View Full Version : 2397 horn - varnish and adapter

09-23-2004, 08:38 AM
I am planning to biuld a 2397 horn for my 2420 driver .

I do have drawings for a 130 horn , 5 island 2167 each other and i need advise for the following .

1. Should I varnish or not inside of the horn ( better or not for the sound ? )

2. I have to make an adpater like 2328 I believe from 1inch round to 4 inch square ( 10 cm ) about
It should be in wood as I can't get original .

An otehr option would be to make a direct opeing 1 inch on the horn instead of 4 ich square but i ma afraid the opening would not allow the air and sound to go in all the side of horn ; wiht zn adapter it would open better the diffraction !.

Any advise .

Best regards


Mr. Widget
09-24-2004, 10:04 AM
I will post a couple of drawings of the 2328 throat adapter and of a prototype 1" to 1.375" X 4" adapter. I will need to convert them to jpgs and scale them. Got to go to work now...


09-24-2004, 10:30 AM
Mr Widget .

Thank you so much i shall wait for it.

Best regards

Gerard Mihel

09-24-2004, 11:10 AM
My god,
Casablanca, Humphrey Bogart, great.
Yes, try a 2397.
It`s the best horn i have heared now for the 2441.
You doen`t hear a horn is working !
Widget knows a mouch about.

Best Regards

Mr. Widget
09-25-2004, 12:28 AM
Here are the interior dimensions for the 2328. The surfaces are quite complex and I can not begin to draw all of the subtle transitions. If you blow this drawing up to full scale you will be able to get reasonably close.


Mr. Widget
09-25-2004, 12:36 AM
This is a simplified 1" adapter that has a conical section that increases in size from 1" to 1.375" in the vertical and to 1.517" in the horizontal plane before changing to a 65 degree sloped side. This adapter will outperform the 2328 and 2327 combo.

I hope this makes sense.
Good luck!


John Y.
09-25-2004, 01:12 PM
Originally posted by Mr. Widget
Here are the interior dimensions for the 2328. The surfaces are quite complex and I can not begin to draw all of the subtle transitions. If you blow this drawing up to full scale you will be able to get reasonably close.

Excellent contribution to our data base. It would help if you could generally define the cross section of the bulge at the point where it reaches the 2.545" maximum point. Is it elliptical, or does it have flat top and bottom with smaller radii to blend with the sides?

This adapter could be made by making a solid and using that as a form with which to mold fibreglas or other resin material. The solid could be made of several pieces that would disassemble for removal from the finished piece.

John Y.

Mr. Widget
09-25-2004, 02:58 PM
Basically the shape is a blend of many radii. It is nearly circular at the bulge with four distinct surfaces becoming evident after the bulge as it approaches the rectangular opening. My guess is that it was described in a multi-view drawing much like the one I have created, but with additional dimensional call outs and then left to the pattern maker to sculpt it out of wood and bondo. The transitions are not very well defined. I have compared half a dozen of these to get these curves. Oldmics lent me one that was from the earliest series. It has a different outer shape and bolt pattern. It is 4" wide at the opening and 4" long. All of the newer ones are shorter and have a variety of opening widths with the widest ones approaching 4".

On top of that, since they are sand cast, they are all a little different changing as the pattern wears. Each new series would theoretically return closer to the original. I would expect the original drawings are gone, but maybe they will turn up.

I started to make a new pattern to sand cast a new run of 2328s, but decided it was easier to buy them so I lost interest in the project. The current eBay prices for 2328s made the idea more interesting, but I would need to sell 20 pairs or so at $125 per pair to make it worthwhile. I don't see that happening.


09-28-2004, 02:49 AM
Mr widget
thank for the drawing .

Question : should I varnish the inside of adapter and horn or not ? or shall i use a special product to get the best reflection ? .

thanks for advise .

gerard .

Mr. Widget
09-28-2004, 10:19 AM
I have been told by two sources more knowledgeable than myself that the interior surface of horns is very critical to the final sound. One swears by a special paint made by 3M called Nextel. It has a light texture and almost rubber like feel. The other source says that you want the surface to be a smooth as glass and as hard as possible... these two sources are absolutely contradictory.

I have heard horns made by both of them and they both sound good.

For my wood horns I finish them inside and out to 600 grit and carefully oil them. I think my horns sound pretty good too.

JBL seems to have made their horns ranging from rough sand cast, texture paint, rubber like paint, sonoglass that is highly polished... I guess they aren't very consistent either. Now in their case I don't think all of their horns sound pretty good, but I doubt it is the finish.


09-28-2004, 10:49 AM

ok I will go to oil inside

bestv regards


09-30-2004, 02:52 PM
Hi Gerard,

I don't want to get you off of your cloud....but I have to tell you that my experiances with 2397 and different drivers like 2441 and 2420 told me (very clear) that it's a big difference in sound to use a 1" driver with the 2328 and an additional 2327 throat adapter on the 2397.
The sound is very different (for my opinion)...short....a 2" driver sounds a lot better.

(my 2 cents)


Mr. Widget
09-30-2004, 08:29 PM

That is exactly why I also included the 1" adapter throat. It should offer a significant improvement over the 2328-2327 combo. I agree however that the 2441 is more ideal.


10-01-2004, 02:28 AM

I have a 2420 so I have to go with it .

i will make the new adapter ....



Mr. Widget
10-01-2004, 09:51 AM
I am building a similar adapter that will allow me to use a 1.5" driver on my "Westlake" version of the 2397.

Let us know how your project turns out.


10-01-2004, 10:56 AM

Nice drawing .
I will advise when I will first finish the 2397 ....


10-31-2004, 05:27 PM
Widget has done great ground work on adapting a 1.5" driver to the 2397 and similar horns. On another thread where this came up Earl raises interesting theoretical questions which suggest that the horn and driver are best designed as a whole.

On a related question I have been wondering if the 4" diaphragm 2447 and the smaller 2435, both of which have a 1.5 opening, use the same horn? I don't see anything in the JBL literature that suggests they can.


Earl K
10-31-2004, 05:36 PM
Hi Dave

re; mating the 2435 to the 2397.


(a) If it was my project, I'd ask Ken Pachkowsky to take an internal lip to lip measurement of the 1" Smith Horn, as found in his Westlakes.

(b) Then I'd look the Mr. Widgets' measurements to derive the average height
inside the more or less horizontal part of the H9800 diffraction portion of that horn.

(c) Then, see if you can get a measurement of the diffraction Slot-Opening for the large Vertec SR box that uses the 2435.

(d) Take a measurement of the ( 2397 ) height between the top & bottom plates.

(e) Compare these four figures. Some design commonalities should come to the forefront. What to determine ; The best ratio of ;Compresson Driver throat exit size to distance between the top and bottom horizontal lenses.

Some History :

The predecessor to the Smith type horn is the "parabolic horn" as described by H. F. Olson ( of RCA ) in the mid fifties. Drawings show a virtually identical horn - though minus any internal vanes. I believe the aspect ratio he used was .5, when comparing the drivers' exit size to height between horn bells. It's the velocity buildup that occurs when forcing sound through a smaller apeture, then followed by presenting a wide low-pressure horizontal zone, that forces the sound to spray and spread. The reason a one exit driver coupled to the 2397 doesn't work is because little to no pressurization actually happens. Additionally, the 2327 adpater goes the wrong direction from a pressure perspective.

My Conclusion : I'd be thinking that I need to shrink the mouth height somewhat for this Smith horn ( for use on a 1.5" exit driver ).

Just my thoughts :)

<> Earl K

EDIT : Alex has asked ; What are the purposes of the vanes in the Bell ?

The original parabolic horn without the vanes shows great dispersion in the upper regions. The book has polar patterns included. It's in the lower octave that dispersion suffers ( without the vanes ). This leads to an assumed conclusion that just can't be tested till someone makes ( & tests ) a large Smith Horn without Vanes. It might be worthwhile to ask Ken if the small 1" Smith Horns ( in his Westlakes ) have vanes .

Ken Pachkowsky
10-31-2004, 07:15 PM
The small Smith horns on my Westlakes have no vanes and are 13 x 3/4 inches at their widest point.

Ken Pachkowsky
10-31-2004, 07:21 PM
The small Smith Horn is used from 4.5K to 20K but drops off very fast after 16K. They are powered by a JBL 2426H


Earl K
10-31-2004, 07:33 PM
Thanks Ken !

- Did you already state it as being 3/4" - if not - again, what was the height of the slot ?

Thanks <. Earl K :)

Ken Pachkowsky
10-31-2004, 07:35 PM
My fault, was not clear.

The opening is 13 inches wide by 3/4 of an inch tall.


Earl K
10-31-2004, 07:37 PM

Alex Lancaster
10-31-2004, 11:00 PM
Love that leery Westlake smile.

Ken Pachkowsky
10-31-2004, 11:03 PM
I just purchased a pair of 2405 alnico's that I ill be adding to the HR-1's. Widget convinced me this could be an interesting experiment.


11-02-2004, 05:33 AM
What is the distance from the throat to the front lip. Just trying to picture the overall shape. Thanks. John

Ken Pachkowsky
11-02-2004, 06:04 AM
The distance from the throat to outer lip is 9 1/2 inches measured at the center.


S Boat
01-24-2006, 09:35 PM
Good evening gentleman

I bought myself a JBL 2397 with the intention to quarter it; scan it to solid works then sent the G codes to my CNC router and make (4) for my boat. Yes boat. Trust me you have not lived until you ride the ocean swells out of the sight of land at 50+ with a 110 db masking the sound of the wind rushing by. Just raw awsom but it takes power and efficiency to do it and that means horns, clean smooth horns.

I Anyway went on line looking for 2328-2327 throat sections and found your site, Seems you all are already on the trail.

I need to drop to 1" because at this point I am attempting to milk suficent high frequancy without seperate hi frequancy horns.

Right now I am tri amped 31hz to 90hz then 90 to 1000 up.

Chasing wooden horns for warmth of tone as boats by nature have very hard reflective surfaces.

Anyone see any reason not to just CNC the horn and adapters all one piece, actually make two open halves and glue them together?


Mr. Widget
01-24-2006, 10:13 PM
I've beat you to it. Send me a PM with your e-mail and I'll send you the 2397 as a Solid Works file.:)

I'd stick with the 2328 due to the structural requirements to support the very heavy 2" throat drivers. I'd also highly recommend you step up to the 2" exit drivers as they are really necessary to get the full potential of that horn. The 2327/2328 combo with a 1" driver sounds very honky. With the 1" exit driver you loose the warmth you are after... it isn't due to the metal either... I've made wooden and plastic adapters.

In the thread below you'll notice that I did thicken the outer section though.



01-31-2006, 03:12 PM
Hi Mr. Widget!

I sent a PM regarding the CAD files!


10 Watt Street
01-31-2006, 03:33 PM
According to the JBL sheet for the 2397:

It mentions "Vertical dispersion is largely dependent on the baffling; with the recommended cylindrical baffle extending at least 3 inches above and below the mouth, a nominal 60 degree vertical beamwidth is achieved."

Is the Westlake profile equivalent to the "recommended cylindrical baffle"?

Mr. Widget
01-31-2006, 03:42 PM
According to the JBL sheet for the 2397:

It mentions "Vertical dispersion is largely dependent on the baffling; with the recommended cylindrical baffle extending at least 3 inches above and below the mouth, a nominal 60 degree vertical beamwidth is achieved."

Is the Westlake profile equivalent to the "recommended cylindrical baffle"?No.

10 Watt Street
01-31-2006, 03:58 PM
Then I don't think I've ever seen an installation with the "recommended cylindrical baffle extending at least 3 inches above and below the mouth".

Why is that?

01-31-2006, 06:00 PM
That would probably be something like this.

01-31-2006, 08:50 PM
Thats very interesting. Could we get some more pics of that speaker please?

02-01-2006, 03:10 AM
Don't know any more than this thread states.

02-01-2006, 04:44 AM
Thank you.:bouncy: