Oh gosh, let me stop you before this even starts. A curve is based on frequency response and frequency response is not even close to the whole picture. You must take into account things like relative phase, Linear phase, group delay of higher slopes in interaural intensity difference(ITD) frequencies.
More importantly though, a curve's sound is based on those things as well as the
way the measurement is taken. For instance, if i sit in my car and take individuals measurements around my left ear, then take those measurements, average them, and over weeks of tuning, come up with a curve that i like. Guess what, if i put that same exact curve on your car with different measuring techniques; such as taking measurements in different spots around my left ear in your car. I would then have a completely difference sound. This is because of three reasons.
1.Your initial response before eq will have different phase than mine and when you add your parametric or graphic eq to change that initial response. You will change relative phase in very significant ways. This changes the sounds clarity, and what many would call "attack" and "resolution"
2. Measurement(s) have to have a linear and repeatable way of recording before they can be considered useful. What my curve looks like would sound terrible in your car because the way that i took the measurements is completely different than the way you took them.
3. Each car has its own unique reflection, phase response, distortion differences, and comb filtering, and sound absortion. Think of having leather seats instead of vinyl. That kind of thing.
The only way a curve has any kind of validity is if the measurements are standardized across the board in all factors. Basically. If i sat in a brand new 2018 vehicle with stock everything that included a factory dsp, the tuned it with that dsp for multiple height differences. I could apply that curve to every single factory dsp in that car across the production line and it would sound the same. This is already done in some luxury cars.
ALL that being said. You can somewhat justify a curve for 0-300hz due to the fact that those wavelengths of those frequencies are longer that most vehicles in production and you can tune to the idea of the Fletcher–Munson curve. Basically its the psycho acoustic idea that we arent sensitive to low freq and we are hyper sensitive to high frequencies(up to about 15k), so if you tune low freq to be loud and high freq to be low. You'll hear everything as having the same loudness..
https://www.teachmeaudio.com/recording/sound-reproduction/fletcher-munson-curves/