Rather than using percentages under the noise readings, it would be much more useful to show the delta.
If the unguarded fan is at 35.5 dBa, and the turbine guard is at 50.2 dBa, the delta is 14.7 dB. This is the same increase in perceived noise as an unguarded 60 dBa fan and a guard that raised the noise level to 74.7 dBa, not a relative difference of 41% and 24.5%.
If the unguarded fan is at 35.5 dBa, and the turbine guard is at 50.2 dBa, the delta is 14.7 dB. This is the same increase in perceived noise as an unguarded 60 dBa fan and a guard that raised the noise level to 74.7 dBa, not a relative difference of 41% and 24.5%.