JBL 4312 cabinets

[dpuopolo]

I was just given a pair of JBL 4312 cabinets and grills in mint condition. They are 100% complete except for the drivers. I would like to find some drivers to fill the holes. I have a new pair of KLH 12 inch woofers that would seem to fill that bill. The mids originally were 5 inch cones and the tweeters were 1.5 inch cones (later upgraded to titanium domes in the 'A' model). Crossover frequencies are 1.5 and 6 kHz. Efficencies of both drivers are around 90 db.

The cutout holes are both 5 inch. The midrange cutouts have 5 inch deep baffles, so an open back mid would work (or a closed back one as well). The tweeters also have 5 inch cutouts.

It would seem to me that these speakers could be made to sound much better then the originals for fairly short money (someone here once accurately called me a frugalphile).

I also have an amp to drive these: a Hafler DH-200 that I picked up for 25 dollars on Craigslist and repaired. I also bought an Adcom GTP500 on ebay for 50 dollars shipped and repaired it (okay, the service manual cost me another 10 bucks). It had bad opamps in it and I replaced them with National LM 4562s (that I got free as samples).

I'm looking to make these a fun project I can do with my 17 year old son. I'm looking for suggestions for reasonably priced new drivers and/or used drivers that someone no longer needs or wants.

Again, I want to do this CHEAP! I want it to be a lesson to my son that sometimes DIY can produce better sound for less money than commercial.

Anyone out there want to help?

[ZilchLab]

Originally posted by dpuopolo
Again, I want to do this CHEAP! I want it to be a lesson to my son that sometimes DIY can produce better sound for less money than commercial.

Unless you have the tools and know-how to do a comprehensive redesign, you're whistlin' "Dixie" here. It's certainly not going to happen using random drivers.

A 17 Y/O is gonna like them better stock "West Coast," anyway, and they'll be worth something when they're done.

http://manuals.harman.com/JBL/HOM/Te.../4312%20ts.pdf

http://manuals.harman.com/JBL/HOM/Te...4312A%20ts.pdf

http://manuals.harman.com/JBL/HOM/Te...4312C%20ts.pdf

http://manuals.harman.com/JBL/HOM/Te...12DBK%20ts.pdf

http://manuals.harman.com/JBL/HOM/Te...312SX%20ts.pdf

I'd use the "A" driver set....

[Richard Ellis]

Unfortunately I must agree with 'Zlab' as the likelyhood of matching or exceeding the 'factory' performance of the 4300 series JBLs is highly unlikely.
Consider the crossover to start....it is designed literally to EXACTLY match the factory drivers...then think enclosure volumes...this is fixed, the port tube is precisely matched"fixed"...and again think of the cutouts that are there.
Granted you can pitch the crossover and make your own...OK.
Then you will have to fabricate an 'adapter' baffle for your "new" drivers...still doable.
The one truely wildcard is getting a driver to match your fixed internal volume.....you could get close I'm sure, but you will most likely be a little off and it would be a compromise.
Then you would most likely have to cut up the port tube...could get very messy.
The 4300 JBL series were used extensively in studios and for good reason as they sounded VERY good......personally I would put the factory drivers back in them....you would be hard pressed to beat em.
_____________________________________________Rick. .........

[dpuopolo]

Thanks for the tech manuals. I see what you mean-the crossovers are simple. The low end relies upon the natural roll off of the woofer-no crossover at all. The mids have a single pole high pass (likely chosen to compliment the woofer-this also explains the fairly high 1500 Hz roll off).

The mids also use the natural roll off of the midrange driver-no high pass at all. Ditto with the tweeter-it's again a simple single capacitor high pass. No wonder why these speakers image so well!

Anyway, I bought a pair of wooders and mids on ebay from a guy who was parting out a pair. Got a good deal - $117.00 for all 4 including shipping.

Now I have to find a pair of suitable tweeters. These really don't have to be JBLs, as all there is a simple series capacitor for the crossover. I'm actually thinking of trying a pair of these:

http://www.partsexpress.com/pe/showd...number=264-840

These have a really smooth response graph and the sensitivity is correct

I've always found the high end on JBL's a bit ragged, likely due to the cone or titanium tweeters they use. I think using a better tweeter will smooth that ragged high end out.

Again, if anyone has something better to suggest, I'm all ears (pun intended).

[sreten]

Hi,

It is true they use crude crossovers, with no lowpass on the
bass unit or the midrange and possibly iffy 1st order highpass
on the treble, but at least you have some L-pads.

FWIW the crossover does not "exactly" match the drivers,
it is very JBL generic and the same as the e.g. L100,
See here for what you can expect with original drivers :
http://www.troelsgravesen.dk/JBL_L100.htm

Both bass and mid must have smooth rolloffs for a chance of
it working with such a simple crossover, but not very likely.

/sreten.

[sreten]

http://www.madisound.com/catalog/pro...oducts_id=1496

Would this fit your tweeter hole ?

/sreten.

[dpuopolo]

I bought drivers for the speakers and they work great!
I got the stock woofers and mids and this tweeter:

http://www.partsexpress.com/pe/showd...number=297-416

The tweeters have none of the 'honky' sound of the cone tweeters nor the harshness of the titanium ones.

The imaging on these babys are superb.

[dermanu]

just to see what we are talking about!