Why use High Voltage rated caps in Xover?

[plmedeiros]

Hi,

Can anyone tell me the reason why a speaker designer would use 650v caps in a xover built for a 250watt rated speaker? Is it that the amp might spike at high output levels? If so, what safety factor is reasonable?

I've been trying to determine the voltage rating of the caps I need for a MTM xover design, (1- 4ohm tweeter and 2- 8ohm woofers). I'm using Tina v6 to analyze the circuit. The bode plots tell me that I won't see voltages greater than 26v peak across my drivers. I'm basing this on my Yamaha receiver that puts out 100 watts/channel, (28v peak for a 4ohm load). I even looked at the transient response using a square wave generator and I didn't see any transient problems with the circuit.

Thanks

 

[Frank Berry]

The designer may have over-designed the crossover or he might have found the caps at a very good price. It does seem like overkill. I could imagine 100 volt caps but 650 volt caps?

 

[bob91343]

No harm, probably just a case of what was available at the time. Sure 100 V rating will be fine.

If you want to be more precise, 250 Watts into 8 Ohms equals about 45 Volts. That means a peak of about 65 Volts. You could add some safety factor, and realize that the tweeter is inductive (perhaps causing some voltage buildup). But the woofer will load the system and prevent any significant buildup.

If it's a solid state amplifier, look at the power supply voltage and make the capacitor rating above that.

 

[raypalmer]

What speaker is this you've got with this massive caps???

 

[richie00boy]

I bet they are polypropylene caps, often used because of stability and good sound. It just so happens that they are only made in high voltages because in industry that is the normal application for them.

 

[woody]

If you read the old article by Walter Jung "Picking Audio Capacitors" his test indicated
that all other things being equal the higher the voltage rating the less distortion.

 

[plmedeiros]

Thanks for all your responses. I'm glad I'm not the only one that thinks a 630V cap is a bit much for a 250 watt rated speaker

What speaker is this you've got with this massive caps???

I've seen too many designs that use high voltage caps to single one out. I have an In wall MTM speaker that I built that I'm trying to tweak. I'm just trying to understand why people spend so much money in Xover components.

Thanks

 

[jackinnj]

If you read the old article by Walter Jung "Picking Audio Capacitors" his test indicated
that all other things being equal the higher the voltage rating the less distortion.

Yes, but that article (with Marsh) was written 30 years ago -- it is on WJ's website, although Audio is defunctorum. Similarly, higher voltage electrolytics seem better than their lower voltage counterparts.

My wife, a famous molecular biologist (in my opinion) is never lacking her opinion that if it hasn't been on the web in the past 10 or 15 years, modern scientists deny its existence -- until she goes to some convention ... "that was discovered and written in a paper in 1973..."

 

[speakerdoctor]

Herein may lie the answer to your question

Hi,

Can anyone tell me the reason why a speaker designer would use 650v caps in a xover built for a 250watt rated speaker? Is it that the amp might spike at high output levels? If so, what safety factor is reasonable?

Thanks

Download the paper I wrote (dismissed by some here and in other forums) at this link.

Capacitor voltage rating vs performance - The Classic Speaker Pages Discussion Forums

Over 600 others have. Check out the Martin Collums paper.
Or, write to Tony Gee and ask him why he generally ranks higher voltage caps better than lower voltage ones.