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Old 19th June 2013, 11:43 PM   #1
Mrhjelm is offline Mrhjelm  Sweden
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Default Crossover explanation

I am quite new to passiv xover design and can not really understand what Troels Gravesen is adding in hos xovers

If you look at Jenzen-Illuminator he adds some resistors in parallell/series. Is this to acheive correct/increase impedance or what are the reason for these? From what I have read the parallell resistors should be of a higher value than the series if this is an L-pad and keep impedance at the same.

Appreciate if someone can explain the need of resistors R2021 & R2051 for the mid and R1011, R1031, R1041 & R1051 for the tweeter.
Also are there any reason why he do not combine R1011 & R1041?

Do not laugh, I am trying to learn from the pros here
/Mattias
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Old 20th June 2013, 12:49 AM   #2
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In some cases, and always so when the Coil and the Resistor have the same number, the Resistor represent the internal resistance of the Coil.

So, R2041 represent the resistance of the wire making up the coil L2041.

The various components in parallel with the various drivers are a Zobel Network which stabilizes the impedance of the driver at higher frequencies outside the working range of the driver/crossover.

In other locations I suspect the Resistor/Capacitor or Resistor/Capacitor/Coils are fine tuning of the frequency response. They are traps to moderate peaks in the response.

And the remaining bulk of the components are just standard crossover components.

I would say, anytime a resistance is a fraction of an ohm, it is the internal resistance of some component or a residual resistance in the circuit.

If a given resistance is 1 ohms or more, then likely it is a real resistor and play some part in the circuit.
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Old 20th June 2013, 04:58 AM   #3
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The legend above the left most illustration says it. the green resistors are physical resistors, while the uncolored open box represents the internal resistance of the coils.

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Old 20th June 2013, 07:49 AM   #4
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Quote:
Originally Posted by bear View Post
The legend above the left most illustration says it. the green resistors are physical resistors, while the uncolored open box represents the internal resistance of the coils.

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Your right, but the general point I made is if the resistors are less than 1 ohm, they are residual resistance in some component. If they are 1 ohm or higher, then they preform some function in the circuit, and a quick check bears that out.

The resistors could be to control impedance in some form of Zobel or Zobel like network.

They could be attenuation, to bring the tweeter and possible the Midrange down to reasonably match to the likely lower level of the Woofer.

They could be tied in with some type of Notch filter to control peaks in the response.

Troels seems to know what he is going and is respected as a speaker design, I think we fairly have to assume every component has a purpose.

STeve
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Old 20th June 2013, 08:13 AM   #5
Mrhjelm is offline Mrhjelm  Sweden
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Quote:
Originally Posted by BlueWizard View Post
Your right, but the general point I made is if the resistors are less than 1 ohm, they are residual resistance in some component. If they are 1 ohm or higher, then they preform some function in the circuit, and a quick check bears that out.

The resistors could be to control impedance in some form of Zobel or Zobel like network.

They could be attenuation, to bring the tweeter and possible the Midrange down to reasonably match to the likely lower level of the Woofer.

They could be tied in with some type of Notch filter to control peaks in the response.

Troels seems to know what he is going and is respected as a speaker design, I think we fairly have to assume every component has a purpose.

STeve
Haha! No I do not think he just put them there to get a nice look to it

Thank you Steve for your explanation, not that I got much wiser
I have never sen this before and if someone can explain more into detail what these circuits are doing to the FR/Impedance would be highly appreciated.

I don't know, maybe this kind of circuit could be very usefull some day. And for that reason I would like more input.

/Mattias
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Old 20th June 2013, 09:26 AM   #6
balerit is offline balerit  South Africa
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The resistance of the coil becomes important, especially when designing L-pad networks for tweeters and the woofer coil's resistance is factored into the calculation.
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Old 20th June 2013, 11:43 AM   #7
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Think about what coils and capacitors do.

L3011 is a coil in series. At low frequencies a coil is a short, at high frequencies the impedance goes up. So, it is going to pass low frequencies and blocks high frequencies.

C3012 capacitor is exactly the opposite. If blocks low frequencies but passes high frequencies. Since it is in parallel with the Woofer, high frequencies are going to by-pass the woofer, and Low frequencies are allowed through.

These two make up a 12dB/Octave Low-Pass crossover for the woofer.

In parallel with the same woofer are R3031, L3031, and C3031. Relative to each other, they are in Series, relative to the woofer, that chain is in parallel.

At some Low frequency, L3031 is going to be a short. At some High frequency, C3031 is going to be a short circuit. Which means we have something of either a notch or band pass filter. Likely a notch filter to bring down some irregularity in the woofer response. This could be the Baffle Step correction, which has to bring down the Woofer between the Baffle Step and the Crossover frequency.

In the Mid-Bass, C2011, with L2021 plus C2041 with their associated resistors appear to be an 18db/octave 3rd Order High Pass. But you have L2041 in parallel with R2042 and C2041. At some low frequency, L2041 is going to be a short, and higher frequencies it is going to have some resistance. So, below some selected frequency, R2042 and C2041 are by-passed. At higher frequencies L2041 become insignificant and R2042 and C2041 dominate the circuit. Again, with this he has made some modification to the response.

On the Tweeter we seem to have a somewhat straight forward 12dB crossover with attenuator, and some modification to the response.

Go through it item by item, it all makes sense, though the above is my best guess.

And every other component will have a similar purpose.

They can be individually analyzed, but more accurately by those who know more than I do.

Steve
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Old 20th June 2013, 12:39 PM   #8
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Bass section: a standard 2nd order LP filter plus notch filter (LRC) for smoothing the 100 Hz region (as described by Troels).
Mid section: a 2nd order HP filter where R2021 probably shapes a bit the response, followed by a 1st order LP filter (L2041 & the resistance of the inductor =R2041) with a notch (C2041 & R2042). The parallel components R2051 & C2051 here seems like a Zobel network.
High section: a 2nd order HP filter (C1021 + L1031 & R1031, again the resistor shapes the response), a notch of the 500 Hz section (LCR) and 2 resistor for attenuation (R1011 & R1041). Using 2 resistor instead only one permit to slightly modify the response in the crossover area.
Unfortunately in this design there aren't showed graphics of the driver responses on baffle without crossover, I could have been more precise about some components.

Ralf
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Old 20th June 2013, 12:49 PM   #9
AndrewT is offline AndrewT  Scotland
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A filter works (achieves the theoretical turn over frequency and roll off slope) when it is fed from a zero Source impedance and feeds into an infinite Load impedance.

You can modify this filter to work correctly when feeding a finite load impedance, that does not change with signal frequency.
This is what we do with speaker crossovers.
We have TWO filters to create the crossover.
Each feeds a load that is the speaker driver impedance when fitted into it's box (or other loading).

BUT that filter ONLY works correctly if the impedance of the load does not vary with signal frequency. That is the really big problem with passive crossovers. The speaker drivers are NOT constant impedance.

Much of the extra components added at the speaker driver terminals are there simply to let the crossover filter think is is loaded with a near constant finite impedance over some of the frequency range.
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Old 20th June 2013, 01:41 PM   #10
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Looking at the mid driver I would say that R2021 is there to fine tune the phase response of the driver. R2051 is almost certainly (in conjunction with C2051) part of a zobel network to flatten out the rising impedance of the mid.

R1011 will be for attenuating the tweeter. R1031 I would say once again is for fine tuning the phase response of the tweeter. R1051 is part of a series RLC network which is a resonant circuit. It is probably some sort of notch filter. R1041 Is probably used for attenuation purposes, but quite possibly also affects the shunt preceding it to change the filter characteristic somewhat.

Getting some actual driver response curves and impedance plots and putting them into a simulation program and fiddling with values, paying attention to what it does to the spl curve as well as the phase curve is very helpful in getting an idea of how different parts of a crossover circuit play their part.

Tony.
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