Whats the point of a Zobel?

[Hybrid fourdoor]

I know that a zobel network is used to cancel out the reactance of the voice coil, but how does it play out in real life?

I added one to my Spheres which have a W3-881S running full range. I used a 8ohm resistor and a 4.7uF capacitor. sitting in front the speakers listening to Vangelis' End Theme To The Bounty which has alot of descent high frequency energy I couldn't here a difference disconnecting and reattaching the circuit.

So what is it really supposed to do? Is it something I have to listen to in stereo? Am I damned with normal ears? Am I cursed to a lifetime of listening to sub $10K stereos, never to make it out of The Absolutes Sounds basement systems??? What should I do?!?!?!

TIA

[jean-paul]

Do we need Zobel with chip amps?

All about Zobel is written in that thread. BTW 8 Ohm in series with 4.7 uF is not correct. Try 8 Ohm with 0.1 uF in series instead. When you don't hear the network when its connected that's only better. It should not have influence on sound but just do its protective job silently

[Hybrid fourdoor]

I used C=(Le/(r²)

So thats C=(0.0003/64) = 4.687uF

[Ouroboros]

A series C-R network gets used for two things.

The first is the real 'Zobel' network, and is used at the output of an amplifier, (usually before any output inductor/resitor combination), to ensure that even with an inductive load, the amp sees an effectively resitive load at high frequencies. This helps to keep the NFB loop stable.

The second use is to go across the voice coil of a bass (or midrange) unit, and makes passive crossover design easier, in that the correct C-R values can compensate for the inductance of the voice coil so that the bass unit has a nearly constant impedance across the audio band. The effect is easily seen with a simple first-order LPF. In this case the ultimate attenuation at high frequencies can be much less than expected, because the speaker impednce at HF will be much higher than the nominal value because of the dominant effect of the voice coil inductance.

With active XO, and with a separate power amp per drive unit, voice coil inductance compensation tends not to be needed.

[phase_accurate]

With active XO, and with a separate power amp per drive unit, voice coil inductance compensation tends not to be needed.

That depends on the amp IMO.
It is never a bad idea if speakers present a real load to the amp even though it might not make a difference in this specific case. But you should be aware that a manufacturer never knows what amp will drive his speakers.
If two speakers are demoed with the same amp and one sounds bad just because of amp/speaker interaction, guess which one will be sold ??
This is particularly the case for amps with high output impedance.

In the aforementioned case I would maybe leave the impedance compensation away, but would keep it in mind if these speakes sounded harsh when connected to an SET for instance.

Regards

Charles

[Hybrid fourdoor]

Originally posted by jean-paul
Do we need Zobel with chip amps?

All about Zobel is written in that thread.

Haha, ya right! By the fifth page it was like trying to run though the ocean.


So for a full range application it doens't help much? I thought maybe it would make high frequency extension better since the impedence would stay relative.

[ashok]

Hi,
Zobel networks on full range speakers will show up on listening tests only if the output impedance of the amp is 'high'.
With Zo ( output impedance ) of say 0.1 ohms or less it should be less audible . With tube type Zo of 1 ohm or more it will probably be more audible.
Since it 'flattens' the impedance at high frequencies it will result in reduced HF and that can sound different depending on the speaker. It could just sound like softer HF or less noisy in 'noisy' speakers. In many speakers I have found it to help in smoothening the audible sound from the speakers.
IMO it is essential for better sound. This is highly dependant on the speaker and amp being used.
I would think it is better to start with it and switch it out if you find it not so audible.
Cheers.

Edit : Don't forget that Zo can vary with frequency. Typically it will rise at HF and also at LF.