375 vs 2440 What is the Difference

[mbottz]

Can any one out there tell me the differences between the 2440 and the 375. Is there a sound difference? Thanks for any info you can give.

[Mr. Widget]

They are functionally identical. They use the exact same diaphragm, throat, phase plug, magnet and cast return pot.

The differences are color, nameplate, terminals, and depending on the vintage, possibly the back cap shape.

In the voodoo that is audio, I am sure there are those that will tell you that one sounds better than the other. The 375 and all of the consumer versions of JBLs are more collectable and therefore more expensive on the used market than their pro counterparts. If you compare a 375 and a 2440 and they do sound different, which isn't that unlikely, it is because one or both are not operating up to spec. Intact "Red Wax Seals" is certainly no guarantee of condition.

Widget

[LE15-Thumper]

Intact "Red Wax Seals" is certainly no guarantee of condition.

Widget

I hear ya Widget. My LE85's would cut out on certain bass notes from the LE15's. Turned out the short 3" wiring inside the driver itself was loose under the screw terminals.
What can you do ? Had to pop those red cherries to fix 'em.

[Roddyama]

The chances that the used 2440's seen more rigorous service than the used 375 is probably pretty good.

[Steve Schell]

You have to be careful when buying these drivers used. As Rodd pointed out, many of these drivers have been used and abused for many years in professional systems. Some have been installed in outdoor systems and suffer from rusting of the internal parts. It is a bad sign if the external paint finish is coming loose and falling off.

One fellow I know has made quite a study of 375, 2440 and 2441 drivers. He often demagnetizes and disassembles them, blasts off the old paint, removes rust, remachines the mating surfaces if necessary, repaints, reassembles and remagnetizes them. He supplies them to another friend who builds complete systems. They were noticing large variations in response curves between drivers of different vintages, and began to notice differences in construction. Ultimately they identified seven distinct versions of the drivers; changes over time in the pole pieces, phasing plug geometries, etc. They found that it is necessary to pair up drivers with similar features in order to get stable imaging from a stereo pair.

The ones to look for should have close serial numbers and a nice external appearance. Chances are they have been used in a hi fi rather than a prosound application.

[Lancer]

Great information guys!

Thanks :)

[Oldmics]

"You have to be careful when buying these drivers used. As Rodd pointed out, many of these drivers have been used and abused for many years in professional systems. Some have been installed in outdoor systems and suffer from rusting of the internal parts. It is a bad sign if the external paint finish is coming loose and falling off.

One fellow I know has made quite a study of 375, 2440 and 2441 drivers. He often demagnetizes and disassembles them, blasts off the old paint, removes rust, remachines the mating surfaces if necessary, repaints, reassembles and remagnetizes them. He supplies them to another friend who builds complete systems. They were noticing large variations in response curves between drivers of different vintages, and began to notice differences in construction. Ultimately they identified seven distinct versions of the drivers; changes over time in the pole pieces, phasing plug geometries, etc. They found that it is necessary to pair up drivers with similar features in order to get stable imaging from a stereo pair.

The ones to look for should have close serial numbers and a nice external appearance. Chances are they have been used in a hi fi rather than a prosound application."


Yeah,That "Sam" guy knows his stuff.

Oldmics

[scott fitlin]

You have to be careful when buying these drivers used. As Rodd pointed out, many of these drivers have been used and abused for many years in professional systems. Some have been installed in outdoor systems and suffer from rusting of the internal parts. It is a bad sign if the external paint finish is coming loose and falling off.

One fellow I know has made quite a study of 375, 2440 and 2441 drivers. He often demagnetizes and disassembles them, blasts off the old paint, removes rust, remachines the mating surfaces if necessary, repaints, reassembles and remagnetizes them. He supplies them to another friend who builds complete systems. They were noticing large variations in response curves between drivers of different vintages, and began to notice differences in construction. Ultimately they identified seven distinct versions of the drivers; changes over time in the pole pieces, phasing plug geometries, etc. They found that it is necessary to pair up drivers with similar features in order to get stable imaging from a stereo pair.

The ones to look for should have close serial numbers and a nice external appearance. Chances are they have been used in a hi fi rather than a prosound application.I have six 2441 drivers purchased new in 1979-80, I have two 2440 drivers I got with a pair of lenses, dated 1972! I have always said they sound different than the 2441 from 79, even with 2441J diaphragms! Everyone said they ( the driver itself ) is the same, except for the diaphragm! The older drivers have a slightly different gap width! THEY DO SOUND DIFFERENT! I never measured the differences, but to my ears, the older drivers with 2441 phragms sound sweeter, to me anyway!

Thank you Steve!

[Roddyama]

At some point in the 70's (and I'm not sure what point that is) JBL started making a titanium diaphragm. To me, these diaphagms, while more tolerant of abuse did not sound as "sweet" as the earlier aluminium diaphragms. Also some prefer the "mellow" sound of the older phenolic diaphragms.

I have also run a fewsets of 2462's with Radian Audio aluminium diaphragms. I had come to like these very much (although I am running TAD's now). I'm sure the mylar surround helps the sound of the Radian diaphagms.

[Steve Schell]

Rodd, the Radian design with its well behaved mylar compliance is the legacy of Jonas Renkus's work; he also designed the Symbiotik diaphragm for Altec. As I have learned from a friend who knew him well, Renkus preferred the direct reproduction of signal energy by the driver, and did not endorse complex suspensions that artificially extend response up high through breakup modes.

I also like the sound of the Radian diaphragms. Though sometimes difficult to center in the gap, these diaphragms measure well and sound very good.

So Scott, you were right all along about the differences, despite the opinions to the contrary. I have also heard for years that these drivers were identical.

Oldmics, you sure get around!

[Mr. Widget]

So Scott, you were right all along about the differences, despite the opinions to the contrary. I have also heard for years that these drivers were identical.


Yes, your friend's research explains a lot of the confusion that we have experienced in the past.

http://audioheritage.org/vbulletin/showthread.php?t=6253

In my own tests I have noticed that different vintages from TAD vary in performance as well. I guess everyone "Reserves the right to make continual improvements":blah:

Widget

[edgewound]

I guess I'll jump in too.


The aluminum diaphragms have better internal damping, partly because the diaphragm itself is thicker, and it's a softer metal...so it sounds "sweeter" to the ears. The titanium diaphragm is thinner and has lots of breakup from spurious resonances in the dome and diamond surround. Add that to the increasing cost of aluminum, lots of shattering diaphragms in the field, and the marketing sex appeal of titanium...lot's of manufacturers making titanium diaphragms. Here's an experiment to try, if you have the equipment...its very revealing. Take a 2445, 2446, 2447, 2450 with titanium diaphragm and apply about 3-3.5 volts signal drive and sweep it up to 18k-20khz and tell me what you hear. Do the same thing with a TAD 4001. I haven't done it with the JBL 2435...haven't had the chance to yet... Radian Drivers do sound very nice, but it took along time to straighten out the diaphragm quality issues...and they rarely did anything under warranty...even when it was obvious

Every tool that is used to make the TAD diaphragms is destroyed in the mfg process...vapor deposition process in a vacuum chamber, and the tool is acid etched away. This was explained to me by Leon Sievers, the marketing mgr at TAD a few years ago. Berrylium is the lightest of the three metals....and very toxic when in smoke or vapor form.

Edgewound

[scott fitlin]

I have always used Al, still do, dont shatter them, and rarely lose a diaphragm!

And, yes, I agree, aluminum sounds sweeter!

[Ken Pachkowsky]

Intersesting read guys.

[Roddyama]

Every tool that is used to make the TAD diaphragms is destroyed in the mfg process...vapor deposition process in a vacuum chamber, and the tool is acid etched away. This was explained to me by Leon Sievers, the marketing mgr at TAD a few years ago. Berrylium is the lightest of the three metals....and very toxic when in smoke or vapor form.

Edgewound

A story of lessions learned.

As I was in the process of setting up my TAD 4001s I first wanted to use them without the 077's on top with direct connection to the Aleph copy on loan from a friend (with "direct" being the focus here). This proved to be a very bad move. After a couple weeks of tweaking I put a DVD in before switching the function and for brief instant heard what a video signal sounded like. It didn't take long to determine that this dumb move took out both of the TAD berylium diaphragms (at $800/ea.).

The moral of the story.

Always use a series hi-pass cap on high frequency drivers.

The up-side of the story.

I replaced the TAD diaphragms with Radian aluminium diaphragms at about $300/pair. It had a 12db peak at about 1500Hz and was only good to about 15kHz. Using a a single hi-pass cap that starts to roll off at about 3kHz gave me a (theoretically) relatively flat response from 1200Hz to 12kHz. I put the 077's in above that and it worked wonderfully. The sound is the best that ever came from my system.

berylium vs aluminium

Inconclusive. I want to say that the sound of the alumium is "softer" than the berylium but its could have been other factors like the series cap on the aluminium diaphragms. I can say that I don't miss the the original TAD diaphragms, and the $1300 I saved by buying the Radians went a long way to making me feel better.:)

[Zilch]

I posit that JBL will migrate back to aluminum now that they have new surround technology worked out.

The difference in sonic character between LE85 (aluminum) and 2425/6 (titanium) is readily apparent to me. Aluminum is better (smoother, less harsh). :yes:

I don't hear any similar difference between Al and Be (2431 vs 2435).

[Mr. Widget]

Always use a series hi-pass cap on high frequency drivers.


I never did when I was using good old 2441s... sure those diaphragms at around $500 a pair aren't free, but I felt with luck I would be OK... never had a problem.

Since moving to beryllium diaphragmed drivers I have always used a series cap. At around $800ea. for the 4001 diaphragm and $1400ea. for the 4003s I am simply not prepared to be out there without a safety net. I have done some demos with the caps in and out of the circuit and so far no one has been able to hear a difference. I use a 47uF polypropylene film cap on them.



berylium vs aluminium

Inconclusive...

I am a huge advocate of aluminum diaphragms. I do think if cost is no object however the beryllium will give you a slight amount of detail that is masked with the aluminum. As one forum member said to me, "With the beryllium you can hear the rosin on the bow." It is true... it is damned expensive, but there is just that much more music revealed... goose bump material.

Widget

[Mr. Widget]

I don't hear any similar difference between Al and Be (2431 vs 2435).

Just speculation here but...

It is possible that the ferro fluid in the 2435s also reduces the benefit of using the beryllium. JBL did forgo using ferro fluid in the 435Be hi-fi version.

Possibly in your temporary workshop listening setup it is difficult to discern the more subtle details...

Widget

[edgewound]

I tend to think that ferrofluid in the gap of a compression driver actually smooths out and calms down the frequency response, when a metal type of dome is used...all titanium anyway. Titanium domes do take alot more abuse in live sound situations because of the tensile strength.The damped domes do sound smoother. At the expense of a little sensitivity, to my ears putting the brakes on the piston motion of the voice coil with ferrofluid cuts down on harmonic resonances bouncing around in the dome, making it somewhat less fatiguing to listen to. It would be interesting to me to hear a carbon/ceramic/silicon or even diamond type of lightweight high internal damping material that doesn't flex at all. These devices are so much more sensitive/efficient than other mid and woofer drivers, what's a few dB less from a slightly heavier material.

As Mr. Widget refers to...unobtanium may be on the drawing boards...?

Edgewound

[Ian Mackenzie]

I would like to try some dusted 275Nd dias at some stage, I think that would be very interesting. It also depends on the genre of music you play, brass come up particularly well on the titanium.

I am also inclined to think there are tonal differences in the ferrite and Alnico versions of the drivers. The outfit I bought both the 2420 and the 2405 said the Alnico were prefered for Hifi and they sell container loads to Japan.

I currently use alnico 2420's with the 2425 dias.

[herki the cat]

I posit that JBL will migrate back to aluminum now that they have new surround technology worked out.

The difference in sonic character between LE85 (aluminum) and 2425/6 (titanium) is readily apparent to me. Aluminum is better (smoother, less harsh). :yes:

I don't hear any similar difference between Al and Be (2431 vs 2435).

My Two Cents:

Gee, I hate to intrude__ but we would all appreciate it very much if JBL would produce again some original LE 85 / 2420 15 ohm Aluminum diaphragms with tangential suspension for replacements. :bouncy:

LE 85 OEM in the LC9-A Horn System, does present Stunning Sound Quality__totaly free of horn honk due to the extremely high level of LE 85's flux density. The 2420 big brother is also recommended. It has a heavier platform to support the diaphragm motion, & it is noticeable.

Enchanted by the prospects of the new JBL dimpled suspensions, I tried the 2425 in my LC9-A' s when it surfaced in the market place. I concluded it certainly will solve many problems, as intended, in high level sound
pressure applications where LE 85 & 2420 would not be welcome.
________________________________
Cheers, herki the cat

[4313B]

I missed this:


The difference in sonic character between LE85 (aluminum) and 2425/6 (titanium) is readily apparent to me. Aluminum is better (smoother, less harsh). :yes:I believe that you were able to source a pair of the D8R275Nd diaphragms? They offer the best bang for the buck.
I don't hear any similar difference between Al and Be (2431 vs 2435).Well then, consider yourself lucky! You just saved yourself a ton of money! :yes: There is an order of magnitude difference in price!



While the Mg diaphragms are quite close to the Be diaphragms, the Al and Ti diaphragms are not. And virtually all of them benefit from the good old aquaplas.

"If it's metal, coat it."

[Robh3606]

It is possible that the ferro fluid in the 2435s also reduces the benefit of using the beryllium. JBL did forgo using ferro fluid in the 435Be hi-fi version.


Hello Widget

Actually you need the Ferro in there it helps seal off the VC cavity. I would more concerned about the amount used as too much certainly does effect the Frequency Response. Too little and you have other issues. If they were used drivers with an unknown amount that certainly could be an issue. I know the ones I had were loaded with the wrong type of Ferro and had way too much in them.

Rob:)

http://www.audioheritage.org/vbulletin/showthread.php?t=14369

[pos]

The messages you are quoting are 4 years old ;)

[Robh3606]

The messages you are quoting are 4 years old ;)


LOL

Thanks well at least it was a correction that set the record straight. You always have to watch these old threads seem to just pop up now and then.

Rob:applaud:

[4313B]

Thanks well at least it was a correction that set the record straight. You always have to watch these old threads seem to just pop up now and then.True.



I think Zilch has moved on to 2452H-SL's as well as other brands in any case. I know he's also mentioned that he liked his stock LE85's which I can certainly understand. Then others have posted how the LE175's sound better than the LE85's and on and on it goes...

[frank23]

Since moving to beryllium diaphragmed drivers I have always used a series cap. At around $800ea. for the 4001 diaphragm and $1400ea. for the 4003s I am simply not prepared to be out there without a safety net. I have done some demos with the caps in and out of the circuit and so far no one has been able to hear a difference. I use a 47uF polypropylene film cap on them.

I hear a large difference in caps on the 2435. I have some top quality chateauroux MKP's that are considered to be all someone would ever need, but the 2435 only sound as sweet as my 2420 on russian paper-wax caps...

[4313B]

Hello Widget

Actually you need the Ferro in there it helps seal off the VC cavity.

I know the ones I had were loaded with the wrong type of Ferro and had way too much in them. Yep.

I hear a large difference in caps on the 2435. I have some top quality chateauroux MKP's that are considered to be all someone would ever need, but the 2435 only sound as sweet as my 2420 on russian paper-wax caps...Weird.



As an aside, as far as I'm concerned anyone posting about 2435's and their sound quality who purchased said 2435's off eBay have dubious samples at best and I consider their opinion highly questionable.

I don't give a rat's ass what the eBay ads stated, I've personally gone through a sufficient number of these second hand drivers and, quite frankly, I wouldn't own a pair if they were given to me. Why? Because I don't want to spend the roughly $1,600 it would take to get them back to spec. That would be a classic case of throwing good money after bad.

I just went through yet another pair a couple weeks ago and true to form they both had suffered surround creep and had virtually no ferrofluid. They'll still make noise and that might be good enough for some unwitting end users but they aren't a 2435 that would pass any kind of QC that I know of. They don't even rate as B stock.

Unfortunately a whole bunch of people bought into a product that requires a higher degree of maintenance than any of the older compression drivers and they now can't afford to bring them up to spec. They would have been better off taking their money and putting it towards some LE85's, 2420's, 2421's or 2425/2426's along with some new aluminum diaphragms and ending up with a more robust long term product.

And to think that people used to bitch and moan about the cost of the aluminum diaphragms... :rotfl: