LH-C,Aeq,T=the energy mean of diffuse-field-related A-weighted equivalent-continuous SPLs under headset (dBA)LB-N,Aeq,T=the energy mean of A-weighted equivalent-continuous SPLs of background noise(dBA)TH =the declared time of the headset usage per working day(hrs)TB-N =the effective duration of nonheadset work activities(hrs)T0 =the reference duration(hrs);T0 =8h