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

[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! )
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/.../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 cabs

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.

[MyLittleViking]

[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, Ron

Thanks!

[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/.../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
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: