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Old 15th August 2011, 01:12 PM   #1
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Default Parallel woofers - independent filter?

On a 2 woofer in parallel setup I wonder if there could be some benefits on using independent filters or just independent zobels.

Drivers are never fully identical and wires+connectors add R,C and L to the circuit...

So, for a simple 1st order + zobel what do you think would be the best filter? (check pic)

On option 2 consider the zobel's are mounted close to each woofer and the inductor is on the back side of the speaker.
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Old 15th August 2011, 01:22 PM   #2
sreten is offline sreten  United Kingdom
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Originally Posted by Aleph 5 View Post
On a 2 woofer in parallel setup I wonder if there could be some benefits on using independent filters or just independent zobels.

Drivers are never fully identical and wires+connectors add R,C and L to the circuit...

So, for a simple 1st order + zobel what do you think would be the best filter? (check pic)

On option 2 consider the zobel's are mounted close to each woofer and the inductor is on the back side of the speaker.
Hi,

Option 2 does not really exist, and its hard to make an argument for option 1.

IMO for 1st order c/o's the series arrangement is better, and you don't need
zobels, if fact mainly you will be better off without them, horses for courses.

rgds, sreten.
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Old 15th August 2011, 01:50 PM   #3
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+1 for not needing zobels If you have measurement gear and a crossover simulation program (especially one with an optimizer) why throw away signal* forcing the driver to fit an impedance that a standard crossover will be happy with, if you can optimize based on the drivers natural impedance curve. You will almost certainly end up with a lower parts count in your crossover and with it better sound

* my subjective impression of implementing a zobel has been that it affected the sound of the driver (in a non positive way) listening to that driver alone running full range. My logic tells me that to get the lower impedance some of the energy is being shunted off to ground via the zobel, strangely when I sim it shows the exact same spl curve as a raw driver if the only network is a zobel, which I don't understand , so take my comments with a bucket of salt

Tony.
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Last edited by wintermute; 15th August 2011 at 01:51 PM. Reason: minor changes
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Old 15th August 2011, 02:01 PM   #4
sreten is offline sreten  United Kingdom
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Originally Posted by wintermute View Post
+1 for not needing zobels
* my subjective impression of implementing a zobel has been that it affected the sound of the driver (in a non positive way) listening to that driver alone running full range. My logic tells me that to get the lower impedance some of the energy is being shunted off to ground via the zobel, strangely when I sim it shows the exact same spl curve as a raw driver if the only network is a zobel, which I don't understand , so take my comments with a bucket of salt

Tony.
Hi,

Yes, energy is being shunted to ground, all the energy going via
the zobel is extra current drawn from the amplifier, driver current
remains exactly the same, (with no filters or series R involved).

With a filter or series resistance the zobel shunts driver energy,
and driver response will be different with and without it, that
does not mean though that it is necessary, often it is not.

rgds, sreten.
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Old 15th August 2011, 02:31 PM   #5
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Quote:
Originally Posted by wintermute View Post

Why throw away signal forcing the driver to fit an impedance that a standard crossover will be happy with, if you can optimize based on the drivers natural impedance curve?

Tony.
Beginners should read this over and over until it starts to sink in.

I see so many projects that have a Zobel to flatten impedance, a seperate bass shelving circuit, etc. In the end the drivers have a natural response (on the cabinet) and there is a target response you would like to achieve. The difference betweent the two curves is the required filter. Figure that out first and the neccessary topology will be revealed.

David S.
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Old 15th August 2011, 02:57 PM   #6
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You only need 1 coil and 1 zobel. The need for the latter depends on the impedance curve of the woofer. Usually, certainly with a first order filter, you will need one. Otherwise, the rising driver impedance will fight the coil to work properly, and you will wind up with insufficient filtering.
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Old 15th August 2011, 04:52 PM   #7
sreten is offline sreten  United Kingdom
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Quote:
Originally Posted by vacuphile View Post
.... Otherwise, the rising driver impedance will fight the coil to
work properly, and you will wind up with insufficient filtering. ....
Hi,

It doesn't for series 1st order c/o's, a rising impedance "helps"
the parallel capacitor, so that zobels are not needed, usually.

rgds, sreten.

Why series 1st order is referred to as quasi 2nd order on the low pass,
the equivalent circuit is 2nd order series with a pure resistance ....
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Last edited by sreten; 15th August 2011 at 04:56 PM.
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Old 15th August 2011, 05:58 PM   #8
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Hi Sreten,

You are economical with words so I may not quite get the gist of what you are saying.

However, in 1st order low pass there is no parallel capacitor. If there is a parallel capacitor, it is 2nd order. Also, with 2nd order, a Zobel might be required to get the desired 12dB/oct slope.

One thing I forgot to mention in my earlier response is that, working with two woofers, you might consider using that configuration for baffle step compensation. In that case, you would need two filters, each tuned differently, and two zobels. However, without ability to measure acoustic response, this would be very difficult to get right. Btw, any xover without ability to measure is matter of getting lucky to get it right.
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Old 15th August 2011, 06:27 PM   #9
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Quote:
Originally Posted by vacuphile View Post
One thing I forgot to mention in my earlier response is that, working with two woofers, you might consider using that configuration for baffle step compensation. In that case, you would need two filters, each tuned differently, and two zobels. However, without ability to measure acoustic response, this would be very difficult to get right.

Be careful here as you can have difficulty with phase shift between units when you start giving them different crossovers. A small amount of phase shift will tilt the best response plane. A large amount can lead to response cancellation. Try to keep the phase difference to 90 degrees or less. This is equally true of 2 1/2 way designs.

Probably better to parallel the woofers and use a common response shaping network to both.

I still question the common ussage of Zobel networks.

David S.
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Old 15th August 2011, 07:34 PM   #10
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Thank you. Following your advice I will then go for the simplest design (pic's option 3) with a single circuit filtering both woofers.

This project is aimed for a 4ohm nominal load, as the amps to be used like this impedance. So, two 8ohm woofers in parallel provide the expected impedance.

What you say about the Zobel makes total sense - it affects the purity of the signal and dissipates energy.
I am using it for impedance equalization and it merely serves the objective of making the filter work as expected. I recognize it's a trade-off or, if you prefer, a shortcut for a unenlightened speaker designer (me).
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