2013Jun04Tu’s practice was the first opportunity since the curtains came down last month to measure the sound pressure level in the ringing chamber with all eight bells going. On 2013May21Tu with eight bells going several ringers noted that it was uncomfortably loud. For this week’s Jun04Tu practice several of the ringers came equipped with ear protection in expectation of all eight going.
Tonight with eight bells going, Thomas’s sound pressure meter gave readings ranging from 86dB to almost 88dB. 85dB is a widely accepted threshold for hearing damage; here is an authoritative discussion from the National Institutes for Health, the third paragraph of which states:
Long or repeated exposure to sounds at or above 85 decibels can cause hearing loss. The louder the sound, the shorter the time period before NIHL [noise induced hearing loss] can occur. Sounds of less than 75 decibels, even after long exposure, are unlikely to cause hearing loss.
The rule of thumb I’ve seen (as a musician and a physics major) is permanent damage after one hour at 85dB. People who ignore this risk soon don’t notice that it’s too loud because their hearing has been damaged. A typical scenario for NIHL is for an unknowledgeable person to tough it out, often commenting that “it’s not really that loud”, especially after a few hours accumulated exposure when their hearing has become less sensitive due to the permanent damage.
We must take measures to prevent damage to the ringers’ hearing. I will bring my supply of foam earplugs to this Sunday’s service ringing, for which 10 ringers are expected. I ordered a box of the 3M “Push-in” earplugs that the Pittsburgh tower gives out (they have 85+dB levels too) which should arrive next week. The push-in earplugs are easier to manage and don’t require clean hands like the foam earplugs do. They are reusable.
Jim is talking of putting up wallboard over the concrete, which probably will reduce the sound level only slightly. The figures I’ve found show gypsum board over concrete reduces the sound level by less than half a decibel relative to just concrete. Just putting up wallboard will make the ringing chamber look better but the sound level will still be above 85dB. The tower should push for something that will eliminate the cumulative permanent hearing damage that the current sound levels will cause.