PDA

View Full Version : 375 and 2440 mid drivers



aust-ted
12-11-2003, 11:56 PM
Hi

I am trying to clarify a question raised in another discussion forum about the 375 / 2440 compression driver.

It has been claimed that there are differences between the 375s and the 2440s although there appears to be agreement that they use the same aluminium diapgragm although there is a later diamond pattern diagraphm.

Other advice I have receive suggests that the 375s and 2440s are identical except for the name plate.

On the other hand I have seen references to early "bubble backed" versions of 375s as compared the later flat backed 375s and 2440s.

Can anyone (eg Don Mc Ritchie) through some light on this?

Also if there are differences, I would appreciate any opinions on any differences on the sound these variants produce, especially for home use.

TIA

aust-ted
Canberra
AUSTRALIA

Mr. Widget
12-12-2003, 02:20 AM
The 375 and the 2440 are the same driver. They are not all identical however. The 375 pre dates the 2440 model introduction. There were several subtle design changes to the 375 between it's introduction in the 1950s and the introduction of the 2440 which occurred around 1969 or 1970 with the introduction of the JBL Professional Series. they were produced concurrently thereafter with the introduction of the 376/2441 around 1980.

The diamond pattern surround on the aluminum diaphragm makes it a 376 or 2441.

For exact dates and possible acoustic differences (probably lore) over the years of production someone else will have to chime in.

You can read about the early 375 and it's Westrex/Altec heritage on the Lansing Heritage site.

aust-ted
12-12-2003, 02:38 AM
Mr Widget

Thanks

So the early 375s differ from the latter ones which are the same as contemporary 2440s. Correct me if I have got that wrong.

I have checked out out the Lansing Heritage site for info on the 375 and could find only one pic of what looked like a later version. Can anyone point out any more detailed info on this site?

I would dearly like to see a pic of the early bubble backed version.

What has excited my interest are claims that the 375s sound marginally better than the 2440s from people interested in vintage audio. I would have expected that JBL would have strived to ensure that the drivers would have improved over the years.

Regards

Mr. Widget
12-12-2003, 03:04 AM
I don't think there are pictures of the early bubble backs on this site. I do believe someone posted photos on a thread, but it may have been the previous forum that cannot be accessed by this search function.


Personally I would be skeptical about the older units sounding better. There is a lot of that audio voodoo out there. For example if the diaphragm is an original with the red wax seals intact, the vintage buffs go nuts for it. The fact of the matter is that the reason JBL went to titanium was for durability as well as extended highs. The old diaphragms will not sound as good as a new 2440 diaphragm. (Unless of course it has never or rarely been played.)

Furthermore the 2441 diaphragm is even better for most applications. The 2440 has quite a peak at 10KHz. For systems that were designed to use this peak, you want to stay with the 2440 diaphragm, otherwise the 2441 is the better choice.

If the bubble backs were better, I am sure that style back would be available from JBL or an aftermarket vendor. For example many people (myself included) prefer the sound of the less durable aluminum diaphragms over the titanium ones. That is why JBL still sells 2440 and 2441 diaphragms instead of only producing the "improved" 2445 titanium diaphragms.

aust-ted
12-12-2003, 03:27 AM
Mr Widget

Thanks again.

I understand the point you are making. I own a pair of 2450s which I have just bought based on advice along the lines you expouse.

It may just be a case of the older the better in the eyes of those who seek out these drivers. However my curiosity got the better of me and I would like to delve into:

1. What are the differences between the various 375s and 2440s.
You have kindly provided some advice on this, and

2. What aspect of the early 375s might attract hi Fi enthuiasts aiming for the golden sound.

It may just be a case of age and rarity but then there may be something else to it not related to the technical specs which certainly appear to improve as new JBL models were introduced.

aust-ted
12-12-2003, 03:39 AM
Mr Widget

A follow up question to your last reply.

Can you describe what it is about the 2440 and 2441 diaphragms that attract you compared to the later Ti ones?

I know this has been discussed before on this forum but I do not really have a feel why quite a few have the same preference.

I know that the later Ti diaphragms, as used in the 2450 say, go higher and that there is some distortion at the top end which I understand is at least partially a result of throat limitations. On the other hand this can be avoided by the use of tweeters such as 2404 or 2405 just as can be used with the 2440.

Trust I have not asked too many questions

Oldmics
12-12-2003, 09:09 AM
Hello Aus-Ted,Here are the pics that I had posted on the old forum.

Starting in the center is the earliest 375 assembly also knpwn as "the Humpback".This first version is labled on the bakolite plate with the Jim Lansing logo.

Next going to the left of center is the second version of the Humpback labled as Jim Lansing signature.

Up at 12:00 "O" clock is the version that I consider the rarest.That would be the grey colored 375.This was introduced after the humpback and has the rounded end cap as do the 2440 series.Still using bakolite for the name tag material.I have only seen 3 of the grey 375 drivers.

Down at 6:00 "O" clock is the first apperance of the black 375 driver.This still uses the bakolite nametag material.

And finally on the right side is the second version in black.This marks the first apperance of the foil decal as an identification plate.More pics in the next post.

Oldmics

Oldmics
12-12-2003, 09:26 AM
This is one that was on eBay awhile back.Its a JBL consumer version 375.The differences are obvious.What has not been discussed are the 375H versions.These came out during the era that JBL was painting there componets blue.So there are a few of these 375H units floating around in blue color.Rare but not much interest-yet!!! And don"t forget the other versions such as 375AB,375FH,375EX,375HP.These were the true mid range 375 assembles that had a larger coil gap at .043.These were similiar to the 2482 driver.
I measured the earliest humpback that I have against the early grey 375 (rounded endcaps) a while back.They were both close with a 3 db down on both units at 10.5K.

The lore of the old drivers is that supposedly the dura-aluminum material was recycled from skins of WW 2 aircraft.This was hi quality salvaged material and is the preferred diaphragm material in the golden ears crowd.The material apparently was not availiable for a long period of time and seemed to dissapear with the black 375 drivers introduction

Oldmics

aust-ted
12-12-2003, 11:49 AM
Oldmics

Thanks very much for the info and the pics. Most interesting

I actually have a pair of 2482s. Would it be possibe to get a pair or Aluminium diaphragms such as used in the 375AB, 375FH, 375EX, or 375HP units you address or can the regular 375 Al diaphragms be modified to work in a 2482?

Mr. Widget
12-12-2003, 11:58 AM
I'll jump back in as I am on the forum and I believe oldmics stepped away.

The 2482 has different guide pins specifically to prevent you from doing that. I believe it is because the gap is wider on the 2482.

Oldmics
12-12-2003, 12:31 PM
Widget is correct about the locator pins being in a different spot and will not allow the 2440 aluminum diaphragm to fit.Also the gap is larger on the 2482 at the forementioned .043.The .043 gap size applys to the 375AB,375FH,375EX,375HP.

The aluminum replacement diaphragm for these drivers has been obsoleted.This being the case even if the holes were redrilled in the 2440 diaphragms to accomidate a 2482 pattern the diaphragm probably would not fit due to the difference in gap size.

Oldmics

aust-ted
12-12-2003, 12:34 PM
Mr Widget
Thanks again

"The 2482 has different guide pins specifically to prevent you from doing that. I believe it is because the gap is wider on the 2482."

I gathered that but as Oldmics wrote there were special versions of the 375 with the same gap. I was asking if these diaphragms are available and if they would fit a 2482?

Also are there any non JBL alternatives which will fit a 2482?

aust-ted
12-12-2003, 12:39 PM
Oldmics Thanks again

"The aluminum replacement diaphragm for these drivers has been obsoleted. This being the case even if the holes were redrilled in the 2440 diaphragms to accomidate a 2482 pattern the diaphragm probably would not fit due to the difference in gap size. "

I responded to Mr Widget's advice before I read your reply

Earl K
12-12-2003, 01:34 PM
Hi

Also are there any non JBL alternatives which will fit a 2482?

Yes, if you want an aluminum diaphragm for a 2482 driver consider buying one from Radian (http://www.radianaudio.com/) . Their model 1282 (http://www.radianaudio.com/products/diaphragms/diaphragms.php4?viewT=diaphragms&viewC=diaphragms&viewI=#radian) is made expressly for this purpose. Radian is a US company that makes aluminum replacement diaphragms for a few companies drivers - plus they make their own line of transducers .

<> Earl K:)

Alex Lancaster
12-12-2003, 04:04 PM
Earl:

20+ Years ago I contacted Radian, and at the time, their pricing was not good, me beeing a JBL pro dealer; things have changed, but how is their quality?

I have been using some P-Audio diaphs, and they sound very good, even replacing Altec 288 and 80x for my "audiofiend" friends who would find the smallest defect. You can look them up in the web.

I would really like Your feedback.

Alex.

Earl K
12-12-2003, 05:04 PM
Hi Alex

I put (8) Radian replacement diaphragms into a batch of 2426 drivers a few years ago. They have that characteristic "Aluminum" sound of being a little bit "duller" ( or better damped ) when compared to a stock 2425/6 titanium diaphagm. IMO, this metal is better used in a near to mid field setup. In my world that means 10' to 30'. After 35', the titanium is my first choice for the metal type for the diaphagms' dome .

Quality: Their build tolerances closely match JBLs' for gap fit - but - I find the plastic used in the ring that holds it all together is a little soft. ie : one has to be very careful to not "strip" the plastic when securing the wiring to the terminal strips.

I also purchased a single Altec 802/902 replacement diaphragm. Its' a very close acoustic approximation of the older 808 diaphragm - meaning - since I prefer the 802/902 - I wouldn't ever pursue buying those.

I'll eventually buy a pair of the Radian large format diaphragms for my 2482s - based on the above impressions.

regards <> EarlK :)

aust-ted
12-13-2003, 05:31 PM
Earl

Thanks for the advice on Al diaphragms for 2482s. It appears Radian is the only supplier of a drop in unit for this driver

I was also very interested in your comment about the sound of the Al as "of being a little bit "duller" ( or better damped ) when compared to a stock 2425/6 titanium diaphagm" .

I assume this is simply an outcome of the Al diaphragm being heavier than the Ti ones and being used in the same motor assembly.

Regards
Aust-Ted

Unison845
08-19-2005, 08:21 PM
I have a single JBL 375H in blue and bakerlite sign, swimming in rain water!

Does anybody know how I can clean this driver, or take it apart? Any assembly diagram would help.

Thanks!


This is one that was on eBay awhile back.Its a JBL consumer version 375.The differences are obvious.What has not been discussed are the 375H versions.These came out during the era that JBL was painting there componets blue.So there are a few of these 375H units floating around in blue color.Rare but not much interest-yet!!! And don"t forget the other versions such as 375AB,375FH,375EX,375HP.These were the true mid range 375 assembles that had a larger coil gap at .043.These were similiar to the 2482 driver.
I measured the earliest humpback that I have against the early grey 375 (rounded endcaps) a while back.They were both close with a 3 db down on both units at 10.5K.

The lore of the old drivers is that supposedly the dura-aluminum material was recycled from skins of WW 2 aircraft.This was hi quality salvaged material and is the preferred diaphragm material in the golden ears crowd.The material apparently was not availiable for a long period of time and seemed to dissapear with the black 375 drivers introduction

Oldmics

Oldmics
08-19-2005, 08:51 PM
Take the diaphragm out.Either use a non-magnetic screwdriver or be very careful unscrewing those phillips screws.

Then drain out the water and see how bad the damange is.

If there is rust scaleing up in the voice coil gap,its probably gonna have to go back to the factory for repair.

Oldmics

Unison845
08-19-2005, 08:59 PM
The diaphragm is damaged. There is some rust in the voice coil gap, also in the throat there is some rust.

Is there any way that I can take it apart?


Take the diaphragm out.Either use a non-magnetic screwdriver or be very careful unscrewing those phillips screws.

Then drain out the water and see how bad the damange is.

If there is rust scaleing up in the voice coil gap,its probably gonna have to go back to the factory for repair.

Oldmics

Oldmics
08-19-2005, 09:03 PM
Is there any way that I can take it apart?


Not really.To do it correctly you need a gaussing and de gaussing machine.

If its trashed-Put it on ebay as is and get a coupla bucks for it.

Oldmics

John
08-20-2005, 12:45 AM
Well I could tell you how to do it without de-gaussing the magnet but I am afraid you could end up crunching your fingers:eek: and you would have to get a new throat for it for sure as it would be toast by the time it was disassembled:(
The magnetic power contained in that driver is beyond belief :D

ralphs99
08-20-2005, 04:10 AM
Hi Aust-ted,
Good to hear from you!
I've been dreaming of buying various 2" parts on Ebay, and have noticed that you've been picking up same. 2397's and some drivers.....
Please let us know what you're building. I for one am very curious.
My 2 cents on the Al vs Ti debate: I had a pair of 2420's that were sounding ragged. I spent a lot of time trying to find replacment Al diaphragms. Finally Mike Caldwell at Vintage Audio Sales sold me a pair of lightly used 2426's at a good price. Big improvement! The new parts sound so much softer and more detailed. I can't say that it's definitely the Ti diaphragms that are the cause of the improvement. But I can recommend anyone with with older comperssion drivers replacing their diapragms either with Ti or Al. New is Good!

Cheers,

Ralph.

aust-ted
08-20-2005, 06:08 AM
Hi Ralph

>I've been dreaming of buying various 2" parts on Ebay, and have noticed that you've been picking up same. 2397's and some drivers.....
Please let us know what you're building. I for one am very curious.

I have built a pair of dual bass boxes each using a pair of 2235Hs. Currently I am using them with 2450/ 2380 CD horns and 2404 baby bums, tri-amped and have been reasoably happy with them. However I have acquired a pair of 2441s which I intend to try out with the Smith horns which I have heard good reports on. Will try both 2440 and 2441 diaphragms.

>My 2 cents on the Al vs Ti debate: I had a pair of 2420's that were sounding ragged. I spent a lot of time trying to find replacment Al diaphragms. Finally Mike Caldwell at Vintage Audio Sales sold me a pair of lightly used 2426's at a good price. Big improvement! The new parts sound so much softer and more detailed. I can't say that it's definitely the Ti diaphragms that are the cause of the improvement. But I can recommend anyone with with older comperssion drivers replacing their diapragms either with Ti or Al. New is Good!

Suspect the improvement you got was mainly related to replacing worn out diaphragms with new ones. I am a novice on this forum but my reading is that most members seem to prefer the Al diaphragms for home Hi Fi over the Ti ones but I must admit my 2450 ones sound pretty good.

You might like to pick up a pair of 2420 or 2421 diaphragms when new ones come up on eBay. Not sure what others say but the Radian ones with the mylar surrounds might also be worth a punt. Then you will have a spare pair of drivers for another project.

Regards
Ted

Unison845
08-20-2005, 08:13 AM
If it is that difficult, well anybody knows how much JBL would charge to rebuild it?
Thanks!


Well I could tell you how to do it without de-gaussing the magnet but I am afraid you could end up crunching your fingers:eek: and you would have to get a new throat for it for sure as it would be toast by the time it was disassembled:(
The magnetic power contained in that driver is beyond belief :D

Unison845
08-20-2005, 08:38 AM
I also have a pair of JBL 150H, one of the driver has the dome pushed in, does anybody know how to fix it without damaging the cone? I figure using a small pin I can poke through and start pulling out, but may be somebody can show me a better way. Thanks!




Well I could tell you how to do it without de-gaussing the magnet but I am afraid you could end up crunching your fingers:eek: and you would have to get a new throat for it for sure as it would be toast by the time it was disassembled:(
The magnetic power contained in that driver is beyond belief :D

Mr. Widget
08-20-2005, 10:16 AM
I also have a pair of JBL 150H...

It is very likely your speakers came from this or a similar setup...

http://audioheritage.org/vbulletin/showthread.php?t=6856


...one of the drivers has the dome pushed in, does anybody know how to fix it without damaging the cone?

Domes are replaceable, or you may try wetting it and applying light suction through a hose or tube.

I would guess if the rust in your HF driver is extensive JBL will not repair it, if it is mild it will cost around $350 to get it fixed.


Widget

Dave Zan
08-24-2005, 02:23 AM
I was also very interested in your comment about the sound of the Al as "of being a little bit "duller" ( or better damped ) when compared to a stock 2425/6 titanium diaphagm" .

I assume this is simply an outcome of the Al diaphragm being heavier than the Ti ones and being used in the same motor assembly.



The Al dome is not heavier than the Ti. It's nominally 10% less.
Ti is denser than Al so the Ti part is thinner to (almost) compensate.
The mass difference is probably within production tolerances anyway - it's about 5% of the total dome + Voice coil mass. .
The differences in response are mainly due to resonances in the suspension itself.

pelly3s
08-24-2005, 05:50 AM
if you get the driver bead blasted its gonna be about $25 or $30 then the cost of a new dia. the dust cap if you are gentle you can pop it back up with the approach widget said, if that doesnt work cut it off and put a new one on.

if there is rust in the gap you can send it to any nut job speaker shop (like mine) and they should be more than happy to restore it for you.