3-Way JBL C-38's

[cjwebber]

Hey guys -

I have been listening to my JBL C-38s for the past few weeks, and have been LOVING them.

They have the 001 load (130a, 175, n1200). They have a midrange that is simply gorgeous and easy to listen to.The midrange and aesthetics actually ousted the 4430s from my living room.

I am looking at doing some additions to dial things in for a wider range of music types.

My thoughts are:


Buy a pair of n8000s (or 3106)
Buy a pair of 2405s
Add a subwoofer crossed around 50


A couple of things:


Any general thoughts?
If I install the 2405s in the open port, the cabinet will be sealed, as there are no other vents. Will I need to cut another hole for venting?
If I do buy a n8000/3106 I may just create a whole new back panel so I can cutout two crossover holes and a vent (if necessary). I'd like to keep the back panel original.



I don't have internal photos right now - just one of the the outside. I've attached two other photos (not mine) that show the layout of the baffle and the layout of the back panel

[cjwebber]

here is my current plan of attack (per toddalin's advise over on AK):

"Add a 1 or 1.5 mfd cap in series with the 2405 and an L-pad on the 175 and also put a 20 ohm, 10 watt resistor in parallel across both the horn and tweeter leads to stabilize these loads."

I'm currently working on sourcing some 2405's. Theres some on eBay, I'm gonna hold out a bit for some alnico.

I will be building a new back panel to accommodate the crossover, L-Pad, and vent (because the front baffle vent will be used by the tweeter)

Still looking for advise on venting/porting on the cabinets.

[cjwebber]

Also - Maybe this thread would be better suited in DIY.

If so, Moderators, could you please move it? thank you!

[toddalin]

Hey guys -

I have been listening to my JBL C-38s for the past few weeks, and have been LOVING them.

They have the 001 load (130a, 175, n1200). They have a midrange that is simply gorgeous and easy to listen to.The midrange and aesthetics actually ousted the 4430s from my living room.


The 130A is sweeter in the lower and upper midrange than the 2235 (boy I miss that), but has no real bottom end to it. The LE175 is warmer at the bottom of its range than the LE85, though the potato masher is not as nice as the long horn/lens.

I had 130As in my EV cabinets and and my Yamaha would ALWAYS denote them as "small" when going through its set-up. When I put them in L200 cabinets, the Yamaha usually denoted them as "small." (Room placement/toe would affect this.)

Almost defies logic except that you need to consider the bass relative to the upper frequencies, and not the size of the cone. The Yamaha reports the 2235s in the L200 cabinets as "large."

[Wagner]

That "001" is difficult to beat for pure musicality and euphony!
And so EFFORTLESS

In my opinion (having owned "001"s for many years) the single best thing you can do to enhance and possibly maximize it's performance, in stock form, is to find a pair of C34 or C40 cabinets (and you are ahead of the game with the nice stiletto legs no matter which way you go)
Use them on a pair of C40s (on which they seldom come nowadays) and they will be stunning, or, you could probably trade those cast legs straight across for an empty pair of C34 boxes if you looked around! The C34 will allow you to stick with the foot print you've got going in your photo.

Night and day difference when you load the "001" into one of those two over the simple C38 type boxes (both of my pairs started out life in C51/Apollo encloses)

That, and use them with TUBE amplification

[toddalin]

There is something else that you can try if you just want to brighten up the top end without investing is a pair of tweeters.

Take a 1 or 1.5 mfd non-polarized capacitor and run it from the hot input lead to the hot horn lead, by-passing the crossover. This will give the highest frequencies a direct path to the horn without the attenuation of the crossover circuit resistance and may be all you need to make you happy. :banana:

If it makes the horn too bright, try a low impedience (e.g., 4 ohm, 10 watt) resistor in series with the cap.

[speakerdave]

Sadly, D130's have metal domes; 130a's do not. They are also different voice coils and frames. The actual cone may be the same, adding to the confusion and sometimes leading repair persons to disregard the real distinctions. The surround and the glue job on the domes both look questionable, but your photos do not afford the resolution for a close inspection. The glue job may mean either a retrofit dome or a recone, and if that, the surround looks more D130ish. The voice coils have different depths and different materials, the 130a being copper, adding desireable mass, and slightly underhung.

If you are really going four-way with a real 130a/2220 as the center of the system, a pretty good idea in my opinion, and are ok with crossing to a subwoofer at 80, all you need is about 1.5 cu ft vented ala Drew Daniels's Ancient Audiophile system, so the C38 vented might reach 50 with a 130a, though I doubt it would closed.

[cjwebber]

no time to respond fully to everything that has been said -

but I thought I should insert some actual photos of my system instead of the stock photos in the first post.

[speakerdave]

Aha! That clears up a few things. My photo inspection supplanted thorough reading.

[cjwebber]

That "001" is difficult to beat for pure musicality and euphony!
And so EFFORTLESS

In my opinion (having owned "001"s for many years) the single best thing you can do to enhance and possibly maximize it's performance, in stock form, is to find a pair of C34 or C40 cabinets (and you are ahead of the game with the nice stiletto legs no matter which way you go)
Use them on a pair of C40s (on which they seldom come nowadays) and they will be stunning, or, you could probably trade those cast legs straight across for an empty pair of C34 boxes if you looked around! The C34 will allow you to stick with the foot print you've got going in your photo.

Night and day difference when you load the "001" into one of those two over the simple C38 type boxes (both of my pairs started out life in C51/Apollo encloses)

That, and use them with TUBE amplification

I've been looking for C34 and C35 cabinets. no luck yet - I've always loved the C34 cabinets. Tubes are on the list as well - I just wish I hadn't sold my 2A3 SET a few years ago. It just didn't play well with the 4430s, so away it went!


If you are really going four-way with a real 130a/2220 as the center of the system, a pretty good idea in my opinion, and are ok with crossing to a subwoofer at 80, all you need is about 1.5 cu ft vented ala Drew Daniels's Ancient Audiophile system, so the C38 vented might reach 50 with a 130a, though I doubt it would closed.

I'd be okay crossing at 80, but closer to 50 would be desirable.

Can anyone help determine my possibilities of 130a frequency range in a closed or vented (rear) cabinet roughly 2.5 cubic feet?

[Wagner]

Can anyone help determine my possibilities of 130a frequency range in a closed or vented (rear) cabinet roughly 2.5 cubic feet?
I cannot answer that question except to say that it will not be very good
2.5 cubic feet is too small

I also don't get your "closed or vented" scenario? Unless you are just asking as for both types? The 130A will be a waste in a sealed enclosure

130As belong in a reflex or horn loaded box

Thomas

[cjwebber]

I cannot answer that question except to say that it will not be very good
2.5 cubic feet is too small

I also don't get your "closed or vented" scenario? Unless you are just asking as for both types? The 130A will be a waste in a sealed enclosure

130As belong in a reflex or horn loaded box

Thomas

Thanks for the response Thomas!

I am asking for both types, yes. Really I'm just trying to find out what I should do if I mount a 2405 in the cabinet (which covers up the only vent in the cabinet)

[Wagner]

Thanks for the response Thomas!

I am asking for both types, yes. Really I'm just trying to find out what I should do if I mount a 2405 in the cabinet (which covers up the only vent in the cabinet)
Set them on top of the boxes
Dozens of threads, with photos, here on the technique and one member hustling brackets to make it happen if you are unable or unwilling to make your own

Just one of dozens:
http://www.audioheritage.org/vbulletin/showthread.php?30788-DIY-2405-refurb

Easy to make out of a variety of materials. Here's just one example:
http://www.westernlabo.com/goods_image/A928_I2.jpg

Thomas

[cjwebber]

Thank you guys for all the insight so far!

another question:

Does anyone know what the proper vent size, port size, and/or port tube length for a C-38 cabinet with a 130a?

In this picture (these are not mine), I see there is a port tube, not just a hole:

[Wagner]

Thank you guys for all the insight so far!

another question:

Does anyone know what the proper vent size, port size, and/or port tube length for a C-38 cabinet with a 130a?

In this picture (these are not mine), I see there is a port tube, not just a hole:

Not going to make that big of a difference with a 130A
Just an opening in the front baffle was how they did things in the early days
If you want to play around with port tubes you will need to do a little arithmetic:
Go to the library here and find the specs for the 130A and then measure your cabinet's inside dimensions
You can then calculate the theoretical size you need
Pick your poison:
https://www.google.com/?gws_rd=ssl#q=bass+reflex+enclosure+calculator
Again, not going to make a tremendous difference though; that woofer was designed with a very simple reflex cabinet (not to far removed from an infinite baffle!) or a horn loaded box in mind

It would/can be fun, I did it. I recently posted in another thread that I made my tubes out of 1/4" balsa and played around around with length. Easy to assemble and you make them so that they just slide in nice and tight in case you ever want to remove them for originality's sake
(my C51s had the rectangular cutouts so it was quick and easy to experiment with)
If your holes are already cut and round it will take a little more effort (and buying some tubes to cut up)

[cjwebber]

Alrighty, been doing some reading!

From this page:

http://www.lansingheritage.org/images/jbl/plans/1960s-manual/page11.jpg

it says I should have a 20 Square Inch port with a 5" tunnel.

If I'm doing my math properly, I should use a 5" hole with a 5" duct.

Am I calculating that properly?

[speakerdave]

According to the '60's enclosure manual in the Library, use a 2O sq in port with a 5" duct. The notes "some bass loss."

Edit note: "Great minds . . ."

[cjwebber]

According to the '60's enclosure manual in the Library, use a 2O sq in port with a 5" duct. The notes "some bass loss."

To achieve 20 square inches, I need a 5" circle or 2"x10" rectangle, correct?

[Wagner]

Alrighty, been doing some reading!

From this page:

http://www.lansingheritage.org/images/jbl/plans/1960s-manual/page11.jpg

it says I should have a 20 Square Inch port with a 5" tunnel.

If I'm doing my math properly, I should use a 5" hole with a 5" duct.

Am I calculating that properly?
Going by your chart, NO tunnel (port TUBE) is suggested except for one set of box dimensions (volume) - 2.1 to 3 cubic foot box (which is also too small, ergo the bass response loss note)
What that chart from the 1960s enclosure manual is essentially telling you is that they need to be in a fairly large box with a hole the appropriate size cut in the front baffle...........they are using the volume of the box to load the speaker

Things have changed as far as calculating these things since then (enclosure precision learning curve and driver evolution)

The chart you are looking at is a general guide..............
Read the last two pages from the document I provided the link to below - JBL's recommendations in this ancient literature is intended for the purpose of illuminating the customer as to which of THEIR enclosures is the appropriate one to choose for the drivers being considered, NOT custom or DIY designs (the last two pages gives a cursory overview)

I'm trying to tell you nicely, you are essentially wasting your time
The "best" objective bass response I was able to get out of a 130A "free range and as JBL intended it" (stock, JBL designed enclosures from the period) was with a C40 box

If you are intent on pursuing this you need to use one of the calculators on the page I provided you the link to using the 130A's specs............but first you need to determine the size of your box

http://www.lansingheritage.org/html/jbl/plans/c35-c39.htm

http://www.lansingheritage.org/html/jbl/plans/2001-guide.htm

The 130A is NOT a bass pump friend no matter what you put it in - what it can reproduce is very nice, tight and smooth but that's about it

That being said, you need to plug in the published specs for the driver AND the box's VOLUME in order to determine a THEORETICAL port size - better than that, the MEASURED specs of your woofers (there is software/hardware available today to allow you to do this yourself if you don't have, or know, anyone who could help you with that, but that's taking things to another level of the "hobby") and work from there

Or, simply verify with measurements that your C38s are built to factory dimensions (they MAY be home builds) and just make sure your "port" (hole size) is the correct one they suggest (if you want to continue working off the old literature) and enjoy the system as designed

OR, if you are still convinced a port tube will make them perform better, once you've done the above, use the calculator, fabricate a port as the results indicate and see how you like it...............who knows, you may realize some notable improvement but am skeptical based on my own similar attempts (but hey, that's what this hobby is all about) Experiment away!

I would strongly advise you to do some reading on just exactly what "loading" is and think it through - the material I have provided here is a good place to start

That, or just enjoy them

Thomas

[speakerdave]

He wants to use his C38's.


To achieve 20 square inches, I need a 5" circle or 2"x10" rectangle, correct?

Close enough. But I just meant that to give you a general idea of where you are. Optimum for that woofer was 8-9 cu ft and that probably had an Fb between 40 and 50. I may have mislead you before. Daniels used 1.5 cu ft for 80hz. How is one more cu ft going to get almost another octave? If you want to use the C38, which does have a nice classic look, plan on running your sub up past 50.

The 130a and the C38 were both devised in the mono era. Sitting in a corner the combination might have given an adequate approximation of what was on the LP's.

[cjwebber]

Thanks for your help speakerdave and Wagner.

I definitely realize the 130a would shine in a different cabinet - larger and/or horn loaded.

My intent is to optimize the cabinet so the 130a can play *best* in the cabinet. I realize *best* means limited bass and that I should not expect modern, pounding bass. The low end and low/mid that I am experiencing so far are VERY pleasant, especially blended with with the 175.

My intent is to add a subwoofer to cover the drop off in low frequency.

I will do some more researching in terms of driver specs to determine my needs. Thank you.


Does anyone have any suggestions on which brands of Capacitors and L-Pads to look at (and which ones to avoid).

[Wagner]

Does anyone have any suggestions on which brands of Capacitors and L-Pads to look at (and which ones to avoid).
That's a loaded question; search it and you'll understand, decide on your own, PM me or anyone if you'd like AN OPINION but please don't get another craps flame war thread started.............................there's already about 500,000 of 'em on the web already

What do you want/need L-pads for? The N1200 uses a 3 position switch?

Many folks here like the stuff that Parts Express sells

[toddalin]

What do you want/need L-pads for? The N1200 uses a 3 position switch?

In my experience, you can get a better match between the woofer and horn volumes if you use an L-pad between the crossover and horn and leave the N1200 at hi or mid.

[cjwebber]

In my experience, you can get a better match between the woofer and horn volumes if you use an L-pad between the crossover and horn and leave the N1200 at hi or mid.

This is what I will be attempting.

I've ordered some Jantzens, L-Pads and Dayton Resistors!


thank you all thus far.

[toddalin]

If you decide that you also want to also put an L-pad on the tweeter, by convention JBL used 16 ohm L-pads on the mids and 8 ohm L-pads on the tweeters.

[cjwebber]

If you decide that you also want to also put an L-pad on the tweeter, by convention JBL used 16 ohm L-pads on the mids and 8 ohm L-pads on the tweeters.


okay good to know!