Help making a low pass filter

[TubsAlwaysWins]

So this is about to get hella sketch but just hang with me. My work has some old speaker amps that I am testing because im broed on a crap 8 inch sub they had lying around. The issue is the amps dont have low pass filters on them, and I dont have any spare crossover racks.

 

Anyways, I know you can make one with a resistor in capacitor. my question is 1: Can I use any resistor and capacitor 2: Where do I put them? (IE in line to the input of the amp (between the phone and the amp), or inbetween the amp and the speaker???) Im guessing its between the phone and amp but Im not sure.

 

Thanks sorry its a stupid question

[Unimportant]

1 hour ago, TubsAlwaysWins said:

Where do I put them?

The ideal filter location depends on the application requirements. If you want a single power amplifier to drive a multi-way speaker (woofer, mid, tweeter - typically) then there's little choice but to put the crossover filters between the power amplifier and the speakers. Since there's only a single power amplifier, it must amplify the full frequency range and filtering can only happen later.

 

Designing a crossover filter is tricky due to various factors. Speaker impedance can vary greatly with frequency and speaker model and your typical RC filter is too lossy in the low impedance path between power amp and speaker (The R in your filter would dissipate as much/more power then the actual speaker).

 

If you want to drive a single subwoofer with a single power amplifier then you can put the filter in the high impedance input to the power amplifier. What R and C values to choose depends on the desired cut-off frequency and the output impedance of the device outputting the audio signal and the input impedance of the power amplifier. One can also design a active filter, using a op-amp, to make the filter independent of the input/output impedances of the devices involved.

 

 

[Fleetscut]

Look into RLC circuits (Resistance Inductance Capacitance), the values of each component cant be anything, the values control how each filter operates and the frequencies that get rejected. If you want to learn the math behind it look into transfer functions

[mariushm]

On 6/29/2018 at 7:27 PM, TubsAlwaysWins said:

So this is about to get hella sketch but just hang with me. My work has some old speaker amps that I am testing because im broed on a crap 8 inch sub they had lying around. The issue is the amps dont have low pass filters on them, and I dont have any spare crossover racks.

 

Anyways, I know you can make one with a resistor in capacitor. my question is 1: Can I use any resistor and capacitor 2: Where do I put them? (IE in line to the input of the amp (between the phone and the amp), or inbetween the amp and the speaker???) Im guessing its between the phone and amp but Im not sure.

 

Thanks sorry its a stupid question

Buy / Rent / Download some audio speakers / amplifiers related books or google ... and those will contain the formulas to calculate what resistor, capacitor and inductor to use (and their technical parameters like peak current etc)

 

Can't use ANY ... obviously.

 

See these, may help :

https://www.v-cap.com/speaker-crossover-calculator.php

 

https://www.electronicproducts.com/Speaker_Crossover_Calculators.aspx

https://www.diyaudioandvideo.com/Calculator/SpeakerCrossover/

 

etc  just google for "audio speaker low pass filter calculator"