The effect of reduced headband force on the attenuation of muff-type protectors

The headband force of five different protectors was decreased in one-half pound increments until the force was less than one pound. Using a dummy head, the attenuation was measured for each value of headband force. The results indicated that four of the muffs were relatively insensitive to a decrease in headband force and loss of 50% of the original force resulted in less than a 3-dB reduction in the value of the Noise Reduction Rating (NRR). One muff, however, was very sensitive and a 50% loss in headband force resulted in roughly a 50% loss in attenuation. To verify the dummy head results, attenuation was measured at selected forces on three human subjects. Although the attenuations measured were somewhat less than those measured for the dummy heads, the effect of changing headband force produced similar results. While all protectors were unaffected by a reduction of one-half pound in force, the effect of greater reductions varied dramatically with the make and model of the protector. Apparently, manufacturers need to set guidelines tailored to their specific models.