Audible noise for service provider enclosures (the last mile)

Service providers are demanding smaller enclosures located closer to the customers as part of their deployment of high density xDSL. The higher density equipment demands more active cooling, which in turn leads to higher audible noise levels. How do you balance the need for larger capacity HE (heat exchangers) or ACU (air conditioning units), (i.e. With more audible noise) with low audible noise requirements coming from the MOE (Ministry of Environment) and local municipalities? When the noise by-laws first became an issue, both the Marconi DEC 33 and CUE 50 already existed and had already been deployed in numerous residential areas. The DEC 33 enclosure complied with the Telcordia generic requirements for electronic equipment cabinet specification namely 65 dBA at 5 feet. The approach taken was to work within the existing product constraints, work with external consultants, vendors and to find a solution which would satisfy the by-law requirement. After detailed research into the general topic of audible noise, several issues came to light with respect to the two enclosures discussed herein. Firstly the prime source of audible noise was fans. Secondly after conducting audible noise testing, it was further determined that the main source of audible noise came from the external fans housed within both the HEs and ACUs used in the Marconi enclosures. Once the main source had been determined, detailed testing led to two very unique solutions for the two enclosures. For the DEC 33, fan speed control methodology with was introduced as a standard produce offering. For the CUE 50, a more complicated noise hood had to be designed for deployment on an as required basis.