Posted By John Donaldson I presume you are referring to an ultrasonic disruptor used in cellular and molecular biology to disrupt cells. If you are there is a possibility that a very basic sound level instrument may not be picking up the higher frequency. High frequency can damage hearing and can be somewhat insidious as it can sometimes not be heard. So it is important that your instrument has a suitable dynamic range. If it does and you are showing less than 85 dB on an A weighted scale you should not have a problem if it is being used for short periods as is often the case with this device. Having said that it is often easier to attenuate high frequency sound with close fitting perspex shielding, which is the approach we have taken here. The latest ACoP from HSE covering Noise at Work is very helpful.