Speaker Crossover Capacitor Values


If the original capacitor for the bass driver is a 72uF Electrolitic non-polar 100 volt, when considering a replacement due to age, why does the value have to be the exact same, such as using a 22uF + 50uF ? What would happen if one used , say a 68uF or a 100uF ? Also for the woofers, does upgrading to a film Cap make sense rather than replacing with a newer electrolitic ?

jim94025

Showing 2 responses by erik_squires

I disagree, based on hands on experience with @timlub a little.

It's important to note exaclty when ESR matters a lot and when it doesn't so much, and also how much we are talking about.  It's usually under an ohm for all types of signal caps, but higher for electrolytics generally, especially older one's.

In series with a driver half an ohm difference isn't a big deal.  The problem shows up with caps going to ground.  2nd and 4th order caps in low pass filter and zobels. A change of 0.4 Ohms there can really change the impedance curve.  This is honestly hard to imagine without the right simulation.  I am afraid I lack the files and memory right now to find them.  In a circuit you'll often see these caps have a very small value resistor in series.  That's where you want to be especially careful.

In the middle of the road here is caps in series with a woofer, whose ESR may act as a bit of a baffle step compensation.  See if you can find the writing by Troels Gravesen where he discusses using this effect.

Stay as close as you can to the intended value.  You can go over the Voltage.

You can replace electrolytics with film caps but you must pay attention to measuring the ESR correctly. Especially with caps that go towards ground and are not in series.  A Dayton Audio DATS will measure this for you.

I've heard good things about replacing electrolytics with film but I wouldn't go too crazy.  Mundorf MKP or Clarity SA is about as expensive as I'd go.