Hi everyone,
I have some 16ohm JBL 2420 drivers that I need to test, but I've read that I'll need to add a protection capacitor before I hook them up. All good, only problem is I can't find the fs of these drivers anywhere so it's hard to know which cap to buy. I'm hoping to cross these at 600hz.
Any help would be greatly appreciated!
I have some 16ohm JBL 2420 drivers that I need to test, but I've read that I'll need to add a protection capacitor before I hook them up. All good, only problem is I can't find the fs of these drivers anywhere so it's hard to know which cap to buy. I'm hoping to cross these at 600hz.
Any help would be greatly appreciated!
You should be able to cross them at 600Hz. fs is probably a bit higher than that. You might have a problem with the capacitor interacting with the resonance impedance peak(s).
That's great thanks.
So a 72uF capacitor should do the job. Will a cheap non-polarized electrolytic cap be okay to use? It's not affecting the frequencies above the crossover point is it?
I'm still trying to wrap my head around note 3... So the resistor, say a 32 ohm one, is simply limiting the impedance peaks to 32ohms? If so, doesn't this reduce the overall impedance of the driver?
I'm hooking this up to a little 2A3 SET tube amp so 50w resistor might be overkill?
Sorry, a lot of questions. I'm new to this.
So a 72uF capacitor should do the job. Will a cheap non-polarized electrolytic cap be okay to use? It's not affecting the frequencies above the crossover point is it?
I'm still trying to wrap my head around note 3... So the resistor, say a 32 ohm one, is simply limiting the impedance peaks to 32ohms? If so, doesn't this reduce the overall impedance of the driver?
I'm hooking this up to a little 2A3 SET tube amp so 50w resistor might be overkill?
Sorry, a lot of questions. I'm new to this.
600Hz might be a little low for the 2420 from experience, 800Hz might be better.
Based on the recommendation 3 I would probably shunt with 47 ohms.
Is the capacitor just for protection?
If it is actually for XO 12.5uF would be about right for 800Hz, and about 16.5 for 600Hz, otherwise I would go for about 33uF and 47uF respectively.
Something else to note is that 2420 and 2440 work better when driven by a low source impedance. SE amps (I use 300B SE) have relatively high source impedance and that results in some variation in output amplitude based on the driver impedance and horn loading at any given frequency. I was able to improve flatness in my 2440 by about 1dB by reducing the source impedance by using the lowest impedance taps (8R vs 16R) I use direct drive - the amps in question have very low turn on/turn off transients. (No problems in 3 years and perhaps 4000 hours of listening.)
Based on the recommendation 3 I would probably shunt with 47 ohms.
Is the capacitor just for protection?
If it is actually for XO 12.5uF would be about right for 800Hz, and about 16.5 for 600Hz, otherwise I would go for about 33uF and 47uF respectively.
Something else to note is that 2420 and 2440 work better when driven by a low source impedance. SE amps (I use 300B SE) have relatively high source impedance and that results in some variation in output amplitude based on the driver impedance and horn loading at any given frequency. I was able to improve flatness in my 2440 by about 1dB by reducing the source impedance by using the lowest impedance taps (8R vs 16R) I use direct drive - the amps in question have very low turn on/turn off transients. (No problems in 3 years and perhaps 4000 hours of listening.)
The note 3 resistor doesn't reduce the impedance of the driver but reduces the net impedance what the amplifier sees.
Here, read the whole thing.
View attachment Protection of compression drivers.pdf
According to my understanding (and Table 2), it's more like 33uF for a 16-ohm driver at 600Hz. I don't think it's a good idea to exceed the recommended values (72uF), don't you think?
There's not much you can do about the resonance-related issues, even with the resistor in Note 3. Nevertheless, you could correct things using paraEQ, since you are already active.
Although there are many capacitor types mentioned by JBL, I use an induction motor running capacitor (polypropylene, self-healing) which is easily available at several values, always high-voltage rated (helps linearity), rugged, and inexpensive.
All the best.
View attachment Protection of compression drivers.pdf
According to my understanding (and Table 2), it's more like 33uF for a 16-ohm driver at 600Hz. I don't think it's a good idea to exceed the recommended values (72uF), don't you think?
There's not much you can do about the resonance-related issues, even with the resistor in Note 3. Nevertheless, you could correct things using paraEQ, since you are already active.
Although there are many capacitor types mentioned by JBL, I use an induction motor running capacitor (polypropylene, self-healing) which is easily available at several values, always high-voltage rated (helps linearity), rugged, and inexpensive.
All the best.
Okay thanks kevinkr. Yep, that cap was just for protection but it's great to have some solid info on what works for these drivers in terms of crossover frequencies. My goal at the moment is not to blow anything up, and then onwards from there.
I have 8ohm and 4ohm taps on the 2A3 amp so you're saying I should hook these up to the 4ohm taps? I've had my amp for a few years and, I don't know about it's on/off transients, but it's never been noisy in that respect.
I have 8ohm and 4ohm taps on the 2A3 amp so you're saying I should hook these up to the 4ohm taps? I've had my amp for a few years and, I don't know about it's on/off transients, but it's never been noisy in that respect.
Once you play with these for a bit you might want to measure. Impedance variations might be significant, and a capacitor in series will transfer the problem into output levels per frequency, in other words peaks/dips in the response.
Okay, got it.
I got that wrong (72uF), realised after I posted.
I was actually going to (eventually) build a passive crossover. Do you think it'd be too tricky with these drivers and the resonance issues?
Yes, definitely want to start measuring these asap. I've heard the Dayton Audio Test System (DATS) along with a decent mic is a good place to start.
Well, that finally solves your problem. With a passive crossover, this capacitor is not required altogether. Cheers.
It can be done passively. Navigating the impedance is probably not the trickiest part of a crossover.
I don't know much about DATS but it can be done with the standard measuring software. When you get a mic, one that connects through your soundcard may be best. Sometimes they need phantom power. USB mics don't lend themselves to timed measurements.