Horn-Ringing with 2390

[Dr.db]

Hey guys,

I listened to my 2440`s on 2390 horn/lenses the other days a little louder. About 2-5 watts...

I haven`t listened to them that loud before and I noticed some annoying horn-ringing... Is that possible or might it has been something else causes by the 2440 driver itself !?
Does this horn tends to ring or is it a rather quiet horn ?

Thanks a lot,
Olaf

[10 Watt Street]

Are they mounted to a baffle?

Horns/lenses that are sitting in the open on top of a cabinet can ring.

[Dr.db]

No, they`re just sitting on top....


Do they loose their ringing when mounted to a baffle due to coupling to more weight ?

[10 Watt Street]

The front baffle adds rigidity. You can also place the horn on a sandbag and place another sandbag on top.

[10 Watt Street]

Are you slant plate diffusers (lenses) mechanically tight? Some of them have small felt damping pads between the plates which works well.

[more10]

Just knock on the horn and you will hear the ringing. Then hold the horn with one hand and try again, ringing should be gone. It is impractial to hold the horns while listening though :)

[ivica]

Hey guys,

I listened to my 2440`s on 2390 horn/lenses the other days a little louder. About 2-5 watts...

I haven`t listened to them that loud before and I noticed some annoying horn-ringing... Is that possible or might it has been something else causes by the 2440 driver itself !?
Does this horn tends to ring or is it a rather quiet horn ?

Thanks a lot,
Olaf

If You are talking of say 4 W, using 2440 driver, expectable sound level at 1m would be about 113dB !!!!
- so, first what was (and what kind of) hi-pass network used. Suggested has to be OVER 800Hz
http://www.jblpro.com/pub/obsolete/Acoustic_Lens_Family1.pdf

regards
ivica

[Dr.db]

Hey,

the slant plate diffusers (lenses) were mechanically tightened, no felt or damping in between... You wouldn`t have a picture of that, would you ?


Crossover was passive and at least 800hz, I believe it to be somewhat higher. But this wasn`t the final solution, just something for a quick try...
My Toshiba`s VU-meters told me aprox. 2-5 watts, but this is for 8ohm.... Might be half of that, because drivers are 16ohms...


I think you guys calmed me down, I don`t have to start rethinking my horn-selection and bother building wooden horns....

[Dr.db]

BTW;
can the acoustic-lense be flush-mounted in the baffle ? So the sides of the lense are masked completly by the baffle...


The JBL L220 uses some lenses to and they seem to be flush-mounted:

http://img.canuckaudiomart.com/uploads/large/125216-jbl_l220_l220_oracle_stereo_speakers.jpg

[10 Watt Street]

http://www.lansingheritage.org/images/jbl/specs/pro-comp/horns-lens/page3.jpg

From the 2390, 2391, 2392 and 2395 Data Sheet linked above:

"The lens requires a baffle to function properly in the crossover region. If the 2390 is not mounted in a cabinet a 20" by 20" baffle board must be included between the lens and the horn. When mounted in normal position the lens is usually exposed to avoid masking the ends of the plates."

"The sides of the lens plates must not be obstructed if proper high frequency dispersion is to be maintained."

Here is the entire Data Sheet:
http://www.lansingheritage.org/html/jbl/specs/pro-comp/horn-lens-series.htm

[Dr.db]

Hey,

thanks for that :)

What`s the disadvantage of masking the ends of the lense ?
"Just" a loss in high frequency ? I´m using a 2405 for UHF, would this compensate the loss or does the decrease of high freq. starts earlier than about 10khz ?
Are there any other downsides with masking the ends such as unwanted peaks, phase-problems etc.. ?


Why did JBL themselfs mask the ends on the L220 ??
http://audio-database.com/JBL/speaker/l220.JPG

[Lee in Montreal]

Felt pad. There's indeed a thin felt pad glued to the aluminum baffle on each side of the horn. It can be seen clearly here. It helps damp any possible ringing.

http://img.photobucket.com/albums/v668/Lee_Vuong/JBL%20parts%20factory/DSCN0906.jpg

http://img.photobucket.com/albums/v668/Lee_Vuong/JBL%20parts%20factory/DSCN0926.jpg

http://www.hifido.co.jp/photo/08/131/13105/g.jpg

[10 Watt Street]

"Why did JBL themselfs mask the ends on the L220 ??"
http://audio-database.com/JBL/speaker/l220.JPG[/QUOTE]

That was a side effect of aligning all three voice coils in the L220/L222.

[Odd]

In L220 I think they mounted a lens just to get a fancy look.
It is a LE 5-9 behind the lens.

[Mannermusic]

The 2390 is a unique animal - not what Lee is showing. The 2390 is the old Hartsfield horn (HL89) that was originally anodized gold. Shown on all the JBL ads! It had 20 pads inserted between the diffuser "fins" (10 per side) to kill the tendency to ring. They cannot be seen unless you look into the end of the lens carefully. They are approx 1 1/4 X 1 3/4 X 1/2 thick (inches). It's a rather firm, black felt of sorts and is inserted 2 1/2" into the lens from the outer edge between each element - and there are 11 elements. The elements / fins are only .040" thick and 20" long so they are gonna definitely ring without some kind of damping. You could make your own pads, but you definitely need something. Like the links above say, that horn has to be used per JBL instructions or you will not get optimum results. Used it for a couple decades in a tri-amp rig. Lots of tubes, Marantz, Luxman, etc. Fun.

[Dr.db]

Thanks a lot, I will consider these felt-pads when mounting my lenses finaly :)

[Mannermusic]

Thanks a lot, I will consider these felt-pads when mounting my lenses finaly :)

Yes, very good! Apparently someone threw them away not knowing what they were before you got hold of them. And, I'd say you could experiment with rubber or other materials - an easy A-B test (just slide 'em in approx 2 1/2"). ;) Mike

[maxserg]

Need felt of different density? Find a piano parts supply (i.e. Shafft) :)

[more10]

If you want to use the horn down to 500 Hz you will also need a baffle. I have searched but not found any JBL documentation on this issue. I believe the baffle should be as wide as the serpentine lens. This will also take care of the ringing.

[Dr.db]

Yes, a 500hz crossover would require a baffle for shure.


Will masking the ends of the lense "just" lead to a loss in high frequency ?
I´m using a 2405 for UHF, would this compensate the loss or does the decrease of high freq. starts earlier than about 10khz ?
Are there any other downsides with masking the ends such as unwanted peaks, phase-problems etc.. ?