I'm designing an L-Pad for my speakers. They attenuate the signal while keeping a consistent effective impedance, which is necessary for the amplifier and crossover circuits.
Typically, these values are computed and hard soldered, giving one 'set' attenuation level.
I want to use a single potentiometer (though it could be a dual-wiper pot) to make this adjustable, and include 0 dB (completely out of the circuit).
Would this be possible to design, without the use of a microcontroller and programmable potentiometers?
It needs to maintain a constant impedance, and I'm using them on 8 Ohm speakers.
Solving for my application:
R2 = Variable from (infinity) Ohms / disconnected
R1 = 8 - (R2 * 8) / (R2 + 8)
Help!
Best Answer
Normally reactive components such as inductors and capacitors are used to provide attenuation within/outside of specific frequency ranges and this by definition is how cross-overs are built.
Reactive components are favorable because they do not dissipate power apart from minimal R losses.
If you want to attenuate the signal being driven into a power load such as a speaker then I believe you will need a fairly robust potentiometer. If you are delivering 40 watts into a speaker, and you want to attenuate it by -3dB, then your potentiometer will need to be 8ohms and capable of handling 20 watts. Something the size of a high school lab rheostat would be suitable, but impractical and slightly inductive. I would suggest you consider attenuation of the signal entering your amplifier rather than the signal coming out of it.
If however you're dealing with 250mW headphone speakers then the potentiometer will work, however you may want to consider a Logarithmic type as the parallel impedance equation is not linear with differences in R.