dBA: One size does not fit all

Perhaps the greatest confusion in the popular understanding of noise surrounds A-weighted sound level, abbreviated dBA.  It’s the most common descriptor used in environmental noise assessment, but it’s not a comprehensive descriptor of noise annoyance.  Problems arise when we use dBA, which is a good descriptor of relative sound levels, as an absolute descriptor.  Keep in mind the actual significance of dBA:

Relative: The annoyance associated with roadway traffic is well understood. Higher dBA predictably means more annoyance.   

Absolute: Your daughter’s piano recital and a neighbor’s chainsaw interrupting the recital have the same dBA reading.  Same dBA, but very different annoyance.

Why? dBA is not a unit, like meters or kilograms.  dBA is the total weighted energy of a sound spectrum.  The weighting (heavily skewed towards high frequencies) dictates what’s important.  Things like strong bass content, prominent tones, spectral balance, and fluctuations in frequency and amplitude, all affect how annoying a sound is based on its character (“sound quality”).  Energy is energy: if the total is the same, the reading is the same.  Important details are submerged in the total.  

But wait, there’s more: Context is also important.  Our brain assigns messages to most sounds.  This is obvious if words or lyrics are present. But the brain also assigns meanings like “that overpriced piece of junk I just bought is about to break” or “they’re making money while my property value declines”. That’s what our brain does: extract information from our surroundings, even when we don’t want  it to. 

“Decibel thermometers”, tables, or charts, associate levels with particular activities.  A typical urban residence might well be 50 dBA, but the converse is NOT TRUE: not all 50 dBA sounds would be welcome outside (or inside) a residence.  A 98.6ºF thermometer reading does not guarantee perfect health.  Similarly, a given sound level reading that’s ok in one context may not be ok in another.    

Sound is multidimensional, it’s not a simple easy to measure unit like distance.  Our perception of sound is very complex and defies physics, and it defies one-size-fits-all simplification.  

Nelson Acoustics has extensive experience assessing and improving the acceptability of products, machines, equipment, and facilities.  For best results noise emission and sound quality can and should be considered at the outset.

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