[Lovecore]

Hello,

I am a new user seeking to use the search function in order to learn how to restore or replace the crossover in my vintage JBL Century L100's which I picked up at Salvation Army for $30!

 I am getting nothing out of my tweeters. I measured resistance through both of them: 4.4-4.6 and 4.0-4.1 ohms, which chatGPT tells me is OK with my multimeter.

I'm assuming the issue is with the crossover or L-PADs. I'm not sure if I should do a like for like replacement, or an upgraded crossover. I know these speakers are known for their character but accuracy might be better for my use case?

I am primarily using these in an Atmos HT setup for movies / shows as my main front L/R channels. Music is secondary but I am mostly interested in Atmos mastered tracks.

I am new to to hobby and almost everything I have is secondary had from thrift stores or marketplace.

[SteveFord]

You'll need a couple of additional posts to use the Search function.
I lusted after those speakers as a kid.

[WGH]

Welcome to AC!

I still have the JBL L100 speakers I bought new in 1972. The crossover is an interesting design, the 12" woofer is run full range without single part in the signal path. A couple of respected speaker designers have measured and designed crossovers to correct the L100's "flaws", the results are a better measuring speaker but no longer have the L100 sound that made them a classic. The L100 will play loud, perfect for home theater and the elevated exciting midrange could increase dialog intelligibility if a phantom center channel setup is used. In a 5.1 home theater, 99% of the dialog comes from the center channel.

A redesigned crossover will require a little more power but that is a moot point, the L100's need at least 125 high current watts per channel to come alive. Notice the sensitivity in the schematic below, 76 dB is extremely low by today's standards. Even with a lot of power the L100's don't go very low. The 12" driver doesn't have a very long excursion, the speaker has terrific 40 Hz output so it gives the impression of great bass but the frequency response drops quickly below 40 Hz. Back in 1972 most vinyl recordings didn't have much content below 40 Hz anyway, especially rock music. A sub will be necessary for a full range home theater where strong 30 Hz - 35 Hz content is common.

Here is my original crossover. My L100's actually started out as the L88 Nova. I bought them new in 1972, on sale for $188 pair. I did major surgery to re-positioning the tweeter, installed a sealed inner box for the midrange driver and the new crossover based on directions I received from the JBL factory. The L88's woofer and tweeter are the same ones used in the L100's in 1972. The 5" midrange is the LE5-2, the same as in the L100 and 4312.




Here is another original JBL L100 crossover. Note the different tweeter that was used in later models:



If you decide on making an upgraded crossover, what design you choose will be based on what tweeter your L100 has. Mine has the original LE20-1 tweeter. I decided to keep my L100 all original.

An AC member changed his crossover and likes how it sounds
The Vintage JBL West Coast Sound becomes the…
https://forums.audioholics.com/forums/threads/the-vintage-jbl-west-coast-sound-becomes-the%e2%80%a6.25014/


One person tried out the Troels Gravesen Crossover, the  Dennis Murphy Crossover and a Like-For-Like Recap keeping the original values and decided he liked the Like-For-Like the best.
JBL L100 Crossover Upgrade
https://audionostalgia.co.uk/jbl-l100-crossover-upgrade/#3_Like-For-Like_Recap_%E2%80%93_cost_approx_55_for_a_pair


Troels Gravesen’s Up-grade pages for JBL 4310/L100 - Except for the tweeter, the 4310 is identical to the L100 Century speakers
http://www.troelsgravesen.dk/JBL-4310.htm
http://www.troelsgravesen.dk/JBL_L100.htm

[FullRangeMan]

Welcome to AC 

[AllanS]

I still have the JBL L100 speakers I bought new in 1972. The crossover is an interesting design…

I guess I shouldn’t be surprised by now, but it never ceases to amaze me how much knowledge is amassed on AC.

Now there’d be an interesting poll; total years of 2ch audio experience on AC.

[veloceleste]

The sensitivity spec is @15 feet or 4.5 meters.  what the sensitivity is at 1 meter?