JBL L100 Century Speakers Upgrade Kit

Written by Wendy Dunham.


If you own a pair of JBL L100 Century speakers and want to refurbish or upgrade them for improved sound by using a modern crossover, I highly recommend the JBL L100 Century Upgrade Kit from Jantzen Audio in Denmark.

Click this link to Contact Jantzen Audio to inquire or purchase this L100 Crossover Kit.

I chose their Level 2 kit – which is the preferred version – because of the top level audio components it contains, such as Superior Z-caps and air core inductor coils. The crossover was designed specifically for the L100 to replace and improve upon the original JBL two capacitor/L-pad crossover. The problem with that cheap design is that, at certain frequency bands, all 3 speakers (woofer, mid, tweeter) are trying to reproduce the same sounds simultaneously. There is a lot of phase cancellation going on and an amplitude spike at 6.5 kHz. Despite JBL's stellar audio reputation, these speakers never handled vocals properly because their crossover design was too simple. Rather than using filters, JBL allowed the speakers to roll-off naturally, which is why – at certain frequencies – all 3 speakers attempt to play the same sounds. This should not be happening.

These '70's era L100's were boomy with lot's of "tizz", which everyone seemed to like. However, it wasn't until the '90's with the advent of computer-aided audio analysis that 1st and 2nd Order crossover filters were being utilized and designed properly. Jantzen Audio has done this work in great detail through extensive analysis and design. Their crossover breathes new life into these excellent JBL audio drivers. You still get plenty of boom, mid and high end, but now with a properly designed crossover network that corrects those out-of-phase cancellation issues, as well as the rolloff and crossover points that previously allowed all 3 speakers to play the same frequencies. The result is a superb L100 speaker whose former muddiness has been replaced by clarity. This new crossover results in a L100 speaker that JBL should have made!

The crossover board is nearly the width of the cabinet, indicating just how large the coils and caps are!
Jantzen offers proper damping padding to replaces the ineffective fiberglas JBL used inside the cabinet.
Click this link to Contact Jantzen Audio to inquire or purchase this L100 Crossover Kit.

My letter to Jantzen Audio after building and testing the crossover kit:

I was able to give the new Level 2 crossovers a thorough testing with my entire music collection, including my own recorded music (I'm a home studio musician). I also ran a sine wave frequency sweep and also analyzed discrete test tones near the crossover zones. The sweep volume seemed level to my ears.

During my first listening experience, I immediately noticed an improved clarity over the original L100 crossovers. I went through my entire music collection and was delighted to hear more clear vocals than I had ever heard since I bought them in the 70's. Back then, I thought these were the best consumer speakers around. I knew they were modeled after the JBL 4311 studio monitors, which I first heard when I worked part time in a studio. At least my L100's were part of the best audio system I had ever owned. And who could argue with JBL? Everyone wanted them! In the 90's, I had the 12 inch and mids refurbished. I thought they were shot and went to buy new complete speakers, but was surprised at their inferior volume and sound. So I called JBL and asked them for advice. An engineer highly recommended I have my L100 speakers refurbished, citing that in order to be competitive, JBL no longer made speakers like that.

Now almost 40 years since purchasing my L100s, I had to do something about the intermittent L-pads. That's how I discovered your crossover kit. After reading your web article, it was clear that you have done some serious analysis and fine tuning of the new crossover design. So for the very same reasons I bought the L100s and held on to them all these years – namely, the quest for decent sound – decided to take a leap of faith and invest in the Level 2 kit. The quality of the Level 2 components is impressive. The inductor air coils are like magic - it's hard to believe they make them so perfect. The final assembly looks cool and adds some weight! Worth every cent.

The result is a pair of L100's like I have never, ever heard them. The transition to this new sound is as refreshing as my long ago transition from toy stereo to a Hi-Fi component audio system with JBLs. But if I had never heard what this new crossover could do, I would not have ever realized what I was missing all these years! I have read one comment that a new crossover could not be better than JBL's original engineering design, but such remarks seem more an attitude than based on fact. Clearly this new crossover is a serious audiophile upgrade that get's it right. The sound is more transparent and clear. The overall muddiness, especially with vocals, is gone. As a recording musician, I have noticed that JBL muddiness compared to my near-field monitors. My music seemed dull on the JBLs, yet I needed to listen on big speakers in order to fine tune my mixes. It was not until I read your analysis of the original L100 crossovers that I finally understood the simple two cap design was contributing to the muddiness from phase cancellation and some frequencies driving all 3 speakers. Now that mess is gone! I also noticed that, for the first time, my L100's play well with in my 5:1 audio video set up. They aren't firing on all speakers with the same frequencies. They take a tiny tad more power now for the same level, but now they are level and balanced. Plus if you want more bite out of the mids, you explain how to bypass one resistor. It's also nice that you provide a choice of two resistors for the high frequency drivers. I went with the higher drive, probably because I'm older and/or all the damping in my living room.

So, to that naysayer who didn't believe anyone could design a better crossover than in the original JBL L100, you stand corrected! Anyone considering this upgrade who has a discerning ear, understands clarity, or is considered an audiophile, you will not be disappointed. This breathes new life into the L100s.

Wendy Dunham
Hopkins, MN
Click this link to Contact Jantzen Audio to inquire or purchase this L100 Crossover Kit.

Contact me if you have any questions about my experience building this upgrade kit.


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