JBL 4331 Studio Monitor education requested for a non expert

I have been given the pictured JBL Studio Monitors from an uncle downsizing from the family home to a senior's living apartment. 40 years ago as a teen I admired these and he remembered thus gave them to me. He had a Macintosh amp on them (which at the time I had never even heard of the brand! ). They spent their life in the living room, literally as furniture that could play background classical music so they are cosmetically in very nice shape.

My uncle says he purchased the entire system new, and he doesn't know if they were modified by the shop he bought the package from way back when. He had the main driver's surrounds replaced a dozen or so years ago.

I appreciate good sound but am totally non-technical so any advice is appreciated. The front cover and inside front panel say 4331, but from online reading on this site I see they have the 2405?? ultra high frequency driver which points to model 4333? So maybe the stereo shop upgraded them? Also the 2 separate rear connection panels don't match anything I've found online.

Regarding hookup, as seen it has the two hookup areas on the back. Is the upper panel with the additional contacts ONLY to be used if they are bi-amped? I have a 6-7 yr old consumer level Yamaha receiver ( HTR-6295, 130W /ch ) so I cannot bi-amp these. Thus I assume I hook up to the bottom panel with just the 2 inputs. Assuming that's correct, does the adjustment knob on the upper panel still adjust something? Or is that adjustment for level balance only if they are bi-amped?

I have hooked my stereo to the lower 2-contact panel and I must say the sound is not overly impressive compared to some not too expensive mid-range Polk Audios that I've had for 30 years, mostly high end is missing. Could it be that the Yamaha I have simply is not good enough to run speakers like this properly? Is there something I'm missing? How can I get the most out of these speakers with the Yamaha that I have?

Lastly and least important, are these speakers anything special and/or valuable? I know they were a gift but someday I'll sell them in a home downsize as well, are they worth $500? $1,000?

They appear to be 4331's that have been loaded with the slot tweeter and additional crossover making them a 4333. The cabinets came with the extra holes pre cut but blocked
over.

Try rotating the knobs on the crossovers, the contacts may be oxidized.

Do you hear any sound from the horn/lens or the tweeter?

You have a pretty good handle on what you've got:) Back in those days ('71-'73), the enclosure was a generic enclosure used for several speakers. The 4331 had a piece of wood screwed behind the front panel where your 2405 tweeter is now. I don't think the back panel would have been cut for the extra crossover. You would have had just the lower speaker connectors which fed a simple internal crossover to split the sound between the woofer and the compression driver and horn for mids/highs. The adjustment screw on the front panel would adjust the output volume of the compression driver. If you listen now, and turn the screw, it probably sounds scratchy, or the mids/highs go away and come back. if so, you can get a can of de-oxit and clean that potentiometer, but you will have to pull the woofer to get to it.

At some point, the output to the compression driver was re-routed to the 2nd crossover (the one on the back panel), which split the mids from the highs, and sent the highs to the 2405 tweeter. There is a knob on the crossover with 4 positions to adjust the volume of just the tweeter. The screw adjustment on the front panel adjusts the output of both the mids and the highs since the upgrade.

The speakers are really directional, especially the highs, so you might try raising them up to get the tweeter closer to seated ear level to improve the sound. Also, the crossovers in these speakers are very simple, and are the weak point for sound quality. However, if you're not going to keep them, it's not really worth upgrading these, as collectors will want them in their original condition. As they are 50yrs old, it's possible the capacitors have leaked or are failing, I inherited a similar set of speakers from my father, and have been able to make them sound much better than they did previous, though they are still very different than modern speakers. These were designed to be really efficient, since good amplifier power was really expensive in the early 70's. Also, they don't have any low bass - 50hz is probably as low as they go, but if you put in some rock with a good kick drum, they'll sound a lot tighter and with more punch than just about anything you can buy today. Highs are going to be bright, but not as detailed as the better dome tweeters you can buy now. In short, you may feel like they sound like a P.A. speaker, which would not be far off. If you do decide to keep them for a while, and we get COVID under control, let me know and I can stop by and show you how good they can sound. My kid goes to university in Squamish, BC, so when they are there, we come through Vancouver 5 or 6 times per year for visits.

What are they worth? If the veneer is clean, probably $2-2.5kUS. Start looking on Canuckaudiomart.com, USAudiomart.com, Ebay, and Audiogon. Just keep in mind that alot of the market for these are sellers that picked them up for a couple hundred bucks at a yard or estate sale, and then advertise them for $4k or more, and they never sell - the ads are there for a year or more. Hope this helps:)

Quote:

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Originally Posted by Mike Caldwell

Try rotating the knobs on the crossovers, the contacts may be oxidized.

Do you hear any sound from the horn/lens or the tweeter?

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Try using a paper-towel tube over the driver to your ear to isolate and make sure the UHF is working. Most likely a network L-pad dirt issue.

Quote:

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Originally Posted by Charleyb

I have hooked my stereo to the lower 2-contact panel and I must say the sound is not overly impressive compared to some not too expensive mid-range Polk Audios that I've had for 30 years, mostly high end is missing. Could it be that the Yamaha I have simply is not good enough to run speakers like this properly? Is there something I'm missing? How can I get the most out of these speakers with the Yamaha that I have?

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A few things.

First, you need to verify that your speakers are working properly. Make sure all drivers are playing, try changing the settings etc. perhaps get help from a more knowledgeable person to take a deeper dive into them.

Second, your amp isn’t ideal to get the most from your speakers, but if you are happy with the sound through your Polks, then I would swap amps after taking care of everything else.

Third, while outwardly your speakers look like a 4333A which is identical to the popular L300, because of their vintage your speakers likely have LE15A woofers and 2307 horns. A clean pair of LE15A woofers (which is what I assume you have) are desirable and could be sold to buy the 2235H woofers and 2312 horns needed to turn your speakers into the 4333A/L300s. From there you could get or build a pair of Nelson Pass L300 crossovers.

I am pretty confident that if you made the changes I mentioned above, you would be very pleased with the sound of the speakers. But yes, it would take a fair amount of work to make these changes and track down the parts.


Widget

Quote:

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Originally Posted by Mr. Widget

A few things.

First, you need to verify that your speakers are working properly. Make sure all drivers are playing, try changing the settings etc. perhaps get help from a more knowledgeable person to take a deeper dive into them.

Second, your amp isn’t ideal to get the most from your speakers, but if you are happy with the sound through your Polks, then I would swap amps after taking care of everything else.

Third, while outwardly your speakers look like a 4333A which is identical to the popular L300, because of their vintage your speakers likely have LE15A woofers and 2307 horns. A clean pair of LE15A woofers (which is what I assume you have) are desirable and could be sold to buy the 2235H woofers and 2312 horns needed to turn your speakers into the 4333A/L300s. From there you could get or build a pair of Nelson Pass L300 crossovers.

I am pretty confident that if you made the changes I mentioned above, you would be very pleased with the sound of the speakers. But yes, it would take a fair amount of work to make these changes and track down the parts.


Widget

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+1!

Welcome to the forum Charley. You are in the right place , even better we've all been where you are , give it time and we'll get you sorted oot eh.

( see what I did there ? )

Mac

A true 4331 should come with the 2312 horn and 2231A woofer in it

Thanks for the input. Yes both the horn and the tweeter on each speaker work as does both the front and rear panel level adjusters. Its just that even with both knobs on max setting the high frequency sound is just not very 'bold'. I get no crackling when adjusting them so I assume that means the contacts are clean.

Maybe its my ear, they require a significantly higher volume setting than my much smaller Polks to output a similar sound level. I presume that's because these are less efficient? If I run them on the same zone as the Polks, so the same volume setting, you literally can't hear them unless you get a foot or 2 away.

So I got intrigued by the comments and pulled the main driver out to see what I really have. The main driver is a 2231A, the horn is a 2312 and the label is not on the tweeter, I guess I could pull the other one to look but I think there was only the one model of tweeter, 2405. Man its a heavy little sucker, as is the main driver. Then there is a box, crossover? on the back panel, 3105, then another bigger crossover box mounted to the base panel, that's a 3131.

Your JBLs should have a sensitivity of about 93-94dB at 1 watt/meter. I imagine your Polks are like most modern speakers and are under 90dB. That said, your JBLs have an impedance of 8 ohms or 10 or more ohms depending on the woofer, and the Polks may have a 4 ohm impedance which would make them appear louder for a given volume knob setting. All that said, if your JBLs are significantly less loud than the Polks, I think you need to have these speakers looked at.

Regarding the tweeters not sounding bright, years ago I added a pair of 2405 slots, the tweeters you have, using the recommended JBL add on crossover similar to your setup. I could never get them to sound bright either. Ultimately I built new crossovers and the sound opened up significantly.


Widget

I agree with the earlier comments.

These monitors are very similar to those in this link

https://www.hifido.co.jp/sold/02-128...-00.html?LNG=E

They are an iteration of the original 4331 (not the 4331A or 4331B).

As mentioned the slot high frequency radiator was added later.

What to do with them?

They are probably not meeting your expectations of sound quality at this point.

What l suggest is to have a look around for a jbl enthusiast in your location for some diy assistance. The horn compression drive may need attention (clean out the gap and a replacement diaphragm). Then find someone to build the Nelson Pass passive crossover. The networks in them right now are fairly crude and not worthy of the quality of the drivers.