Tap "Enable" up top once when the page loads, then Start Session each drive.
Audio: —
Drivetone generates its engine tone directly — no sound files needed. It reacts to speed; Bass/Mid/Treble below control each layer's volume live as you drive. Exterior boost and Play continuously live under Settings → Playback.
Bass/Mid/Treble each drive an oscillator layer — slide up for more of it, down to quiet it. Needs Web Audio (see the Audio status line above); there's no fallback if it's blocked.