Noise Reduction Percentages Explained

How Good is 90% Noise Reduction?

Several quiet rack manufacturers represent the performance of their soundproofed cabinet as a percentage. For example, you may see statements like '90% server noise reduction'.

90% sounds very impressive, doesn't it? One could even be forgiven for thinking that the result would be almost near-silent.

So, how are we to interpret this information?

Percentages Explained

The following scenario will help us to explain:

2 x low form factor servers each with average CPU loads will operate at around 62 dB(A). What would be the impact on their noise level were we to house these inside a quiet rack rated at 50% noise reduction?

Would the result be a halving of the noise to a very impressive 31 dB(A)?

The simple answer is no, because decibels, being a logarithmic scale, don't work in that way.

In reality, a sound power reduction of 50% will always be a reduction of 3 dB(A) – a change that is barely perceptible to the human ear.

So, going back to our original manufacturers statement of '90% server noise reduction'. In terms of sound power, this will give us a more moderate sounding 10 dB(A) reduction, which is generally perceived by the human ear, as a halving of the original noise level.

This table shows sound power level differences and their impact upon human hearing:

Conclusion

In terms of noise reduction, percentages are not a very helpful tool in assessing the performance of a quiet rack. Wherever possible, we recommend that Sound Power Level readings, in decibels (dBA), are used.

Remember, the only place that coherent performance data can be obtained is from a Quiet-Rack.com approved reseller partner.