General Opinion on JBLs' 4" diaphragms
Hi Scott
As promised, here's my subjective opinion / bias about JBLs' larger format / 4" metal diaphragms .
I find them all ( excluding the 2450SL & 2482 ) to sound somewhat underdamped ( & that includes the 2441 ). I've never listened to a "bubble-backed" 375 ( or the other K2 diaphragms ) so I have no opinion there . I'm talking about listening to them in smaller rooms and not in large areas where the air volume helps mitigate some of these impressions . It's somewhat like " Don't point that thing at me !!! " :die: or " I'm out of here " :dancin: .
That's usually my thought process when confronted with these large beasts ( on small or big horn or softened up by diffusers) . My Altec 288-8K drivers aren't like this ( of course, that dome has only 1/2 the surface area which immediately rebalances the all important paper to metal ratio ) . The 2450SL/2440 has the ability "to get up close & personal" without it being hurtful :biting: . Maybe my combos are actually in a misfit situation with the whole drivers ( especially 1st gear ) torque curve thrown out of whack . Don't know / won't know until that time comes that they ever do a high level SR job - but not planning on that . I do know I like this combo alot . :bouncy:
regards <. Earl K
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Speaking of Torque Curves
Hi Scott
Glad you like your 4002s. In my case, I've been ruined, in as much as I have a tough time listening to 1.75" diaphragms ( no matter who makes them ) - the loss in resolution or clarity is just too great to accept - when I know I can easily restore it by just grabbing some larger format drivers (off the proverbial shelf).
In addition to the berylium diaphragm , I think the addition of the 5th slit in the 4001/2 phasing plug makes a big difference to the response of the large TAD drivers. Even the Radian replacement diaphragm ( the 1292 ) has roughly an extra 10 db of top end when compared to the JBL replacement type. Both Radian types use a .08 mm aluminum dome with mylar surround - strongly implying, it's not all about the metal type.
I've heard those mesh screens on the back of the diaphragms are a protection feature in case the dome ever particalizes ( I believe the theory was to prevent the berylium parts from being inhaled - since berylium oxides are cancerous ). For a hoot, here's a picture of an early "blast-screen" - this is from a 50s vintage RCA driver meant for naval duty . I might eventually turn these 180° and create a phenolic based, 093 standin .
regards <> Earl K