375 diaphragm question

[spinboy]

i've come across 6 drivers (375), all in varying shape. they have paint chipped off the outside, as they were part of a FOH system.

4 of them have diaphragms with a red dot at the top center; they also have lines 'embossed' onto them which resemble latitude and longitude. the other 2 are totally smooth.

the aftermarket diaphragms i find are all smooth. would i be presumptuous to assume the 4 with red dots are original JBL diaphragms? it's a little confusing as some places i read talk about the original "red wax" factory seal, but that doesn't quite seem right to me. (to put a drop of red wax on a midrange driver?)

[grumpy]

pictures might help... sounds like much more recent 2446-style diaphragms
(with embossed lines)... could still be aftermarket, I suppose.

Wax was on the screws for the rear cap, I believe, not the diaphragm.
(you might just have 16 ohm diaphragms ... green on 8 ohm) -grumpy

[spinboy]

aha. makes sense.
will see if i can make a picture link appear here.
the driver body says 16ohm, so that makes sense too.

ok, i'll try the pic link. unfortunately i think it is very large. sorry. http://www.soundcurrent.com/production/375diaphragm.JPG

[grumpy]

the red/green 16/8 ohm marking has been on the (+) terminal for
the diaphragm (between the screws) on the units I've seen...
I don't recall if there is significance to the dot/sticker on the diaphragm
center.
..still looks like a JBL D16R2450 diaphragm to me (used in 2446J).

don't know about the smooth ones...

-grumpy

[spinboy]

thank you for your quick replies. i'll check into it a bit more.

[subwoof]

The "red dot" appears to be a customer-added visual aid to reflect the impedance - red is 16 ohms and green is 8 by JBL's labeling. This is also painted on the + terminal.

The ribbed ones are indeed D162450 and I would bet the smooth ones are D16R2445.

The original aluminum diaphrams had a very short lifespan when on the road and I can almost bet that your magnets are going to need to be recharged.

It will be no small change to bring these back to original status. Just what do you plan to do with them??

sub

[spinboy]

i'd not heard about recharging the magnets, nor seen it mentioned on any which have been sold on ebay...

[scott fitlin]

That is indeed a 2450 diaphragm.

[louped garouv]

i'd not heard about recharging the magnets, nor seen it mentioned on any which have been sold on ebay...


read up on "Alnico regaussing"

http://www.audioheritage.org/vbulletin/showthread.php?t=279

[Mannermusic]

i'd not heard about recharging the magnets, nor seen it mentioned on any which have been sold on ebay...

Yep, has to be done if you want the original high frequency performance. I had mine done by Orange County Speaker Repair. Good job but difficult to ship without damage - the plastic throats tend to get sheared off from jousting in the UPS truck - finally had to use airmail. But, they sounded like new. :o:

[Robh3606]

Before you go tearing your drivers down read this

http://audioheritage.org/vbulletin/showthread.php?p=110522#post110522

Rob:)

[spinboy]

thanks for the alnico re-charge info. for a $25 charge to do the work, the shipping just kills ya don't it.

on the issue itself: it seems a lowered flux would offset the total output, not a frequency dependent situation (i saw one post say it would affect the HF rolloff, but it makes more sense that the driver simply couldn't produce as much sound). of course if i have a system, i'd be wanting to have matched drivers, or would simply offset any level differential by doing so by adjusting the amp for that driver (say, in a bi-amp or tri-amp application).

oh, on the diaphragm, JBL transducer parts listing shows a 375H diaphragm as the part D16R2440, although a previous posting said it was a 2450; JBL shows them listed for $204 in their 2006 price list.

[scott fitlin]

The 375 is the 2440. 375 was the JBL Signature Series ( consumer ) and 2440 was the pro variant. Except for the paint, and foilcal, they are identical, same diaphragm, same motor.

I personally prefer the sound of the aluminum diaphragm, D16R2440.

[spinboy]

so the 2440 is the smooth aluminum and the 2450 is the ribbed pro variant?

[scott fitlin]

so the 2440 is the smooth aluminum and the 2450 is the ribbed pro variant?No, both the 375 and the 2440 use the same diaphragm. Smooth aluminum.

The 375 and 2440 are 1 in the same, the only differences are the model numbers, the consumer version used in their studio monitors and TOTL hi fi speakers were labeled 375, and the drivers for the pro market were labeled 2440. But, other than that, they are the same drivers!

The 2450J is a neodymium driver, that uses the ribbed Titanium diaphragm.

[spinboy]

so the 2450J diaphragm will fit the 375 then... i see. and you prefer the aluminum.... just confirming, sorry to be a bit slow on this one. thank you.

[grumpy]

so the 2450J diaphragm will fit the 375 then... i see.

yeah, and the 2445 (which came with a smooth Ti dome), and the 2446 47 50 51
(which in 16ohm form use the D16R2450, ribbed Ti dome), and the ... :blah:

Note these are not -necessarily- drop-in and go. Some alignment can be necessary.
There are other threads here devoted to that, as there are other threads that cover
what diaphragm fits in what motor. :)

-grumpy

[Zilch]

I'd go directly to Aquaplas-damped "-SL" diaphragms.

[If they'll fit.... ;) ]

[subwoof]

I agree...The only diaphram I use for the 4" stuff is the D8R2450SL. Smooth, predictable and handles all the oomph you throw at it.

When I install the newer diaphrams in the older structures I drill out the guide pin holes and align with an oscillator / amp combo...

It is important to couple the driver to a long horn ( I use an old 2355 with the front squared off that is faced down on a rug ) so it can be swept down to 300 during the test.

sub