models.py

from django.db import models
from polymorphic.models import PolymorphicModel


class Audio(PolymorphicModel):
    name = models.CharField(max_length=255)


class Sony(Audio):
    pass


class Pioneer(Audio):
    pass


class Car(models.Model):
    name = models.CharField(max_length=255)
    audio = models.ForeignKey(Audio, on_delete=models.CASCADE)