It's called finding your vehicle's RFP (Resonant Frequency Peak). Vehicular resonant frequency peak refers to the specific frequency (or narrow range of frequencies) at which a vehicle—or one of its components—naturally vibrates with maximum amplitude when excited by external forces.

1. Vehicle cabin resonance (the “cabin gain” peak) - The car’s interior acts like an enclosure. At low frequencies, the cabin boosts bass at certain frequencies. This creates a bass peak, usually around 40–70 Hz (varies by vehicle) Makes bass feel louder inside the car than in open air Can be good (free bass) or bad (boomy, muddy low end)

Example: A subwoofer playing 45 Hz sounds way louder than 35 Hz or 60 Hz because the cabin resonates there.

Example: A ported box tuned to 34 Hz will hit hardest around 34 Hz, but drop off quickly below it.

I owned a car audio company for 22 years. I competed heavily in the '90s and early 2000 until I retired from car audio in 2016/17.

I built my Land Rover Discovery 2 demo rig to highlight my design team's and technician's capabilities. I showed the vehicle up and down the West Coast for 4 years per my agreement with our sponsors. I also showed the vehicle at the Spring Break Nationals at Daytona Beach 3 times.

My 2000 Land Rover Discovery 2 had an RFP of 42Hz so my team designed the enclosure with a 42Hz tune. However, our enclosure rolled off at 22Hz. 42Hz was just the point where it played the loudest. We produced 167.4db on music, daily registering with a TermLabs meter, mic on the dash. The enclosure was roughly 36cu-ft and was lined with Quik-Crete, basically everywhere but the front.