Crossover help for 2405

[Sootshe]

I'm running a set of 12 inch Altecs in Onken enclosures crossed over at 500Hz through an Altec 500 Hz crossover to a 2450.

I'd like to add a 2405 for more HF extension, but I'd prefer to leave the existing system as is & just run the 2405 with a cap on it.

Can anyone tell me what value of cap I should run so that the 2405 will run just above 7K?

Many thanks,
John

[rudy sesztak]

If the 2405 is 8 ohms, use a good quality cap( solen) - 2mfd in series& a.26 mh coil across it.The crossover frequency will be around 7 kc.- Rudy

[Sootshe]

Thanks very much Rudy, that's a great help.
I'm very sorry, I should have mentioned that the 2405 I have is 16 ohms....will this make any difference?

Thanks,
John

[rudy sesztak]

Dear John, Some JBL speakers rated 16 ohms are really around 8 ohms. I'm not sure on the 2405. If it is a16ohm tweeter,then you would need a 1 mfd cap in series& a .5 mh coil across it. Try both crossovers, they should sound almost the same. by the way the 2405 and my 077 are great tweeters. you will be happy with the sound.- RUDY

[Sootshe]

I'll check the resistance, even though it's stamped as 16 ohms.
Rudy, I really appreciate your help, as I'm all thumbs when it comes to X-overs. Give me a cabinet to build & I'm OK.
Regards,
John

[HCSGuy]

Checking DC resistance won't tell you what you need to know. Regardless, the D16R2405 and D8R2405 are the same part, with the same impedance - the 8ohm and 16ohm versions of this driver are actually the same thing. If you really want to be precise, you will need to check impedance of your driver at the desired crossover frequency. However, as this is an experiment, take Rudy's advice, build both (they will have different crossover points), and see what you think. Let us know!

[Sootshe]

Interesting....& way above my head!!!
I'll try both & let you know.
Thanks,
John

[1audiohack]

The impedance of a 2405 is right about 8.3 Ohms from 5500Hz through 9000Hz and rising to about 9 Ohms by 10kHz. They are all the same regardless of what the label says, 8 or 16 Ohm.

The JBL 7kHz passive crossover #3105/N7000 built for these uses a 0.6mH inductor and a 1.5uF capacitor. The 8kHz 3106/N8000 uses 0.3mH inductors and the same 1.5uF cap, easy as that.

All the best.

[Sootshe]

You guys are just great....what a wealth of knowledge you have here.

[ivica]

I'm running a set of 12 inch Altecs in Onken enclosures crossed over at 500Hz through an Altec 500 Hz crossover to a 2450.

I'd like to add a 2405 for more HF extension, but I'd prefer to leave the existing system as is & just run the 2405 with a cap on it.

Can anyone tell me what value of cap I should run so that the 2405 will run just above 7K?

Many thanks,
John

JBL in networks 3133, 3143 and 3145 used 3-rd order C-L-C network with 1uF-0.16mH-1.5uF (with additional resistor -in 3145 of about 17 Ohm parallel with inductor (in order to reduce "overshoot" on frequency about 8~10kHz).
In 3155 network 1.5uF-0.16mH-1.5uF with 20 Ohms resistor.....
In any case 8-Ohms "L-pad" is used....

[ivica]

Does anybody tried to put "serial' inductor of about 0.16mH 'in series' with the second capacitor (1.5uF) in networks 3133, 3143, 3150 or 3155 before 8-Ohm L-pad fro 2405...
I expect that would rise UHF frequency over 15kHz, and maybe compensate some UHF losses 240x driver