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Koelboy
01-07-2015, 06:03 AM
Hi all,

I have a nice vintage system with JBL 2405 and JBL 2470 / 2345 horns. Using a single direct radiating 12" below them and two 2x15" subs below 100 Hz (12" and subs are a Dutch brand called Stage Accompany).

Currently crossing the 2470's actively at 1600 Hz and the 2405's at 8 kHz. My crossover also allows crossing the 2470's at 1100 Hz, but I'd need to get or make the filter cards. Would this be worth a try or would the 1100-1600 Hz range be more at home with the 12"?

Hoping to get the best sound, PA durability is not relevant. Any other recommendations most welcome :)

Thanks
Jan

Horn Fanatic
01-07-2015, 09:50 AM
Hi all,

I have a nice vintage system with JBL 2405 and JBL 2470 / 2345 horns. Using a single direct radiating 12" below them and two 2x15" subs below 100 Hz (12" and subs are a Dutch brand called Stage Accompany).

Currently crossing the 2470's actively at 1600 Hz and the 2405's at 8 kHz. My crossover also allows crossing the 2470's at 1100 Hz, but I'd need to get or make the filter cards. Would this be worth a try or would the 1100-1600 Hz range be more at home with the 12"?

Hoping to get the best sound, PA durability is not relevant. Any other recommendations most welcome :)

Thanks
Jan

There is no sense in crossing over a phenolic diaphragm at 1.6K. Crossing over the 2470 at that frequency is counter productive to what the diaphragm was designed for. You could safely cross that driver over at 500Hz. The 2470 has a rapid roll-off beginning at approximately 10K. Although the 2345 is considered an 800Hz horn, you could cross it over as low as 700Hz, or perhaps 600Hz. Using that as a starting point you can find a crossover frequency to determine the best acoustical match between the horn and mid-bass driver. If you do it right the effect should be seamless. I am not one to use stock crossover frequencies.

As for the 2405, JBL typically used 7K as a crossover frequency, but also used 8K in some systems. You could safely cross the 2405 over at 5K. Keep in mind, all JBL ring radiator diaphragms are the same. The lowest crossover frequency JBL used for the bullet was 2.4K, a bit too low for the 2405 only due to the horn mouth area. Phasing problems will occur when the wavelength of crossover frequency approaches, or is at unity with the circumference of the horn mouth. With respect to the 2405, the horn mouth is the slot, not the diameter of the horn, as it is the same horn used for the 2402.

High frequency horns are designed as such that the recommended crossover frequency is one octave above the cut-off frequency flare rate. The ALTEC 811 for example is roughly a 400Hz horn, the 511 is roughly a 250Hz horn, both based on the horn mouth area, and the cut-off frequency flare rate.


H.F.

1audiohack
01-07-2015, 12:30 PM
Keep in mind, all JBL ring radiator diaphragms are the same. H.F.

No sir that is not correct. There are three witht 076/2403 being obsolete.

Barry.

Allanvh5150
01-07-2015, 01:19 PM
Yes indeed. 2402, 2403 and 2405.

Allan.

Koelboy
01-07-2015, 02:31 PM
There is no sense in crossing over a phenolic diaphragm at 1.6K. Crossing over the 2470 at that frequency is counter productive to what the diaphragm was designed for. You could safely cross that driver over at 500Hz. The 2470 has a rapid roll-off beginning at approximately 10K. Although the 2345 is considered an 800Hz horn, you could cross it over as low as 700Hz, or perhaps 600Hz. Using that as a starting point you can find a crossover frequency to determine the best acoustical match between the horn and mid-bass driver. If you do it right the effect should be seamless. I am not one to use stock crossover frequencies.
H.F.

Seems like I'm on the right track to get the best out of the 2470's by lowering the XO frequency, then.

Horn Fanatic
01-07-2015, 09:17 PM
No sir that is not correct. There are three witht 076/2403 being obsolete.

Barry.

I believe you misinterpreted my comment. There are actually four ring radiator motors that take the same diaphragm. You forgot the 2404. Same diaphragm, four different horns, four different cross over frequencies.

H.F.

jerv
01-07-2015, 11:05 PM
I believe you misinterpreted my comment. There are actually four ring radiator motors that take the same diaphragm. You forgot the 2404. Same diaphragm, four different horns, four different cross over frequencies.

H.F.

Sorry - this is not correct.

There are three different ring radiator diaphragms: the "heavy" one normally used in 2402/075 and 2404H-1, the "light" one normally used in 2405/07 and 2404H - and the one in the 2403.

Three different diaphragms, four different horns. Many possible combinatons. And endlessly many different crossover frequencies.

speakerdave
01-08-2015, 12:59 AM
I think your idea of trying a crossover around 1100 or 1200 Hz may be worthwhile. JBL used that horn and driver that way in some of its PA systems.

ivica
01-09-2015, 01:13 AM
Sorry - this is not correct. There are three different ring radiator diaphragms: the "heavy" one normally used in 2402/075 and 2404H-1, the "light" one normally used in 2405/07 and 2404H - and the one in the 2403. Three different diaphragms, four different horns. Many possible combinatons. And endlessly many different crossover frequencies. Hi jerv, I believe that ring-radiator diaphragms used in 2402-2403-2404-2405 mainly differs in the "suspension size" ( or in other words in the radius of the aluminum rings -inner and outer- that hold the diaphragms...., and the phase-plug-horn combo too. Here the real weight of the diaphragm itself is not important - I think reagrds ivica

jerv
01-09-2015, 03:20 AM
The diaphragms with the biggest "suspension size" has of course the least diaphragm area (as your illustration clearly shows), and therefore also has the least moving mass (i.e. "lighter") in comparison with the diaphragms with smaller suspension and more area.

ivica
01-09-2015, 07:23 AM
The diaphragms with the biggest "suspension size" has of course the least diaphragm area (as your illustration clearly shows), and therefore also has the least moving mass (i.e. "lighter") in comparison with the diaphragms with smaller suspension and more area.

Hi,
Just for better mutual understanding, when I said suspension, I had in mind parts of the diaphragm from the fixation rings ( blue or gold color) to the "V"-shape diaphragm part. So Blue or Golden rings, in my view, are not suspensions....

regards
ivica

jerv
01-09-2015, 11:48 AM
No matter.
The bigger the fixation rings - the smaller (and lighter) the diaphragm.

d8r075 have the smallest fixation rings, and is standard in 2404H-1 and 2402/075. Heavier diaphragm: more rugged, and less HF exension.
d16r2405 have bigger fixation rings, and is the standard for 2404H and 2405/077. Lighter diaphragm, more HF extension.