2328/2397 transition

[jim henderson]

My 2397's have a 4.25" wide mouth and my 2328's have a 3.75" wide mouth. Shouldn't that transition be smoother?

[Mr. Widget]

Hmmmm... you seem to have a pair of each that are at the far end of their tolerance range. All of the 2328s I have measured have been under 4" (typically 3 15/16") except for the very early one I borrowed from Oldmics that was pre JBL Pro. It is an entirely different casting with the same internal geometry and a different external shape. It has an opening of exactly 1.375" by 4". The 2397s are supposed to be 4". I have noticed that they can vary and even the vanes can be mounted crookedly in the horns. When I did my research to generate the 3-D geometry for machining them I found that original JBL 2397s were not even axially symmetrical.

You have to remember that these were built pre CNC using templates and guides.

Widget

[subwoof]

I had a group of 2397's that also were all over the map on width.

When I rebuilt them I used a sheet of 1/16 3 ply birch plywood that was machined with a router and gorilla glued them to the particle boardface. Then I used a file / filler ( if needed ) to make the transition to the horn sides smooth.

These were NOT held to a good tolerance - much like the particle board cabinets of the 70's...

sub.

[jim henderson]

Here's the 2328's.

[Mr. Widget]

Hi Jim,

I am afraid there is little you can do. You do seem to have some parts that are at the fringe.

Are you happy with the sound? Realize there is a bit of a mid peak that is best tamed with delicate EQ to get the smoothest sound from the 2397s.

Widget

[Mr. Widget]

The 2397s are supposed to be 4".

I would like to make a partial retraction. While I do believe the JBL target was for a 4" throat opening on the 2397, I believe they are meant to be slightly over that dimension as you would never want the 2328's exit to be bigger than the 2397 throat opening.

I had measured several 2397s before generating these drawings... I recently dug them up for a fellow forum member and noticed the dimensions.

Widget

[aust-ted]

Jim

Just had a thought from left field. How about using a piece of wood to as a transition piece fit between the 2328 and the 2395 with angled sides to the rectangular hole, like a thick gasket.

That would put the throat back about an inch. Would that pose a problem?

Regards
Ted

[Mr. Widget]

Jim

Just had a thought from left field. How about using a piece of wood to as a transition piece fit between the 2328 and the 2395 with angled sides to the rectangular hole, like a thick gasket.

That would put the throat back about an inch. Would that pose a problem?

Regards
Ted

Here is a custom throat I have tested. It has a smoother response above 1500Hz than the 2328. There is a sacrifice in lower frequency performance.

Widget

[Mr. Widget]

For anyone wanting to build their own 2397s you can blow up these details to full scale and use them as templates along with the other drawings posted.

Widget