Start with a fundamental sine wave at ~50Hz.
Add harmonics in one or some of these ways:
- Additive synthesis
- Additional oscillators
- Lowpass another wave eg saw, square, triangle, etc
- Saturate/waveshape
- Overdrive a preamp
- Overcompress
Add movement by automating modulation of:
- Frequency
- Amplitude
- Filter (even on a pure sine wave for a different tremolo effect)
- Saturation drive/wet
Or by adding portamento
Get it to to agree with the kick using any of:
- Highpassing the kick between 50-100Hz (eg 80Hz)
- Using non-100Hz overtones eg 150Hz, 75Hz. Squares and Triangles have odd overtones.
- Side chaining.
Then your snare’s fundamental sits around 200Hz, so pay attention to that if necessary.
The reason higher sub notes sound louder is because of the equal-loudness curve which compressing will not solve. You will have to manually adjust the velocity.
https://upload.wikimedia.org/wikipedia/commons/4/49/Lindos4.svg