Today I finished designing my crossover. Here’s what I have come up with.
I have to give a special thanks to DIY Audio and Video.
I’m building a speaker for an old radio that, in addition to a new loudspeaker, I’m creating a cool new case. It’s not a stereo, so I just need one loudspeaker.
Here’s what I’m using for speakers.
The woofer is an 8 ohm speaker with a frequency range from 29 Hz to 3,000 Hz. The tweeter is also 8 ohm, but with a range of 2,000 Hz to 20,000 Hz.
The woofer’s maximum decibels is 88 db and the tweeter’s is 96 db. Using an l-pad circuit, I plan to pull that tweeter down to 88 db to match the woofer.
And to calculate a proper Series Notch Filter, I need the free air resonance of the tweeter, which 1,800 Hz.
So based on this tutorial, I came up with the following two crossovers.
For the tweeter, I’m going to create a 3rd order Butterworth 800 Hz crossover. For the woofer, I’m going to build 1st order Butterworth 3,000 Hz.
Those are the crossovers, now I need a Loss Pad circuit. A l-pad circuit, or driver attenuation circuit, is supposed to decrease the output levels of the louder speakers to match the output of the more quiet speaker.
In my case, the tweeter outputs up to 96 db and the woofer is 88 db, so I need to pull the tweeter output down 6 db.
A l-pad is two resistors, one in series and one in parallel.
Using the fabulous DIY Audio and Video l-pad calculator, here’s the circuit for the tweeter. I entered the values 6 db, 100 watts and 8 ohms.
The last thing to do is design the Series Notch Filter.
I’ll be honest, I’m not sure exactly what this one is for, but the purpose of this filter is to block frequencies within a certain range, letting through all others.
To build the series notch filter, I’m using the free air resonance (Fs) of the tweeter, which is 1.8 kHz.
Using the awesome Series Notch Filter Calculator at DIY Audio and Video, I was able to determine the necessary components.
Re = 8 Ohms
fs = 1800 Hz
The last step to do, which I haven’t done yet, is to combine all of these circuits into one. I’m going to sketch it out on paper. Then I’ll pull my parts and prototype it on breadboard.
- 3rd Order Butterworth (Tweeter)
- C1 16.58 uF
- C2 49.73 uF
- C3 33.16 uF
- L1 1.19 mH
- L2 2.39 mH
- L3 .8 mH
- 1st Order Butterworth (Woofer)
- C4 6.63 uF
- L4 0.42 mH
- R1 3.99 Ohm 49.88 watts
- R2 8.04 Ohm 25 watts
- C5 16.68 uF
- L5 0.42 mH
- R3 8 Ohms