Library / Vibration exposure / VIB-06
Vibration exposure
Seat effective amplitude transmissibility (SEAT)
Percentage of the floor vibration that reaches the person after the seat, using the same weighting, axis and duration on both.
- Ref
- VIB-06
- Rev
- v1
- Field
- Vibration exposure
- Result
- SEAT [%]
SEAT = 100 × aw,seat/aw,floor is the weighted RMS vibration at the seat as a percentage of that at the floor, using the same axis, weighting and duration for both. Below 100 % the seat attenuates the vibration in that measured metric, and above 100 % it amplifies it. It is a single-number summary, so a seat can do well on one terrain and poorly on another.
Percentage of the floor vibration that reaches the person after the seat, using the same weighting, axis and duration on both. Below 100 the seat helps, and above 100 it makes the ride worse.
Calculator
- Attenuation by the seat30 %
- Seat acceleration if SEAT were 100 %1 m/s²
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 seat level of 0.7 m/s² against 1 m/s² at the floor gives a SEAT of 70 %, so the seat takes out 30 % of the weighted vibration on this journey.
- If the floor level fell to 0.5 m/s² with the same seat level, SEAT would be 140 %: a lower SEAT means a better seat only when the floor level is the same.
Chart data as tables
Ranked variables
| Variable | Typical range | Lowest result | Highest result | Swing (%) | Local step | Change in result |
|---|---|---|---|---|---|---|
| aw,floor Weighted RMS at the floor | 0.1 to 3 m/s² | 23.33 | 700 | 676.7 | +10% | −9.09 % |
| aw,seat Weighted RMS at the seat | 0.1 to 3 m/s² | 10 | 300 | 290 | +10% | +10 % |
Sweep of Weighted RMS at the seat
| Weighted RMS at the seat (m/s²) | Seat transmissibility (%) |
|---|---|
| 0.1 | 10 |
| 0.4625 | 46.25 |
| 0.825 | 82.5 |
| 1.188 | 118.8 |
| 1.55 | 155 |
| 1.913 | 191.3 |
| 2.275 | 227.5 |
| 2.638 | 263.8 |
| 3 | 300 |
Sweep one variable
Variables and how each one contributes
Seat transmissibility
What the equation gives you. Everything else feeds it.
Weighted RMS at the seat
The weighted RMS acceleration measured at the seat surface, in m/s². Raises SEAT in proportion. Raising it by 10 % (to 0.77) moves the result by +10 %, from 70 to 77 %.
Weighted RMS at the floor
The weighted RMS acceleration measured at the floor, in m/s², in the same axis and duration. Lowers SEAT in inverse proportion. Raising it by 10 % (to 1.1) moves the result by −9.09 %, from 70 to 63.64 %.
Worked example with the values above
- Ratio of the weighted levels: 0.7 / 1 = 0.7.
- Multiply by 100.
- SEAT = 70 %.
Assumptions and limits
- Same axis, same frequency weighting and same duration for seat and floor.
- A steady journey, so the RMS values are representative.
Common mistakes
- Comparing SEAT values from different terrain or speed.
- Mixing weighted and unweighted values.
Statistics and uncertainty
SEAT is a ratio of two weighted RMS values, each with several per cent of measurement error and run-to-run variation of up to 10 %, so differences below about 10 points between two seats are not reliable.
Where it is used
- Comparing seats, cushions and suspensions on the same vehicle and terrain.
- Specifying a seat requirement for a vehicle.
Maths you need
- Weighted RMS: frequency-weighted root mean square acceleration
- Percentage: ratio times 100