Should I install a blocking cap in series with my subwoofers to protect them? How many volts are appropriate? The speakers (Peavey LO Max) are rated at 1200 watts continuous. (ill be using a pair)The amp is rated (at four ohms bridged) @ 2200 watts RMS. I can figure my values myself if someone will give the necessary formulas.
m
m
Better stability, less heating of the amplifier... unless you have to squeeze the last watt from the amplifier. Nothing wrong with bridging the amplifier with the 4-ohm load if the amplifier is a good quality, though. Amplifier with lesser quality struggle with 4-ohm load when bridged.
Which make and model is the amplifier?
Which make and model is the amplifier?
a blocking cap could be useful to protect in advent of an amp dumping its rail - but it can alter the impedance of some systems and effectively give a useful "boost" (sized correctly) - or unwanted bump and excessive cone excursion
An externally hosted image should be here but it was not working when we last tested it.
contact Peavy factory technical support for bridging recommendations. Some amplifiers are set up for bridging but not really ready for prime time, at max power, stuff can break.
good bi-polar blocking caps at that power level are not easy to find, again contact the factory concerns for protection advice. IDK they should know better than most all opinions. back to back electros can do in a pinch but I wouldn't.
Polarized power electros want to have bias voltages to fully form the dielectric.
good bi-polar blocking caps at that power level are not easy to find, again contact the factory concerns for protection advice. IDK they should know better than most all opinions. back to back electros can do in a pinch but I wouldn't.
Polarized power electros want to have bias voltages to fully form the dielectric.
Last edited:
A blocking capacitor is useful only with sealed designs with Qtc=1.1 or so. Low
Qtc designs with less than 0.7 will show SPL loss of 2 or 3 dB (see the simulation
above) in the important bass range from 70 to 150 Hz (gain below 70 Hz is OK).
The majority of powerful PA 18" subs are vented designs, so blocking capacitor is not a good solution here. More appropriate here would be a line-level capacitor filter (first order).
hey DJK - (I've no mobility to do PA/DJ work and know nothing about it - ) do you think my 600uF caps would hold down a fair amount of current? - sorry for blurry pic - old cheap camera. Thanks Sonce - I was thinking of a home situation where a turn-off transient destroyed 4 Seas woofers - do pa amps ever dump their rail or are they failsafe in that regard?
An externally hosted image should be here but it was not working when we last tested it.
Last edited:
The reason for doing this is to protect the driver/s under DC fault conditions. Most power amps these days should have auto protection in place via a relay etc. But if you want to do it with caps, you could. It's not what i would do though.
A quick way of "approximating" the value of the capacitor/s is, knowing that for eg, 20Hz @ 4 Ohms = 2200uf - 8 Ohms = 1100uf But that's using non polar types. You can use 2 x polar types in series, provided either the +'s are joined together, or -'s. Putting caps in series halfs their uf, so instead of 2 x 2200uf you would need 2 x 4400. Nearest would be 2 x 4700uf.
For safety, the combined series AC voltages should be capable of @ least more than the highest voltage the amp can output under fault conditions. Take the power supply voltage of the amp as a reference. For eg, + - 100V DC i would use 63V DC - 100V DC caps. Of course these MUST be high current types, capable of @ least twice the expected current, & low esr power supply types are ideal.
Whether the amp is bridged, or not, only 1 pair is needed per output.
A quick way of "approximating" the value of the capacitor/s is, knowing that for eg, 20Hz @ 4 Ohms = 2200uf - 8 Ohms = 1100uf But that's using non polar types. You can use 2 x polar types in series, provided either the +'s are joined together, or -'s. Putting caps in series halfs their uf, so instead of 2 x 2200uf you would need 2 x 4400. Nearest would be 2 x 4700uf.
For safety, the combined series AC voltages should be capable of @ least more than the highest voltage the amp can output under fault conditions. Take the power supply voltage of the amp as a reference. For eg, + - 100V DC i would use 63V DC - 100V DC caps. Of course these MUST be high current types, capable of @ least twice the expected current, & low esr power supply types are ideal.
Whether the amp is bridged, or not, only 1 pair is needed per output.
Attachments
I used 6 200uF 400V AC rated 100A film caps for a undersized Beyma 15g450. Hitting this driver and encloser with 3000w/peaks.
Only because they where trashed at our company after a few minutes of testing them for use in high power frequency inverters.
Each one was more expansive than a cheap active crossover with highpass.
Do you think a cap will really helb with faulty amps.
It is fine to bridge the amp. It sees exactly the same stress running each speaker off one channel each, as it does to both speakers in series and bridged. In fact bridged will mean less stress on the power supply as it loads each half equally rather than double whammy on each then changing over as polarity of the signal changes.
Last edited:
Something is wrong with your amplifier, it should not do that. Quality PA amplifiers are bomb-proof.
Capacitor is of little help with turn-off (or turn-on) transients - leading edge of the transient will run through the capacitor straight to the loudspeaker. Capacitor will block only the steady-state DC voltage, not the transient.
Bridged amplifier connected to two parallel 8-ohm loudspeakers sees 4-ohm impedance, and that is the same as 2-ohm impedance loading to each channel. Only good quality amplifiers will survive that, especially on prolonged time with output power close to the maximum. That is why I asked OP for the make and model of the amplifier.
Yes, that is the advantage of bridging the amplifier.
OK.... Sonce and others have laid out the obstacles to using a series cap definitively. (Good thing no golden-ear person has added more complaints about the "sound" of different types of cap!).
So.... what's the latest thinking on protecting drivers? (BTW, since I am going back to motional feedback experiments, I sure need protection for my drivers having destroyed an expensive woofer last time I experimented.)
Ben
So.... what's the latest thinking on protecting drivers? (BTW, since I am going back to motional feedback experiments, I sure need protection for my drivers having destroyed an expensive woofer last time I experimented.)
Ben
Sealed cabs? No problem with a cap in line except the huge value needed. About 1600/1800uF for a 4R driver will do, half that obviously for an 8R driver
Series the caps if all you can find/afford are 100V caps
Won't be cheap but it did stop my HT passive sub from bottoming out on Infrasonic signal
I used 100V caps as only 400 watts amplifier but even so that's a lot of bulk
Series the caps if all you can find/afford are 100V caps
Won't be cheap but it did stop my HT passive sub from bottoming out on Infrasonic signal
I used 100V caps as only 400 watts amplifier but even so that's a lot of bulk
If turn off thumps are destroying woofers, either the speakers are too small and the amp is too big (30 watt speaker, 4kW amp, for example) or there is something seriously wrong with the amplifier. Going to the rail for a few milliseconds won't hurt anything unless the speaker/amp is terribly mismatched. If it lasts longer than that you need to get it fixed. If it's a home brew design and not settling out in a reasonable time it needs redesign.
PA amplifiers and most home amps have muting relays to gate out the transients (and DC faults) and to trip in case of overload.
If the transient is due to switching off the preamp while the power amp is till on you deserve your fate. Those transients are far worse than anything a power amp usualy creates and totally preventable.
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.