Capacitor only filter for a twitter 2

[LucasBS]

I need to make a High pass filter for a twitter (allowing 1kHz or more)

I thought about putting a capacitor in series, but been reading that it needs a resistor too

None of the answers have convinced me of why

Plus, a resistor across (?after or before the capacitor?) will (?) reduce the current of the hi freq as well, and I don't need to say that that is undesired...

Why can I not use a capacitor only, in THIS case? It seems to fit perfectly in my conception

 

[MacGyverS2000]

You're looking at RC filters. The intent is to slow down the speed at which the signal "fills" the capacitor. It is this speed (i.e., frequency) which you're designing for. There is an inherent resistance in any wire (and any non-ideal capacitor), but it is likely to be too low to get you to the frequency range you care about, hence the need to add resistance.

Dan - Owner

http://www.Hi-TecDesigns.com

 

[LucasBS]

But what about the capacitive reactance ?
Won't this reactance slow down the speed at which the low frequency fills the capacitor ?

 

[VEBill]

A 'tweeter' (small high frequency speaker) ?

There are many (2-way) speaker designs where the only cross-over is that the tweeter has a series capacitor.

Resistors in the tweeter circuit would impact the frequency response, but may actually be included for the primary purpose of balancing the frequency response (bring the tweeter level down to balance the woofer, to avoid being too "bright"). The resistor may even be adjustable, or a combination of fixed and variable.

The best approach to speaker builds is to follow an existing deign.

The box that the tweeter came in may include a data sheet with a recommended typical value for the series capacitor.

Failing that, perhaps experimentation. Trying to predict the correct value might well require more data than is available to you.

 

[LucasBS]

"There are many (2-way) speaker designs where the only cross-over is that the tweeter has a series capacitor."

That's what I thought. It makes all the sense.

I have no documentation at all. All the components I have been scavenging. The box I'm doing myself
This small speaker is one of those cheap computer pairs (but it sounds good and is loud). Seems full range, but I'm not confident. That's why the filter.

The woofers are already dominating the sound. Now I'm adding the small ones, so no need to reduce their strength

Still today, before your answer, I found one of those online RC filter calculators. One of the ideas that came was to put a very high resistor across (1M ohm).
The site shows the Bode diagram, and it seems to behave pretty much as if there was no resistor at all. It only shifts the cutout frequency.

I think the problem is resolved

 

[MacGyverS2000]

Ah, I couldn't figure out what a twitter was... never dawned on me we were discussing a "tweeter"/speaker.

The cap-only configuration is more than likely an LC filter, where the 'L' is the speaker coil, rather than your RC filter. Equations for determining cut-off frequency works the same...

Dan - Owner

http://www.Hi-TecDesigns.com

 

[LucasBS]

Yep. Loudspeaker is the subject
Blame it on regionalism...


But I've learned a lesson here: I can cheat a similator, not real life
My "infinte resistor" approach that I used on the RC calculator demands in real life a huge capacitor

Let's try your LC idea now. Makes more sense

 

[OperaHouse]

Actually, many tweeters now are piezo. They call the series capacitor a shelving capacitor. So it is more of a frequency selective capacitive voltage divider.

 

[VEBill]

...many tweeters now are piezo...

I'm not a 'serious audiophile', but I'm still here grimacing at the thought of a piezo tweeter. Perhaps they've improved since the "fingernails on chalkboard" versions I've heard over the years.

Dipole Ribbon, now that's a tweeter.

;-) !!!

 

[OperaHouse]

People will listen to anything. Many years back the Infinity 1001 has a 12 inch woofer where the weighted the voice coil with modeling clay. Added to that was a tiny tweeter. It was Tizz, tizz, boom, boom. Big hole in the midrange, but people liked them. I still have a pair of Magnaplanars.

 

[jimkirk]

If the issue is that the woofer is "dominating the sound", a simple solution might be to add a resistor (an ohm to ten ohms or so) in series with the woofer to reduce the bass. Be sure to use one with a suitable power rating.