I am having an issue with the signal pint to the rear woofers in my classic car. They are receiving a signal down to 20hz. This is causing a noise like a blown speaker. I thing I need a 750uf or 760 uf capacitor. Thing is I am struggling ro find the. Any advise for uk based member welcome
Yes, you need a bipolar electrolytic capacitor, probably with a substantial ripple current ratings.
Something like these should work.
https://www.ebay.com/itm/125897992481
Something like these should work.
https://www.ebay.com/itm/125897992481
1000uf would give a frequency pass off 40hz which would be to low for the speakers. They operate from 50hz
That was just an example. Capacitor companies make a wide range of values, but you'll have to look.
Given the likely response of the system, I'd personally think that a lower value may be fine too. What about a first order crossover, where the -3 dB point is 50 Hz? That'd be about 380-400 µF for an 8 ohm speaker. Or 560 µF if you'd prefer to cross -3dB closer to between 35-40 Hz. Those should both be much easier to find and purchase.
Remember, a capacitor in series is just a first order filter.
Remember, a capacitor in series is just a first order filter.
@Weekatie
You can use 2 easy to find electrolytic capacitor connected like below:
Capacitance will be in series so, if you need 500uF, use 2x1000uF.
What is your amp power rated at? And what is the speaker impedance?
You need to check RMS current to make sure it handles the current and has a reasonable life span (capacitor datasheet).
I use at least 160V capacitors.
You can use 2 easy to find electrolytic capacitor connected like below:
Capacitance will be in series so, if you need 500uF, use 2x1000uF.
What is your amp power rated at? And what is the speaker impedance?
You need to check RMS current to make sure it handles the current and has a reasonable life span (capacitor datasheet).
I use at least 160V capacitors.
OK so they system is 40w rms per channel and on an 4ohm system. So if I used 2 375uf caps that would work? Sorry still kinda new to this
Both caps still see reverse current flow. If the caps can't handle this, don't. This is not a great solution.
Don't worry about getting such specific values. The amount of difference it'll make for you to use two standard value caps or one standard value cap is not that big that you'll notice. Assuming these rear car trunk speakers aren't the only speakers in the car, you can probably cross them over around 50 Hz on a first order filter, which will be -6dB by the time it gets to 25 Hz, or roughly half the power.
820µF would give you around 50 Hz -3dB. 40 watts per channel would be around 3 amperes and under 16 volts, which would be the minimum specs your caps should be rated for, for ideal results.
Hi,
In terms of maximum continuous current through the capacitors you have P=R*I^2 which yields to 3.1A.
But with music, you can consider 1:4 peak to average, so 3.1/4 = 0.79A.
2x1000uF will give you a frequency cut at 79Hz. As mentioned, this is a 6dB/oct filter (1st order) so the roll off is very smooth.
2 Capacitors in series gives you C/2, so an equivalent 500uF.
From TDK standard electrolytic datasheet, 1000uF/100V you can see that if operated below 50C, it will last more that 50,000h.
So, 2x1000uF/100V in series connected with opposed polarity will work for you.
If you need to cut a bit lower, just increase the capacitors, but always keep them equal values.
In terms of maximum continuous current through the capacitors you have P=R*I^2 which yields to 3.1A.
But with music, you can consider 1:4 peak to average, so 3.1/4 = 0.79A.
2x1000uF will give you a frequency cut at 79Hz. As mentioned, this is a 6dB/oct filter (1st order) so the roll off is very smooth.
2 Capacitors in series gives you C/2, so an equivalent 500uF.
From TDK standard electrolytic datasheet, 1000uF/100V you can see that if operated below 50C, it will last more that 50,000h.
So, 2x1000uF/100V in series connected with opposed polarity will work for you.
If you need to cut a bit lower, just increase the capacitors, but always keep them equal values.
It works as long as you respect the voltage and average RMS current.
I have a number of deployments since 1978, when I think I built my first speaker.
Reverse current is not an issue for an electrolytic capacitor - its actually the normal operation when charging and discharging.
You cannot reverse the voltage.
Bipolar electrolytics are just two "anti-series" electrolytics, in one package. No functional difference with two identical discrete caps.
You can't have the current reverse if the potential difference is never changed so as to allow the charges to flow the other way. If the potential difference is maintained as "right way around" then the current will not change its direction either. It "flows high to low" in terms of potential.
After digesting everything that's been said, I have went with a single 560uf capacitor. Not going to lie my head was fried last night with numbers. Had to ho distract my self fir an hour then come back to this and it dunk in
If you had access to the center node inside an NPE you would find a slight negative voltage on it after it has been in operation a while. The leakage current from the reverse half cycle charges the caps. Once that happens, the leakage current decreases. An new unformed NPE probably has significant distortion till the bias builds up.
In audio, we have alternating current, so the capacitors are under constant voltage variation (up and down) but not necessarily forward and reversed polarity.
If a capacitor is at 10V and it is forced to move to 12V you have current flowing through in one direction (let's call forward direction).
When it is forced to go from 12V to 10V, negative current flows, thus current is constantly rerversing.
Just make sure this is a non polarized capacitor - you cannot use a single eletrolytic capacitor in alternating current system such as in an audio system.
If a single eletrolytic is inserted in series with speaker, it will eventually blow up as well as cause a strong distortion.