Is There a Difference Between a Tangential 2420 and 2410 Diaphragm?

[toddalin]

I always favored the LE175 to the LE85/2420 because of its "warmer" sound. But at one time I came across a pair of 2420s with tangential diaphragms. These had much of the warmth of the LE175, but a bit more extended at the top end and these became my L/R replacing the LE175s.

But my center channel has a 2420 with an aluminum diamond surround (typical). I came across a single, reported original, unused, 2410 tangential diaphragm and am wondering if this would be identical to the tangential diaphragms in the 2420s. I guess I'm asking if the 2410 and 2420 used the same tangential diaphragm back in the day or if the 2420 had a slightly different piece in there, like they did in the ring tweeters?

One for the old timers.

Thanks

[1audiohack]

From memory;

The difference between the 175/2410 vs the 185/2420 is the silver ring on the pole for better HF on the latter. Later the 2421 got the diamond surround and kept the silver also.

Barry.

[toddalin]

Both did.


http://www.lansingheritage.org/images/jbl/catalogs/1971-pro/page11.jpg

[1audiohack]

Memory jog;

I forgot that 2410's are the little ones. There is something different and I don't recall exactly. There is a 2410 being used as a door stop at my friends shop because he couldn't get a phragm for it. He would have loaded a 2420-2421 in it if that would have worked.

I just looked and it appears JBL has D16R2410's on the shelf, no D--R2420's though.

I get that none of that answers your question. If no one else gets to it I will find out tomorrow and let you know.

Barry.

[1audiohack]

I am at a dead end on this one. Since there is a part number specific to the 2410 there must be some difference.

The 2410 door stop my pal has is fitted with an aftermarket phragm that is dead anyway. Neither of us wants to buy one just to know.

If you find something definitive I would like to know.

Barry.

[Doc Mark]

Greetings,

I have 2420's, with original diaphragms, and also one LE175. I have never opened the 175, and seem to recall that it has the red JBL sealing wax on the screws. How can I help you learn what you want to know, Todd? Want me to crack open the 175, and compare it to the 2420? Let me know, and I'll be happy to help you, if I can. Take care, and God Bless!

Every Good Wish,
Mark

[Earl K]

I am at a dead end on this one. Since there is a part number specific to the 2410 there must be some difference.

The 2410 door stop my pal has is fitted with an aftermarket phragm that is dead anyway. Neither of us wants to buy one just to know.

If you find something definitive I would like to know.

Barry.

I was curious as to what you might uncover ( since you have some good sources ) .

Anyways Todd ( Barry ), the diaphragms are indeed different ( not only do they have different part numbers, but they also officially had different DCR's [range wise ] from each other ).

An ancient JBL Pro-Note ( never published here at LHF ) made mention that contractors might "temporarily" substitute a 2410 diaphragm into a blown 2420 ( when a replacement D16R2420 wasn't immediately available ) with the understood consequence of decreased power handling .
- That's enough for me ( that the info strongly implies ) that the 2410's VC is made with a lighter gauge winding.
- The diaphragm might also have been made of lighter Al stock ( or perhaps a different amalgam or maybe just a different glue technique ) .

An interesting experiment would be to do a distortion test of a 2410 diaphragm working in a ( up to spec ) 2420 magnetic assembly .
If increased HF performance ( as well as distortion ) was measured, then the results would point to the lighter diaphragm theory .

Here's a bit of Altec trivia regarding the construction of their different voice-coils ( this is mid to late 70's info gleaned from an eBay seller whose mother wound voice-coils for the company ).

http://www.audioheritage.org/photopost/data//500/Altec_Tabulation_Block_.jpg

:)

[1audiohack]

Hi Earl;

Hmmm that is enticing information. I found in the literature while looking that the dome was the standard 0.002" thickness. Another added possibility is the dome is closer to the phase plug to extend the HF. That combined with a smaller coil loaded into the stronger 2420-2421 (tel:2420-2421) motor might be a sweet combination for home level playback.

Damn! Now I might have to buy a pair and see.

Barry.