R-weighting provides better estimation for rat hearing sensitivity

Since sounds may induce physiological and behavioural changes in animals, i t is necessary to assess and define the acoustic environment in laboratory animal facilities. Sound studies usually express sound levels as unweighted linear sound pressure levels. However, because a linear scale does not tak e account of hearing sensitivity-which may differ widely both between and w ithin species at various frequencies-the results may be spurious. In this s tudy a novel sound pressure level weighting for rats, R-weighting, was calc ulated according to a rat's hearing sensitivity. The sound level of a white noise signal was assessed using R-weighting, with H-weighting tailored for humans, A-weighting and linear sound pressure level combined with the resp onse curves of two different loudspeakers. The sound signal resulted in dif ferent sound levels depending on the weighting and the type of loudspeaker. With a tweeter speaker reproducing sounds at high frequencies audible to a rat, R- and A-weightings gave similar results, but the H-weighted sound le vels were lower. With a middle-range loudspeaker, unable to reproduce high Frequencies, R-weighted sound showed the lowest sound levels. In conclusion , without a correct weighting system and proper equipment, the final sound level of an exposure stimulus can differ by several decibels from that inte nded. To achieve reliable and comparable results, standardization of sound experiments and assessment of the environment in animal facilities is a nec essity. Hence, the use of appropriate species-specific sound pressure level weighting is essential. R-weighting for rats in sound studies is recommend ed.