The 12" JBLs are at the intersection of vintage HiFi and crystal clear guitar tones of the '60s and beyond. I've seen quite a few of the same questions pop up about JBL speakers as used in Fender amplifiers and with Jerry Garcia rigs so I decided to create an entry to aggregate the information as I understand it, in one place. I'll update this entry often as I stumble upon new information.
JBL D131/D120 High-Level Specs
Originally with a 131-404 (D131), 21032 (D120) part number untreated paper surround cone
25 to 50 watts approximate continuous power handling depending on the frequency
102 dB sensitivity
4" voice coil with a .053" gap
AlNiCo magnet
13.5 lbs
JBL D120F (Including Orange Frame) High-Level Specs
Originally with a 21032 part number untreated paper surround cone later was replaced with a treated cloth surround which is a different tone compared to paper surround (more bass, less perceived mids, still sparkly top end)
35 to 100 watts approximate continuous power handling depending on the frequency
101 dB (paper surround) 103 dB (cloth surround) sensitivity
4" voice coil with a .057" gap. Reduces efficiency slightly over D131/Early D120s.
AlNiCo magnet
13.5 lbs
JBL K120 High-Level Specs
Treated cloth surround which is a different tone compared to paper surround (more bass, less perceived mids, still sparkly top end)
150 watts approximate continuous power handling depending on the frequency
103 dB sensitivity
4" voice coil
AlNiCo magnet
12 lbs
JBL E120 High-Level Specs
Treated cloth surround which is a different tone compared to paper surround (more bass, less perceived mids, still sparkly top end)
300 watts approximate continuous power handling depending on the frequency
103 dB sensitivity
4" voice coil
Ceramic magnet
22 lbs
JBL Alternatives
There is a hand full of new speakers available that achieve similar JBL tones. Some of the specifications are different as no faithful reproductions exist as far as I have found. Beyma Liberty 8 is very close in specifications to an E120, but may not be suited for everyone.
JBL D120 Paper Surround
Weber California Alnico - https://www.tedweber.com/cali12a - 2" voice coil, aluminum dome is available, cone seems similar to an original paper D120.
JBL E120
Weber Michigan Cermaic - https://www.tedweber.com/mich12f - 2.5" voice coil, 100watts, 10.6lbs, aluminum dome is available, cone is cloth surround but not exactly double rolled like a JBL. Favored for JBL K120 & E120 similar tone with less weight.
Beyma Liberty 8 - https://usspeaker.com/beyma%20liberty-1.htm - Closest specifications to a JBL E120 available as a new production. 22lbs, 103dB sensitivity, 300 watts, cloth surround, 4" voice coil ceramic.
According a poll hosted on the Grateful Dead Musician's Facebook group, Weber Michigan and Beyma Liberty are both favored. Other models were mentioned but are currently not available as a new purchase.
JBL 2130 is functionally the same as a JBL K120
You can sometimes find 2130's for less money on eBay and Reverb. No difference in components other than a fancy cover on the back.
AlNiCo D131/D120/K120s Should Be Recharged!
AlNiCo will lose its strength over time called "degaussing" at a rate of 50% over 100 years. I recommend having your speakers recharged before the demand for this work is dropped entirely (or businesses close shop).
My thoughts on JBL Ownership and Alternatives Experience
I own a pair of JBL D131's that have been recharged and reconed by Speaker Repair Pros. This is the speakers I use in my Steel String Singer #004 clone since the original Dumble cabinet had JBL D131's with a E120 cloth surround. The tone works really well with that amp and I understand now why folks love the old JBLs. The AlNiCo has a natural compression to the tone and high sensitivity so it's addicting to play and feel the thump in your chest while you play. Before having the speakers reconed, oned of the D131s had the original paper cone and I had a chance to play it. My take is that it definitely is a different tone compared to the other D131 that had the E120 kit already installed. It lacked the bottom end that was on the E120 kit but that might be desirable for some for the true-vintage tone. I do know I can tell a difference when the speakers came back as far as magnet strength. The touch response was much stronger and I'd imagine it's pretty much a brand new speaker.
For alternatives, I own a Weber California AlNiCo and a Weber Michigan Ceramic. Both with aluminum domes and I swapped both in my Fender Deluxe Reverb. Comparing both reminded me a lot of my memories of the JBL D131 experience. The California has controlled bottom end but not as extended bottom end as the Michigan. I continue to go back and forth without a clear winner in my mind. I am curious to try a Beyma Liberty but I don't have a need for another speaker. In the coming months, I'll do a comparison between a California and a Michigan.
A JBL Story By Harvy Gerst, Retired JBL Engineer
Post on Grateful Dead Musician's Facebook Group provided by Edwin Hurwitz quoting Harvy Gerst
9/20/97 alt.guitar.amps
…let me take you back to the late 50s, early 60s. JBL was a small company with their main offices above a candy store, and the manufacturing scattered in a number of buildings up and down the street, near Glendale, on Fletcher Drive.
They made the following speakers; the D130 a full range 15", the D131 a full range 12", the 130A a 15" woofer, the 130B (same as the 130A, but 16 ohms), and the 150 - a 15" woofer with a heavier cone.
The D stood for a metal dome and the A and B were for woofers of different impedances. I don't remember if we made a 131A. We also made a D123 (full range pancake 12" speaker) and the D208 and D216 (both 8" speakers but with 8 and 16 ohm voice coils).
Fender was buying D130s for use in their Dual Showman systems, but they were experiencing problems in surrounds drying out from outdoor use, and burnouts from improper mounting techniques. I wrote a memo to the president of JBL, outlining a plan to let me design a series of speakers made specifically for musical use and he agreed. My plan called for modifications to the D130 and D131, plus an all new bass 15" speaker, and a new 10" speaker.
Since Fender was our largest purchaser, I did not want the headache of trying to reintroduce a whole new series so I kept the D130 name for the 15" and simply added an F (yes, the "F" is for Fender - don't know why to this day I did that, but I did). Since I was making up new model numbers, I decided where possible to keep it simple, so the 12" (originally the D131) became the D120F, and the new 10" became the D110F.
That left the new bass speaker. I didn't want to leave it in the 13x range because it was different and the 150 was already being used by our theater woofer. The 140 was not being used, so I named the new bass speaker the D140F.
After I left JBL, I understand they came out with the black crinkle finish and renamed them E series. The first major modifications were made in the K series, as I understand it.”
-Harvey Gerst
An additional interview with Harvey Gerst about the difference in models.
"Okay, lemme clear this up once and for all:
The only reason I raised the power rating on the "F" series is because the program source material had limited range. Typically, electric guitars go down to around 80Hz, but most of the energy is an octave above that, around 160Hz. The "why" has to do with string length, tension, and diameter - let's just say there's not as much fundamental there as most people think.
So, I knew that guitars were mainly putting out from about 160Hz to around 3kHz, with some harmonics probably going out to around 6kHz. Not exactly the hardest range to handle for a big ass 12" or 15" JBL speaker.
When it was time to really rate them, I brought them into the lab, hooked them up to our "monster Mac" - our tube 200+ watts McIntosh, and started to play guitar, while we watched where they started to crap out.
Everybody felt comfortable that increasing the published power ratings was a reasonable step. We weren't playing pipe organs or symphonies thru these things; they could handle more power simply because the instrument's range was severely limited.
Hopefully, that should clear up some misconceptions."
-Harvey Gerst
