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I am running an active tri amp rig. I keep blowing soft domes and ribbons. My active crossover is a 48db slope to the soft dome and ribbon at 3 KHz. I have a 2nd order passive crossover between the soft dome and ribbon at 9 KHz. A 20 uf blocking cap is used prior to both drivers and crossover. Where am I going wrong, and how can I prevent furthe rfried divers?
Follow Ups:
I think Presto totally misunderstood your post. He is active going to both the ribbon and dome, and passive between the dome and the ribbon. He is using a protection cap before the ribbon, a common thing. I personally don't like them, but whatever. What I am confused about is that you say you are using the protection cap before both the crossover and the drivers. Is that correct?Normally a protection cap is only used on purely active systems, where DC or LF transients from the amplifier can be presented directly to the ribbon from the amp. If a passive crossover is used the crossover iteslf acts as the protective filter for the ribbon. A protection cap alone essentially creates a 1st order high-pass. The high value, like 20uf brings the filter point down to say ~1K depending on the impedance of the driver at the filter frequency. However in your case you are already using a 2nd order crossover at 9K, so why do you even need the protection cap if its DC or LF transients you are concerned about? They are already being attenuated by the 2nd order crossover. Not so for your dome though. It is suceptible. However since you're blowing both, this precludes LF impulses or DC as the culprit, since the ribbon shouldn't be seeing any due to the 2nd order passive.
In most cases, blown drivers are a result of exceeding either a drivers thermal limits or operating the driver outside of its frequency range. Without knowing which drivers you are using I can't say for sure if your crossover points are OK. However, based on what you did mention I suspect you are fine especially with sharp slope of 48dB/oct on the dome low point and the 9k 2nd order on the ribbon low point. I would remove that protection cap, especially if it is before the second order. You may be having a phase issue here, reducing output and forcing you to play at higher levels to achieve the desired SPL's. Which leads me to the following ...
What is probably the culprit more than likely is lack of power for the levels you are playing at. If clipping, even a small amount, is occuring on peaks a "protection cap" will not prevent the drivers from exceeding their thermal limits. It might be counter-intutive to some people, but having more power than the rating of the loudspeaker is better than having less. Some would say, "Well ... the amp is only rated for 200W and my speakers can handle 250W so I should be safe". In fact the opposite is true. Generally, I use amplifiers with double the power of my loudspeakers RMS ratings and use my ears and common sense to govern how hard I drive my loudspeakers.
Understand that a clipped signal has a significantly higher RMS value than an unclipped one. Therfore, a 100w clipped signal will cause a driver to "go thermal" much sooner than a 100w unclipped signal. Also remember, clipping is not always audible.
Why don't you give us a list of the gear (Active cross, amplifier, driver makes and models) and what kind of music you like and how loud you like it. Don't worry, we won't judge ... much! :-)
JRL
Edits: 11/03/12 11/03/12 11/03/12 11/03/12 11/03/12 11/03/12
If he's going "active to dome and ribbon" and adding in a highpass cap (which seems to be the wrong value) then he's doing it wrong.
Whether he does it active or passive, he needs a lowpass filter for the dome at 9khz. Unless he intentionally wants a big boost in SPL above 9khz, he's going to get a very sizzly sound.
Then again, some fellas think this is synonymous with "more inner detail" so who can say...
If he wants the right answer I think he needs to sketch out a quick circuit diagram (or even block diagram). I still think his cap might be the wrong size.
Cheers,
Presto
"A 20 uf blocking cap is used prior to both drivers and crossover."
How many 20 uF caps do you have in total? And why 20uF? I think you want a 2uF in there. 20uF gives you a 900Hz crossover with an 8 ohm driver.
So for the dome you are doing 3kHz active high pass and 9khz lowpass? The 9khz 1st order electric lowpass should will be a coil in series, not a cap.Something sounds amiss here. Can you sketch a schematic and scan it or just do a crude sketch in paint? Indicate the nominal impedance and efficiency of both drivers.
If you have a 1st order at 900Hz, that would be why you're frying ribbons in a second. Also remember that a first order at 9kHz is only 6db down at 4500 Hz and 12db down at 2250Hz. This is not a lot of attenuation if you're playing at very high levels. Thing is, the ribbons SHOULD be at least as efficient as the domes if not moreso. If they are super efficient ribbons, then you can get away with a shallower slope because of how much you will be padding them down. If they're only as efficient as the domes, you will need to observe "typical" ribbon protection thumb rules.
First thing to do: verify cap size. Did you mean 2.0uF?
Cheers,
Presto
Edits: 10/22/12
Hello Ozzie,
you seem to be already on the right track - amplifier turn-on or, more likely - your pre-amp / crossovers. Depends on what your set-up consists of, as a general rule in active rigs you want to turn on first the pre-amp, then the crossovers, then the amplifiers.
Turn everything off in the reverse order. There are power strips available to "program" sequential turn-on / turn-off as well as delay times between the steps. Every active rig I've seen utilizes those as a "pop" at turn-on of the pre-stages with power-amps on (and all the way open) does tend to blow the tweeters and mid-range drivers.
Your power amps should have a topology that either soft-starts or connects the speakers after the circuit has stabilized, though audiophiles scoff at relays between the output devices and the speaker-outs. That does no good of course if the amp gets presented with something bad at the input stage when already on.
Seems to me adding components in front of your HF / Mid-drivers is the worst when it comes to degrading the performance.
When flying commercial you want the aircraft to be maintained and operated by sound standards.
I faithfully follow the turn on and off sequence. The circuits I am using for the crossover is somewaht similar to that of the original. The planer is exact. Still I get the occassional open driver. I have a new amp set. Threshold SA3s. Hopefully my results will improve for the better.
Do you actually "witness" driver overload or is (hopefully was..) it something that you'd find out at the next power up?
Had a Stasis 5, great amp but would make a good "pop" on power-up with the Maggies it was driving then. Never had a ribbon blown, though.
Hope it get's resolved with the new amps, did read up on Mr. Pass again after looking at your set-up. One of my favorite designers.
What do you mean by "The planer is exact"?
Back in the 80'ies we'd put fuses on drivers in the studio, some clients would always manage to make a bad decision on the board with the mains too loud already.
Good luck, active is the way to go.
When flying commercial you want the aircraft to be maintained and operated by sound standards.
Oops, I meant that the planer crossover at 9 K is exactly as the stock crossover was. The crossover on the soft dome is different as I don't need a three pole band pass since the electronic Xover is providing > 3 KHz. I am using a simple 2nd order on that as well.
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