Hello,
At the exact moment i began reading this thread i had the opportunity to buy a pair of JBL 2397. I have a pair of 2445H with Radian diaphragms on Iwata horns.
I put the 2445 on the new horns, and ... not better, Iwata rules.
I decided then to measure them outside in the garden.
I then compared my measurement of the 2397 with the one made by Widget
very interesting, thank you for posting that!
That 700Hz suck-out appears clearly on both measurements, I wonder what could be its cause.
550 and 350 are opposite, 700 is the same, except that on Iwata it's smaller.Originally Posted by pos
I think all the irregularities below 1000 are caused by the mouth and the brutal change of direction of the sound waves in the 2397, less on the Iwata which has lips more curved. J M Le clea'ch has showed the importance of the mouth, look at his circular horns. If the mouth is cut sharply, the waves go back in opposition.
The Iwata expansion is made on all directions, everything is curved, the 2397 has straight lines which are interrupted suddenly. (i have some difficulties finding the words to express myself clearly)
I'm pretty disappointed by the 2397, i'll stick to the Iwata.
550 and 350 are opposite, 700 is the same, except that on Iwata it's smaller.
I think all the irregularities below 1000 are caused by the mouth and the brutal change of direction of the sound waves in the 2397, less on the Iwata which has lips more curved. J M Le clea'ch has showed the importance of the mouth, look at his circular horns. If the mouth is cut sharply, the waves go back in opposition.
The Iwata expansion is made on all directions, everything is curved, the 2397 has straight lines which are interrupted suddenly. (i have some difficulties finding the words to express myself clearly)
I'm pretty disappointed by the 2397, i'll stick to the Iwata. Being smaller i intended to use it from 1000Hz, but the response is not smooth enough.
Re the 700Hz suck-out, I was thinking about yours and Widget's measurement of the 2397.
Maybe using some putty to smooth the 2328/2397 transition would help in this matter?
Sorry, i misunderstood. But the explanation should be the same, because it's the same horn, surely a phase problem at the mouth.
I imagine that it all comes from the desire to spread the directivity widely on a horizontal plane, which makes it particular, and the straight walls (easy to do).
It pleased me to see that, with a different driver, certainly different measurement tools and more than 6000 km between Widget and me, the results were pretty close. The only thing we had strictly in common was the horn, so the problem lies there.
What bothers me is not especilally the 700hz suckout which is a bit narrow but the general hole between 600 and 1200 with only a few peaks
I don't know if puttin putty will be enough to remodel the mouth and stop the phenomenom but it is worth trying, another option could be to absorb those waves at the mouth with anything, maybe a baffle with rockwool? But in any horn the most important thing is the shape and that can't be changed
Another option is to cut them above 1000 Hz in a 4 way system but the response is still a bit cahotic. Maybe a little EQ ?
Best regards,
Jean
JBL recommand to use 3" lips above and under the horn:
http://www.lansingheritage.org/image...2397/page1.jpg
Maybe that would help wirth.
One could also fill the 2397 with reticulated foam, ā la Geddes...
Concerning your measurement, I guess the iwata horn was much taller than the 2397, so at 50cm the diffraction from the mouth was less of an issue.
I guess the differences would be less obvious at 1 or 2m.
Far from that, the farther you go the flaws of each horn grow bigger. To show you i join the measurements made at 2 meters, still in the garden.
By seeing the response, it's easy to see why the Iawatas are filtered at 600Hz.
This should make You doubt about the measurements.
You should measure in the far field, and away from reflecting surfaces. The ground plane is one.
If You can't do that, and if You can't do neither a ground plane measurement nor a gated measurement, then You should try to find an explanation for the peaks and dips.
You could make a measurement with the loudspeaker pointing up, and some measurements off-axis. Maybe this sheds some light on what is happening there.
ruediger
hello,
i'm well aware of the limitations of my measurements, and i take them for what they are, and i invite anyone who can do more accurately to proceed and post the results because i don't see many.
I went to the garden with no wall around but there is always the ground plane. I could try to put the horns and the mic higher but the Iwatas are very heavy. I will try pointing up next time, but there will still be the ground effect. The close measurements already tell the tale, i made those from 2 meters just out of curiosity.
Anyway, i usually listen on the ground, so how they behave in that position concerns me
I have just bought the 2397s, and wanted to compare them to the Iwata to make a choice. All things being equal, it's obvious that the 2 horns are very different, i don't think that the ground should affect one more than the other.
As it is the 2397 has a very wide vertical dispertion, and needs 3" lips to achieve 60°. That might be a part of the problems shown in your measurements.
You could try to mount two 3" curved baffle around the mouth to see how things improve.
You could use thin mdf or even cardboard
Yes, that's an option, i will try it in a few days , but it will not take away the sudden change of expansion between the horn and the lips or baffle. I will try all the options before taking a descision on their fate.
I looked at post #21, JBL sure have nice graphs on their brochures! I see also that the lowest recommended crossover frequency is 800 Hz, which i would push up to 1200 (in a 4 way system that i'm building with a 2123H for the low-mids), so the problems below are not that important to me.
I'm more concerned by the response above 1000. I was trying to replace the big iwatas (crossed at 600 in a 3 way system until now), but it appears that they still might be better from 1000 to 8000 (with a little compensation they are flat up to 8000).
to be continued....
When You do new measurements:
1.) write down the exact height of horn and microphone, and the distance from horn mouth to microphone,
2.) take measurements at several distances between horn and microphone, vary the distance irregularly, not in equidistant steps,
3.) do some off-axis measurements as well.
ruediger
i agree , i did many of that but did not post it : 30 cm, 50cm, 1.50m, 2m 30°, 45°, i did some indoors also. In similar positions and distances, each horn kept his own personality. I suppose that if i put them both in better diverse positions the differences will still be there.
The goal was for me to see if 2397 could replace the iwatas in a 4 way speaker (more convenient size). I'm not doing 2397 bashing, i bought a pair based on the beautiful models presented in this thread, i've got 2 pairs of horns now and must decide which one to use.
In a few days i will try a new set of measurements to let no stone unturned, but it would be great if among the readers of this thread (who might have 2397s or westlakes) some would make some measurements for a more wide perspective.
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