Resistors in series in speaker crossover?

Discussion in 'Electronics & Electrics' started by O-B-E-L-I-X, Oct 12, 2013.

  1. O-B-E-L-I-X

    O-B-E-L-I-X Member

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    Hi,
    Wondering if anyone with more knowledge in the speaker crossovers could shed some light on what the resistors in series do and how are the values calculated?
    Did some research on the web, however can't find anything definite on the subject. Thanks in advance.


    + --------R=1.8------C=10uf------R=3.3----Speaker Tweeter R=7.2DC

    In the above there is an inductor L=0.134 in parallel, after the capacitor.


    + --------R=2.2----- polyswitch------C=3.3------Speaker Tweeter R=4.9DC
     
  2. mtma

    mtma Member

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    ED- Sorry crossed my wires and gave you a bit a bum steer there.

    The series resistances will be used to form the overall highpass filter in conjunction with the cap. In addition to this the total resistance reduces the sensitivity of the tweeter which has to match with the mid/woofer.

    The probable reason as to why there are two resistors in the first circuit is because the designer wanted to use 5.2 ohms to get the frequency characteristics and level to the points they had desired. The only reason why it might be connected in that manner is because somebody felt like that was going to be easier - in the series circuit the component order doesn't matter.
     
    Last edited: Oct 12, 2013
  3. OP
    OP
    O-B-E-L-I-X

    O-B-E-L-I-X Member

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    The first one is a 12db roll off, so the capacitor and the inductor form the high pass filter. So, you are saying that those resistors form some sort of attenuation circuits?...instead of a L-pad?

    Wouldn't the second resistor increase the impedance of the speaker?...to over 10 Ohms?
     
  4. Fishface

    Fishface Member

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    The usual reason for resistors is to attenuate the tweeter to match the woofer output.
    The arrangement here is unusual and looks like an amateur attempt to do that.
     
  5. OP
    OP
    O-B-E-L-I-X

    O-B-E-L-I-X Member

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    Amateur? The 12db is Mission and the other Wharfedale...
    Any idea how would they be calculated? Trial and measurements? I know there are L-pad calculators
     
  6. /invariance\

    /invariance\ Member

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    They would start off with the T/S paramaters (Thiele/Small) and frequency plot of the tweeter (supplied by the manufacturer if out-sourced or tested if made in-house), then punch the data into the standard formulae for the type of crossover desired.

    From there the speakers would be tested (frequency responce) and the crossover tweeked a number of times.

    A very simplistic overview of how I think it would be done, anyway.
     
  7. mtma

    mtma Member

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    That's pretty much right as far as a scientific method goes. Test your devices for simulation inputs and then simulate and tweak a circuit until you get ballpark results you desire (either on paper or in a program), then implement, test and measure, and adjust inconsistencies until you are happy.

    Whether rightly or wrongly there are a lot of 'dark arts' surrounding design of audio stuff so the method employed can vary a lot from designer to designer.
     

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