Myth Busting : NRC, and its cosmic significance

Here, many unsuspectingly enter into a spot. There are acoustical tiles available, whose “NRC” ratings are x, and people blindly assume higher the rating, more the absorption.  That is only true to an extent.  NRC itself is an average of the absorption at 4 different frequencies, and  inevitably, the performance of the acoustical tile at low frequencies is poorer than the stated NRC value.  Further, lab reports show that the shape of the tile has significant effect on the NRC value. I am writing this as caution to the hordes of professionals in the audio industry who rely entirely on NRC values for judgement.

Lab reports sometimes show NRC of 1.3. This should baffle most people who go by accepted definition that NRC is roughly the percentage of the sound absorbed by a tile. So does it mean that a tile of NRC 1.3 absorbs 130 % of the sound incident on it? Where is the extra sound coming from?

If this isn’t enough ambiguity, the fact that lab tests are always more ideal than real life situations should be enough to make you think again. There’s flanging, there’s external noise, there’re differences in performance depending on the way the tiles are mounted, ..etc.

Acousticians have answers to all this, and beyond a point, their value lies in their sheer experience with products.  Add to this, many products are touted to be acoustical in nature, and very few have been clinically studied and experimented with.

With so many factors affecting the way a room sounds – the interiors, the decor, the upholstery  the positioning of speakers and listeners, the sound transmission properties of the surrounding walls, the noise from surroundings,  the mounting and installation of products, the very shape of the room, etc., it is vital to have some scientific basis as a starting point before giving in to the variables.

The lucky part is, a wide variation  in ambience is tolerated and enjoyed rather well by human ears.  Plus the variations in “perception” of music are profoundly influenced by many factors – physiological, cultural, environmental, etc. So regardless of accurate or faulty calculations, home theaters continue to sound acceptable to some, and unacceptable to others, always. Hallelujah!


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