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View Full Version : JBL 4425: oiling the veneer, and bass boom



carolax
06-19-2003, 12:27 PM
I recently obtained a pair of 4425 Studio Monitors from the late 80's. Now that the woofers have been re-foamed, a couple of questions:

The cabinets are in great shape, but appear dried out. Should I use linseed or tung oil on the veneer, or what?

No matter where I put them in a large, vaulted listening room, no matter how high off the floor, there is a strong bass underline. A giant, one-note boom. Is this normal for a 4425? Could the refoaming or age of the speakers cause this?

Otherwise they're great home theatre speakers. Thanks.

Mr. Widget
06-19-2003, 08:51 PM
For the wood finishing portion of your post, my preference is "Watco Danish Oil". You wipe it on, let it set a bit depending on temperature and humidity and then wipe it off. I usually do this a couple of times, followed by a good buffing of the oil residue that is left behind. If the surface is in decent condition, that is all it takes. You should use their "Natural" color unless there are scratches, then you might want to use their "Walnut" color.

As far as boomy woofers goes most JBLs are tuned to be a bit boomy. Are yours in original condition with the original woofers?

I don't know much about the 4425, but typically JBL tunes their systems with a bit of a bass bump. Retuning the port to a slightly lower frequency should help. This is done by lengthening the port... I wouldn't recommend that you do anything permanent, but it can't hurt to temporarily add an inch or two to see if it helps. Ideally this would be done while being fed from a signal generator in a test set up so that you can monitor the impedance rise on both sides of resonance.

Hopefully someone with experience with this monitor can add some helpful information here.

4313B
06-19-2003, 09:19 PM
Yeah, you might want to measure the tuning frequency of those enclosures and make sure they are 34 Hz or lower. What is the port again? 2.5" diameter port x 6" duct? You might want to measure the free air resonance of those 2214H's as well.

herve M
06-22-2003, 03:51 AM
Yes, It's difficult to adjust: loudness effect (medium frequency level is lack)
Solution: enclosure to heighten ( stand: 60 cm )
or upside down ( stand 1 meter!!!!!)


herve M
4425 old user

Tom Loizeaux
06-22-2003, 06:08 PM
I'm not sure there is a big difference in what oils do for wood, but after using a number of other oils, I've become a fan of Tung Oil. It has the ability to be waterproof, stay in the wood longer then most other oils and hardens with age making the wood more resilient.

Tom

Mr. Widget
06-22-2003, 07:17 PM
Tom,

What brand of Tung oil do you use? I believe all of the products labeled as "Tung Oil" have some percentage of Tung oil with a mixture of other ingredients. I haven't used any in several years, but I remember some working much better than others. For the most part they create a bit more luster than the "Watco Danish Oil" which is fine if that is the desired result.

boputnam
06-22-2003, 08:01 PM
Hey, Mr. Widget...

I've used "Jasco" brand Tung oil with great results. The bottle doesn't give details on %, so I assume it's 100%.

It's kinda "goopy" (eek! Giskard is bound to Thesaurus me! ;) ). I use paper towels to apply (wearing rubber gloves) and then rub off excess after a few minutes.

Depending upon the desired gloss, after drying, I rub with 0000 steel wool.

Just thought I'd toss this into the mix...

GordonW
06-22-2003, 11:45 PM
Carolax,

How long have you listened to the speakers since the refoaming? IME, having refoamed LOTS of drivers of all kinds (including several LE15s, my pair of L77s, several L166s. a pair or two of L112s, a couple vintage LE8s, etc), new foam sometimes has to "break in"- ie, it gets more compliant after being played a few hours at a decent SPL level. A foam surround with too much stiffness, can raise the resonance frequency and the Q of the driver, making them boomy.

If you haven't done something similar, I'd try playing something with good bass content, at a good high volume level (don't overdrive anything, of course) and let them percolate like that for an hour or two. Let them sit for a short while afterwards, and them see if they sound any better...

As for cleaning and wood rejuvenation- I've had good luck with Old English lemon oil, applied medium-lightly with a Scotchbrite scrubbing pad. Gets all sorts of airborne debris back out of the woodgrain, and BOY, they just look IRRIDESCENT afterwards. What depth and sheen!

I'd do this, before applying anything like tung oil... if the speakers later start to look dry again after the lemon oil, then I'd escalate to something like tung oil or whatnot...

Regards,
Gordon.

Tom Loizeaux
06-23-2003, 06:45 AM
Mr. Widget, and others,
I use Waterlox "Original" sealer/finish which is thinned tung oil.
Though lemon oil can be good for cleaning old hardwood surfaces, "lemon oil" is almost always mineral oil with thinners and lemon scent! It dries out and often leaves the wood in need of a higher quality, penetrating oil that flows in to the wood fibers. I still feel that tung oil is the best for adding a rich, wood-enhancing oil to porous wood surfaces (like walnut).

Tom

carolax
06-23-2003, 10:20 AM
First, until I ran across lansingheritage.com and this forum, I thought I was the only fan of old JBL's left on this earth. For a numer of years I worked for a JBL sound contractor and did some semi-pro recording. During those years I owned or used the following JBL's: 4310, 4311, 4320, 4315, 4343, 4350 (yikes!), 4410, 4412, and my current LSR-32's and 4425's. It's nice to know I'm not the only member of the cult!

I appreciate the company, and the sage advice (as opposed to cerulean advice?). I'm going to go slather my 4425's with tung oil, play some Moby real loud for a day or two to see if the 'wooferitis' gets the cure, then check to see if my wife is still living at home.

IDF
06-23-2003, 11:44 AM
No matter where I put them in a large, vaulted listening room, no matter how high off the floor, there is a strong bass underline. A giant, one-note boom. Is this normal for a 4425?

Certainly not :)
JBL's literature recommend that "the monitor should be monted against a wall. Other mounting location, such as away from a wall or at the intersection of room surfaces, cause uneven bass response".
In my experience (43xx series) that point is important. Maybe try to play a record with huge bass and find the best point.

Norbert
06-24-2003, 09:15 AM
What amp are you using?

Myself owning a pair of 4430 monitors I found out that these monitors are really hard to drive in the bass area. Efficiency and therefore power is not a problem but you have to be careful selecting an amplifier with a low output impedance (equals high damping factor). Certain tube-amplifiers like single-ended triodes are not really able to control a heavy 15" cone (155 gr. for the 2235H). Something similar might apply to your 4425 speakers. I would try a power amplifier having a damping factor at least one magnitude higher than the one you are currently using.
If you look at the schematic of the current K2-S9800 dividing-network you will notice user configurable resistors in parallel to the bass driver in order to adjust damping. Adding damping resistors in the 4425-network is also something you could think about.

Best regards,

Norbert

4313B
06-24-2003, 09:38 AM
Excellent point Norbert. I personally can't stress the importance of lots of amplifier control for JBL 3-inch and 4-inch coiled LF transducers. I've harped (:p) on this since the first forum. Tubes are fine for everything else, but they really don't belong in the VLF and LF unless someone is specifically going for that particular sound character.

IDF and Gordon are right. You have to "break in" refoams. Not quite the same as a recone with a new spider but nevertheless...
That's why I recommended that you might want to measure the free air resonance of those 2214H's. You might want to measure the tuning frequency of the enclosures as well. If the enclosures measure too high above 34 Hz you have a problem.

*****

I just examined the 4425 schematic and it already has 50 ohms of resistance across the 2214 which drops the impedance peaks; the largest from ~ 112 ohms down to a reasonable 35 ohms.

carolax
06-24-2003, 09:42 AM
Good question about the amplifier. I'm using an Adcom GFA-5400 which I originally bought to power JBL LSR-32's, and which it has done very well. I also use an Audio Research LS2 preamp because there should always be at least one tube!

I'm going to borrow a different power amplifier this weekend and see if it helps. Adding resistors to the crossover sounds like fun...maybe next weekend :>)

4313B
06-24-2003, 09:46 AM
I've personally never had any trouble driving JBL's with Adcoms... I'd be very interested to know if swapping out amps solves your problem :)

boputnam
06-24-2003, 09:55 AM
Norbert...

You make a great point that has been touched on on another Thread here, of late. (http://www.audioheritage.org/vbulletin/showthread.php?s=&threadid=347 - an interesting mix of technical info and salesmanship...)

This might be of interest to some: http://www.crownaudio.com/pdf/amps/damping%20factor.pdf

Or, here's the .pdf for direct download.

I have no relationship with, nor do I own or use any Crown gear (but they articulate this real well :p )

I'm lately using QSC CX502 (LF) and CX302 (MF/HF) - each have damping factor "Greater than 500". The improvement over my prior rig-up is astonishing and largely attributable to (at least coincident with...) a materially increased damping factor.

4313B
06-24-2003, 10:04 AM
Nice find Bo! :)

boputnam
06-24-2003, 10:23 AM
Hey, this one's cool, too!

http://www.trueaudio.com/post_013.htm

It validates Giskard's harping (oh NO!!) on using Monster Cable to reduce cable resistance, and another friend's imploring me to solder the speaker cables right to the network binding posts! Whoa...

:cool:

4313B
06-24-2003, 10:57 AM
Yes, and it has good points as well which perhaps indicate where PSS AUDIO is coming from.

The earliest article I have on DF is from 1966 when George L. Augspurger (James B. Lansing Sound, Inc.) authored "The Damping Factor Debate". This particular article definitely reinforces PSS AUDIO's stance on published DF figures.

In any case DF alone does not a good amplifier make.
It that Yoda speak?

boputnam
06-24-2003, 10:59 AM
Completely! :rolleyes:

Got a copy of that Augspurger article to share? I can't imagine what I can offer as fair trade...

4313B
06-24-2003, 11:12 AM
I'll scan it at some point and send it via email to those interested. I think John Murphy expanded on the concept pretty well. His examples are definitely worth reading.

boputnam
06-24-2003, 11:30 AM
Thanks - keep me on the list! :D

Yea, I'm glad I "re found" Murphy's site. I had used the PC-based RTA some years back, and thought it quite good. Re-looking at things, his site is very comprehensive.

Cool. :cool:

Paul Joppa
06-24-2003, 08:22 PM
OK, up front here: I'm an SET enthusiast. There have been several comments in this thread about the importance of high damping factor, which SET amps don't have. So it seems a good place to say my piece. Which is basically that the damping factor should be matched to the speaker.

The total resistance - voice coil plus cable plus amplifier - is part of the cabinet design. The oldest JBL woofers (130A and its relatives) have an incredibly low Q, which provided great efficiency and worked well with amps of high output impedance, as was common before the Williamson amp made large amounts of negative feedback popular.

A modern Theile-Small optimum design for a 2220 with a high damping factor amplifier is 0.75 cubic feet, and extends down to 130dB - not much of a woofer! In a 5 cubic foot cabinet (such as JBL designed and recommended in the late forties/early fifties) you could get down to 60Hz, with a 3dB ripple and a strong, narrow hump at 70Hz. Pretty poor. But double the electrical Q by driving it with an amp whose resistance equals the DC resistance, and suddenly you get a beautiful maximally-flat Butterworth alignment down to 50Hz.

Now the 130A had a VC resistance of around 5-6 ohms, but was labeled 16 ohms in those days. An SET amp, or a triode push-pull such as was popular at the time, with no feedback, has a damping factor around 3 - i.e. an output impedance of about 5 ohms on the 16 ohm tap.

Put a 2235 in the same box, and you can get deeper bass, very flat to 35Hz with a high fedback, high damping amp. But drive it with the high impedance amp, and it acquires a giant booming peak of 6dB or more around 60Hz, unless you put it into a huge 25 cubic foot box.

So yes, an SET amp (or any amp with little or no feedback) will make a modern speaker design boom. But a high-feedback, high damping amp will generally make a well-designed vintage speaker boom too. Combine an SET (typical damping factor 2 to 3) with a speaker designed for that amount of amplifier damping, and it works just as well as a modern amp/speaker except the vintage setup is more efficient.

Some amps from the fifties, including my own pair of Heathkit UA-1's, had a complex feedback scheme so that a unity damping factor could be generated even with high amounts of feedback. Presumably this was so they could drive the "original JBL/Altec/etc" kind of speakers correctly.

And now, back to your regularly scheduled entertainment ...

4313B
06-24-2003, 08:40 PM
"Which is basically that the damping factor should be matched to the speaker."

How true! But pretty impractical for the person who is exhausted after programming a VCR.

Your points are one reason why I really enjoy the computer software packages of today because all these factors can be taken into account if desired. It sure beats all the myriad formulas I used to have to work through! :(

GordonW
06-24-2003, 11:37 PM
Hm, 2214 12" deep-basket woofer, huh? So, would the 4425 sort of be like the "pro version" of the L100T? Because if so, the bass sbould NOT be boomy in any way!!

Regards,
Gordon.
wish I could find an abandoned pair of L100Ts, or even better, L80Ts... that series seriously sounded GOOD...

Norbert
06-25-2003, 12:00 PM
Originally posted by Paul Joppa
So yes, an SET amp (or any amp with little or no feedback) will make a modern speaker design boom. But a high-feedback, high damping amp will generally make a well-designed vintage speaker boom too. Combine an SET (typical damping factor 2 to 3) with a speaker designed for that amount of amplifier damping, and it works just as well as a modern amp/speaker except the vintage setup is more efficient.
I think you're absolutely right Paul. It is the question of finding an amplifier with the right amount of damping for a speaker with a given amount of damping. Or vice versa ...
As a lover of SET amps (I have a 300B Uchida amp which I don't use currently), I must admit that it was quite difficult to find a satisfying combination for my 4430s. I'm currently using a KT88 (triode) push-pull amp in my system. From time to time I swap with my Hafler 9505 (excellent MOSFET amp with almost no sonic contribution). I think the challenge is to design an amplifier (tube or SS or both) with SET sound, low output impedance and no feedback.
I'll face that ...

Best regards,

Norbert

Ken Schwarz
07-01-2003, 09:42 PM
Bass boom can be caused by floor resonance. Is yours a suspended wood floor? If so, you could have bass problems which are not the speaker's fault.

carolax
07-05-2003, 10:31 PM
A final followup (from me, at least): a different amplifier (a Bryston) sounded better than my Adcom, but it didn't alter the resonance. Time and Moby, however, seems to be doing the trick. I played some bass-heavy material at 'non-residential' volume for a few hours a day for several days, and the bass hump is leveling off. Thanks to everyone for their input.

4313B
07-06-2003, 05:56 AM
Which Adcom?
Which Bryston?

carolax
07-06-2003, 08:29 AM
Adcom GFA-5400
Bryston 3B

Although I only had it overnight, driving the 4425's it had better deep bass and less 'glare' in the upper midrange. I'll stop before I begin to sound like an audiophile [at this point carolax cracks open a can of Schlitz and spits into, or nearly into, a nearby waste basket].