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.

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/vbullet...IY-2405-refurb

Easy to make out of a variety of materials. Here's just one example:


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...ure+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)