Decibel
From Memory Alpha, the free Star Trek reference
A decibel is a measurement of the loudness of sound.
According to Quark the usual sound level at Quark's was 65 decibels, and with Klingons present up to 85. When the soldiers of a Klingon task force visited Quark's in 2372, the unusual quietness of less than 30 decibels worried Quark. Later, when the Klingons had left, the noise level was back up to 72 decibels again, which greatly pleased Quark. (DS9: "The Way of the Warrior")
In order to get two meters of electro-plasma conduit from the Defiant in 2373, Nog listened to Worf's Klingon operas at eighty-two decibels to filter out subharmonic distortions. (DS9: "In the Cards")
