375 and 2440 mid drivers

[aust-ted]

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]

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]

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]

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]

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]

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]

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]

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]

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]

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]

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]

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]

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]

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 . Their model 1282 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]

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.