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Old 6th July 2009, 02:04 PM   #1
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Default Impedance Equalizer

I'm wondering how an Impedance Equalizer (a capacitor & resistor connected across the speaker terminals) should be intergrated into a low pass circuit where two 8 woofers are connected in parallel resulting in 4?

Should I use an Impedance Equalizer for each woofer (basing the values of the equalizer on 8) or just one Impedance Equalizer prior to the branching off of the wiring to each woofer, where the impedance is 4 & obtain the values for the resistor & capacitor based on 4 & the voicecoil inductance of a single woofer?

Also, correct me if I'm wrong, but as the parallel woofer connection will result in the Low Pass filter reading 4, I am basing the values of the inductor & capacitor (2nd order Linkwitz-Riley) on that specification.

Thanks for any help.
Steve:
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Old 6th July 2009, 07:23 PM   #2
mjf is offline mjf  Austria
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Default Re: Impedance Equalizer

[QUOTE]Originally posted by sparkless

Should I use an Impedance Equalizer for each woofer (basing the values of the equalizer on 8) or just one Impedance Equalizer prior to the branching off of the wiring to each woofer, where the impedance is 4 & obtain the values for the resistor & capacitor based on 4 & the voicecoil inductance of a single woofer?

with two equal speakers you can do as you want.but take care of the power rating of the resistors,they shoukl withstand a few watt.

Also, correct me if I'm wrong, but as the parallel woofer connection will result in the Low Pass filter reading 4, I am basing the values of the inductor & capacitor (2nd order Linkwitz-Riley) on that specification.

yes,the speaker load is 4 ohm.
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Old 6th July 2009, 10:15 PM   #3
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I tend to Zobel each individual driver, even if it does cost a little extra.
Use 5 watt resistors at a minimum, depending on how much power your system needs to handle, some published designs use 10 watt ceramic resistors.

I usually mount the Zobel onto the driver backplate using silicon
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Old 6th July 2009, 10:20 PM   #4
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I think you should be using the measured value of Re, not the nominal impedance.

EDIT: actually, you can choose any impedance to Zobel to, though for flattest impedance probably best to use the min impedance on the impedance curve...?
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Old 6th July 2009, 11:37 PM   #5
infinia is offline infinia  United States
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Using two 8 ohm drivers in parallel with a single LPF. Zobel with a single network where Le and Re is 1/2 the value of a single. If you use a 1.5 bass ie two different LPFs, zobel would be seperate. Zobels are a form of conjugate matching.

Another approach is to use a 3rd order LPF with Le (or 1/2Le drivers in parallel) as part of the filter. This is called absorption. This has some risk as Le varies dynamically, more so with large Xmax subwoofers.
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Old 7th July 2009, 11:19 AM   #6
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Thanks for the responses all.

This info leads me to another question.

Using two 8 ohm woofers in parallel with a single low pass filter
& a single "Zobel" will result in a 4 ohm impedance at the speaker terminals. The transistor amp I use is rated 8 ohm, thus the speaker impedance needs to be equal to or higher than 8 ohms.

How & where in this low pass filter circuit can a resistor be placed
so as not to interfer with the crossover frequency or Zobel, but raise speaker impedance to around 8 ohms?

It seems the more I learn the stupider I feel.

steve
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Old 7th July 2009, 11:38 AM   #7
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Most transistor amps "Should" handle 4 ohms with ease.

Don't waste power and SPL with resistors,
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