How to reduce audio output?

Thread Starter


Joined Jan 27, 2004

I like to "putter" around with electronics; I'm still in the beginning, learning stages.

I have a question about reducing power output. What I have is a siren that requires a speaker that can handle between 60 to 100 watts. I would like to know if a resistor would work to reduce the power so that a small speaker would work without burning out. What I would like even more is to be able to input the sound to my computer to record it as a sound effect. The unit takes 12 volts DC to operate. Can this be done without opening it up and messing around with the internal electronics?


P. S. This site is just plain amazing!


Joined Jan 24, 2004
:) The following web page shows a T Pad Attenuator used to reduce the output level to the speaker along with a table of values to select the desired attenuation.
This type of attenuation will keep the load on the siren circuit at the origional level.

This Impedance matching was required with vacuum tube amplifiers with transformer coupling however it probably would work fine to simply use a single resister in series with the speaker to reduce voltage and wattage at the speaker.

An 8 ohm resistor will cut the voltage across an 8 ohm speaker by half. The current will also be cut in half therefor the power (in watts) will be 1/4 of what would go to the speaker without the resistor.

To feed the output into your computer line in input to record you will need to drop to a signal level around 0.3 volts AC with no measurable DC, This might best be done through an audio transformer to achieve isolation from the voltages generated in the siren circuit. Radio Shack will have something that will do this, just a small transformer will work if you limit the current with a high enough resistor on the primary.

Good Luck