noise vibration harshness tests for Caruna’s swivel seat mechanisms
posted on - 2025-03-20
Octave analysis used to measure vibration and continuously improve Caruna swivel seats and our wheelchair devices:
The human ear doesn’t perceive frequency linearly; a small change in frequency at low frequencies sounds like a larger change than a similar change at high frequencies.
Logarithmic scales, like octaves, help to represent these perceived changes in a more meaningful way.
For example, an octave is a doubling of frequency, and the difference in pitch between two notes an octave apart is perceived as the same, regardless of the starting frequency.
An octave analysis of vibration measured at specific part in an normal internal combustion engine car vs electric car is a usual example.
If one is being crude, one uses the 1/1 octave analysis where the upper and lower limits of the octave band are determined by the centre frequency.
upper limit = 1.41 x centre frequency
lower limit = 0.707 x centre frequency
this is the calculation for the band related to centre frequency 4 khz. for example.
At Caruna, for accurate car research works, we use the 1/3 octave analysis with human ear weighting parameter specific to the measurement.
We try and sample data over various road conditions, small potholes to large, small speed breakers to large, as the car reacts differently to each type of vibration. We continuously study the vibration of our swivel seat mechanism also under various conditions.
We sample data with respect to time, as seen from the graph in the bottom and sample the time frame where you observed the worst vibration (shown in red). We then proceed to us our own fast Fourier transform to convert to the decibels vs frequency octave graph (shown as the big graph on top).
Once we convert to octave bands, we note the decibel levels. We then isolate disturbances like honking etc.. We redo whole process till satisfactory to consumer.
image source : obserview
Ashwin Shreshta
Founder, Caruna mobility
MSc. Automotive RWTH Germany
www.caruna.in
