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Old 16th November 2007, 08:31 PM   #1
arc2v is offline arc2v  United States
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Default Parallel inductors (dumb question) w/ Zobel followup

Maybe this is because it's friday at 4:30 and my brain is fried, but I have a parallel inductor question.

I'm familiar with the L=L1*L2/(L1+L2) math for parallel inductors and resistors.

My question is is the DCR in this arrangement the same? DCR=R1*R2/(R1+R2)?

The reason I ask is for Zobel network calculations.

I have drivers in parallel with 1mH inductance and 6.4Ohm DCR.

Should I use separate Zobels for each driver, or one at the end of the crossover, calculated for the drivers in parallel?

I think it's simple and the answer is: design a zobel for 0.5 mH and 3.2 Ohms, but my brain keeps second-guessing.

Thanks in advance, and I did search, but didn't come up with anything on this topic.
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Old 16th November 2007, 11:47 PM   #2
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If I understand, you simply have the two drivers in parallel. Two woofers or mids? In that case one Zobel; but a larger problem I have is why an LR Zobel? A Zobel is a series RC across the driver terminals, to prevent a rise in high frequency impedance caused by the drivers' inductance.

A conjugate is an LRC network, designed to maintain a relatively flat impedance through the LF resonance region.

I just awoke from a nap... am I muzzy-headed still?


There are a lot of sources for this sort of information, I tend to be partial to the Vance Dickason Cookbook.
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Old 17th November 2007, 12:41 AM   #3
arc2v is offline arc2v  United States
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No the LR is the woofer, modeled as an inductor and a resistance (as they are usually put into the calculators).

I was planning on a traditional R-C parallel circuit (R and C in series, parallel to the woofer pair).
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Old 17th November 2007, 04:50 AM   #4
jnb is offline jnb  Australia
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There isn't any compelling reason to use more than one RC (at least in my opinion). You are correct about halving the driver impedance for two in parallel. Just calculate the RC for a single driver and halve the resistance and inductance.
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Old 17th November 2007, 08:39 AM   #5
Svante is offline Svante  Sweden
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Quote:
Originally posted by jnb
There isn't any compelling reason to use more than one RC (at least in my opinion). You are correct about halving the driver impedance for two in parallel. Just calculate the RC for a single driver and halve the resistance and inductance.
...you mean halve the resistance and double the capacitance ?
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Old 17th November 2007, 09:39 AM   #6
jnb is offline jnb  Australia
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Yes, thank you Svante. Guess I'm having one of those days
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Old 17th November 2007, 11:41 AM   #7
arc2v is offline arc2v  United States
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Got it. Thanks all.

I knew I was overthinking it.
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Old 18th November 2007, 02:21 AM   #8
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Quote:
Originally posted by jnb
Yes, thank you Svante. Guess I'm having one of those days


Thanks, I feel better now .
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Old 19th November 2007, 01:00 PM   #9
arc2v is offline arc2v  United States
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Okay, I did the calculations and the capacitor it wants to use, is, well, huge!

What do you all use for your Zobels? 'lytics? Or do you enjoy spending $30 on a capacitor that isn't in the signal path ?

I built the crossover without the Zobels (woof and mid) and so far it sounds great. I know I still need it, though, due to some nasty breakups that occur about 3 octaves above the woofer X frequency and then a really loud ring in the upper octaves. I'm hoping the zobel will help the normal crossover damp those out without needing a special notch filter or higher slope.

Thanks again for the help, all!

I'll be posting measurements and pics this week of the prototype.
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Old 19th November 2007, 02:33 PM   #10
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Default Big caps


When I was building my main dipoles, I listened to just the woofer section (d/c the mid/tweeter part of the xover) to determine what effect the zobel had... then subbed different values until the "voicing" was correct; the calculated value was pretty close.

You might consider motor start caps for this, larger values are pretty cheap compared to poly's/ other types... I've heard no ill effects, but, as always... ymmv.

What value of cap did you come up with... what frequency does the impedance of the woofers double?

John L.
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