L100...Severe make over: history, pics and test results.

[Akira]

These original Century L100’s were purchased in 1974, at a cost of $650. (CND) when I was but a mere teen. What I did not know that day as I joyfully unpacked my prize, was that these very speakers would literally change my life...spawning a 28 year odyssey of sound ending in 2002 with the sale of my last system. The console from my studio now wrapped in plastic, only an engineer's personal microphone collection remains. The digital basement has slain the once mighty analog facility. Who would have thought the meteor would land? It seems I must surrender to an undeniable fact. I am a dinosaur of sorts.......
Systems have come and gone. First the horns, then the compression systems, then the designer names, the technical ryders always demanding more. But through it all, JBL has always been there. The workhorse of the industry, not always seen, sometimes hidden underneath the glory of another grille's name. An old friend, the reliable soldier once flanked by an army of peers, the fierce sonic warrior...through it all, JBL has always been there.
Of my past JBL inventory only a pair of 4411’s and the speaker that started it all, these original Century L100’s remain.

[Akira]

(2) Yorkville cubes, D120 with Atlas sound horns (1969) my first P.A.
(2) Decade 16
(2) L100
(2) 4411
(2) 4430
(4) 4663 3 way (2205/2470/2x2405)
(4) HF clusters (2470/2x2405)*
(2) 2395 slant plates (2482/EV tweets)
(8) dual 18’s (2241)*
(8) dual 12’s with 2” (2xE120/2445)*
(4) dual 15’s (E140’s)*
(4) single 12’s with 1” bi-radial (E120/2420)* pictured below
(11) 4602 stage monitors
(2) 4604 stage monitors (clones)
(2) dual 12/'s with 1" stage monitors (2xE120/2420)*
(1) dual 15”/2” drum fill (2225/2441)*

[Akira]

OK...I know that no matter how much you modify an L100...it is still an L100.
A hippo in a dress is still a hippo, albeit a prettier one.
But, keep in mind the purpose of these mods which are 80% based in sentiment. These speakers are rarely used, but in a limited way are still useful. They will become a mobile system, mainly for outdoor activities. BTW, after accidentally stumbling on this site and seeing the remarkable work many of you have done, I got the inspiration to carry out this project. Almost all parts and peripherals are from left over existing inventory, so to a large extent that dictated what I would do. What I lacked, i just traded with friends.

Modification #1: road case mounting

In the mid 70’s there was no second option for a portable studio monitor. As I was in the habit of dragging these babies to live gigs and location recordings they got hacked up, so eventually I mounted them into road cases. I think they look cool but, the wife says they are the ugliest speakers she has ever seen. (not allowed in the house) Well that is not it’s purpose anyway. While I still use them for the odd mobile recording, they are now retired to a life of summer barbecues, outdoor parties and just listening in my backyard. These speakers can go anywhere, are fast to setup as an integrated system and they are not delicate. While I hear no difference in sound, the extra stiffness provided by the road case 1/4" of mahogany can only help their particle board construction.

[Akira]

A sealed female 280 input jack was added for speed, convenience and no polarity mix up. I always hated those little springy things anyway.

[Akira]

This box is a little boomy around 60-80Hz. I thought i would try some extra dampening. When I opened up the box I was surprised to see that only 3 of 6 surfaces were insulated. Adding insulation on the exposed sides yielded very little change, but a slight change nonetheless which I convinced myself (or imagined) was a tiny improvement. So more is better right? I filled the box loosely packed...It sounded horrible! No life in the speaker. My guess is the low end bump was intentional to make up for a shortened bottom end. The tuning (2" unducted pipe) is different from other 4310/11/L100 series. This anomaly falls in the "just have to live with it" category.

[Akira]

As you are aware, shortly after it’s introduction the LE20 was replaced with the LE25 which simply out preformed it. But, how good (bad) is the LE 20. The original 4310 monitor design goal was to mimic the dominant Altec 604, and to this extent the LE20 succeeds marvelously, due in no small part to it's near seamless interface with the LE5 midrange. This tweeter is in fact a very small speaker and sounds like an extension of the mid. The obvious downfall is a smoothly falling off response above 10K...again 604 attribute. I just EQ the top.

As I no longer have use for these drivers they are FREE TO A GOOD HOME.
I would rather see them put to good use than have them collect dust. So any forum member can contact me at: [email protected] I just ask that you full fill the following criteria: 1) have a project on the go or at least planed for the future. I want these drivers used and enjoyed. 2) prepay your shipping so it is not a problem for me. 3) after you receive these drivers and are satisfied they are in good working condition, make a very small contribution to this website. I will not guarantee these free drivers spec out but they sounded fine the last time I used them. They were re-magnetized 6 years ago, one was reconed and they have seen very limited use. As you can see from the pic, the badges have fallen off and the paint on one of them is starting to rust, but they can be cleaned up.

[Akira]

New high end systems all boast specs well above 30K. I have not heard JBL's beryllium super tweeter...maybe it sounds amazing...any opinions? From what I gather the extended response adds to the performance of the entire box??? Not sure what that means... My favorite HF is the slot. It sounds like air and totally opens up the box. There is no sizzle, spit or sparkle that some people mistake for great top end. To me, the 2405 has the best reproduction of hi-hat, ride cymbal and acoustic guitar harmonics and does an excellent job of creating that breathy air on a vocal.
Luckily, the original L100 (early line array) is the only 4310xx version which can accept the 2405 slot. It's wide horizontal dispersion coupled with a narrow vertical dispersion make the slot an ideal candidate for a line array configuration. By tracking the serial numbers of the L100's I was able to find the exact cross over schematic and was pleasantly surprised to learn that this was the only model that did not use the 6db/octave 1st order slope @ 6K. This model uses a 2nd order 12db/octave bessel slope @ 7K5, which puts it in 'slot' territory. However, for this conversion I would have preferred a non additive Linkwitz Riley filter.
Problems:
The 2405 slot is 9db more efficient than the driver it replaced, which means while the L100 can accommodate it, there is no room left on the Lpad for level adjustment.
Even with a 12db slope @ 7K5 the slot can develop a rough metallic sound when driven really hard and the resulting interference can result in the cross over frequency having a beaming effect. I tried increasing the slope of the 2405's and was never quite happy with the result. As it turns out the LE 5-2 mid is the irratating factor not the slot as can be seen in the rising response of the test graph. Zero reference standard on the mid has always been too harsh, even when I was young and could take it.
Time to cheat:
Even though the speaker falls in between +/- 3db, I was not happy with the response graph so I tried a little cheating. I moved the mic around to a position where the graph looked the best and adjusted the crossover to where the picture looked the best: 4.5' away, mic aimed directly between mid and slot. Mid decreased to -9db, slot increased 1.5db to -7.5db. The response graph flattened out and looks pretty good averaging +/- 2db. (above 500Hz) When I played a program the result was immediately noticeable...much smoother and less irritating. By turning down the mid 3db and raising the slot 1.5db, the sound improved considerably. Obviously the LE5-2 is the offensive problem, not just in frequency response, but also in tonal signature. It should be noted that the upper mid region dominated by the LE5 is also one of the easiest regions to tailor where EQ can actually be effective.

[Akira]

One of the first questions I asked when I found this site was, which 10" bass drivers would be appropriate for a high Q response mainly in the 25Hz to 50Hz range. Got some bad scolding but, I wanted dual 10's for many reasons. Mitigating factors aside, IMO they are quicker. (received some flames for that!) I wanted the ability to run stereo or mono sum. They must have a strong presence down to 20Hz. I did not want to hear them so much as feel them. They are compatible with a full range system and I could use existing inventory to power them. BTW, someone built a fabulous single 1500AL which almost changed my mind...beautiful job. While over all it may be superior to my sub, the dual 10's suit my application better.

So my speaker of choice is............OMG car speakers!!! OK, now you can throw flames!#%*&#!! Made in China%*!!%#

These are good speakers in spite of their off shore heritage. They are relatively inexpensive at around $200. USD The construction is excellent but, of course the only thing that matters is their performance. They peak at 26Hz with a combined sensitivity rating of 101db referenced at 2.83V both channels independently driven.
OK, what sucks? Well the only thing that really bothers me outside of sending my money off shore is the damn stupid painting on the cone. A ridiculous peak rating whose only purpose in life is to show off in your car!!%&*# These speakers will be played with covers on.
So the verdict is: Absolutely Perfect.
They are everything I was hoping for-- tight, quick and earth moving. Not a bass driver, lower than that, a true sub driver. The L100's can not keep up with this sub. Again, as can be seen from the RTA test result graph...absolute perfect response!

[Akira]

The beauty of this system lies in it's packaging--self contained, pre wired, quick, mobile and rugged...touring company inspired. I decided that the system should be able to be split up. 3 piece, for a quick 5 minute setup using the L100's with main EQ/power rack. 5 piece, for heavy bass and pounding adding dual sub with Xover/power rack.
Main rack: Klarke Teknic 1/3 octave EQ Bryston 3B 100W/side @ 8 ohms
Sub rack: 24db/octave BSS crossover Bryston 4B 400W/side @ 4 ohms

[Akira]

Tests were conducted out doors to create an anechoic environment. While results were fairly consistent above 600Hz, lower frequencies were a little misleading as we had to wait for the slight wind conditions to calm down--thus the peak values can be seen in the following graphs. A calibrated mic using a DBX digital cross over system's RTA was employed. Due to wind conditions this was a very unscientific testing but, it does give an idea of what is going on. I would have liked an RTA with half scale increments. In all cases the microphone was aimed approximately at the middle of the box between the woofer and mid range. Only on the very last graph was the microphone moved into a position where it looked the best in a picture. (4.5' aimed between mid and slot) All distances are approximate.

[Akira]

notice the double hump in the high end which marks the upper limit of the mid and the lower end of the slot. keep in mind the Xover point is 7K5

[Akira]

(first pic) top curve only set to: -1.5 @ 5K/ -3 @6K3/ -1.5 @8K
(second pic) right side, distance 10' EQ as above, mid -3, high -9

[Akira]

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[Akira]

much better response with mic position changed to between mid and high. mid down/slot up slightly
note that wind turbulence gives a deceptive reading below 600Hz, mic was also mistakenly set to +24db, fast response.

[Akira]

(sorry for the flash) EQ out. 24db/octave BSS crossover with Linkwitz Riley filter set @ 60Hz. PERFECT RESPONSE! note that the 4th bar from the left is the crossover point; thereafter the effect of the electronic slope can be seen.