Why resistor in parallel with inductor in low pass crossover? - diyAudio
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Old 6th April 2013, 05:12 AM   #1
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Default Why resistor in parallel with inductor in low pass crossover?

Hi,
I am struggling to understand the purpose of the 60 ohm resistor in this crossover:

I simulated it with "5 spice", I understand the purpose of the other elements, but this appears to reduce the attenuation of the woofer at high frequencies to just a few dB below the output of the tweeter? Is this for transient response? Doesn't it make one prone to hearing the effects of the cone break up?
thanks

(ps. This comes from Mark K's speaker pages: The Seas ER18DXT ported two way
Looks like an interesting 2 way)
tx

Last edited by Pano; 7th April 2013 at 03:42 PM. Reason: image problems
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Old 6th April 2013, 05:27 AM   #2
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Sorry - the image may not open - not sure how to post images - but you can see the crossover in the supplied link. It has a 1st order low pass filter with a notch filter at 5KHz added. The 60ohm resistor is across (in parallel with) the main inductor for the low pass filter. Why bother? Only affects the woofer at well above cross over right?
THANKS!
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Old 6th April 2013, 06:05 AM   #3
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http://en.wikipedia.org/wiki/RL_circ...rallel_circuit

Seems like it reduces the strength of the low-pass filter and alters the phase of woofer.

Last edited by ruinevil; 6th April 2013 at 06:27 AM.
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Old 6th April 2013, 02:22 PM   #4
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Quote:
Originally Posted by ruinevil View Post
RL circuit - Wikipedia, the free encyclopedia

Seems like it reduces the strength of the low-pass filter and alters the phase of woofer.
Thanks Ruinevil - You are right - I hadn't looked at the phase closely enough around 2-5Khz cause the attenuation wasn't changing much there with or without that resistor - but is does change by 25deg or more in that frequ range. Though seems crazy to allow only ~ 5dB of attenuation relative to the high pass filter at 20kHz just to get that phase "correction" so I was wondering if that aspect of the design had some explicit purpose...
thanks
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Old 6th April 2013, 04:33 PM   #5
Davey is offline Davey  United States
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The 60 ohm resistor is more about the notch filter.
A shunt-connected, series RLC needs a series resistor element to create the voltage divider which yields the notch. The inductor itself becomes a series element when out of band, but this combination must have worked well for Mark.

A series-connected, shunt network would be an option also, but Mark's preference in this case was probably chosen because of impedance concerns.

Cheers,

Dave.

Last edited by Davey; 6th April 2013 at 04:54 PM.
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Old 6th April 2013, 05:06 PM   #6
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Quote:
Originally Posted by Nvr2manybikes View Post
I am struggling to understand the purpose of the 60 ohm resistor in this crossover
The 60 ohms in parallel with a 2.5mH is a Bass Shelving Filter. Basically, it attenuates the higher frequencies.

Following that is a Notch Filter. There is no Conventional Crossover. The combination of this Shelving Filter and the Notch Filter serves as a crossover (blue trace in FR plot)
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Old 6th April 2013, 10:42 PM   #7
system7 is offline system7  United Kingdom
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Well, what MarkK COULD have done is just put a 0.1uF capacitor in line with the 60R resistor, and finished the 10kHz (tank) notching of the rather good SEAS ER18RNX. That would have been a conventional sort of smooth 2nd order speaker with excellent phase alignment and no cone breakup worth mentioning.

But NO!!!

He decided to simulate all the HORRORS of a metal cone with it's breakup and midband phase problems. He set out his TARGET RESPONSE, and succeeded in implementing it.

Doubtless the cloth-eared brigade said it sure sounds GOOD and LIVELY like a low-order should and it's got flat "power response" apparently! And went home with their ears ringing...

The treble filter is frankly, equally baffling with its mainly random notches. But as I said to Mark, the Mark 2 version could be great. Really.
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File Type: png MarkK_Metal_Cone2.PNG (16.0 KB, 448 views)
File Type: png MarkK_resistor_effect.PNG (17.3 KB, 447 views)
File Type: png system7_double_notch.PNG (15.7 KB, 444 views)
File Type: png system7_double-notch_circuit.PNG (13.7 KB, 448 views)
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Old 7th April 2013, 12:50 AM   #8
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Quote:
Originally Posted by Michael Chua View Post
The 60 ohms in parallel with a 2.5mH is a Bass Shelving Filter. Basically, it attenuates the higher frequencies.

Following that is a Notch Filter. There is no Conventional Crossover. The combination of this Shelving Filter and the Notch Filter serves as a crossover (blue trace in FR plot)
I don't think this is correct - I have done the simulations both with and without the resistor. The resistor REDUCES the high frequency attenuation
thx
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Old 7th April 2013, 12:56 AM   #9
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Quote:
Originally Posted by Davey View Post
The 60 ohm resistor is more about the notch filter.
A shunt-connected, series RLC needs a series resistor element to create the voltage divider which yields the notch. The inductor itself becomes a series element when out of band, but this combination must have worked well for Mark.

A series-connected, shunt network would be an option also, but Mark's preference in this case was probably chosen because of impedance concerns.

Cheers,

Dave.
I believe the 5uf Cap in series with the 0.22mH inductor is actually the notch filter in this ckt.
thx
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Old 7th April 2013, 01:03 AM   #10
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Originally Posted by system7 View Post
The treble filter is frankly, equally baffling with its mainly random notches. But as I said to Mark, the Mark 2 version could be great. Really.
Yes - but at least I knew they were notches and thus knew what was being attempted. Just trying to learn a bit about crossovers by seeing what folks are doing and "reverse engineering" them to the extent I can - your comments were very helpful. Thx
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