Library / Vibration exposure / VIB-02
Vibration exposure
Measured transmissibility
Ratio of the acceleration measured at a response point to the acceleration at the base that drives it, at one frequency.
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- VIB-02
- Rev
- v1
- Field
- Vibration exposure
- Result
- |Ha|
Transmissibility is the ratio of the response acceleration to the base acceleration driving it, at one frequency. In general it is a complex frequency-response function; this entry uses magnitudes. A value above 1 means the seat, mount or structure amplifies the vibration at that frequency, and below 1 means it isolates it. It differs from the model transmissibility of a single-degree-of-freedom system by being measured, not predicted.
Ratio of the acceleration measured at a response point to the acceleration at the base that drives it, at one frequency. A value above one means the structure or seat amplifies the vibration.
Calculator
- Attenuation in decibels, −20 log10|Ha|1.938 dB
- Reduction of the vibration20 %
What drives the result
Each variable is moved across its typical range while the others stay at the values above. The longest bar is the key driver.
- A response of 4 m/s² to a base of 5 m/s² gives a transmissibility of 0.8, so the mount removes 20 % of the vibration at that frequency, or 1.94 dB.
- A seat suspension that works above its resonance gives values well below 1, but near resonance it can exceed 1, so a single number can be misleading without the frequency.
Chart data as tables
Ranked variables
| Variable | Typical range | Lowest result | Highest result | Swing () | Local step | Change in result |
|---|---|---|---|---|---|---|
| |Abase| Base acceleration | 0.1 to 30 m/s² | 0.1333 | 40 | 39.87 | +10% | −9.09 % |
| |Aresponse| Response acceleration | 0.1 to 30 m/s² | 0.02 | 6 | 5.98 | +10% | +10 % |
Sweep of Response acceleration
| Response acceleration (m/s²) | Transmissibility |
|---|---|
| 0.1 | 0.02 |
| 3.837 | 0.7675 |
| 7.575 | 1.515 |
| 11.31 | 2.262 |
| 15.05 | 3.01 |
| 18.79 | 3.758 |
| 22.52 | 4.505 |
| 26.26 | 5.252 |
| 30 | 6 |
Sweep one variable
Variables and how each one contributes
Transmissibility
What the equation gives you. Everything else feeds it.
Response acceleration
The acceleration amplitude at the response point, in m/s². Raises the transmissibility in proportion. Raising it by 10 % (to 4.4) moves the result by +10 %, from 0.8 to 0.88.
Base acceleration
The acceleration amplitude at the base, in m/s², at the same frequency. Lowers the transmissibility in inverse proportion. Raising it by 10 % (to 5.5) moves the result by −9.09 %, from 0.8 to 0.7273.
Worked example with the values above
- Response and base amplitudes: 4 and 5 m/s².
- Divide: 4 / 5.
- |Ha| = 0.8.
Assumptions and limits
- Accelerations at the same frequency and in the same direction.
- Linear response at that frequency.
Common mistakes
- Comparing amplitudes at different frequencies.
- Reading a value just below 1 as a good isolator when it is near resonance.
Statistics and uncertainty
As a ratio of two measurements, the relative errors combine in quadrature (±3 % each gives about ±4 %). Accelerometer mounting and cable noise typically dominate at low levels.
Where it is used
- Reading the performance of a seat, a mount or a hull from two accelerometers.
- Checking a measured result against a model.
Maths you need
- Frequency response: output over input at each frequency
- Decibels: 20 log₁₀ of an amplitude ratio