Zobel networks in an active speaker/crossover

[SteveVaiRules]

I am designing a speaker around an active crossover. and the only passive component I had in mind was a tweeter protection circuit.

But I am wondering if by using 1 amp/driver I would really benefit from the introduction of a zobel network(s). If so should I attach one to every driver or just a specific driver. Of course I am designing the crossover points around the frequency response curves of the drivers and am largely ignoring the impedance curves (doing this because I have gone active). Now I don't know if this is to become a detrimental choice. And how should I fit a zobel network into this equation, if at all? 😕

These are the drivers I am using. And this isn't my first speaker.
accuton® Carefully selected loudspeaker drivers.
accuton® Carefully selected loudspeaker drivers.
accuton® Carefully selected loudspeaker drivers.

Looking at the impedance curves I don't really think that I will be really anywhere near the peaks in the curves for any of the drivers. So does that mean that a zobel network in this case is just extra hassle for little to no gain?


Matt

 

[mrfeedback]

Amplifiers always prefer resistive load, so yes I would compensate the rising impedance characteristic.
Even better results are obtained ime by compensating the electrical resonance of the drivers also.
This does take more time and incurs more cost but is well worth while, especially considering the prices of the Accutons that you are specifying.

Eric.

 

[SteveVaiRules]

this is my first active build, so I am wondering if there is going to be any negatives to having a zobel in the signal path; other then the time, cost, and complexity issues, which I am willing to go through if it's worth it? Considering I am using accutons as a sign that I will be pushing the boundaries and willing to spend the extra time and money and willing to put up with additional complexity.

Will the zobel network have a negative impact on the sound or is the trade off of a flatter impedance and a nice resistive load on the amplifier be more then an ample consolation?

I don't really have a tonne of experience with zobels in my own designs, my only experience is in implementations of others work.

Thanks for the reply Eric!

Matt

 

[Henry8]

I would concentrate on getting right your active setup, crossover points, amp choice, achieving desired acoustic response via the xover etc.
A amp driving a sole driver is the easiest load for it, since there are no caps and inductors.
Once the system is running then if your bored you can add a zobel to flatten the inductive rise, and evaluate its benifits....
If your really bored then you can try to add l-c-r for the imp res peak.
Zobel design via software is easy if you have the actual measured imp.
Imp res peak is slightly more tricky.
I can say zobels can offer a very slight, smoother sound with some tweeters.

 

[mrfeedback]

Thanks for the reply Eric!

You are welcome.
My experience is that the effects are only positive.
One thing to note is that the networks should be right at the driver away from the magnets as far as is practical, and not on the cabinet input terminals.
If you impedance eq the individual drivers correctly you get smooth highs way out past your hearing, lows that are clean all the way down to the floor, and mids/vocals that sound right.
Another benefit is being able to run the system significantly harder (higher spl) before nasties creep in, and therefore better reliability of drivers.
Cooler running of amplifiers and perceived higher efficiency is another plus.
Sweep your drivers from the amplifier end of your cables at realistic sound pressure levels and mounted into the cabinets to get correct component values by selecting on test.
Some more background....you can do more searching if you like.
Zobel network - Wikipedia, the free encyclopedia
Passive Crossover Network Design

Any more info, just ask.

Eric.

 

[sreten]

Hi,

FWIW I cannot see any point in zobelling the drivers in a fully active setup
with low output impedance amplifiers, it only makes some sense with high
output impedance amplifiers, and that effect can be alternatively EQ'd.

rgds, sreten.

 

[mrfeedback]

Cheap Speakers Don't Bother To Do It, But Good Ones Do...

Hi,

FWIW I cannot see any point in zobelling the drivers in a fully active setup
with low output impedance amplifiers, it only makes some sense with high
output impedance amplifiers, and that effect can be alternatively EQ'd.

rgds, sreten.

Sure.....in a perfect world. Reactive load = return energy that the amp and internal feedbacks have to deal with.
Resistive load means one way transmission of energy and is ideal as can be.
Reducing load inductance is always better ime, and that includes speaker cables.
Matt is forking out $2k++ for drivers + cabinets +++ etc.
Extra passives are not going to break the bank and will polish his project.

Eric.

 

[bigfishe]

I'm with you on that Eric .I run a DEQX and find the zobel smooths out the sound of my two way fullrange/sub system.brines fb20/goldwood H frame

 

[benb]

Hi,

FWIW I cannot see any point in zobelling the drivers in a fully active setup
with low output impedance amplifiers, it only makes some sense with high
output impedance amplifiers, and that effect can be alternatively EQ'd.

rgds, sreten.

I agree with this, a zobel would be much more important sound-wise for any driver(s) driven by a tube amplifier where its higher output impedance would cause a rising voltage where the driver has a rising impedance.

 

[Charles Darwin]

Personally I think that any inductor in the signal path between amp and driver does more damage than an uneven impedance with regards to transistor amps.

 

[SteveVaiRules]

Cool!!! Lots to think about!!

Thanks guys!

I am going to try the speakers with and without the zobel, both by measurements and with my ears.

I know it's extra expense and time, but hell, why not right? 😀


Charles Darwin, how would the sound be effected? Like, what characteristics of the sound would change?

Thanks again guys.


Matt

 

[BobEllis]

Matt, I am in the Sreten camp - It doesn't seem like it would make a difference in most cases when using a solid state amp with low output impedance. I tried a couple times and found no audible difference. Some drivers, like some full rangers, benefit from high driving impedances. Perhaps this is why certain tube amps make certain drivers sing and others don't.

Good for you conducting your own experiments to see if it matters to you in your system.

I don't think of an impedance flattening conjugate network as in the signal path between amp and driver like a baffle step or series notch would be. It's a series connected RLC across the driver terminals.

Of the many advantageous characteristics attributed to active systems over passive, better driver control due to direct connection of the driver to a high damping factor amp seems to make sense. I suspect that effect combined with the potential signal distortion generated by series inductors are the effects that CD implies.

You'll probably get as much debate on this as the value of zobels in an an active system. The way to verify is make active and passive crossovers that generate identical response curves and see if you hear a difference. I haven't done that experiment, because one of the reasons I started down the active trail was to avoid buying a collection of inductors and caps. I did replace a passive crossover with an active one and found much improvement, but the transfer functions were not identical.

 

[Pano]

I did replace a passive crossover with an active one and found much improvement, but the transfer functions were not identical.

I applaud your honesty.

 

[SteveVaiRules]

Matt, I am in the Sreten camp - It doesn't seem like it would make a difference in most cases when using a solid state amp with low output impedance. I tried a couple times and found no audible difference. Some drivers, like some full rangers, benefit from high driving impedances. Perhaps this is why certain tube amps make certain drivers sing and others don't.

Good for you conducting your own experiments to see if it matters to you in your system.

I don't think of an impedance flattening conjugate network as in the signal path between amp and driver like a baffle step or series notch would be. It's a series connected RLC across the driver terminals.

Of the many advantageous characteristics attributed to active systems over passive, better driver control due to direct connection of the driver to a high damping factor amp seems to make sense. I suspect that effect combined with the potential signal distortion generated by series inductors are the effects that CD implies.

You'll probably get as much debate on this as the value of zobels in an an active system. The way to verify is make active and passive crossovers that generate identical response curves and see if you hear a difference. I haven't done that experiment, because one of the reasons I started down the active trail was to avoid buying a collection of inductors and caps. I did replace a passive crossover with an active one and found much improvement, but the transfer functions were not identical.

Interesting points.

I still want to build both and test, but part of me is really wondering if this will be worth it. I will be using solid state amps and the crossover frequencies really won't be near the huge impedance peaks (i don't think) I will still need to test the drivers to see of course.

Seems that there is positive points to both approaches, and that there is no clear winner. So despite my leaning towards it not being necessary I am still going to go through with a test and see what if any difference it really makes in my particular system.

I'm still looking for other peoples opinions on the subject though. 🙂

Matt

 

[BobEllis]

Another thing to keep in mind is tweeter protection. I use a large value cap to protect my tweeters from DC. Not everyone agrees on the need for this, but it makes me feel better. I was surprised how much it affected the overall response even with the roll off an octave below the crossover point.

Next time the cap will either be one pole of my filter or at least 50 uf to get it really out of the way. Of course, this will give you another experiment to determine whether the cap is audible...

 

[SteveVaiRules]

Another thing to keep in mind is tweeter protection. I use a large value cap to protect my tweeters from DC. Not everyone agrees on the need for this, but it makes me feel better. I was surprised how much it affected the overall response even with the roll off an octave below the crossover point.

Next time the cap will either be one pole of my filter or at least 50 uf to get it really out of the way. Of course, this will give you another experiment to determine whether the cap is audible...

I am going to use a cap for the tweeter protection. But I am going to be using a DEQX unit with a 300db/octave filter. Also I don't plan on using a really high cap value just enough to keep things from getting hairy. I do plan on testing the audibility of the protection circuit and will adjust accordingly.

Thanks for pointing that out though 🙂


Matt

 

[BobEllis]

Keep in mind that using an 8ohm nominal tweeter and 24 uf (2x12uf that I used) roll off begins above 1500 Hz. Even with a brick wall filter you still want to keep the F3 of the filter formed by the protection cap more than an octave away from your cutoff to avoid impacting response in the pass band.

 

[SteveVaiRules]

Good to know. Thanks!


Matt

 

[AudioEngineer]

Personally I think that any inductor in the signal path between amp and driver does more damage than an uneven impedance with regards to transistor amps.

The RC Zobel network does not use any inductor in the signal path. Even the RC components are not directly in the signal path i.e. in series, rather they are connected in parallel and only come into effect at higher frequencies.

 

[speaker dave]

Amplifiers always prefer resistive load, so yes I would compensate the rising impedance characteristic.

Eric.

Measurements that I have seen have shown that amplifiers are quite happy with inductive loads and can actually give lower distortion than into resistors. The phase angle for the typical driver is fairly modest (45 degrees or so) and in the right direction.