Vehicle Cabin Transfer Function

Canonical Definition

The vehicle cabin transfer function is the frequency-dependent complex ratio between a defined source reference and sound pressure at a stated in-cabin position and vehicle state.

Hcabin(f) = Pseat(f) / Reference(f)

There Is No Universal Cabin-Gain Curve

Automobile interiors can increase low-frequency pressure, but the amount and slope vary with geometry, source location, seat position, modes, leakage, panel motion, trim, and openings. A fixed 12 dB-per-octave assumption is not a substitute for measurement.

State Must Be Recorded

• Vehicle, trim, enclosure, source location, and orientation
• Driver, passenger, and nearby microphone positions
• Doors, windows, hatch, seatbacks, cargo, and trim state
• Source voltage or acoustic reference and gain settings
• Smoothing, bandwidth, timing reference, and averaging method

Measure More Than One Seat

A response that is strong at the driver's head can contain a deep null at another seat. Use single-seat optimization only when that is the stated goal. For a multi-seat system, measure and weight the intended region rather than averaging unrelated traces without a defined method.

Use Transfer Data In The Design Loop

1. Measure or model the enclosure near field or in a controlled reference state.
2. Measure the installed source-to-seat response with the same source condition.
3. Compare source positions and enclosure alignments.
4. Choose the response, output, and protection tradeoff for the intended seats.
5. Repeat after changing windows, hatch, seats, orientation, or large trim panels.

Openings Create New Conditions

A partially open window or hatch can produce a resonant and strongly position-dependent condition. Treat it as a separate measured vehicle state, not as a guaranteed extension port or fixed third chamber.