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    Replacing car radio speaker with dummy load

    Hi,

    I have system for sampling signals from a car radio.
    It is done by placing the sampling circuit in parallel to one of the speaker.
    The system is working fine.

    My problem is that when I need to run many tests and in different volume levels it is very inconvenient to work in the room with the radio playing all day long.
    I would like to replace the speakers with a dummy load.

    The speakers have impedance of 8ohms.
    Should I place a resistor of 8ohm instead or can I put any size resistor?

    Thanks
    Tomer

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    Re: Replacing car radio speaker with dummy load

    Use an 8 Ohm resistor or something close to it. When a loudspeaker is described as 8 Ohms it means 'nominal' as the real impedance will vary across the frequency range and to some extent on the enclosure it is fitted in. Don't forget the resistor power rating must be sufficient to handle the output of the radio.

    As 8 Ohms isn't a standard value, you could consider making one from four 33 Ohm resistors in parallel (8.25 Ohms total) then each only has to be rated at one quarter of the radio output as well.

    Brian.
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    Re: Replacing car radio speaker with dummy load

    Thanks Brian,
    That was my thought as well.
    What will happen if I put a larger value resistor?
    Will it damage the amplifier?

    - - - Updated - - -

    Thanks Brian,
    That was my thought as well.
    What will happen if I put a larger value resistor?
    Will it damage the amplifier?



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    Re: Replacing car radio speaker with dummy load

    A higher value, within reason probably will work but depending on the amplifier configuration, going too high (> 100 Ohms) might cause problems.
    A low value may overload the amplifier and cause damage. If you can't get close to 8 Ohms, aim for higher value rather than lower if possible.

    Brian.
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    Re: Replacing car radio speaker with dummy load

    Car radio speakers are usually 4 ohms but some are 2 ohms. 8 ohms is almost never used in a car that has a 12V battery because the output power will be almost half. Home speakers are usually 8 ohms.
    The output level from a car amplifier does not change when its load resistance is increased.



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