ACHIEVING THE IDEAL: Quiet Space and Optimal Power Quality
Part II -- Power Quality
July 30, 2003
Appeared in ProSound News
In any sound studio, excellent power quality – a power supply at a constant voltage, current and frequency, free of harmonic distortion and the transfer of common mode noise that can create an audible hum in sensitive audio equipment – is critical to enable the generation of quality recordings. Achieving this requires careful planning and coordination among the owner; architect; mechanical, electrical and plumbing (MEP) consultant; and acoustical consultant.
The volume of equipment in recording studios almost always necessitates an upgrade in electrical service and distribution, whether the facility is in a free-standing warehouse/industrial building or a multi-tenant high-rise office building. Typically, an existing warehouse will have either 200A, 120/240V single-phase service; or, if it has two incoming services, 100A, 240V three-phase service. These always would need to be doubled to 400A or 200A, respectively, as a minimum based on average 20-30 watts/sq. ft. In a multi-tenant building that may have been designed as an office space power can be augmented in the floor by adding more panels, boards and transformers, sometimes getting feeders all the way back to the service equipment.
It also is essential to provide recording studios and associated technical rooms with excellent power quality. Not only are studio components sensitive to voltage, current and frequency variations in the power source, they are themselves a source of disturbances in power quality, including harmonic distortion -- and the coaxial cables that interconnect the vast array of equipment are a “perfect” conduit for carrying electrical noise throughout the network.
Begin at the source
To provide clean power -- i.e., free of harmonics and voltage distortion -- begin at the source by providing separate electrical distribution for technical equipment and non-technical equipment. A facility with an uninterruptible power supply (UPS) system gets the added advantage of clean power thanks to its isolation transformer or power conditioner, which assures constant voltage in the electrical distribution system.
If a UPS is not required to prevent data loss in the event of a power outage, a separate power conditioner or isolation transformer should be installed to ensure clean power. In any case, it is essential to install surge protectors to mitigate large voltage surges.
The most common practice to mitigate single phase harmonic distortion is to utilize a Zero Sequence Filter at the panel serving sensitive equipment. The Zero Sequence Filter provides a low zero sequence impedance path which is intended to trap single phase harmonic (3rd order) current from flowing back to the electrical system. This design approach will also allow maximizing the usage of electrical system capacity since mitigating harmonic current flow will reduce the True RMS (please spell out) current of the system.
Proper grounding design will mitigate common mode noise, or hum, in the network. In many cases, electrical noise in existing systems can be traced to an undersized neutral conductor, and the problem can be solved through proper sizing and by placing all technical equipment on the same grounding system to ensure equal potential among all equipment.
Non-grounded transformers: pros
While most engineers feel that a grounded system is both safe and effective, many recording studio owners are interested in using non-grounded systems to supply their technical equipment. This type of system takes a conventional 208/120V grounded system and converts it to a 120 volt ungrounded single phase system. This is done by using two 60 volts between phases (exempting the system from National Electrical Code (NEC) grounding requirements).
One difficulty with the balanced 60V system is that it has a smaller capacity, i.e., a more limited number of output circuits, compared with a conventional transformer/panel board system; therefore most recording studio installations require multiple transformers. Another problem is that these systems need to be located as close as possible to the source, while a conventional transformer and panel board can be located in a central electrical room. Furthermore, to comply with NEC, the circuit will require ground fault protection to ensure safety.
A professional recording studio is dependent on an adequate supply of clean power. While not that difficult to achieve from a technical standpoint, as described above the are a host of design issues that must be addressed in order to ensure the optimum recording environment.
Hisham Barakat is a Vice President, Sports and Entertainment
Group, with the Los Angeles office of Syska Hennessy Group (www.syska.com),
a leading consulting,
engineering, technology and construction firm.