The Electronic Theatre Controls Unison Equipment Rack, model ER4, equipped with ETC part # B123 Fan will emit 22.5 to 23 dBA. The rating is taken from the fan running at full speed. The fan noise is the only negligible noise generated from an ER4. Therefore, the noise level of 22.5 to 23 dBA can be used as an accurate total noise level for the ER4.