[JLM]

What is the design like?

Why do some speakers have them and some don't?

What are it's effects/advantages?

TIA

[Vapor Audio]

Traditional use is to flatten the impedence curve on a woofer.  Typical woofers have significant rise with frequency, the Zobel makes it a flat line, and allows the network to function correctly as frequency rises.  But there are many other uses for Zobel like networks, I use one in my Cirrus on the AudioTechnology woofer which has effectively NO inductive rise.  It's function there isn't to flatten impedance since it's already flat, but to adjust the woofer rolloff in order to meet target which then aligns phase between woofer and tweeter.

A Zobel on the tweeter can be used to flatten the peak at the Resonance Frequency, also called a trap in this application.  On tweeters you basically try the network with and without, listen closely and see if there's any benefit. 

Many times speakers that should have a Zobel on the woofer don't because of extra cost, same with the tweeter. 

[JLM]

Thanks, but what does the circuit design look like and what are the sonic impacts?

[richidoo]

The voice coil in a dynamic driver has the same low pass filtering effects as any inductive coil. The rising impedance is what causes the low pass filtering effect with a voltage source amp. A zobel filter lowers the Q of the inductor and flattens the rising impedance.

But different types of amplifiers react in different ways to the rising impedance. Some amps will play softer into higher impedance, while others will play louder, like current source amps, or tube amps with low damping.

With single driver speakers the zobel can be used to tune the high freq response, but only if the amp would otherwise be affected by the rising impedance. With a super low output impedance like your Hypex, the zobel will have less effect - that's one of Hypex's claims to fame, flat response no matter what the load.

Some insights on source impedance and load impedance in this.


edit:

Thanks, but what does the circuit design look like and what are the sonic impacts?

It is a resistor and cap in series put in parallel with the amp or load.


http://en.wikipedia.org/wiki/Zobel_network
http://diyaudioprojects.com/Technical/Speaker-Zobel/

[Quiet Earth]

I think there are very good answers in this post.

what are the sonic impacts?

After you get your fill of reading about zobels, try a simple experiment with your single driver speakers (if they don't already have a zobel in them). All it would take with your amp and speaker is a 6 or 7 ohm resistor and a 2 or 3 microfarad film cap to make a zobel that will let you hear the ballpark effect of what you just learned.

Make sure you get a 5 or 10 watt resistor, but don't worry too much about the quality of these parts for the experiment. Keep it cheap.

[jeffh]

Good stuff.  You guys make this a great place.

So, don't you need measurements of the speaker to figure out the value of the components?

[Vapor Audio]

Good stuff.  You guys make this a great place.

So, don't you need measurements of the speaker to figure out the value of the components?

Yes, you do need an inductance sweep of the driver to figure out proper Zobel component values.  What Earth was saying was you can plug in some generic values and see what happens, although more like an 8-10uf cap is typical instead of a 2-3.

[richidoo]

Another good article about zobels, from John Murphy of True Audio.  I like his explanations.

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

[Æ]

You might also want to look up "Boucherot cell."