JBL L100 crossover kit--Murphy or Troels Gravensens
Al Japely
New Member
Well thanks for the info. You are suggesting replacing the midrange and tweeter while leaving the old crossover in place?
R Swerdlow
Active Member
The LE5 mid range driver is the source of most of the trouble, above roughly 1500 Hz, in the L100a. Here's it's unfiltered frequency response from one of my L100s:
It was much easier to smooth out it's response and properly blend it with the woofer & tweeter by adding a few extra crossover parts, instead of replacing it.
What does the 104 H-2 frequency response look like?
Yes, the woofer must be rolled off. The Murphy redesigned crossover uses a 2.5 mH steel laminated-core 15g inductor combined with a 40 µF capacitor that rolls off the woofer at about 950 Hz. That's high for a 12" woofer, but the LE5 mid range's ragged performance prevented a smooth transition any lower.
The JBL LE25 1½" cone tweeter is clearly not a modern 1" dome, but it's performance is not a problem in the L100a, and doesn't need replacing. See it's frequency response below. That break-up resonance at about 15 kHz isn't really audible. The Scan Speak 9130, at $81 each, is hardly inexpensive.
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Al Japely
New Member
The LE5 mid range driver is the source of most of the trouble, above roughly 1500 Hz, in the L100a. Here's it's unfiltered frequency response from one of my L100s:
It was much easier to smooth out it's response and properly blend it with the woofer & tweeter by adding a few extra crossover parts, instead of replacing it.
What does the 104 H-2 frequency response look like?
Yes, the woofer must be rolled off. The Murphy redesigned crossover uses a 2.5 mH steel laminated-core 15g inductor combined with a 40 µF capacitor that rolls off the woofer at about 950 Hz. That's high for a 12" woofer, but the LE5 mid range's ragged performance prevented a smooth transition any lower.
The JBL LE25 1½" cone tweeter is clearly not a modern 1" dome, but it's performance is not a problem in the L100a, and doesn't need replacing. See it's frequency response below. That break-up resonance at about 15 kHz isn't really audible. The Scan Speak 9130, at $81 each, is hardly inexpensive.
I’ll begin working with the Murphy crossoverThe LE5 mid range driver is the source of most of the trouble, above roughly 1500 Hz, in the L100a. Here's it's unfiltered frequency response from one of my L100s:
It was much easier to smooth out it's response and properly blend it with the woofer & tweeter by adding a few extra crossover parts, instead of replacing it.
What does the 104 H-2 frequency response look like?
Yes, the woofer must be rolled off. The Murphy redesigned crossover uses a 2.5 mH steel laminated-core 15g inductor combined with a 40 µF capacitor that rolls off the woofer at about 950 Hz. That's high for a 12" woofer, but the LE5 mid range's ragged performance prevented a smooth transition any lower.
The JBL LE25 1½" cone tweeter is clearly not a modern 1" dome, but it's performance is not a problem in the L100a, and doesn't need replacing. See it's frequency response below. That break-up resonance at about 15 kHz isn't really audible. The Scan Speak 9130, at $81 each, is hardly inexpensive.
using existing drivers first. Since I’ve already replaced walnut frames and tweeter foam and binder posts I’ll try and keep close to 1973 originals. These are very useful forums
thanks to both of you guys.
R Swerdlow
Active Member
It seems the availability of crossover parts changes over time, and people have often wondered what other parts can substitute. If you run into this or any other questions as you work on this, I'll be glad to try and answer them.
Good luck with your project. We always like to see photos.
Al Japely
New Member
Richard
Components placed following your parts list. Question - you used 10 watt Dayton Audio resistors and I purchased the 15 watt Madisosound resistors you suggest on your Dec 12,2017 parts list. Also I went with the Dayton Non-inductive .05 (004-.51) resistor. Why are the resistors different wattage? Photo of my 2 unwired boards here:
R Swerdlow
Active Member
The last time I ordered those parts, on 12 Dec 2017, I ordered everything from Madisound. Shipping costs were lower than if I split the order between Madisound and PE. No other reason. I wouldn't worry over a difference between those 10 or 15 watt resistor failure ratings. I simply ordered what was available at the time. I'm certain you won't hear differences with those different resistors
.To be honest, I usually get those sand-cast resistors from PE because they have the resistance value printed on them. Other resistors have those color-coded stripes. I never remember what stripes mean what resistance value.
Thanks for the photos
.I have a set of 70’s era L100a Century IIs that have been sitting around collecting dust for the last 25 years. I have noticed the Bass and Tweeter on one shows some level of damage. I am angling to repair the Bass and replace the Tweeter.
While I am at it, I have been intrigued by the conversations about upgrading the crossover and particularly the one from Dennis Murphy.
Is anyone able to provide me a parts list I can begin with?
Thanks all, stay safe.
Richard
While I am at it, I have been intrigued by the conversations about upgrading the crossover and particularly the one from Dennis Murphy.
Is anyone able to provide me a parts list I can begin with?
Thanks all, stay safe.
Richard
R Swerdlow
Active Member
I've attached the Parts List and the Make Over info below. Both were last revised in December 2017, so it is possible that those parts may not all be available now. If you have any questions please feel free to ask.
R Swerdlow
Active Member
I've only seen the schematic diagram for the Gravesen crossover, but it never showed the component values. They were available only for those who bought the Jansen kit. Apparently, the kit's crossover details were copyrighted.
I remember learning a few years ago that this kit was no longer available in the USA from Parts Express. Does Jansen still sell it in Europe? I wonder if someone has posted the component values. I looked but found nothing.
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R Swerdlow
Active Member
As far as I understand, the 4311WX speakers came in oiled walnut cabinets, and the earlier 4311Bs came in painted gray cabinets. Other than the cabinet finishes, they were the same. The switch to 4311B involved woofers with ferrite magnets instead of the AlNiCo magnets. Their performances are similar but probably not identical.
Is it safe to use the crossover design with the ferrite magnet woofers? It certainly is safe, but may not be completely ideal. But I'd go ahead and use it just the same. The biggest changes in the crossover occur between the mid-range and tweeter, which are the same in the 4311WX / B as in the original L100A / 4311.
Here is the full write up with crossover parts and prices as of April 2021.
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@R Swerdlow . Thanks for your great work and constant update regarding the design, explanation, and parts sourcing. I’m in the process of building a pair of crossovers for my JBL 4311B speakers. I understand the driver’s layout is different, however I’ll give it a try and see if I can get any improvement. There were only two parts I couldn’t source, first the 2.5mH inductors that were out of stock, but I'll try to get them locally. The other was the 4uF caps, also out of stock, so I will use four 2uF caps in parallel.
I still have one question though. As I’m restoring the 4311s I would like to keep the l-Pads functioning. Is there any way to incorporate those in the design? Perhaps I will not use them at all, but for the sake of having the original function of the speakers, it would be great If I could somehow incorporate the L-Pads.
Thanks again
Nick
I still have one question though. As I’m restoring the 4311s I would like to keep the l-Pads functioning. Is there any way to incorporate those in the design? Perhaps I will not use them at all, but for the sake of having the original function of the speakers, it would be great If I could somehow incorporate the L-Pads.
Thanks again
Nick
R Swerdlow
Active Member
Nick
The new crossover already incorporates the resistance needed to balance the mid-range and tweeter for an overall neutral sound. I wouldn't know which of those resistors to skip if working variable L-pads were used, without a lot of trial & error. In my opinion, the balance achieved in the new crossover sounds good. I never found myself wishing to adjust them.
I also don't recommend variable L-pads because the original ones got badly corroded. If you can clean them well enough, they will still corrode again. Even new replacements easily corrode. In my opinion, they simply aren't worth the trouble. That's a good reason why you don't see them used on modern speakers.
Good luck finding suitable 2.5 mH inductors. I did a quick search and found three possible substitutes.
Two use 18g wire instead of 15g:
https://meniscusaudio.com/product/2-50mh-18sl/
https://www.parts-express.com/Dayton-Audio-IC182-5-2.5mH-18-AWG-I-Core-Inductor-257-556
This more expensive inductor uses 15g wire, but is 2.7 mH instead of 2.5 mH. You can unwind wire until it reads 2.5 mH with an inexpensive handheld LC meter (such as this one from Amazon). Then cut most of the wire off, leaving about 6" unwound wire to allow making a connection:
https://www.parts-express.com/Jantzen-5118-2.7mH-15-AWG-P-Core-Inductor-255-110
Dale Hobbs
New Member
Good morning- new to this forum, as Ive gone down the rabbit hole on upgrading my L100a's Ive had since the early'70's . I use them daily. I was looking to buy a pre-made crossover board, as building them myself looks out of my skill sets. I've attached a pic of a replacement available on e-bay from LoudspeakerChief.com. In comparing to Dennis Murphys project, these look a bit anemic. I value your experts opinion on what route to take. Thanks in advance.
Attachments
R Swerdlow
Active Member
After a quick glance, that pre-made crossover board looks to me like it's the same crossover design as was originally put in the L100a. The parts, including the variable L-pad resistors, are new, but they will suffer from the same flaws in the original design. The woofer and mid-range have no upper limit to their frequency responses. Those drivers have no low-pass filters at all.
The woofer seems to behave alright at higher frequencies, but it still should not be allowed to compete with the mid-range driver. And the lack of a high frequency cut-off for the mid-range contributes to significant problems at it's higher frequencies. It should be cut off at frequencies well below the 6-7 kHz where the worst trouble occurs. (See pages 4-7 in the JBL make over PDF file attached to post #34 above.)
The new crossover uses steeper crossover slopes (4th order) between all three drivers. As a result, it has more parts. It allows each driver to operate in it's band, mostly without significant sound coming from the other drivers. That's how any 3-way speaker crossover should work. The original crossover design of the L100a was simply not up to the job. Replacing it with new parts, while keeping the same design, won't make it sound any better.
The last 2 pages of the JBL make over write up shows a photo and a labeled diagram of the crossover board I built. If coming up with your own layout seems complicated, you can simply copy my layout.
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Dale Hobbs
New Member
Thank you for the quick reply. Agree that replacing the current crossover with the same design does not make sense.
donprice
Wound up workin' at a gas station....
Welcome to AK!
10-15 minutes of practice with a soldering iron is probably all you need to learn how to do a simple crossover. YouTube University offers classes every day.
I think removing the foilcal without damage is a bigger challenge.
It doesn't have to be pretty since it will be inside the cabinet. I would recommend testing them outside the cabinet (run long wires through port tube) until you are sure they are right.
I thought about this same project years ago before I sold off my L100s. I would try the Dennis Murphy version over the TG version.
Last but not least, keep the old crossover intact just in case you go to sell them and someone wants to revert to original (or use as an excuse to beat you up on price). Ditch the old twist-style speaker wire connectors and replace with decent 5-way binding posts if you didn't do it already.
Good luck!