# Cap size for tweeter 2200uf??



## Skierman (Mar 3, 2008)

What will a 2200uf capacitor, 50wvdc in line with power wire cross over a tweeter? Running active but want to protect the tweeters. The are about the size a C cell battery


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## minbari (Mar 3, 2011)

lol, i suppose if all you want is dc blocking, it will work. 2200 uF will be a 1st order HP at about 20hz


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## Skierman (Mar 3, 2008)

20hz? Wow. Just want some protection incase of some pop from the amp, if that ever occurrs. Guess it's not even worth it for that cap, have the right ones coming in the mail hopefully.


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## minbari (Mar 3, 2011)

i am assuming 4 ohms, would 10 hz if it is 8 ohms


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## circa40 (Jan 20, 2008)

Try this site: 6 db Crossover Table


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## brianhj (Apr 9, 2009)

Just out of curiosity, does adding a capacitor in-line like that with a driver (if you already have it actively crossed) affect SQ in any way?


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## TokoSpeaker (Nov 12, 2010)

Usually we use 10uf capacitor for tweeter.

Thank you.


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## kyheng (Jan 31, 2007)

Blocking DC should use light bulb....
And with that big value of cap, better don't put...
The right value of cap used shall be 2X from the tweeter's FS value.....


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## amomacko (Sep 14, 2010)

A light bulb in series to protect a tweet against DC?

How does that work?

Typically a light bulb is represented as a temperature dependence resistance with negligible inductance and capacitance (assume to be zero at audio frequencies).

So effectively a light bulb is a resistor in series with a tweeter. This forms a voltage divider so the DC voltage across the tweeter will decrease but will not be zero. This voltage drop will occur at all frequencies (as capacitance and inductance are assume to be zero) so this light bulb will effect the volume level of the tweeter and in a system using a passive crossover it will also change the cross over frequency.

A much better approach seems to be a cap in series or parallel inductor to the tweeter.


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## kyheng (Jan 31, 2007)

If your amp are working properly, it will only sending AC to your speakers, not DC.... You will be sending DC when the amp got problem, like the MOSFET driver failed or push your amp to the limits(wire your amp at 1ohm load)....
You will only need 4-5V of DC to fry your speakers....


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## minbari (Mar 3, 2011)

which is why he wants to add dc blocking protection. if you amp goes, that is bad enough. dont need speakers going with it.

5V into a 4 ohm load is only 6watts. highly unlikely that will hurt anything. but 50V might


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## 14642 (May 19, 2008)

10uF is the right answer if it's a typical 1" tweeter. 20uF will work too. Anything in between. Not all that critical. I usually use something that has a -3dB point at about half the crossover frequency.


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## amomacko (Sep 14, 2010)

Andy is correct 

A light bulb is wrong


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## 14642 (May 19, 2008)

A light bulb is often used in crossovers to protect tweeters, but not from DC caused by a failed amp, although it does offer some indirect protection. The light bulb is simply a resistor that has increasing resistance with increasing voltage. The more power you apply, they brighter the bulb, whic means more voltage is dropped across the filament because the resistance increases with heat. The reason the filament doesn't burn is quickly is because there's no air in the bulb. It's imprecise but effective in making a system relatively foolproof. However, it doesn't sound good, especially if the designer makes the mistake of putting the bulb between the passive high pass filter and the tweeter. Seems like an obvious mistake, but I see it all the time.


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## amomacko (Sep 14, 2010)

Andy:

Thanks for the detail - it all makes sense.

I just wanted to clarify to the OP that light bulb does not provide DC protection. However as you have pointed out there is a use for a light bulb albeit not an optimal solution to help prevent tweeters from burning up due to thermal overload.

As a side note, and not related to speaker protection, Nelson Pass has used a light bulb in one his Zen amp variations.

http://www.passdiy.com/pdf/zenlite.pdf

In this case, the light bulb is used as a constant current source in an amplifier design.


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## Skierman (Mar 3, 2008)

The 2200 UF is wired in with the tweeters now, but I have these being delivered, Amazon.com: Dayton Audio DMPC-2.0 2.0uF 250V Polypropylene Capacitor: Electronics Caps make me feel like an idiot, I have no clue what these are rated. 2.0UF means what?


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## minbari (Mar 3, 2011)

lol, from one extreme to the other. that will be a HP at about 18kHz. pretty useless unless you just want to piss off dogs.


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## gokiburi (Jul 20, 2007)

Maybe this article by Richard Clark will help.

IN THE KNOW: Nov/Dec 2001

And this.

Tweeter Crossover Capacitors

More good stuff:

http://www.diymobileaudio.com/forum/diyma-sq-forum-technical-advanced/36855-tweeter-protection-circuitry.html


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