2402/2405 Diaphr

[Hofmannhp]

Hi Forum,

is anybody in this forum who can tell me if the diaphragma for the 2402 (bullet) and the 2405 (slot) are the same?
Whats with the gap space?

I place this question, cause Cannonsound tells that they only have the dia for 2405.

thanks for any reply

HP

[4313B]

The 075/2402 uses the D8R075 diaphragm. Possible alternatives are the D16R076 and the D16R2405.

The 077/2405 uses the D16R2405 diaphragm. Possible alternatives are the D8R075* and the D16R076.

* Note that I personally have never seen where JBL has specifically stated that the D8R075 can be used in the 2405, only in the 077. I have no idea why.

Both the D8R075 and the D16R2405 are formed from 0.0022" aluminum alloy. Both have a 0.025" gap. Both have a DCR range of 5.7 ohms to 6.7 ohms.

[Mr. Widget]

Originally posted by Giskard


Both the D8R075 and the D16R2405 are formed formed from 0.0022" aluminum alloy. Both have a 0.025" gap. Both have a DCR range of 5.7 ohms to 6.7 ohms.

Hey Giskard,

Are you sure about that? I read somewhere that the difference between the D8R075, D16R076, and the D16R2405 was the moving mass, with the 075 being the one with the most mass and the 2405 having the least mass. Ignoring the D16R076 for this discussion, if the VC and diaphragm material are the same, then how could the mass be different?

Widget

[Earl K]

Hi there

- I have 20 yr old ( Fall, 1983) JBL service info that supports a contention for a different diaphragm mass ( or maybe different coil - though not likely with the duplicated DCRs ) . It comes from a service bulletin ( # 231183 ) that describes the difference between the regular 2404 and the 2404H-1 ( as found in the 4612 ). The published statement is; the replacement of the regular D162405 diaphragm with a D8R075 ( giving a 2404H-1 ) enables a lower cross-over point that's 1000 hz lower than whats recommended for the typical 2404H .

HP : FWIW, those Cannon Sound knock-offs are made with titanium vs JBLs' aluminum diaphragm type. You'll need to collect some opinions on what this swap in metal types may mean to your listening experience.
- On the other hand; the low worldwide prices charged by Cannon Sound put those diaphragms into a category of "Buy it & Try it - You Might Like It" . I'm thinking of buying a pair for my Altec 288s - just to compare against the original Altec aluminum types.

regards < .EarlK

[Dieter]

Hi,

look at:
http://www.jblproservice.com/pdf/Goe...nto%20List.pdf

in this list JBL wrote that the D16R2405 is for 2405 and 2404 and not for 2402.
The D8R075 is for 2402, 075 etc.

I've bought in the past from a guy 2 2405. I wondered, why they sound different. i opened them and i saw that the dias looked different. at one the aluminium dia was wider ( 1 or 2 mm ) than the other.
i asked him, and he said, that a german distributer (Thomann) told him the dias from 2402 and 2405 are the same, but i don't believe. yes they fit the 2402 and 2405, but they are different!
But i don't remember which one was the right one: the wider or smaller.

I hope this helps

Dieter

[4313B]

Originally posted by Mr. Widget
Hey Giskard,

Are you sure about that? I read somewhere that the difference between the D8R075, D16R076, and the D16R2405 was the moving mass, with the 075 being the one with the most mass and the 2405 having the least mass. Ignoring the D16R076 for this discussion, if the VC and diaphragm material are the same, then how could the mass be different?

Widget

What I posted is from JBL's own data. Whether that is correct or not is anyone's guess

Back when I was actually messing around with the 075/2402 and 077/2405 transducers it never occured to me to mix and swap diaphragms so I never actually held both diaphragms side by side to note their similarities/differences. I guess I'm boring in that I only replace a D8R075 with a D8R075 and a D16R2405 with a D16R2405. It would never occur to me to buy an aftermarket diaphragm for a JBL so I can't really help in that respect.

[Hofmannhp]

Hi folks,

first of all....thanks for your ideas....but I'm a little more confused in some points.
Whatever....I learned a lot.....I think I follow the words of EarlK ( the price for testing)...he maybe right....I will try it with some 2405 dias (with least mass). The different mass may be called " a different dynamical mass"-----(called Compliance). The result with a dia with less mass can only be better for what I want. Maybe I can push the high freq section a little over the 15k.
The main thing what I wanted to know was ...does it fit mechanicaly?.....ok.


thanks again

HP

[Mr. Widget]

The aftermarket diaphragms being made of titanium will inherently have higher distortion than the original aluminum ones. This of course may or may not be audible, only a careful listening test will reveal that.

In my experience the titanium diaphragms used in the midrange do suffer a bit from this added distortion, but at UHF frequencies it will likely be much less of a problem.

[boputnam]

Originally posted by Hofmannhp
Whatever....I learned a lot.....

What I've learnt here, and elsewhere, is while swapping can work, best is sticking with design. Anything other is experimentation in something other than ideal (anechoic...) conditions.

But, as has been said, here, so long as no one loses an eye...

[subwoof]

All the diaphrams are interchangeable ( 2402 / 2403 / 2405 ) and are color-coded to distinguish.

As far as the gap, I use a plastic shim set to clean the gaps and all but the 1950's 075's seem the same. Alnico or ferrite.

The PITA alignment posts are sometimes out of alignment and require judicial elongation of the replacement diaphram to make them fit. This then required manual alignment with an oscillator before tightening the horn/wedge/plug located in the center.

If the coil rubs, suspect the magnet is weak and has shifted. ALL that holds them together is the magnetic strength...look ma, no screws! This is the same for the alnico 1" and 2" drivers

As far as thickness, since all else is the same, it seems logical that it's the only significant difference..???

BUT since these can go pretty high, it seems a minor issue if the 2402 can kill a bat while the 2405 can kill a teenage bat.

I have a wall of blown diaphrams that stretches back 30 years for reference sake - all the tweets are in one place and look the same.

One interesting variant was the "OEM" model sold to the railroad industry. They had special diaphrams that **seemed** to me to be stainless steel....?? I have to look and see if I can find one.

sub

[Oldmics]

Quote from Giskard
"Back when I was actually messing around with the 075/2402 and 077/2405 transducers it never occured to me to mix and swap diaphragms so I never actually held both diaphragms side by side to note their similarities/differences. "

Well today I had that very opportunity.To do a side by side comparison.And you know what,appearance wise they are identical.HOWEVER- Now I question the application that is suggested from JBL in Earls post above.
The only reason that I did this is because the opportunity presented itself and I am personally looking for the differences in the older original 075 diaphragms that are rated at 16 ohms.
The D.C. resistance was found to within specs quoted by JBL.The voice coil former height and winding height was found to be the same on both units.
The weight however was found to be different between the diaphragms.This supports both Widget and Earls comments.
Weight was found to be heaver on the D16R2405 diaphragm at 6.5 grams.The weight of the D8R075 is lighter and weighs in at 5.5 grams.I weighed 4 of the 2405 diaphragms and 2 of the 075 diaphragms.The weights found were identical on each of the particular series of diaphragms.So if you don"t know whatcha got-weigh it for the answer!

I measured the thickness of the diaphragm and found the 2405 to be thicker at .050 and the 075 thinner at .045.(I suspect a potential for greater margin for error in my measurements due to the potential "crush factor" of the sandwich of materials).Again ,makes sense.If its thicker it will weigh more.

If the service manual that Earl is quoting from, recommends that the lighter weight 075 diaphragm can be used at a lower crossover point.How is this possible?How can a diaphragm that has less density be subjected to a greater operating range on its low frequency reproduction end where a greater number of non-linear vibrations are prevelant?
Or am I just splitting hairs over 1000 Hz?
Well thats it for todays saga.

Oldmics

[4313B]

Interesting Oldmics! Thanks for the info

[Earl K]

Hi Oldmics

- You've certainly brought forth some conflicting information. You're right, all other things being equal a heavier diaphragm should have a lower Fs. The problem here is that you've measured the weight of the whole assembly including mounting ring .


(A) So, to further your study on the matter here are some suggestions;

(1) Measure the Fs of each diaphragm type when mounted in a 2404. It would be useful if this was done in two ways; with and without the BiRadial horn in place. I suggest a 2404 because the horn should present a noticeable/readable load .

(2) If you have "cooked" diaphragms of each type ; cut away all the diaphragm from the mounting ring and then measure the weight of the mounting rings of the two types.

(B) An offered Adhoc explanation;

- It might be that the 2405 ( 077 ) is "purer" aluminum stock while the 2402 ( 075 ) is built wth a sort of Duraluminum alloy. These 2 alloys will have different Fs points. These two alloy distinctions used to show up in older JBL literature. The two alloy types would have different "fatigue" points .
- And it might be, that we are looking for a "higher" Fs to work within the 2404 horn. Apparently (I've never measured this ) - a properly loaded/constructed horn will "lower" a drivers' Fs. So ; the softer / thicker 2405 may actually have an Fs that drops "too" low when the horn is added. This Fs shift or "unloaded" condition might drive the need for a higher crossover point .

Just a couple of thoughts <. Earl K

[Guido]

Originally posted by Giskard

Both the D8R075 and the D16R2405 are formed from 0.0022" aluminum alloy. Both have a 0.025" gap. Both have a DCR range of 5.7 ohms to 6.7 ohms.

Thats what I found

2402H and 2404H-1 use D8R075 0,0015" diaphragm

2404H and 2405H use D16R2405 0,0010" diaphragm

Of course they are interchangeable

JBL Data somtimes confuse

[Oldmics]

Quote from Earls previous post

"The problem here is that you've measured the weight of the whole assembly including mounting ring ."

Correct

"(2) If you have "cooked" diaphragms of each type ; cut away all the diaphragm from the mounting ring and then measure the weight of the mounting rings of the two types."

This thought came to me as I was ascertaining weather the weight difference came from including the mounting rings or not.The particular diaphragms that I was replacing were cooked and pieces of the voice coil were missing.The required disassembly procedure would have to be preformed on a diaphragm that has all of the materials still intact so correct weight could be calculated.

I am sure that I am not explaining anything new to you here Earl.I just want clairification for anyone else who reads this thread.The real info lays in the fact that the weights were all exactly consistant in the various series of diaphragms.I feel confident in identitfying the two different diaphragms through the weight of each.I also wondered if the stamping angle may be different on the top edges of the aluminum.

If I have another opportunity to do Fs measurements on the driver I will do so.As you know reverse engineering is a job really based upon the tools availiable for the research.My little shop trying to second guess JBL-I don"t think so.

Best regards and thanks for the views,Always appreciated.

Oldmics