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ONS MMTMM Crossover Design - is something off?

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  • DeZZar
    commented on 's reply
    It just changes the load the amplifier sees but a parallel resistor all by itself, per OP's question, has no effect on the "volume" of the tweeter - it only has an effect in combination with series resistance like an lpad. You can reduce output without a specific series resistor if there are other series components providing a level of resistance already - then a parallel resistor can reduce the output without a specific series resistor.

  • Jeremy White
    replied
    Here is what Paul had in his writeup for reference...

    Any thoughts are welcome. I'm learning.

    Click image for larger version

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  • Jeremy White
    replied
    Here is my ham-fisted attempt at running the simulation in vituixcad.

    (Note - I am VERY new to this - and some things are likely wrong. For instance the inductors all have the default resistance set.)
    All drivers are at 0,0.

    With the 8.2 ohm resistor I'm getting a better curve - but what I notice is that with 4 drivers I get significantly more SPL before the crossover, which seems wrong. (Or is it? I'm learning here.)

    Also, my woofers that are supposed to be lower, seem almost the same response as the inner ones that are supposed to be mids. I don't have the separation that Paul had in his simulation.

    (I assume the summed total power is the olive green line above the woofers and tweeters?)

    Click image for larger version  Name:	crossover.png Views:	0 Size:	198.9 KB ID:	1472510
    Last edited by Jeremy White; 07-06-2021, 12:16 AM.

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  • rpb
    replied
    Originally posted by billfitzmaurice View Post
    Only if wired in series. As I understand it the OP has it wired parallel. Please read my post again.I don't believe you understood what I said.


    It only plays a part in so far as the current demand on the amp goes up with a parallel wired resistor. It doesn't affect the tweeter output, which is voltage sourced, not current sourced. The voltage to the tweeter is unaffected by the presence of a parallel wired resistor.
    OK... a tweeter with a 4 ohm, and 8 ohm pad vs the same tweeter with a 4 ohm and 4 ohm pad. Which is louder? The 8 ohm would be in parallel with the tweeter, and changed to 4 ohms in the second sim.

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  • rpb
    replied
    There is also a series resistor. Any current through the tweeter, and through the parallel resistor goes through this series resistor. If more current goes through the parallel resistor due to changing its value, then more goes through the series resistor as well. Voltage drop across the series resistor is dependent on the current through it. If more current flows, there is more of a voltage drop across the series resistor. This reduces the voltage seen by the tweeter, and changes its spl.

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  • billfitzmaurice
    replied
    I wouldn't say the parallel resistor benefits the amp, but yes, both it and the tweeter see the same voltage, just as two tweeters parallel wired will see the same voltage. In that case the higher current draw would serve some purpose, as two identical tweeters driven with the same voltage will have 6dB higher output than one.

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  • Steve Lee
    replied
    Originally posted by billfitzmaurice View Post
    Only if wired in series. As I understand it the OP has it wired parallel. Please read my post again.I don't believe you understood what I said.


    It only plays a part in so far as the current demand on the amp goes up with a parallel wired resistor. It doesn't affect the tweeter output, which is voltage sourced, not current sourced. The voltage to the tweeter is unaffected by the presence of a parallel wired resistor.
    OK - so the parallel resistor is for the amp's benefit and has no effect upon the tweeter since it (tweeter) sees the same voltage as the parallel resistor?

    Leave a comment:


  • billfitzmaurice
    replied
    Originally posted by rpb View Post

    Changing the resistor will change the spl.
    Only if wired in series. As I understand it the OP has it wired parallel. Please read my post again.I don't believe you understood what I said.

    Bill - does current NOT play a roll here?
    It only plays a part in so far as the current demand on the amp goes up with a parallel wired resistor. It doesn't affect the tweeter output, which is voltage sourced, not current sourced. The voltage to the tweeter is unaffected by the presence of a parallel wired resistor.

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  • rpb
    replied
    Originally posted by Steve Lee View Post
    I am watching this discussion closely and thanks - OP --> Standby, this may get interesting but much learning can be obtained as this progresses.



    RPB - keep going.

    Bill - does current NOT play a roll here?
    I feel like I had this argument before, and lost, but I change the parallel resistor sometimes to make small changes. I can't run a sim right now, because I don't have a computer with the software available. Try any 8 ohm tweeter with a 4 ohm, and 8 ohm pad, and then change the 8 ohm to 4 ohms, and see if I'm correct. Use a big cap, or no xo to see if the effects are strictly from the resistors. Maybe the effect is very small. Sometimes a small change is what's needed.

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  • Steve Lee
    replied
    I am watching this discussion closely and thanks - OP --> Standby, this may get interesting but much learning can be obtained as this progresses.



    RPB - keep going.

    Bill - does current NOT play a roll here?

    Leave a comment:


  • rpb
    replied
    Originally posted by billfitzmaurice View Post
    I'm not familiar with the design, but that being the case the resistor won't affect the volume of the tweeter. It will affect the load seen by the high pass filter, which will alter the filter transfer function and the tweeter response. The resistor would only affect the volume of the tweeter, and the transfer function of the filter as well, if it was series wired with the tweeter. This is why we use LPads to lower the volume of tweeters. They do so without altering the load seen by, and therefore the transfer function of, the high pass filter.
    Changing the resistor will change the spl. The combined impedance of the tweeter, and resistor change, thereby causing a change in current flow through the series resistor, and that will cause a change in the voltage drop across the series resistor. That change in voltage drop changes the tweeter output. It may also change the roll-off, but the spl does change as well. A sim can show this to be true.

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  • Steve Lee
    replied
    Thanks for the clarification, Bill.

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  • billfitzmaurice
    replied
    Originally posted by Steve Lee View Post

    The resistor and tweeter are in parallel so they both see the same voltage.
    I'm not familiar with the design, but that being the case the resistor won't affect the volume of the tweeter. It will affect the load seen by the high pass filter, which will alter the filter transfer function and the tweeter response. The resistor would only affect the volume of the tweeter, and the transfer function of the filter as well, if it was series wired with the tweeter. This is why we use LPads to lower the volume of tweeters. They do so without altering the load seen by, and therefore the transfer function of, the high pass filter.

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  • Steve Lee
    replied
    Originally posted by Jeremy White View Post

    Shouldn't that divide the voltage by 8 instead of 6? Making it quieter?

    -Jeremy
    The resistor and tweeter are in parallel so they both see the same voltage.

    The parallel resistor is a shunt/shorter circuit to ground bypassing CURRENT away from the tweeter - The lower the resistance the higher the current therefore a higher resistance is needed to reduce the current in the shunt so the tweeter gets more of it available to play louder.

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  • Jeremy White
    replied
    Originally posted by Steve Lee View Post
    Try the 8.2 Ohm across the tweeter and it should be louder/more present.
    Shouldn't that divide the voltage by 8 instead of 6? Making it quieter?

    -Jeremy

    Leave a comment:

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