooden lenses and the extra pair of pristine 066 slot tweeters).

Good luck on your project! Have great fun!

Ah, I see that now. I was looking at the pair in the background.

Thanks!

[badman]

It was not sub-optimal. The impedance of that LE15B was affecting the crossover point and the driver is more sensitive than the 136A which the network was designed for. Padding it down reeled in the the output level and put the crossover point where it should be. I did a frequency sweep to confirm that the resistor had the desired effect. The 3dB drop was known and intended for the application.

The level of design precision of these older systems is not high, so it's perhaps not a biggie, but in a well optimized system, there are a lot of negative impacts to resistive padding. It impacts bass alignment, crossover slope behavior, and other factors, it sounds like you took a pretty simplified analysis approach here- again which is fine, because the JBL systems of yore didn't benefit from modern design elements which have improved dramatically. Resistive padding also can increase distortion (drastically lower damping).

[nikster22]

The level of design precision of these older systems is not high, so it's perhaps not a biggie, but in a well optimized system, there are a lot of negative impacts to resistive padding. It impacts bass alignment, crossover slope behavior, and other factors, it sounds like you took a pretty simplified analysis approach here- again which is fine, because the JBL systems of yore didn't benefit from modern design elements which have improved dramatically. Resistive padding also can increase distortion (drastically lower damping).

Simplistic is an understatement with this system, particularly with the original crossover. It is a fairly crude network and doesn't even utilize an L-pad to attenuate the horn, just a selectable in-line resistor much like what I did on the woofer. I also didn't realize the true impedance of the LE15B before building the L200B crossover, hence the after-the-fact fix using the in-line resistor. The LE15B's don't dig very deep, and I've only driven these with transformer-coupled amps so any hope of a respectable damping factor was out the window before the mods. Prior to the tri-amplification, my plan was to replace the LE15B with 2235's, however the cost of going that route and questionable history on some of the eBay units (not knowing if the mass ring was present, etc.) deterred me from ever doing that and I decided to save the cash for the 077/2405 modification instead.