# crossover component

#### Jerry Calà

##### Member
Hello,

I have to buy a 82uF capacitator for the crossover circuit of the tweeter. I will use it in parallel to prevent the tweeter playing too low frequency, so there's no need to be high quality cap I will use a bipolar.

Raugh or smooth bipolar cap? What's the difference? From the specification it seems Raugh has a higher voltage ratingso it should be better.But I've seen that smooth caps are used in a lot of kit.

Another thing I don't understand is VAC, VDC terms.

http://www.lautsprechershop.de/hifi/condens_en.htm#elko_glatt
So a smooth bipolar cap with 82uF has 100Vdc/35Vac
How many watts in 8ohm will support that capacitator?

From my raw calculation the tweeter with my choosen cross point will be feed with max 25W at full amplifier power.

Thank you

#### Cal Weldon

Paid Member
Yes, please tell us more about what you are trying to do. The people here will be able to help more if you have info on the drivers and XO point etc.

#### BlueWizard

##### Member

Vac = Volts Alternating Current, meaning that the applied voltage will go both positive and negative.

Vdc = Volts Direct Current, meaning the applied volatage will be on a continuous single (either positive or negative) polarity.

Notice that Volts DC is typically higher than Volts AC. You want to use Volts AC as your standard, and you want to rate your Caps at twice the anticipated voltage.

To determine the maximum voltage of your amp, use this formula -

Voltage (E) is the square root of the Power(P) times the Resistance(R).

E = SqRt(P x R)

Example-

Assuming 100 watt amp and 8 ohm speakers

E = SqRt(100watts x 8ohms)
E = SqRt(800)
E = 28.3 volts

Meaning you need at least a 60 Vac capacitor.

Using the Capacitor calculator I linked to, and using 3 sample crossover points, assuming 8 ohm speakers, and assuming a Butterworth crossover design, I come up with -

2,000 hz = 10uF
3,000 hz = 6.6uF

That seems far off from the 82uF you estimated.

The values above are consistent with the formula -

C= 1 / [2(pi)fR]

Where C = capacitance, (pi) = 3.14159, f = the crossover frequency, and R = the rated impedance of one speaker.

Steve/bluewizard

#### Jerry Calà

##### Member
thank you for the formulas!

Thanks to all I will start building my own speaker the next time. Now I decided tui build a kit, then in the future I will try to make my own speaker once I've got expirience.