4312A make-over, new cabinets; question about tuning frequency

[Serum]

When i was a 13 year old, i bought a set of the JBL 4311B monitors, which i grew fond of. I bought them with blown mid-ranges and tweeters. Over the years i've reconed their tweeters and their mid-ranges, and restored their cabinets.

At a certain point (i was 19) i needed money for my study, so i needed to sell them. Some time ago i've bought a set of 4312A's, with damaged cabinets, i'm currently rebuilding them from ground-up using mahogany fineer and blue HPL from abet laminati in this color; (it's the best match i could find in respect to the JBL blue color) one thing i'm going to change though, is their orientation. I liked the decal/L-pads on the bottom better, just like the 4311's
This is the color of HPL as used on the front and rear-panel;
http://www.abetlaminati.com/wp-content/uploads/wpsc/product_images/838SEI_L.jpg

I'll get some pics of the enclosures later.

A few questions though; The 4312A monitors use an L for the reflex-port, as well as glass-wool dampening. Mine use a 70mm rain-drain type of thing, but it seems to be shorter than the once i know from other 4312's and the 4311's. They seem to be cheaper made, for some odd reason. Using particle-board for the front-panel, as well as particle-board for the filter-board. their wadding is polyester wool, instead of the glass-wool.

Since these reflex-ports seem to be shorter than some of the other 4312's i'd like to know what their original tuning-frequency was?
Any help is greatly appreciated!

[Serum]

here are some pics of the make-over;

[Serum]

some more;

Thinking about adding a frame to the front, their dimensions look a bit off without the tiny bezel.

[BMWCCA]

Nice craftsmanship on the baffle veneer. :applaud:

[Mannermusic]

When i was a 13 year old, i bought a set of the JBL 4311B monitors, which i grew fond of. I bought them with blown mid-ranges and tweeters. Over the years i've reconed their tweeters and their mid-ranges, and restored their cabinets.

At a certain point (i was 19) i needed money for my study, so i needed to sell them. Some time ago i've bought a set of 4312A's, with damaged cabinets, i'm currently rebuilding them from ground-up using mahogany fineer and blue HPL from abet laminati in this color; (it's the best match i could find in respect to the JBL blue color) one thing i'm going to change though, is their orientation. I liked the decal/L-pads on the bottom better, just like the 4311's
This is the color of HPL as used on the front and rear-panel;
http://www.abetlaminati.com/wp-content/uploads/wpsc/product_images/838SEI_L.jpg

I'll get some pics of the enclosures later.

A few questions though; The 4312A monitors use an L for the reflex-port, as well as glass-wool dampening. Mine use a 70mm rain-drain type of thing, but it seems to be shorter than the once i know from other 4312's and the 4311's. They seem to be cheaper made, for some odd reason. Using particle-board for the front-panel, as well as particle-board for the filter-board. their wadding is polyester wool, instead of the glass-wool.

Since these reflex-ports seem to be shorter than some of the other 4312's i'd like to know what their original tuning-frequency was?
Any help is greatly appreciated!

A number of members messed with these. I measured a 4312 some years ago and seem to recall it was 40 Hz or so. But, it is pretty much the consensus here that the thing sounds best with the port plugged - closed box. It tightens up the bass a bit and is generally more listenable over the long haul. But, depends on what you are looking for. Most of us find that when we take that "sentimental journey" we discover our ears/taste have changed.

[Serum]

I'll have a look at what they are tuned to now.

They are nearly finished! i like the combination of the veneer and the blue HPL.

[Serum]

And one more!

[ramin_audio]

What a beautiful job on the cabinets! Congrats.
All you need is a new crossover from scratch (with L-pads).

Mine is in the original cabinets (but with simple bracing added the ports sealed). New crossover is made for them by a speaker-designer (Frank Fabian). In their original form, they were the worst speakers I had ever auditioned in my life (very bad bass and fatiguing mids and highs ... terrible!), but now, they are the best speakers ever made in their size. They are almost flawless. I am sure of that. :applaud:

[4313B]

Those look great!


In their original form, they were the worst speakers I had ever auditioned in my lifeWhile I am no fanboy of this particular series of loudspeakers they are definitely not the worst I ever auditioned. :rotfl:

I did have the opportunity to compare them against many other designs of the day and they definitely weren't the worst of the lot.
What is impressive is that they did as well as they did.


The worst implementation ever had to be the dozen of them around the ring of the Griffith Observatory. What an embarrassment! Gates Planetarium had the good sense to use 4345's. :D

[ramin_audio]

While I am no fanboy of this particular series of loudspeakers they are definitely not the worst I ever auditioned. :rotfl:

I did have the opportunity to compare them against many other designs of the day and they definitely weren't the worst of the lot.
What is impressive is that they did as well as they did.I really have to listen to those speakers then. :eek:

[Serum]

All you need is a new crossover from scratch (with L-pads).

Funny you mention this; i've made a few filter-boxes that help me in this department; (i actually used these 4312's to test the filter to see if it was as convenient as i've hoped)

Internally, they turned out rather complex, (all coils are hand-wound with different cutt-offs at the default common points (,27 ,33 ,39mh etc etc.) In combination with the measuring tools i'm using (dlsa-pro, fuzzmeasure and REW, i'm able to easily tweak/listen/measure to the actual filter in stereo (i've made two of these boxes)
long story short; they can do a 3 way passive filter.

tweeter is highpass 6,12 or 18db/oct
mid is bandpass, 6,12 or 18db/oct on both ends
low is lowpass 6,12 or 18db/oct.

The 3 switches on the bottom left are to switch the mid/low or high on and off, handy for measuring..

On the mid and high there is a resistor network to adjust different efficiency of both mid and high

Silver is capacitor, red coils, and blue resistors.

The boxes are roughly 21"x17,5"x8" and weigh about 33lbs each they took me a while to get finished, but they turned out to be more than convenient at several projects for me and a few Friends.