How to think about a Zoebel?

[johngalt47]

I put a zoebel all by itself across my woofer to see how OmniMic and WT3 measured it.

I was surprised that the fr in OmniMic was nearly identical with and without the zoebel. The only difference was that with the zoebel it was down about 3 db.

I did expect a change in the impedance graph in WT3 and sure enough it straightened out the rise. What surprised me was that now WT3 says the driver has NO Le and that Re is about 1.5 ohms higher.

But...the combination of the Zoebel and the driver's inductance only results in a pure resistance at the resonant freq of that combination, right?

[Jeff B.]

I put a zoebel all by itself across my woofer to see how OmniMic and WT3 measured it.

I was surprised that the fr in OmniMic was nearly identical with and without the zoebel. The only difference was that with the zoebel it was down about 3 db.

I did expect a change in the impedance graph in WT3 and sure enough it straightened out the rise. What surprised me was that now WT3 says the driver has NO Le and that Re is about 1.5 ohms higher.

But...the combination of the Zoebel and the driver's inductance only results in a pure resistance at the resonant freq of that combination, right?

You shouldn't have any difference at all in frequency response. A zobel by itself without any series elements will not affect frequency response, only impedance.

A zobel, if properly designed, will counter Le and flatten the impedance all the way up, not just at one resonant frequency (of which there isn't one). If it's done its job, you won't measure an Le.

[dthomas]

I put a zoebel all by itself across my woofer to see how OmniMic and WT3 measured it.

I was surprised that the fr in OmniMic was nearly identical with and without the zoebel. The only difference was that with the zoebel it was down about 3 db.

I did expect a change in the impedance graph in WT3 and sure enough it straightened out the rise. What surprised me was that now WT3 says the driver has NO Le and that Re is about 1.5 ohms higher.

But...the combination of the Zoebel and the driver's inductance only results in a pure resistance at the resonant freq of that combination, right?

Well first the fact that the FR response was the same is a good thing. Your amplifier is a voltage amplifier and regardless of impedance it should deliver the same voltage level to your loudspeaker.

The reason it could have been down was due to the change in impedance but be careful that you had the same voltage applied from your amplifier.

The zobel won't make your woofer's resonance go away it should flatten your woofers rising impedance as frequency goes up and make it easier to cross. So in short no that is not the purpose of a zobel. What did you use to calculate the values of the zobel. If you used it to flatten the woofers resonance that is not really a zobel, but it would explain why your WT does not like it.

With modern crossover tools there is no reason to use a zobel.

[dcibel]

But...the combination of the Zoebel and the driver's inductance only results in a pure resistance at the resonant freq of that combination, right?
You tell me, you've got the WT3 and the speaker with zobel applied!

3dB is a bit much to lose with a zobel applied, check your measurements and levels again. You should lose, roughly zero.

[dthomas]

Sorry Jeff beat me.

[dthomas]

You tell me, you've got the WT3 and the speaker with zobel applied!

3dB is a bit much to lose with a zobel applied, check your measurements and levels again. You should lose, roughly zero.

You are right... But since he affected the TS parameters I expect his WT miscalculated for a new efficiency.

[johngalt47]

Ok, guys....I'm trying to get a feel for what happens when certain circuit elements are applied. The way I learn is to make an application and actually see it in action. I can't just do a calculation and automatically know what will happen when it is applied. I'm just not that guy. I have to build it and play with it to get a feel for it.

I didn't change the volume control on the amp after I applied the Zoebel.

I used this web site to do the calculation: http://www.diyaudioandvideo.com/Calculator/ImpedEqual/

[dthomas]

Ok, guys....I'm trying to get a feel for what happens when certain circuit elements are applied. The way I learn is to make an application and actually see it in action. I can't just do a calculation and automatically know what will happen when it is applied. I'm just not that guy. I have to build it and play with it to get a feel for it.

I didn't change the volume control on the amp after I applied the Zoebel.

I used this web site to do the calculation: http://www.diyaudioandvideo.com/Calculator/ImpedEqual/

Well you did change the impedance and may have been enough to dramatically affected the spl. The amplifier maintains the same voltage level but it is dependent on impedance.

[Chris Roemer]

Well first the fact that the FR response was the same is a good thing. Your amplifier is a voltage amplifier and regardless of impedance it should deliver the same voltage level to your loudspeaker.

The reason it could have been down was due to the change in impedance but be careful that you had the same voltage applied from your amplifier.

The zobel won't make your woofer's resonance go away it should flatten your woofers rising impedance as frequency goes up and make it easier to cross. So in short no that is not the purpose of a zobel. What did you use to calculate the values of the zobel. If you used it to flatten the woofers resonance that is not really a zobel, but it would explain why your WT does not like it.

With modern crossover tools there is no reason to use a zobel.

Well, it's really possible to make a Zobel for about $1 that can save you many, many more by dropping down the size of the coil needed to do the job.

Chris

[dthomas]

Well, it's really possible to make a Zobel for about $1 that can save you many, many more by dropping down the size of the coil needed to do the job.

Chris

For a $1? Come on a cap and a resistor cost's more than a dollar well I shouldn't say that I know where you can get a film cap and a 15W resistor for about $1.40. God forbid you have to pay shipping on it too. It depends most midwoofers don't see a significant rise in impedance until well above 2KHz so not sure that coil is going to be much smaller if any. On a woofer in a 3 way there would be no advantage to a zobel on the size of the inductor even a 2 way crossing at 2 to 3Khz is not going to see a significant reduction in the inductor value. Model it and you will see what I am saying.

[Chris Roemer]

For a $1? Come on a cap and a resistor cost's more than a dollar well I shouldn't say that I know where you can get a film cap and a 15W resistor for about $1.40. God forbid you have to pay shipping on it too. It depends most midwoofers don't see a significant rise in impedance until well above 2KHz so not sure that coil is going to be much smaller if any. On a woofer in a 3 way there would be no advantage to a zobel on the size of the inductor even a 2 way crossing at 2 to 3Khz is not going to see a significant reduction in the inductor value. Model it and you will see what I am saying.

Well, I've done 100's of models, and what I should have said is that if someone is trying to roll off a woofer using just a coil, the Zobel can significantly reduce the coil size.

Even going 2nd order electric though, by adding that resistor to the shunt cap you have a LOT more control over the rolloff shoulder than using the cap alone. Typically the Zobel won't help much for the woofer on a 3-way, since it's crossed down near Zmin where the profile is pretty flat. Even on my Nano Neos/ntns I used a Zobel ALONG with a series coil and shunt cap to contour the rolloff. Those Zobels ran 0.80c to $1.00. Npe caps and wirewounds.

Chris

[dthomas]

Well, I've done 100's of models, and what I should have said is that if someone is trying to roll off a woofer using just a coil, the Zobel can significantly reduce the coil size.

Even going 2nd order electric though, by adding that resistor to the shunt cap you have a LOT more control over the rolloff shoulder than using the cap alone. Typically the Zobel won't help much for the woofer on a 3-way, since it's crossed down near Zmin where the profile is pretty flat. Even on my Nano Neos/ntns I used a Zobel ALONG with a series coil and shunt cap to contour the rolloff. Those Zobels ran 0.80c to $1.00. Npe caps and wirewounds.

Chris
Why are we discussing zobels. What you are really creating is an overdamped 2nd order electrical network using software tools to meet a target acoustic roll off. My point is you don't have to use a zobel to flatten the impedance of a typical driver not with the currently available tools. Especially create a zobel that is calculated using an online calculator like the OP stated.

[Whitneyville1]

Dave, I understand (I think) what you are saying, but the DC160 is the case where "candy is dandy, but liquor is quicker" with a Zobel being the liquor. For the price of a cheap NPE, a resistor and a tiny metal film by-pass cap, you can save yourself $$$ worth of XO components to accomplish about the same thing. I think the Zobel network is a really marvelous thing both from a practical standpoint and from a conceptual standpoint. I'm not ready to throw it out my toolbox yet, warts and all.

[Jeff B.]

Why are we discussing zobels. What you are really creating is an overdamped 2nd order electrical network using software tools to meet a target acoustic roll off. My point is you don't have to use a zobel to flatten the impedance of a typical driver not with the currently available tools. Especially create a zobel that is calculated using an online calculator like the OP stated.

You are correct. Crossovers should be about achieiving a target transfer function to produce a very specific roll-off for the driver in the application. When you go down this road there is no point in ever using a Zobel, and most of the time if you try to put one in the circuit you only end up adding additional and unncessary components and expense. I haven't used a Zobel on any crossover in over twenty years.

[dthomas]

Dave, I understand (I think) what you are saying, but the DC160 is the case where "candy is dandy, but liquor is quicker" with a Zobel being the liquor. For the price of a cheap NPE, a resistor and a tiny metal film by-pass cap, you can save yourself $$$ worth of XO components to accomplish about the same thing. I think the Zobel network is a really marvelous thing both from a practical standpoint and from a conceptual standpoint. I'm not ready to throw it out my toolbox yet, warts and all.

Maybe my point is unclear. The OP talked about using a textbook zobel. I think you are talking about using a series RC network to achieve a target slope. I bet when you did this with the DC160 you were looking at the acoustic roll off instead of what it was doing to the impedance. The difference here is achieving the target slope. Textbook zobel calculators are about flattening rising impedance based on a generalized formula that does not account for your drivers real complex impedance. If you are using a series RC network in PCD with an inductor you are just damping a 2nd order network to get the right acoustic transfer function. You are not doing anything at all like a textbook calculator is trying to do.

My point is that using a textbook zobel for it's intended purpose is usually a wasted effort especially when you have tools in front of you that will get you to a target slope.

[Whitneyville1]

OK, I'll ask for help (once again). The Murphy Blaster Revised Crossover for the BR-1. His Zobel network is the same as the stock BR-1, while the other low-pass components are quite different. Is this a place to look for sonic improvement? A bad download of Office Pro 2007 (grr!) was the explanation for my problems with PCD, but it's set me back alot on my "learning curve" both with Excel and PCD.:o

[dthomas]

OK, I'll ask for help (once again). The Murphy Blaster Revised Crossover for the BR-1. His Zobel network is the same as the stock BR-1, while the other low-pass components are quite different. Is this a place to look for sonic improvement? A bad download of Office Pro 2007 (grr!) was the explanation for my problems with PCD, but it's set me back alot on my "learning curve" both with Excel and PCD.:o

Depends on what you are after. The DC160 is notorious for mediocre midrange I have heard both but it has been some time. IIRC the Murphy revision was a bit brighter with less baffle step. Both crossover seemed to be well implemented but neither overcame the inherit issue the DC160 has with high odd order distortion in the upper midrange.

[Whitneyville1]

Better mid-range since I missed-out on the Peerless 6.5" buyouts.:o Keeping on a tight budget is limiting. Less BSC is fine due to where these speakers will have to be placed in my room.