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jim henderson
03-09-2005, 09:22 AM
The 2397 data sheet says "recommended cylindrical baffle at least 3 inches above and below the mouth." I haven't seen any discussion here of such a baffle, I've only read of this horn being used in a free-standing configuration or mounted on a flat baffle. Would this horn benefit from a cylidrical baffle?

Chas
03-09-2005, 09:24 AM
I have wondered about that too. I assumed it was meant as a recommendation to somehow maximize vertical dispersion.

Mr. Widget
03-09-2005, 10:04 AM
That combined with aesthetics is why I made my 2397 clones a bit taller. When I mocked them up digitally I found 3" looked butt ugly so I blew that off.

I believe the primary difference is improved vertical dispersion. A problem that I didn't feel needed fixing as I am a "sweet spot" listener. Stupidly I never compared my 2397 clones with the real deal in regards to vertical dispersion.

Widget

Zilch
03-09-2005, 11:20 AM
I am a "sweet spot" listener.Our task is to assist Mr. Widget in rediscovering the unique pleasures of constant directivity. :p

aust-ted
03-10-2005, 03:33 AM
Jim

I have also been wondering about that. I note that a lot of 2397 installations including some I have seen here appear to have the 2397 built into a flat baffle with the curved part sticking out like a pair of lips (eg like the one Ken Pachkowsky uses as his signature pic). Is this what JBL meant by a "recommended cylindrical baffle at least 3 inches above and below the mouth." or did they truly mean a cylindrical baffle? I have never seen a pic of such a beast.

Regards
Ted

Ian Mackenzie
03-10-2005, 04:09 AM
Nice horns Widget.

Ian

Mr. Widget
03-10-2005, 10:04 AM
I have also been wondering about that. I note that a lot of 2397 installations including some I have seen here appear to have the 2397 built into a flat baffle with the curved part sticking out like a pair of lips (eg like the one Ken Pachkowsky uses as his signature pic). Is this what JBL meant by a "recommended cylindrical baffle at least 3 inches above and below the mouth." or did they truly mean a cylindrical baffle? I have never seen a pic of such a beast.



They mean something like this.

Mr. Widget
03-10-2005, 10:07 AM
Here is a shot of 2397 horns in an installation that the original designer of the horn is using. I would guess he knows how to get the most out of them.:) Actually he does... he gave me a couple of pointers which did prove useful.

Widget

paragon
03-10-2005, 10:13 AM
Look this,

jim henderson
03-10-2005, 10:15 AM
What were the pointers? :)

Mr. Widget
03-10-2005, 10:20 AM
I can't give away all the secrets. :)

There wasn't a one size fits all, do this and the horn is better solution. If it were that simple we'd change it and market it.

Widget

John Y.
03-10-2005, 10:21 AM
Jim

Is this what JBL meant by a "recommended cylindrical baffle at least 3 inches above and below the mouth." or did they truly mean a cylindrical baffle? I have never seen a pic of such a beast.

Ted

Ted,

I went through an exercise a while back in a thread I started called
Gone are the 'gons, but why?
In this I showed a concept of a 2397 mated with a metregon-like cylinder which I thought was really cool. It was for a center HT speaker, which I dubbed the "Centregon". A comment was made that I should turn it upside down, but the reviewer didn't understand that I was trying to make a system to fit on the top of a large RPTV, so I needed the horn at the bottom. He sent back an upside down image of my front drawing. I think this would be a wonderful solution for the case where the center would be mounted under the TV display.

Someday I may construct this concept when I change TVs. Meanwhile, there is not enough room above my RPTV sice my back wall slants forward 45 deg. starting 6" above the TV and I could not fit the design into that constraint. My current "Centreflex" design will, and is modular so that I can at least try out a 2397, though probably with less than 3" high lips. I expect to post my centreflex in a few days on a new thread.

John Y.

Mr. Widget
03-10-2005, 10:24 AM
I expect to post my centreflex in a few days on a new thread.

Cool!!!

Widget

paragon
03-10-2005, 11:15 AM
Isn`t it, that a horn has a lower cutoff and a smoother response with a baffle ?

Eckhard

paragon
03-10-2005, 11:50 AM
Ich hab alle Fehler gemacht ! (Marius Müller Westernhagen). = Made all mistakes!
Time is running out. Only five minutes.

Eckhard:D

Mr. Widget
03-10-2005, 12:15 PM
Isn`t it, that a horn has a lower cutoff and a smoother response with a baffle ?


I am not sure... I know that was not the intent of JBL's recommendation, but the low end may be helped slightly. I would rig up a quick test and measure it, but I just sold my last pair of 2" drivers earlier this week.

Here is a plot comparing the TAD 4001 and JBL 2441 both on the 2397 horn. They both show a roll off below about 1500Hz. Interestingly they also show their very similar response curves... it shows how important a horn is in determining the response curve.

Widget

10 Watt Street
03-10-2005, 12:56 PM
There is an article from the January 1951 Audio Engineering by Bob Smith on the Distributed Source Horn at:
http://home.earthlink.net/~buddhaboy2/smith/

Take a look at Fig.6 on pg 2 for a flat front installation!

Steve Gonzales
03-10-2005, 03:49 PM
That is some NICE work there Widget! :applaud:

aust-ted
03-10-2005, 04:55 PM
[QUOTE=Mr. Widget]Here is a shot of 2397 horns in an installation that the original designer of the horn is using. I would guess he knows how to get the most out of them.:) Actually he does... he gave me a couple of pointers which did prove useful.


Widget Thanks. Interesting pic. Is that a small super tweeter mounted directly above the middle of the horn?

Regards
Ted

Mr. Widget
03-10-2005, 05:49 PM
Yes it is a Tannoy super tweeter, It is a pro version of these. http://www.usspeaker.com/Tannoy%20Supertweeter-1.htm

Widget

jim henderson
03-11-2005, 10:40 AM
Is the front-to-back position of that tweeter critical? It's my understanding that time alignment is not an issue around 10 KHz, but I imagine it should be phase aligned.

Mr. Widget
03-11-2005, 10:48 AM
This is what happens at 10KHz when you are about 8" away from time alignment. (Blue trace... Red is with no tweeter.) Can you hear it? Maybe... Would it be better if it were aligned? Sure, all other factors being equal, but they typically aren't all equal. There are reflections to worry about, there is the fact that accurate alignment only occurs at one infinitely small point in space... none of these questions lead to really simple answers... unless of course we are writing ad copy.:applaud:

Widget

For the record this plot is of Project May which is still in development.

Ian Mackenzie
03-11-2005, 12:36 PM
Jim,

I have owned the 2397 and used the 2405 under the front lip lip.

It worked well enough. Of more importance is the true alignment of the midrange driver to the horn especially if using a 1-2 inch throat adapter.

My friend who is an acoustics engineer bought over a digital delay unit one day with an active crossover 3 way and he adjusted the delay to align the mid range driver with the horn driver and we did comparisons.

I was amazed at the difference it made to the imaging. Time alignment is far more crucial in the 800-2000 hz region.


Ian

Mr. Widget
03-11-2005, 01:08 PM
My friend who is an acoustics engineer bought over a digital delay unit one day with an active crossover 3 way and he adjusted the delay to align the mid range driver with the horn driver and we did comparisons.

I was amazed at the difference it made to the imaging. Time alignment is far more crucial in the 800-2000 hz region.

I agree that it is interesting how the time aligning does improve imaging. While true alignment can really only occur for one location in space (as in one ear not both), I did do digital time correction for Project May using the DEQX digital active crossover/DSP and was quite pleased with the improvement. Moving the mic from one position to another did show that the "time alignment" was no longer absolute, but still the sound quality and imaging was significantly better. It also reduced the ripples in the crossover regions.

Unfortunately the only practical way of achieving this is with digital correction and units that are of high enough quality not to cause other problems are still fairly costly. If you try to physically align the drivers you will likely never properly align them and you will also find them physically interfering with each other.

Widget