JBL2328 adaptor

[Flemming Skov]

Hi,

I hope this is a small question. Does somebody know the characterisitc or so to say the behaviour of the adaptor?

The inlet has a area of 0.002 m2 and the outlet is rectangular with an area of 0.0032 m2. Is it a exponential development or???

I want to use it in my design of a radial woodhorn due to the fine attachment to the horn and driver

My horn calculations start with the throat size of the rectangular area. Should I keep an area, in the room just in front of the 2328 free as seen on the smith horn (so to say a half circle with the radii of half the width of the 2328)?

Any comments is appreciated and already thanks to yggdrasil.

Flemming

[reVintage]

Hi Flemming,
I have done some approximate calculations for various horn types for 375/2441+2328. The problems is the two parts differ as Exp flare is ca 180Hz for 2441 and around 160Hz for 2328! These are my findings for 11,5cm2-32,5cm2, length 17,3cm from phaseplug:

Exp: 2441 alone 180Hz, both 165Hz
Hypex 0,8: 2441 alone 210Hz, both 185Hz
Hypex 0,707: 2441 alone 230Hz, both 200Hz

(Tractrix&Kugelwellen: 2441 alone 180Hz)

Have done these calculations as my idea is to design my midrange horns around the drivers flare, even if they are to be used from 4-500Hz:

They will be Hypex 0,707, 90 degree(as the 2328 has 90 degree opening) 3,5cm Smith, followed by a radial expansion the last 35-40cm. The length without driver and 2328 will be just above 60cm with a mouth height of 23cm and 90cm width.

But will not build until I have tested my "511 massacre".

Brgds
Lars

[reVintage]

I now remember I have seen figures of 160Hz flare for the OS JBL 2" drivers in a Tech. paper from JBL. I did my measurements from the mesh, 38mm dia, and to the front of the driver, 49mm dia, and length 75mm. This corresponds ruffly to 180Hz. Maybe one should take the phaseplug in account too?

[reVintage]

Had to recheck the 2441 and I was wrong! These are the right figures:
L=69mm
Dia1=38,5mm
Dia2=48,5mm
This corresponds to 183Hz for an exponential flare.
About the 2328 it still measures around 160Hz flare.
If we add the gasket we get a total length of 16,8cm and 170Hz if we only check initial and final area. But the section will then be a litte wide in the middle part.
If the final height of the 2328 was 3,8cm the whole section would be 183Hz flare.
But as the 2328 is a 90 degree radial adapter maybe there are some hidden secrets in it!

[reVintage]

Hi again Flemming,
Sorry to trash your thread but I think I finally have solved the 2328 mystery!
In an old thread Mr. Widget mentioned that he had measured a pair of "pre JBL Pro" 2328s and they where 35,6cm2 at the mouth. This means that the 2328 also was thought to have a flare of just above 180Hz.

[yggdrasil]

Hi Flemming.

Have you downloaded David McBean's Hornresp program? http://audioheritage.org/vbulletin/s...light=hornresp

This program is very useful when you deal with different throat's and throat adaptor's.

The program takes a few iterations to get used to, but after a while it gets you there.

You will have to enter the driver throat as section one and the throat adaptor as section 2. You will also have to do some research in order to get the driver parameters close to correct.

reVintage: I don't think you should assume the phase plug as a section, rather a front chamber.

Additional, very interesting reading in audio express: http://www.audioxpress.com/magsdirx/...olbrek2884.pdf
http://www.audioxpress.com/magsdirx/...olbrek2885.pdf

The authors homepage: http://www.geocities.com/la1zka/

[reVintage]

Hej yggdrasil,
First I want to say that I am impressed by your homemade radialrouter! About the phase plug you might be wrong about the front chamber but I am not completely sure.
Did a checkup on an Altec 808-8A without dia that I had lying around and the flare seems to be just below 300Hz even measured from the beginning of the plug. Measured after the plug it also seems to be about the same. It would be interesting to check one of the Meyer/2441s I have but will not do it until they need service.

About Hornresp I am not so impressed by it´s virtues for other than bass horns. For instance neither kugelwellen(spherical) nor tractrix is accurate enough. I have made a model of 2441 as driver in Hornresp after a tip from leCleach but I am not sure how accurate it is. Think it needs a little more work.

IMHO it is better to use the formulas in an Excel spreadsheet to begin with. This also goes for Exp and Hypex. To calculate a radial horn you really have a great help by Excel, too.

About the later 2328s I think it will be an easy task to machine them become their intended 3,5*10,2cm mouth to get the same 180(183?)Hz flare as the driver. Mine are 3,5*9,5 and the casting does not look to impressive. I also measured the opening angle and it is 88degrees on mine. This also indicates that they should be widened. Probably they will be 90 degrees when widened to 4".

Brgds
Lars

[reVintage]

Theory of the 2328 form:

It is nearly equivalent to the first part of a 511 horn, but for 2" driver and exponential 183Hz flare. Of course everything is smoothed out, refined and rounded in the 2328. Also the 2328 is different from the theoretical model as it is a little widened at the throat and diminished at the mouth. The first part is a round to square adapter of about 7,5cm length. The second part begins where the 90degree sides have the same width as the square first part(and the second and first part areas are the same) and ends when the width is 4". I hope the sketch I made in MSPaint is understandable:

[Flemming Skov]

Hi reVintage, Johnny

Thanks for your effort and posting. 14 days after my thread was started, I did a trip to Antwerpen to pick up two 2350 horns, which are, as you can see on my little icon, what I'm using now a days. I have completly forgotten this thread

But a question anyway, should I understand your findings (fc=182Hz) as the lowest possible frequency, by use of the 2328 adaptor, is around 364 Hz?

Regards
Flemming

[reVintage]

Hi Flemming,
The lowest frequency to be used depends on what type of horns you use. But you can without problems make a horn that works well below 300Hz. For example if you make a 180Hz Tractrix it will work down to where the length (from phaseplug of the 2441) corresponds to 1/2 wavelength. In this case ca 240Hz but the driver should not be used lower than 300Hz for use at home and 500Hz for PA.

[Jan Daugaard]

I know the adapters in the H2600, 2346 and Everest DD66000, and they are all conical, i.e. they have a linear expansion of the cross-sectional area.

There is an exact way of making the transition from circular to rectangular while retaining the linear expansion, but a CNC mill is required to make such adapters. The picture below shows the two halves of my DIY Everest DD66000 adapter.

[Joe Alesi]

Hi reVintage, Johnny

Thanks for your effort and posting. 14 days after my thread was started, I did a trip to Antwerpen to pick up two 2350 horns, which are, as you can see on my little icon, what I'm using now a days.

Hello Flemming,

Nice to meet. For some time I have been thinking of buying some 2350 horns that are available to me, but always thought that when I get around to using my 2440/1s I would make a nice wooden Smith horn just as you planned. Things are moving slowly- I have yet to take the plunge. I would therefore be interested in your opinion of the sound of your 2350 horn. Which driver are you using with it?

Thanks in advance.

Best
JA

[Flemming Skov]

Hi Joe,

Nice to hear, that someone else is planning to use the 2350's

I'm using the horn with the 2445J (PL) driver. I have been using 2380 (the first, and also the worst sound due to no eq. of the signal, in my set-up), then 2397 which is very linear and good sounding, but lack's the low end.

I'm using the 2350 on axis and maybe +/15 deg. and very pleased by the sound. I have measured it in the "chamber" and was surprised by the flatness. My LF 24dB/oct filter gives a littel surplus around 2K, where I'm using a kind of notch to take out 1.5 to 2.5 dB. I'm driving it from 440Hz and up to 7K. The horn is the best I have done for my set-up!

Regards Flemming