The Workbench

JBL D120F Questions


Bluecap, i cannot thank you enough. Enormously unselfish of you to post such great photos. I will have to repay you somehow with help in the future. Thank you very much. Mine is Orange like this too (D120F) , but way different cone number.


Toxophilite Thank you very much for the suggestion that it is possibly a K120 cone and motor. AFAIK the pre 70s D120s (non F) seemingly had flatwound aluminum coils (this was news to me when I read it) I am not sure if it is the same for the D120F's but mine has normal copper wire wound and no flat aluminum tape coil. I will try and find out if the K120 coils were normal copper wire.

Actually a crazy complex beast these JBL's. No wonder they are so unique. No ordinary speaker. I lived in the Celestion/Fane/Goodmans world which is a nice but completely different speaker universe.

Not easy to peel this D120 onion, but we are getting there.


I did some more digging and found the following:

1) Tracing the cone numbers, 21032 is the correct cone number for a D120F and bluecap seemingly has a completely original specimen.

2) The D120F seemingly was by the request of Fender altered to rather include a cloth surround to replace the less rugged paper surrounds.

3) There seems to be confirmation what Toxophilite claims that therefore the coils used were K120s, which is arguably more rugged for guitar amps.

4) Orange label on gray frame was seemingly introduced around 1969-1970.

5) Not sure if the Orange label on gray frame had paper or cloth surrounds (anyone has one to check)

6) Not sure when the complete orange version of the D120F first appeared. (anyone knows)

7) The pre fender D120s seemingly had a thinner cone with a totally different sound.

I will try to see what the difference is comparing a D120 pre-fender with a D120F Gray and D120F Orange. Very needed comparison as the voice coils definately differ enormously as well as the cones, surrounds and most curious the former that is either aluminum or phenolic based. The motor part is still pretty mysterious and I will try to contact the person Toxophilite suggested to try and get this information.


His name is spelled Harvey Gerst and he is the one who designed many of the JBL drivers we lust after. It is a very good read and dispels a lot of myths. thanks John


I knew Harvey when he was designing amps for Acoustic. Very interesting guy.


Thanks all for pointing me to the Altec group. Did not even know it existed. I will post back a summary here when I completed my questions there to at least complete this thread.

Gee, so he designed acoustic amps, amazing. One of my favorite Bass amps and one of, if not THE solid state bass pioneering amp.

Thanks all for helping.


Gerst, not Gearst! I corresponded with him a few years ago. He was happy to share what he knows. He's still around!


Gerst, not Gearst! I corresponded with him a few years ago. He was happy to share what he knows. He's still around!

– seadevil

I think it's actually spelt Geartsch


I see a pattern.

Seems to me that; Everything that ends with "sch" is gold and everything that starts with "sch" is crap

Cant find any word I like. Link

On the other hand I have Geartsch and Gretsch and like all the words ending in sch. Link

On a serious note, I will report back what I found regarding my questions to Gaertsch.


Schaller makes nice pickups And certainly not everything Gretsch did is 'gold' . They did some really shoddy work at various points.. JBL on the other hand made quality speakers back in the day, and it is evident just looking at them.

P.s It's spelt Geartsch not Gaerstch. Gaerstch is the original Gaelic spelling which was further anglicized when the family moved to North America.


It was meant to be humor.

Schecter makes my favorite Stratocasters other than Charvel.


I registered at the Lansing Group 6 days ago, but I am still not accepted. That group seems to be quite dead. Most posts are from way back with spurious new ones. I did find a lot of new information but will hold off before posting it here and see if i can first verify it on the Lansing group. Till then about that.

In the mean time. Anyone has any experience between the difference in sound between the two versions of D120F ?
One version has a phenolic (Kapton) former and the other has an aluminum former.

This is going to be a very difficult question as it is almost impossible to answer that question unless you reconed the speakers after the comparison or removed the dust caps. I might be able to answer that question in the near future as I will recone blown ones with the two different factory JBL motors but the same factory cone. I think it will be obvious that the aluminum former will much brighter.


The Waldom original cone with surrounds that was in this speaker weighs 18g The replacement I received that is supposed to be a 100% replica and made on the same machines as was used for these JBL D120F weighs 32g.

That is a massive discrepancy. Not that I expect the Waldom is correct. The heavier cone is going to make the speaker darker, but the aluminum former and cap is going to still give cry. So I expect it will be a somewhat scooped sound, with the upper mids scooped out but not the highs and bass. That is usually NOT what I am after. I like mids to be very present.

I still could not get accepted at the Lansing group. My registration was just silently dropped.

Anyone know an alternative way how to get in contact with Geartsch ?


Okay I hope you know I was kidding about the spelling. I'll assume you do. Have you searched his full name?? Harvey Gerst . There a bunch of hits on his name. Here's one which is the studio I remembered being associated with him. Do a little digging.


Okay I hope you know I was kidding about the spelling. I'll assume you do. Have you searched his full name?? Harvey Gerst . There a bunch of hits on his name. Here's one which is the studio I remembered being associated with him. Do a little digging.

– Toxophilite

So it is Gerst then, I was looking for a person by your correction of the name. No wonder I came up short everywhere. The joke became quite practical lol!

I will try again thanks for the correction. .


Sorry. I wasn't in any way actually intending to lead you astray. Good luck with your JBL quest.


Sorry. I wasn't in any way actually intending to lead you astray. Good luck with your JBL quest.

– Toxophilite

No problem, dont feel bad. The fault is mine for not seeing it, I should have been sharper and see it coming. No harm done. You gave me great info. What is life without humor.


At 4:45 to 4:48, I can clearly see what seems like D120's in a 4x12 behind Alan Wilson. As far as I am concerned they basically created the sound that became ZZtop of which this song is an example of a few in the same style. That shuffle was around before them but to my knowledge not the deliberate later zz-type "Tush era" guitar work. But I am sure someone would come up with earlier versions of the exact same sound. ZZ's earliest work 1968 "Salt" as I can remeber, and 1970's recordings had nothing that even resembles the "Tush" era sound while Canned Heat already exactly did that kind of playing in 69.

I never noticed what seem like D120s associated with Canned Heat.. Amazing where the D120's pop up.


And I recently saw that Skynyrd has at least one guitarist during 70s playing JBLs No wonder it was so difficult to get their exact tone. I clearly recognize the JBLs in "Sweet Home" now.

How silly I have been all these years ignoring D120s .


The JBL Binocular view from hell.

That is ... excluding Joni's Jc120s which are presence dome but Japanese and not in the binocular sweep. Pat Metheny seems to have a D120 and what looks like a Fane Pa Crescendo in one of his 2x12's. Check Jaco's 15" JBL. Weird I have been watching this show a lot in the past, but never noticed the extreme use of what seems to be JBL and similar.

JBL Binocular View


Nope; For some reason I am not allowed on the Lansing/JBL group. after trying for more than a week, I got this.

Dear retnev, Unfortunately your registration at Lansing Heritage Forums did not meet our membership requirements. Therefore your registration was deleted. Sorry, Lansing Heritage Forums

so that is that, wont get any info there.


JBL Motor Centering and gluing.

And a video of the finished Recone. D120F Reconed- Video

I was willing to pay a high price for an all original D120F with all original Cone and coil/motor assembly, but after receiving one I had to return it as it was not original and as touted. So I decided to rather get a blown one and recone as close to original as possible, as I have been reconing my speakers as needed since the 80s. It also gave me a great opportunity to find materials as close as possible to the original. Sadly I could not get on to the Lansing Group to nail down the exact specifications, but I think I am close. I bought a couple of cones and some custom made for what I want and one made on the same machines as the JBL's were made on. I opted for the lightest stiffest cone as that would, from experience reconing loads of British speakers, give me the sound I hear from the D120's. The motor is the correct former material and the windings are aluminum tape as needed. The dust cap turned out to be a challenge as I found three different dimensions for dust caps for the D120F and bought examples of each. I chose the one that would fit snugly over the former as it is important to have the high frequencies transferred to the cap. The Dull sounding D120s people report, clearly has the larger, wrong dust cap with no direct connection to the former. I epoxied the cap to the former to make sure I have a hard non-flexible connection.I found the glues supplied for reconing really wanting. I let myself be lead by a supplier to buy their glue kit for a D120F. Well I wont use that again. The epoxy is extremely fast setting and sets before you can place the dust cap (which is necessary to do in one go with the damper and the cone if you want the former and dust cap to have a solid joint which is crucial). Of all the glues supplied I only used the acrylic white glue for surrounds, but next time I will go back to my two part black glue for surrounds I used for decades. The damper and the cone attachments to the frame I went back to my old time-tested nitrile glue. The glue I recieved was too modern and wonky. Similarly the cork was glued with good old nitrile. Never failed me.

Speaker works well and will go into one of my tweeds.

Thanks to all who helped in the two threads regarding the D120. I learned a lot about the history and materials used in the D120's and could in the end do a recone that matches as close as possible. A lot of the comments in the two threads went into this recone


BTW: The reconed D120 sounds enormous and i am glad I did all the reading to find the correct materials. I am quite happy. It has that trademark clack or bash the metal garagedoor in your face when you turn up an old tweed with it. I guess I am trying to describe the enormous attack these D120s seem to have. There is only one Celestion I played that is remotely similar and which is still one of my all-time favorites. The Bass Cone G12's I used to play back in the day, which turned out to be quite an efficient and responsive speaker. Otherwise it is about as opposite from a Celestion Vintage 30 than you can find.

I am really amazed how bluesy this speaker is even though it has a lot of presence and snappy as hell. I tried it with several of my amps. My Tonemaster 214 Accordion amp is what I consider a "prettyshitty" amp, came alive quite a lot when I tried this speaker on it. It made an honest attempt to turn itself into a Tweed Deluxe once it found the D120. The deluxe however took off like a rocket.

I can see what you long-time D120 users are raving about. I totally get it now.


I since also got all original E120 and K120's

The K120 is spectacular also and the D120 and the K120s really transforms my amps.

The E120 is a different beast I haven't figured out what it can contribute.

Beautiful speaker but sound quite different from the others and something I do not know where it fits. Might try it as a Bass speaker and see how it works there. It might just have to be driven harder to be equivalent due to the larger power handling.

The E120 has a ceramic magnet (obvious) as Alnico became prohibitive in price and they try to get exactly the performance of a D120 with the Ceramic replacement. Well that obviously failed. It is a great speaker but no D120. Therefore they used the large ceramic to try and mimic the field of the alnico exactly. Soundwise I would guess it is slightly more towards a brighter Celestion Vintage 30, which is a speaker I just cannot seem to like. Have 4 of them and they underwhelm compared to the older G12's or Creambacks, but that is my taste. It is nothing in the direction of an old celestion alnico blue either. To me, more like an EV Force which is the closest comparison I can make.

Just saw that the power rating on the E120s are much higher compared to the D & K. The E's are therefore great for PA and Bass I would guess, or for +100W 1x12 combos, such as Mesa Boogie Fillmore etc.

  1. "The D (F) series power rating is 200W peak and 100W RMS with an SPL of 100db" (Still debatable info)
  2. I confirmed from Lansing group that the D120 (paper surround) is exactly the D131 paper surround speaker rated at 25W RMS continuous: Peak not stated but probably 40W. Link
  3. "The E series power rating is 300W peak and 150W RMS with an SPL of 103db"
  4. The K series power rating is 200W peak and 100W RMS with an SPL of 101db"

What really is the difference between K and D speakers ? It seems to me as if the K really is maybe a power upgrade of the vintage paper surround D. It arguably shares the power handling of the D120F.

Is the gap the same on both ? K-DataSheet

But I see some people claim 60W RMS for the D's, There are several versions of D's so that is probably why. If so the D120F must be the 100W RMS version and the paper surround non-F the 60W version which creates the confusion on the web. (However I now know from Lansing that this 60W claim is Bogus at least for the paper surround D120) The web wisdom and numbers quoted as in this paragraph above seems to be completely false from data received from Lansing Group so be careful relying on that.

Anyone has JBL-sourced specsheets for the D120F ? Thanks

UPDATE: "I confirmed that Such a Datasheet doesnt exist for the D120 as JBL never issued one."

There are so many crap and dubious claims about these speakers on the web, it is mind boggling. Once you get the datasheets and get info from the designers web wisdom quickly fall apart. No wonder there are so many paper surround blown D120's. People drive these at 60W RMS continuous.!


As a final post in my long Monologue:

I got in contact with someone on the Lansing group a few days ago who owns "Upland Loudspeaker Service". Seemingly the last active person that serviced JBL speakers with the sanction of JBL. If you want to recone as close to a JBL original as possible, his kits might be the closest you can get to the original. Speakerexchange and SimplySpeakers worked really well for me too on the other hand.

So, my conclusions I reached above in my previous post are basically correct: He confirmed my suspicion that a D120F ORANGE cage is exactly a K120 rated at the same as the K120 specs 100Wrms. (Gerst recommended 60WRms, but he obviously rated it for a sine input, not wide band noise "musical" which would be much higher. The discrepancy is resolved that way. This is my own conclusion). Gerst used a bass guitar for this test, and was not really a scientific test. A bass guitar would be closer to a Sine wave rating than Music or noise rating. The Paper surround gray D120 is a D131 and rated much lower at 25Wrms. So be very careful not to use the Gray D120s (paper surround) above 25WRMS

So, everyone is quiet on Gretschpages in this thread but I hope my long quest and monologue did yield some useful information for someone. It sure was not easy to peel this onion. Most info on the web is blatantly false or at best half-truths regarding the D120s and that is why so many are blown.

Thanks all who helped out peeling the onion.

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