Tweeter protection Cap

[static]

Hi

I would like to protect my tweeter, as I plan to go from passive X-over to an active one.
So I'd like to slap a good quality film cap on both tweeters.
The question is what value should it be? These are two ways with X point @ 3kHz, so ideally i'd probably want the cap to filter out anything else below like 1kHz or so (suggestions?)

I remember reading that Peter Daniel has a single cap on his tweeter, what value is it?

Thanks
Alex

 

[tiroth]

Ideally you would want the corner to be at least 2 octaves below crossover, unless you are using it as a pole in the real crossover network of course. So, corner at 750Hz would be ideal, 1kHz should be fine if that is what you have the parts for.

 

[static]

wow - that was a quick one 😱

well, the figure of 1kHz I just guesstimated

So what value of the cap should i get for 750Hz, as per your recommendation?
Also what brand: i was looking at Auricap and more $$$ Hovlands.
Do Hovlands make a noticable difference?

Thanks
Alex

 

[Pan]

Not that I´ve done it myself but it really makes sense to use the DC blocking cap as a pole together with the active.

You can use a smaller cap, which means higher quality for the same money.

/Peter

 

[tiroth]

The only downside to using the cap as a pole is that the pole will vary as the tweeter's impedance varies, throwing away some of the benefit of going active. It's cheaper though.

For a tweeter that doesn't dip below 7 ohms you would need a cap of (2*pi*750*7)^(-1) or ~30uF.

 

[static]

sorry guys, but you will have to be a little patient with me 🙄 😀

First of all can anyone explain the "pole" cap concept? Never heard about it, unfortunately.

30uF!?! are you sure? Then how can 20Hz make it through a 2.2uF DC blocking cap almost unaffected (not rolled off). I will have to pay dearly for a very good quality 30uF cap.

Thanks
Alex

 

[fdegrove]

Hi,

Then how can 20Hz make it through a 2.2uF DC blocking cap almost unaffected (not rolled off).

Because it's working with a much higher impedance.

For a tweeter that doesn't dip below 7 ohms you would need a cap of (2*pi*750*7)^(-1) or ~30uF.

If you look at the figure 7 in the formula, that's the 7 Ohms of the tweeter.

BTW...If you don't have DC at the output of your tweeter amp then I don't see any point in using a blocking cap for the tweeter.

Cheers,😉

 

[sreten]

BTW...If you don't have DC at the output of your tweeter amp then I don't see any point in using a blocking cap for the tweeter.

Cheers,😉

Protects the tweeter against a DC amplifer fault, 🙂 sreten.

 

[Pan]

"Protects the tweeter against a DC amplifer fault, sreten."

Girly girly... 😉

/Peter

 

[static]

Thanks for the explanation on capacity and impedance. It all makes sense now.

Girly girly...

thats unless you have $$$$ tweeters in your speakers.
Since I have $20 tweeters in mine, i guess i can avoid the cap.

Sorry for the bother.
Alex

 

[fdegrove]

Hi,

Sorry for the bother.

Don't be...

I can understand you want to protect your investment but when things go wrong on the amp side, the cap isn't even going to protect.

It'll block DC allright, but what if the amp starts to oscillate at ultrasonic frequencies?

It will fry the tweeter in a few seconds...
So, from my POV, better have a stable amp than to take a false insurance.

Cheers, 😉

 

[roddyama]

Hi,



Don't be...

I can understand you want to protect your investment but when things go wrong on the amp side, the cap isn't even going to protect.

It'll block DC allright, but what if the amp starts to oscillate at ultrasonic frequencies?

It will fry the tweeter in a few seconds...
So, from my POV, better have a stable amp than to take a false insurance.

Cheers, 😉

The bigest culprit will be all the full power high frequencies generated when the amp goes into clipping that are passed uninhibited through the protection cap and fry the tweeter.

 

[static]

These are all good points.
However what I had initially in mind is that since I am trying to go active, if I ***** up something in the active crossover and very low frequencies will make it to the tweeter, from what i had heard, it can kill it.
The passive Xover at least doesnt have this problem.
By the way, is active Xover that much better? I mean does the improvement justify the extra amps and active circuitry?


Thanks
Alex

 

[fdegrove]

Hi,

However what I had initially in mind is that since I am trying to go active, if I ***** up something in the active crossover and very low frequencies will make it to the tweeter, from what i had heard, it can kill it.

Nope...not likely to happen but it's not impossible.

That part isn't going to have to work hard or is it?
Not the X-over nor the Amp...Milimiliwats here.

Still, thing can go wrong and according to Mr. Murphy they always go the most wrong where you'd least exprect it....

The passive Xover at least doesnt have this problem.

It's exactly the same thing, except with an active x-over I'd say that tweeter is even better protected.

By the way, is active Xover that much better?

Depends on the x-overs, but bi-amping is certainly worthwhile.

I wouldn't implement any of it before I were up to speed on the theory though...

Call me old fashioned,😉