JBL 4315's

The 4315 is kind of unique, in a way, as it was a 'special project' that Greg Timbers oversaw in the 70s.

Ad is still up. Showing eleven days so far. Somebody call Bill and help him get these to a good home.
 
I'm actually really surprised these haven't sold yet. If they were close to me, I'd pick them up in a heartbeat.
 
What I found intriguing with the 4315 was that they had great room "presence" at fairly low output levels, driven by a modest amp. In the apartment I had at the time, that was a great combination as I could enjoy listening to them w/o having to crank the system up to the point that my neighbors started banging on the walls or ceiling (my ceiling). I was using a Tandberg TR 2075 MkII for power, and that 75-80 WPC was more than adequate with these speakers to get them to any output level I wanted. I suspect that is true of most of this series of pro monitors, but that model was the one I got to experience firsthand.

Just as well this pair is thousands of miles away. There's no way I could bring home another big pair of speakers w/o at least seriously looking at selling something else - both to help pay for the 4315's and also to make space for them - and I'm consciously trying to avoid making decisions like that about my L150A's or ADS L1230 & L1290/2 at this point.

John
 
I ended up picking them up. Definately keepers I think. They did/do have some minor issues.... one cabinet had water damage one one corner. I flowed some penetrating epoxy in and then glue and pulled it together with a clamp. I went over the cabinets a little with a sander and applied oil and howards. The mids and woofers were refoamed but on the woofers the foam was glued over the cone edge instead of under. Not sure if I can correct that without ruining the cone. seem to sound great anyway though. Also the grills smalled of cat pee and the badges were missing. I sprayed some product on them before bringing them into the house... wife doesn't seem to smell it lol
 
I ended up picking them up. Definately keepers I think. They did/do have some minor issues.... one cabinet had water damage one one corner. I flowed some penetrating epoxy in and then glue and pulled it together with a clamp. I went over the cabinets a little with a sander and applied oil and howards. The mids and woofers were refoamed but on the woofers the foam was glued over the cone edge instead of under. Not sure if I can correct that without ruining the cone. seem to sound great anyway though. Also the grills smalled of cat pee and the badges were missing. I sprayed some product on them before bringing them into the house... wife doesn't seem to smell it lol

Nice! Post some pics if you have them. Sounds like the veneers were good. Recommend using some Feed 'n Wax over the Howards and apply monthly.

Who did the woofer refoam? A lot of times a generic 12 inch foam is used, especially if glued on top of the cone instead of behind (No understanding of OEM JBL woofer specs). In my limited experience, the foams are too thick and stiffer, and the roll is too wide compared to the correct foam. IMHO, if the foam surrounds can be removed without too much trouble, I'd have them redone with correct foams sourced from Rick Cobb and fitted correctly to the back of the cone. For sure, for less than $30, get the correct foams and compare them to the ones on there. If I'm correct, the incorrect foams will alter the T/S parameters, making the driver stiffer and less compliant, accentuating the midrange and decreasing mid-bass and bass output. The bass cutoff frequency will also be pushed higher in that cabinet and tuning.

Are your woofer and mid drivers the alnico (no letter or A models), or the later ferrite versions (H models) on the driver labels?
 
Here are some pics. My listening room is quite small but they don't seem to overpower the room. I am powering them with a pair of Heathkit W-5m tube monoblocks that I got at the same time. I actually have yet to use my solid state amp with them.

The seller told me they were professionally refoamed but seems to me a pro wouldn't have done the woofers like that. I wonder if the seller did them himself. I might eventually try to correct them but for now just enjoying them.
 

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You are correct. Way too wide of a glue line and I don't think the woofer foam was front-mounted on the original, although in fact "pro" JBL service places will also do that in some cases if you don't specify that they mount from the rear. Works fine but doesn't look correct.

How's the sound so far? Do you find you get pretty respectable output from the combination?


John
 
Well so far the sound is great. My prior speakers were JBL 4411s which I traded plus some $$ to another AK member for the Heathkits. These monitors sound more accurate than the smaller ones. There are quite bright though and I have the super tweeter and tweeter tunred back to -3. For most casual listening the tube amps do fine, but if I really wanted to make it loud I have a feeling I would need the 150 watts of my Onkyo Integra M-506RS. I haven't tried it yet.... just been enjoying the tube amps.
 
I ended up picking them up. Definately keepers I think. They did/do have some minor issues.... one cabinet had water damage one one corner. I flowed some penetrating epoxy in and then glue and pulled it together with a clamp. I went over the cabinets a little with a sander and applied oil and howards. The mids and woofers were refoamed but on the woofers the foam was glued over the cone edge instead of under. Not sure if I can correct that without ruining the cone. seem to sound great anyway though. Also the grills smalled of cat pee and the badges were missing. I sprayed some product on them before bringing them into the house... wife doesn't seem to smell it lol


Issues smissues! 4315s are serious speakers! Keep restoring that prize!
 
Thanks for the pics. Can you identify by pulling the woofer and mid if they are alnico or ferrite? Can you see any letters after the serial numbers?

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I would be concerned about the way the 2108 midbasses were done. That black stuff around the last 3 rings of the cone is definitely not OEM. At best, its damping material like used on the corrugated cloth surround of the JBL 123A woofer (from the L100), at worst, its the same black glue used on the center cap glue line. That would stiffen the cone in a ring shape and likely introduce some odd resonance patterns. The only reason to use this would be to repair tears in the cone or loss of material if the previous surround job had been on the front and tore off bits of cone while being removed. Or it could have been there to cover up sloppy glue job where glue got onto the front of the cone.

Certainly, a better repair could have been made and a light misting spray of matching grey-ish paint could give it a better cosmetic appearance, and not add mass to the cone, especially a mid-bass. Center cap glue line is about 2-3 x wider than needed. Pics above show properly resurrounded and OEM appearance.

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The woofer cone looks ok, but yes, the surround looks too wide, and being glued to the front, looks like its glued over the 6th outer rib, because only 5 ribs are visible instead of the OEM 6 as in the other pictures. If the inner rim of the surround appears to be higher or pointing slightly up instead of down into the edge angle of the cone, then it likely is glued over the last rib - a consequence of the too wide roll and using the wrong surround.

You probably should take a good look at the crossover wiring and all the wiring of the speaker. The mid/high balance seeming too bright suggests the woofer and/or mid may be miswired out of phase with each channel or to each other, lowering the apparent volume of the bass and mid bass and upsetting the balance this unit is known for.

You may also want to check the crossover itself for any changes, substitutions, or damage, as well as cleaning the L-Pad controls with DeOxit and exercising them a bunch. They are not easy to get to and require careful removal of the front baffle label - search AK for step to remove the JBL Foilcal, but don't do it if you don't have the requisite tools - heat gun and broad scraper or putty knife.

It is also possible the crossover needs some restoration work too. here's the crossover schematics:
http://www.jblproservice.com/pdf/Network Schematics/3114 Network.pdf

http://www.jblproservice.com/pdf/Network Schematics/3114A Network.pdf
 
Wow, thanks for the comparison with correct ones. Your analysis is spot on. Makes me wonder how much these mistakes effect the sound.

I have done a fair amount of re-foam jobs but I have never undone an incorrect one. Its proabably hard to say how to loosen the glue that was used but what do you guys think I should try? Acetone? Alcohol?

Or should I leave well enough alone for now and just enjoy them?
 
For the woofer, I think you should be able to remove the current surround without having to resort to solvents. The companies I worked with (OCS, Upland) feel that solvents may weaken the cone fibers at the edge of the cone. You probably have experienced the fact that most adhesives are either hard and will come off in a chunk (epoxy), or sheer easily so come off in a layer (PVA, some cyanoacrylics), or are flexible and sometimes need to be scraped off (contact or rubber cements).

So removing the old surround may not be as difficult because its right there on top, once you separate the glue line, you may be lucky enough to get a separation with a bit of old glue left. Or you may lose, hopefully at worst, a minimal top layer of the paper cone. For many, the issue is more of not losing a chunk of cone edge, and the possible discoloration leading to a cosmetically visible evidence of the repair. As mentioned, you could mitigate that with a slight spray of a matching color spray paint before or after the new surround is placed on the back of the cone. Of course, you will need to prep the back of the cone as would have been done if the first resurround had been done to OEM standards.
 
If I had a chance and the cash I'd jump on a pair of those in a heartbeat, especially in good condition. I've heard a pair of those before and they sound really great. :thmbsp:
 
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Wow, thanks for the comparison with correct ones. Your analysis is spot on. Makes me wonder how much these mistakes effect the sound.

I have done a fair amount of re-foam jobs but I have never undone an incorrect one. Its proabably hard to say how to loosen the glue that was used but what do you guys think I should try? Acetone? Alcohol?

Or should I leave well enough alone for now and just enjoy them?

MS, any update on how you and the 4315's are getting along? Did you ever do anything regarding the surrounds on the woofers and mids?
 
Hi, I haven't done a single thing with them except enjoy them. Been busy with records and other gear. These are definately keepers though and eventually when I get some time I might reform them correctly. I recently had a Sansui 1000A tube receiver restored and now I am finally getting some good bass out of the 4315s. Going from 25 wartts to 35 tube watts made a big difference. I Actually see the woofers moving now!
 
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