Late 70's Custom JBL Builds - Info gathering mission - All help truly appreciated

[medwardb]

Hi folks,
I purchased a pair of custom JBL builds from an old gentleman (86) recently who built these back in the 70's. The cab dimensions are:
18"in wide, 14-1/4"in deep & 28-3/4"in high.
The driver compliment, [ea.] is:12"in 124H woofers, 2105 mids & 2405 HF rads. At the time of purchase the 124H's needed to be re-surrounded, and this I accomplished with the very kind assistance of Rick C. in Florida and his high quality JBL surround kits.
[Thanks again Rick! Breakin' them in as I write. They're great. I'll be talking to you again soon. Very soon.]
The cabinets are almost as impressive as the driver compliment. 7/8"in think solid marine grade ply w/ walnut vaneer. Nice and heavy.
There is also a 1/2"in lag bolt goning through the rear straight through the front baffle, half-way up from bottom up but slightly "inside" from center (hmm?). Each "plane" "sandwiched" between a pair of nuts & 1.5"in washers inside & out. I imagine for front baffle and overall support. [The horizontal line on the right speaker is a stain drip, not a crack]
Grills are quite solid also with 3 lateral 7.5" x 1."in. slots in each side due to their 2-3/4"in. thickness.
Cabinet construction is s.o.l.i.d. solid. Not sure about which model the design que was taken from though not like any cab design I've seen as I recall.
As for the crossovers they're HUGE. I'd say that the layout takes up most of the inside of one side of the 28"in. high cab!
They provide two controls similar to that which is found on L100's/4311's etc. But I'm not sure if they are "Brillience & Prescence" or just [0-100 or cut-unity-boost] attenuation for mids and tweets.
(I'm exploring the possiblity of opening one of one cabs for a clear pic and possible upgrade of the crosssovers, as the rear panels seem to be connected using "Allen" head type screws at the very least.)
Crossover component quality is high, and build quality is capable though, from what I can see, was done by someone that had obviously built on this level before. The 3 inductors (at least the size of hocky pucks) are hand built and very well done.
So, I've included some pics and am open to all impressions, info and hints.
If and when I get the rear off of one I"ll include pics of the crossovers and attempt an interpretation of a schematic.(..uh,huh..)
I'm very curious about whether there were home designed or taken from existing crossover design.
Thanks to all for reading through this and letting me benefit from your cumulitive knowledge and experience. This is a great site and I truly appreciate everyones participation. Things are kind of rough here in Michigan but when I get the chance I will be making a $ contribution to the site in appreciation. Peace everyone,
M.Edz

[robertbartsch]

Was the seller 86 when he built the boxes or when he sold them to you? ...Anyway, 86 is not old.

The pair look like a great score to me. If that time period is correct, I would have expected the slots to be 077s, but I could be wrong.

It would be interesting if you could post a picture of the crossovers.

What else can the young man who sold them to you tell you about their history?

[hjames]

Generally, access to the big boxes is by removing the clamps and the woofers.

Lay a towel or something like a small rug down on the floor.
Lay the speakers down on their back.
Loosen the clamps and carefully lift the woofers from out of the cavity.
Using masking tape or a sticky tab, LABEL THE WIRES and the back of the woofer so you KNOW which wire connects to which connector.
Remove the woofers and carefully put them aside.

Now you can photograph or examine your crossover or whatever on the inside.

[medwardb]

Was the seller 86 when he built the boxes or when he sold them to you? ...Anyway, 86 is not old.~
...What else can the young man who sold them to you tell you about their history?

Rob,
The gentleman was 86 when he sold them to me. [He'd be over 110 otherwise.]
This was just before he relocated to, I believe, an assisted living community. He was a chemest and built them in the late '70's. As for the high freq rad.
I"m not ab.positive about it being a 2405 or an 077. I didn't take it out though I did take out the woofer and the mid. Since he's moved I no longer have accesss to him. He had a beautiful pair of 3 way Dynaudio cabs he had built around that time also. Sounded great.
They weren't for sale:D So, I can learn no more about them from him.
His name is G. Valentine. A very nice man indeed, he was to me.
I realy wish I could have spent more time with him.
Thanks Rob,
M. Edz

[medwardb]

Generally, access to the big boxes is by removing the clamps and the woofers.~
....Remove the woofers and carefully put them aside.
Now you can photograph or examine your crossover or whatever on the inside.

hjames,
thanks for the reply and instructions. I thought I mentioned in the original post that I had replaced the surrounds, so, I'm good with a good deal of repair. But thanks, I do appreciate it. Honestly I realy didn't think about putting a digi-cam inside the cab and trying to take an individual or composite pic of the crossover w/the aid of a flash.
Hence, not needing to open the back of the cab. There's a good deal of insulation, and the inner enclosure for the mid, but hopefully it should be possible.
Though that would be the only way to do any repairs on it. As I mentioned it's on a rather large board that has to be at least 18"x14" I'd guess. So taking it out of the woofer port is in no way possible. I"m going to attempt to take photos of the crossover now. Wish me luck, and thanks again for your reply.

-M.Edz>

[Russellc]

Looks sort of like a DIY JUBAL, or L-65. Is the piece inside the tweeter slot black or glass?

Russellc

[medwardb]

Looks sort of like a DIY JUBAL, or L-65. Is the piece inside the tweeter slot black or glass?

Russellc

..it's black.

-M.Edz>

[Allanvh5150]

To me it looks like a DIY cab as well. The 2405 came out very early 70's so it could be either. If the phase plug is metal it will be a 2405, if plastic it will be an 077. So people have been known to paint the clear plastic phase plugs black for some strange reason. But either way they would be a good find.:)

Allan.

[medwardb]

To me it looks like a DIY cab as well. The 2405 came out very early 70's so it could be either. If the phase plug is metal it will be a 2405, if plastic it will be an 077. So people have been known to paint the clear plastic phase plugs black for some strange reason. But either way they would be a good find.:)

Allan.
Hi Allan,
thanks for the info about the phase plugs. As far as I can tell without
taking the thing apart the phase plug is black and metal. I tapp'd it lightly
with a piece of plastic and got a metalic sound, so..
When I get around to photographing the crossovers, hopefully soon, I'll attempt popping them out for a look see.
Thanks again Allan,

-M.Edz>

[Doctor_Electron]

Can you put up some pictures of the crossovers, and component values?

[spkrman57]

I was curious why use ports and stuff them???

Ron

[medwardb]

Can you put up some pictures of the crossovers, and component values?

Hello Doc, and thanks for the reply.
I have been planning to try to get photos of the crossovers while still inside
the cabs (..the crossovers, not me) as they are too large to remove without
removing the back of the cab. But I've just been too busy to get to it lately.
I will accomplish this though. Hopefully within the next few days as I myself
am very interested in their makeup.
I'll then try to accompany the pics with component values as well.

Thanks again Doc,

-MEdz> *

[medwardb]

I was curious why use ports and stuff them???

Ron

Hi Spkrman57, thanks for the question? I myself kind of wondered this as I was replacing the woofers that I had re-foamed. I didn't design these and I didn't build them either. (Please refer to first post for thier history)
I've been meaing to unstuff them and see what I get and I think I'll do that today if I get a chance to A-B them in this fashion.
I'm curious as to wether anyone else does this with their ports and for what reasons.
I'll let you know what I hear soon with the A-B testing of the stuffed and unstuffed ports.
Thanks again SpkrMan57,

-MEdz> *

[spkrman57]

You could test it in the current state of the ports stuffed, then test it without.

Regards, Ron

[duaneage]

Stuffing the ports at best could be described as a aperiodic vent. Dynaudio pioneered this approach. Basically it is a restrictive vent for a sealed box system that allows some relief at resonance. Usually they are on the rear of the cabinet. A proper sealed or vented box would probably be a better bet, I am not familiar with the `124 driver enough to comment on tuning or box size but it looks large enough to be vented.

In the end if you like the performance that is what counts. Just watch out for unloaded drivers at low frequencies that can jump the gap at high volume. Almost any tuning works at low power, at higher volumes the box and respective tuning protects the driver and controls excessive cone movement.

[medwardb]

Thanks duaneage for your oh so informative reply.
I do believe that it is, in this respect, an aperodic vent as they were made by a gentleman who also made a pair of Dynaudio speakers back in '79/'80
that were supurb.(..I tried to buy those too but he wouldn't sell 'em! :D)
Well, I did try them with and without the ports "stuffed" as it were.
At low to mid volume an unstuffed port did indeed forward the low end quite a bit. It was almost too much in fact. But I still take into account the fact that they probably only have 8 hours on them since I re-surrounded them and they're probably still a little stiffish. At high'ish volume they seem to disrupt the ballance over all. I'm thinking that it is indeed allowing excessive if not be'laboured cone movement and we don't want that now DO we?! (..shakes head)
So, back in goes the waddage. And I'm good with this. Having met and spoken to the builder of these cabs, a rite young 86 year old chemist named George Valentine, and having seen the beautiful walnut and redwood Dynaudio's that he built also I am quite sure that he knew what he was doing. I realy wish that I could have chatted with him quite a bit more, in fact. Quite a nice man.

Thanks again "duaneage" for a most informative reply.
I do appreciate it.

MEdz



Stuffing the ports at best could be described as a aperiodic vent. Dynaudio pioneered this approach. Basically it is a restrictive vent for a sealed box system that allows some relief at resonance. Usually they are on the rear of the cabinet. A proper sealed or vented box would probably be a better bet, I am not familiar with the `124 driver enough to comment on tuning or box size but it looks large enough to be vented.

In the end if you like the performance that is what counts. Just watch out for unloaded drivers at low frequencies that can jump the gap at high volume. Almost any tuning works at low power, at higher volumes the box and respective tuning protects the driver and controls excessive cone movement.

[MyLittleViking]

Looks VERY similiar to the component series, dimensions are close to the EN3 cabs... betcha he mimicked those plans... at least the interior volume.. And its similiar to the S21 system...

http://www.lansingheritage.org/html/jbl/catalogs/1979-comp.htm

I'd sure love to see if those are homemade LX-30 networks...


No need to stuff the ports with insulation, about the only speaker that sounded good that way was the Dynaco A-25

[4313B]

I was curious why use ports and stuff them???Well, the 124/2203 was kind of tricky, rediculously overdamped.
dimensions are close to the EN5 cabsIf those are EN5 volumes then they are way too big, the EN3's were even a bit of a stretch. I suspect he was merely trying to achieve some kind of low frequency balance which really isn't going to happen with that driver in that size volume without lots of boundary reinforcement or EQ (think 4315 soffit mounted and EQ'd in a studio).

The original target tuning frequency for the 124/2203 and 136/2231 was ~ 26 Hz and that was just too low for the 124/2203. JBL later changed it to ~ 32 Hz.

One solution for the 124/2203 used as a regular woofer was something around 1.8 cu ft tuned in the high 30's. Very strong and punchy with adequate damping.

Another solution for the 124/2203 used as a subwoofer was something around 2.8 cu ft tuned in the low 30's.

If I remember correctly Wayne Parham also had a nice solution for the 124/2203 many years ago.

[MyLittleViking]

http://audioheritage.org/vbulletin/attachment.php?attachmentid=11059&stc=1&d=1132370921

[spkrman57]

If I remember correctly Wayne Parham also had a nice solution for the 124/2203 many years ago.

I just happened to have Wayne's obsolete Pi alignment figures laying around. He came up with 2.35 cu ft tuned to 38hz with a Q factor of .9(Wayne's Q factor that is).

Just thought I would throw that in if anyone was interested.

Regards, Ron

[4313B]

I just happened to have Wayne's obsolete Pi alignment figures laying around. He came up with 2.35 cu ft tuned to 38hz with a Q factor of .9(Wayne's Q factor that is).

Just thought I would throw that in if anyone was interested.

Regards, RonThanks! :)

[medwardb]

Hey Scott,
I'm goning to try to get into these fella's tonight.
Wish me luck!

-MEdz> *


Looks VERY similiar to the component series, dimensions are close to the EN3 cabs... betcha he mimicked those plans... at least the interior volume.. And its similiar to the S21 system...

http://www.lansingheritage.org/html/jbl/catalogs/1979-comp.htm

I'd sure love to see if those are homemade LX-30 networks...


No need to stuff the ports with insulation, about the only speaker that sounded good that way was the Dynaco A-25

[medwardb]

Hey 4313B, thanks for the input. I just love this forum and it's because of the accumulated wisdom of folks like yourself and the others that have chimed in on this situation of mine. I am truly very appreciative.
Nice info, gives me a little homework to do :D
I hope to have more info later tonight as I'm going to try to get a gander at these crossovers in a minute here...

Thanks again,

-MEd> *


Well, the 124/2203 was kind of tricky, rediculously overdamped. If those are EN5 volumes then they are way too big, the EN3's were even a bit of a stretch. I suspect he was merely trying to achieve some kind of low frequency balance which really isn't going to happen with that driver in that size volume without lots of boundary reinforcement or EQ (think 4315 soffit mounted and EQ'd in a studio).

The original target tuning frequency for the 124/2203 and 136/2231 was ~ 26 Hz and that was just too low for the 124/2203. JBL later changed it to ~ 32 Hz.

One solution for the 124/2203 used as a regular woofer was something around 1.8 cu ft tuned in the high 30's. Very strong and punchy with adequate damping.

Another solution for the 124/2203 used as a subwoofer was something around 2.8 cu ft tuned in the low 30's.

If I remember correctly Wayne Parham also had a nice solution for the 124/2203 many years ago.

[medwardb]

OK, I flipped 'em and clicked 'em. And man are they heavy! (I'd almost forgotten) And here's what we've got...
Pic: 1 ..the inner reaches...(equiped with, shall we say.."adjustable port"!)
(...Note to self....)

[medwardb]

Pic: 2 ..It was a 2405! And detail of inner LE5-? enclosure. Not bad..

[medwardb]

Pic: 3. Here it is et. al. Not bad... 4.Hand wound inductors; decent quality caps all around; good solders, seems like he knew his way around an iron;
Over all not half bad I'd think. Had I wired it myself I would have layed it out a little cleaner (..I'm just like that about this kind of stuff, a real sucker for sweetly hand wired circuits!)

[medwardb]

Here are a couple, kind of top half bottom half close up'ish images.

I'm realy anctious to hear what folks have to say about these guys.
Because it's late I haven't taken down all of the values as yet. That'll have to wait until tomorrow. I very interested to see if these were taken from an existing blueprint or if he calc'd it himself. (He struck me as the kind of guy that could do it. I remember that he had a home made jig for testing components. Very spartin but effective. A seriously cool ol' dude!)

[medwardb]

Well, until I can get values and attempt to make a schematic that'll be it for now. It's going on 1:00 and I've got to do sound at a church here in A2 tomorrow AM. Thanks again to all who have taken the time to give their opinions and wisdom. For a JBL lover like me you all make this forum the best that there is anywhere. Period!

..mata ne..

-MEdz> *

[4313B]

Here's the schematic of the LX30 that JBL suggested for those components:

[medwardb]

Wow, that was quick! Thank you for the, oh so accurate submission of the correct schematic. Should I ever have problems (..knock on wood) with them and decide to do a little clean up / re-wiring in the process of repairs this will be invaluable.
Thanks again,

-MEdz> *


Here's the schematic of the LX30 that JBL suggested for those components:

[MyLittleViking]

Looks like a great home-made job... with great components from that period... leave them alone, of course you could change them... but I am sure they were built for "his" listening preferences as its obvious he knew what he was doing... not worth selling IMO as they are not factory JBL enclosures.. yeah you could part them, but why? You have a unique and interesting speaker that I know will sound like nothing else in the world...

just play them and enjoy them... Like driving a kit Shelby vs. the original..

[MyLittleViking]

I'd pull the foam out of the ports... Can u confirm the model number of the woofers??

[medwardb]

Hey Viking,
Yes the woofers are 124H's. I just re-did the surrounds and they're breaking in very nicely. As I mentioned before, without the port "stuffing" listening is restricted to low to mid volume levels, in my opinion, as at louder volumes the bass becomes quite dominant. And I"m not sure about whether or not the excursion of the cone is being compromised had they been calculated to perform best in the aperodic vent structure model. At high volumes, with the "stuffing" in, the bass is deliciously tight & crisp & hit's you right in the chest!
I never thought I'd be such a fan of the 12"in. 124H but in this config they work quite nicely.

Thanks for the suggestions "Vik", but I never had any intention of selling them. As far as I know I have the only George Valentine JBL's on the planet! And because I believe that he did a bit of research before designing them I think that he's taken a lot of the best qualities of various designs and incorporated them into his own special design. With fabulous results indeed!

-MEdz> *

I'd pull the foam out of the ports... Can u confirm the model number of the woofers??

[4313B]

At high volumes, with the "stuffing" in, the bass is deliciously tight & crisp & hit's you right in the chest!Well, that's what the 124/2203 does best. It's an extremely powerful, grossly overdamped transducer.

[medwardb]

Well, that's what the 124/2203 does best. It's an
extremely powerful, grossly overdamped transducer.

That's good to know. I'm going to check the Max cone excursion in the specs, pull the port wadding and see what I've got at high volume. If while playing some reggae or something I don't get an inordinate amount of movement then
I may play around with a less constricting baffle material. Right now it's just the regular white/poly-synthetic insulation type material that's being used.
If I find a less constricting material I may be able to find a nice sweet spot.

Thanks "4313B"
Take care,

-MEdz> *

[medwardb]

[quote=medwardb;248592]That's good to know. I'm going to check the Max cone excursion in the specs, pull the port wadding and see what I've got at high volume. If while playing some reggae or something I don't get an inordinate amount of movement then
I may play around with a less constricting baffle material. Right now it's just the regular white/poly-synthetic insulation type material that's being used.
If I find a less constricting material I may be able to find a nice sweet spot.

Well, it looks like the 124's will need some sort of repair. I may have to redo- the surrounds and shim them this time as there seems to be a bit of rub on one. It may be the spider as they seemed a bit loosish when I did the surrounds. The tollerance for these is quite small so shimming may be the only way to go. I've done dozens of JBL re-surrounds but these are the only pair I've had trouble with after the job was finished. Hmm?
Anyway, I"m also looking for something that may be a good substitute for the 124's if anyone has a suggestion. I also have a pair of minty 123-A1's that I've been thinking about selling or trading as well.
So, again all suggestions / offers welcome.

Thanks all,

-MEDz> *

[musicaudition]

This is my first note in this web site.
I just purchased a pair of JBL factory built speakers using the same components as yours with original LX-30 crossover networks.
They looks very similar to JBL L-65 Jubal speakers but a little bit taller than Jubal.
It produces excellent bass compared with other 12" woofer speaker.

The all units are built with all Alnico magents, 124 woofers, LE-5, 077 tweeters. All 8 Ohm units.
Someone did woofer reconed a while ago.
It sounds good but I found a little bit mid-range is thin compared with my other speakers.
I am wondering the woofer polarity was reversed or not.
Would anybody kindly suggest what the correct connection is for the set?
According to the LX-30 schematic, woofer red terminal is opposite polarity to the mid and tweeter terminals.

Thank you very much.
Music Lover in Chicago.