Biamping and Zobel Networks

[lohk]

ps: By the way, Andrew, did you get my mail ?

Klaus

[lohk]

It is strange, but we all are talking about loudspeaker crossovers so often - but on the other hand we all know very well that active systems are so much better most of the time !
How many passive crossovers I already tried to adapt, modify or make it better with little or doubtable effort ?
But, alas, active systems are, besides being more expensive, even more tricky to set up, they can be much more of a go-no go affair. I mean proper active systems, not the biwiring or biamping "bastards".
In virtually no recording studio in the world the musicians and the engineer listen only to passive monitors, even smaller sized monitors are getting almost inevitable. Have you ever listened to, say, a Genelec 1029 ? These are very small loudspeakers in heavy non-resonant aluminium cases and can sound very un-hifi-ish clear, neutral and punchy. All this is in a cheap opamp powered active two way system package. It may not be the best loudspeaker of the world, but it is a slap into the face of so many much more expansive systems.
And there are, btw, no zobels needed anymore.

I am sorry to have left the path of this thread almost, but should we better not search better ways of getting our systems active ? I am asking myself this question quite often although I know that it is not that easy.
There must be better active crossover schematics or different ones for the critical cases. Then discussions about zobels in passive networks could be a thing of the past.
In a different thread maybe...

Klaus

[Won]

Thanks for everyone's replies.

And of course, the original thread was motivated by building an actively xover speaker system.

-Won

[hakalugi]

Originally posted by lohk
Zobel networks in the loudspeaker crossover obviously do not correct the damping factor of the amp.

I don't know about correction, but they can surely change it.

If Zobel's flatten (by lowering a portion of) the impedence curve they could alter an amp's daming factor at a given freq.

DF = speaker impedance / amplifier output impedance

Say an amp has a DF of 300 at 2khz where the driver's impedence is 13ohms 'before' Zobel. If a Zobel circuit is applied and the load 'seen' by the amp is droped to 8 ohms at the same 2khz, the amp's damping factor would now be 184.

(unless i'm mixing Zobels. And we know what can happen when one mixes Zobels- whew! don't even think about it)

[jam]

It is easy to proclaim that Zobels do not affect the sound of drivers in an active speaker without trying it but let me assure that there is a difference most of the time. The difference may be small at times but it is there none the less, after all are we not trying to get every last bit of performance from our designs.
To prove what I say hook up an amplifier to a driver and feed it with a square wave (say 1k keep the amplitude low to avoid harming the driver) and observe the output with a scope. Repeat the test with the zobel attached and you will see what I mean.

Jam

[Won]

Very coy of you Jam.

Well, don't leave me hanging...what happens?

-Won

[jam]

Won,

Sorry to keep you hanging.

When an amplifier drives a reactive load you will notice a certain amount of ringing or overshoot on the tops of the waveform. A zobel will change the amount and character of this overshoot.

I suggest you try Zobels on an active system and judge for yourself. If it works use it, if not leave it out. I have found that Zobels work in most instances, even in subwoofers.

Cheers,
Jam

[walker]

Jam, I believe I know where your coming from ,buuuuut. The ringing that you will see without reactive correction is worst with correction. You just need to know where to look for it.

If you were to monitor the current between the Zobel network and the driver you will find the ringing alive and well. If you look for voltage ringing between the amp and speaker, (or in this case the Zobel network) you should see less ringing.
With reactive correction the amp has very little control over the LC circuits oscillations without correction the amps dampening has more control. These conclusions I have reached from a purely theoretical position. I have not tested it, I could be wrong but I don't think so. I will setup the experiment tomorrow if time allows.

Look up tank circuits.

The other misconception is that a Zobel network flattens the drivers rising impedance. Well it does and it doesn't, the driver's rising impedance doesn't change but there is a new element with falling impedance, (with rising frequency).

Look I could be missing the point here, feel free to shoot this down, we'll all gain from the outcome.
Regards WALKER

[jam]

Walker,

I am glad you are about to put this to the test.
I should have clarified that I mount the speaker Zobel network right in the driver terminals themselves, which I believe is important.
I have found instances when the Zobel was determental but rarely. I will be waiting for the results of your experiments, please also listen to the results.

Cheers,
Jam

[Edited by jam on 12-05-2001 at 08:27 AM]

[walker]

Jam, having the network at the driver is, as you said, the way to go but the oscillations will still increase over connection without the network I suspect.
I will listen but I won't have the time to measure it I suspect. I can take oscillograms but I still don't know how to post images, HELP?

Regards WALKER