RCL, RL, Zobel.

[Juggy]

All,

I've been reading, and am a little confused as to when we use which filter.

From what i understand,

The RCL is generally used on tweeters because of the large inductor that would need to be used in a zobel.

A Zobel is generally used on woofers and mids to compensate for the rise in impedence at Fs.

I've seen RL and RC filters as well, can someone please shed some light on those filters and their use as well?

Thanks again and i apologize for my basic questions.

[Horexx]

In detail:
http://users.ece.gatech.edu/~mleach/...obel/zobel.pdf

[Svante]

The main reason to use impedance equalizing networks is that a frequency dependent impedance sometimes causes problems for the crossover filter.

Basic filter therory usually relies on a purely resistive load, and using impedance equalization can be a way to achieve that. In that case, textbook filters behave more like the theory predicted.

Today, when simulation is so easily available for anyone with a computer, the need for impedance equalization is less. One can mostly modify the filter to behave as desired without these solutions.

Anyway, to answer the question:

An RC link compensates for the rise of the impedance toward high frequencies caused by the voice coil inductance. There is rarely a need to do this.

An RCL link compensates for the impedance peak at resonance. This can be useful for tweeters; the system resonance is often (too) near the crossover frequency and it may be hard to make the filter behave well without the compensation.

An RCL link can also be used on woofers that are crossed over low (100-300 Hz), also due to that the resonance is near the crossover frequency.

I encourage anyone to try some simulations on this. It is rather enlightening to put a cookbook filter and connect it to a real loudspeaker impedance.



All the above is for passive filters.

[69stingray]

Info on Zobel Networks:

http://www.trueaudio.com/st_zobel.htm


Zobel Calculator I like to use:

http://www.the12volt.com/caraudio/crosscalc3.asp#cc

Series Notch Filters (RCL):

http://www.carstereo.com/help/Articles.cfm?id=23