It is the responsibility of the client to ensure that his facility’s Heating, Ventilation, and Air Conditioning (HVAC) equipment, AC power, and grounding are all sufficient to maintain the proper operating environment for the audio/video system. A healthy environment for broadcast quality audio/video equipment requires the proper Heating, Ventilation, and Air Conditioning (HVAC) equipment. Also, and just as important are: proper AC power; proper grounding; control of humidity and static electricity.
Environmental conditions play an important part when considering the implementation of a professional audio/video facility, e.g., a TV production facility. Keeping electronics cool is vital to the system’s smooth and continued operation; temperature control is equally important for the comfort of the humans who must operate and maintain the audio/video equipment; and also for the performers and crew who work in the studios. Controlling relative humidity reduces the risk of damage to electronic circuits caused by electrostatic discharge. Filtration of airborn contaminants (dust and lint) will prevent degradation to the film transfer process and also reduces VTR noise, head clogs, and drop-outs while extending VTR head life. Every effort should be made to keep the area clean and free of dust and lint fiber. All technical equipment rooms should have positive air pressure relative to adjacent areas serviced by non-filtered HVAC equipment.
Mechanical air filters are recommended over electronic filters (unremoved electrostatically charged contaminants would be “stickier” in a magnetic tape environment).
The following specification summary applies to all areas in the facility where project audio/video technical equipment is located.
The AC power line into a broadcast plant is the lifeblood of any operation. It is also, however, a frequent source of equipment malfunctions and component failures. The utility company AC feed contains not only the 60 Hz power needed to run the facility, but also a variety of voltage sags, surges, and transients. These abnormalities cause different problems for different types of equipment.
An AC voltage sag is generally defined as a decrease of 10-35% below the normal line voltage for a period of 16 milliseconds to 30 seconds. A surge on the other hand, is a voltage increase of 10-35% above normal lasting 16 milliseconds to 30 seconds. Sags and surges may occasionally result in operational problems for the equipment online, but generally automatic protection (or correction) circuits will take appropriate actions to ensure there is not equipment damage.
Transients, however, are not so easily identified or eliminated. Many devices commonly used to correct for sag and surge conditions, such as ferro-resonant transformers or motor driven auto-transformers, are of limited value in protecting a load from high energy, fast rise-time spikes on the AC line.
Transient suppression is important to broadcasters because the sensitive, high-speed solid state equipment in use today can be disrupted, or even destroyed by random shortduration spikes riding on the AC waveform. If not attenuated, these brief pulses (sometimes only a few microseconds in duration) can destroy semiconductors, disturb logic operations, or latch-up microcomputer routines. Experience has shown that the vast majority of unexplained problems resulting in allowed states of operations are actually caused by transient overvoltages on the utility feed.
Implementing the following AC Power recommendations will greatly increase the SIC audio/video system’s ability to suppress interference. While these standards and practices do not absolutely guarantee freedom from interference, they do provide the first line of defense.
Two basic electrical power services are recommended for the areas where technical equipment is located: Technical AC Power and Utility AC Power.
Technical AC Power supplied to the electronic equipment in the technical areas should be a separate system from the utility AC power supplied for lighting, HVAC, and other general office requirements. Power conditioning and isolated grounding should be a major part of the power supplied to the technical areas. (The selection of Power Conditioning Systems is determined by the size of the audio/video system requiring the Technical AC Power.)
The power supplied to the technical areas shall be single phase 117VAC power, isolated and conditioned with an isolated safety ground tied to the system technical power ground plate; also called the Reference Ground Plate. (See Section 0: Reference Ground Plate.) Distribution of the service from the breaker panel should be via dedicated outlets throughout the technical area. Separate 20 Amp circuits should be assigned to each isolated ground receptacle powering the equipment racks.
This equipment grounding system shall be a separate system from the ‘isolated safety ground’ system associated with the Technical Power circuits. The ‘equipment ground system’ is created to shunt any paths to ground that may be created by the interaction for the ‘signal ground’. ‘Equipment ground’ and ‘isolated safety ground’ systems, and therefore have the largest amount of copper and lower resistance.
When symmetrical AC power is used, grounding tends to be more forgiving. Every professional audio/video production facility that has tried a symmetrical power system has demonstrated a significantly lowered noise floor. The symmetrical 120-volt system is unique in that it deals specifically with balancing all power and load elements with respect to a single-point grounding reference. This is the only prescription for maintaining a clean ground regardless of how big the facility or how much gear is turned on. (Refer also to Section 0: Grounding.)
A specially wound isolation transformer with a center-tapped 120-volt output is basically the heart of the system. Both the load and the power signal are balanced with respect to the common output terminal (center tap) on the transformer. This is the true single-point grounding reference for a studio. The earth ground now functions only as a reference for electrical safety and for shields, as it should be, not as an ineffective sink-hole for reactive current.
Understandably, such a simple explanation of noise problems can invoke a kind of kneejerk skepticism or denial. But, requiring proof is not an unreasonable demand. In locations using symmetrical 120-volt power systems, the results speak for themselves.
When balanced power is applied systemwide, the results are often quite dramatic. On the average, a 16dB improvement in background noise has been noted. Where audio and video wiring is properly installed, in no known case has balanced AC failed to substantially lower the noise floor.
Utility power shall be supplied for general room requirements and lighting. The isolation of technical power from utility power and other building power loads minimizes the risk of equipment damage or malfunction due to power line noise and voltage spikes.
When three-phase power was developed as a standard to suit heavy industrial users, little was known at the time about harmonic distortion or the adverse effects on power systems created by impedance loads. The three-phase wye design enables single-phase fluorescent lighting, three-phase motor loads (e.g., elevators) to be fed by one power distribution grid with the load current evenly distributed across the system--ideal for commercial use. But this system has one glaring fault. The level of interference created when a three-phase wye system is split up and used as three single-phase circuits is truly something to behold. For example, as much as 20% (or more) of the power used by fluorescent ballasts is repelled back onto the power grid in the form of reactive or harmonic currents.
Standard power is unbalanced. Even when a high-quality 120-volt isolation transformer is installed, one side is grounded (made neutral, which isn’t much different at all. The way that AC voltage is referenced and carried by the circuit has everything to do with electrical interference in a grounding system. If an aspect of the circuit is applied or loaded in an unbalanced manner, noise will appear in the ground.
Grounding noise is one of the most common complaints from audio engineers, but it’s difficult to explain noise and grounding without addressing power. Grounding noise is closely linked to AC power under a variety of impedance load conditions.
The ground conductors of the ‘signal ground’, ‘equipment ground’, and ‘isolated safety ground’ systems should be run to the one single central point, generally a “ground plate” located near the breaker panel which is bonded to the ground rod or building Buffer ground. All ground systems should be kept separate from one another except for when they are bonded at the Reference Ground Plate.
All conduit, breaker panel cases, circuit neutrals and safety grounds, equipment ground and the transformer secondary wye ground, case neutral shall be bonded at the Reference Ground Plate.
A safety ground system is required by the National Electrical Code (NEC). In television facilities, an ‘isolated safety ground’ conductor satisfies this requirement. This is a separate, green insulated # 12 AWG ground wire which is run to each electrical outlet’s third (grounding) pin. This safety ground is isolated from the conduit, building steel, electrical boxes, and equipment ground.
Only orange or orange triangle receptacles having an isolated third (grounding) pin should be used on all outlets providing technical power. This ‘isolated safety ground’ should be tied to the ‘equipment ground’ at one point only, which is the Reference Ground Plate.
Improper equipment grounding in an electronic production facility is often the largest single cause of hum, buzz, and noise in program production. It is very important to provide a technical ground system for all SIC audio/video equipment.
Typically a large diameter copper welding cable and compression fittings connected into a star or tee network allows for any one point in the system to have only one very low impedance path to the Reference Ground Plate.
The equipment grounding system shall be a separated from the ‘safety ground’ system required by the National Electrical Code (NEC). Equipment grounding shall be done as a backbone ground system with all equipment having one low impedance path to a reference ground point (the Reference Ground Plate) which in turn has only one path to the building ‘buffer ground’. The copper bus bars provided within the racks shall be connected to this very low impedance copper equipment ground system.
In order to begin development of the HVAC and electrical systems for each of the facility’s areas, e.g., studio, edit suite, main equipment room, etc, the onsite engineers will require heat load and electrical load information for the equipment and lighting in the technical spaces. Sony SIC recommends the following:
An Audio/Video Production Facility has some fairly specialized requirements for its HVAC systems. Like computer equipment rooms, the technical spaces in this facility contain sensitive electronic equipment for which a relatively cool environment with strict temperature and humidity control must be maintained. In order to define criteria for the HVAC systems, the technical spaces can be considered as belonging to one of four different types:
It is usually impractical to provide sufficient cooling to handle the maximum heat loads in these rooms for more than thirty minutes to an hour. To keep the room comfortable for a longer period of time, it is typical to pre-cool a video studio before a session begins. For this reason, it is usually best to establish an average temperature of 70 to 72 degrees F, but allow a tolerance of 5 degrees, with some means of manually precooling the room (e.g., a two-speed fan).
All of the technical spaces, but especially the Studios and Technical Operations Center, will have a high concentration of the equipment heat loads within the facility, and will require high airflow relative to their footprint. Humidity must be controlled in these rooms to prevent the buildup of static electrical charges during periods of low humidity, and to prevent condensation and corrosion during periods of high humidity. A year-round specification of 50% relative humidity is usually acceptable, although shortterm humidity control (e.g., within a given month) should be limited to a 5% swing.
Good circulation and a frequent exchange of air within the technical spaces must be maintained to eliminate stale and possibly smoke-laden air during long work sessions. Since the electronic equipment is also highly susceptible to damage from dust and smoke particles, proper filtration is important.
The equipment in an Audio/Video Production Facility is usually left on continuously, and any combination of rooms may be in operation at any time of the day or week, so 24- hour HVAC is required.
Humidity affects us on a personal level within our comfort zone. Low and high humidity affects the way we feel; low humidity dries our throats and mouths, while high humidity makes our skin feel clammy. It is important to note that humidity is just as important to other activities that must operate in controlled environments, such as broadcast video facilities.
Humidity levels must be maintained within a range of 50% ±5%; if the air is too dry, Electro-Static Discharge (ESD) becomes more of a problem (See also Section 0); if the air is too moist, video tape sticking problems can arise.
Air conditioning’s major activity of cooling the air also has the secondary effect of removing humidity. The Heating, Ventilation, and Air Conditioning (HVAC) equipment’s criteria must be to maintain the temperature range of 70 to 72 degrees F 2 degrees and also the humidity range of 50% ±5%.
Calibrated thermometers and humidity gauges are requirements in each of the environmentally controlled areas; they should be good quality instruments.
Risks from static electricity (ESD) arise in many ways in the electronics industry. People, work surfaces, garments, tools, circuit board surfaces, support fixtures, test jugs, and packaging can all become easily charged by rubbing against other surfaces in the normal course of production and product-handling activities.
If these charged surfaces contact sensitive semiconductor devices or circuit-board assemblies, damage can occur. For example, contact from a person at 100 V and <1 µJ of energy can impair circuit operation. This is 200 times less that the minimum needed for ignition of common flammable atmospheres, and 1,000 times less than that of a perceptible feeling of shock.
Apart from device damage, static discharges can upset the operation of microelectronic systems. Electric fields from charged surfaces can attract airborne dust and debris. Various actions can be taken to avoid these problems First, ensure that all conducting objects are reliably bonded to earth; for example, wrist straps for operators and conductive footwear and flooring.
The main problem area is materials. Plastics are widely used for their many desirable properties, but nearly all are naturally good insulators that easily acquire a charge when rubbed and retain the charge for long periods of time.
The simplest way to avoid problems and risks from static electricity is to ensure that any charge released by touching or rubbing materials together can easily migrate to earth. This encompasses both easy charge movement on all materials in proximity to sensitive devices and adequate electrical leakage paths to earth.
Take advantage of the multitude of products available on the market for testing and controlling static electricity. ESD products such as gloves, smocks, shoes, chairs, flooring and floor mats, air ionizers, and ESD testers, to name but a few, are available to help control the static problem.
It is also essential that relative humidity be controlled to maintain the previously listed specification of 50% ±5%. Keeping the relative humidity within this range helps to control ESD.
This section provides Acoustic guidelines for HVAC system noise control. HVAC systems designed to service the Television Broadcast Facilities should satisfy the specified Noise Criteria. Additionally, the HVAC system servicing technical equipment areas should reduce external ambient noise by a factor of 60 dBa SPL, as measured at the interior of each technical space.
The HVAC system should be designed to meet the specified Noise Criteria (NC) rating as measured at a point 1 meter from the air diffuser/register.
All mechanical units possessing motor driven systems that are to be used in the HVAC system (i.e., compressors, etc.) should be appropriately vibration isolated. In general, vibration isolation systems employed should be of the spring type possessing a minimum static deflection of 2 inches. A 95% or greater reduction in potential vibration transmission should be adopted as performance criteria.
All motor driven systems should be checked for proper rotational balance subsequent to installation. Any deficiencies in this system should be corrected by proper alignment. Fans used in the HVAC system should be of the multi-speed variety. However, the speeds should be fixed once selected. Variable-speed fans should not be used for acoustically critical applications. In addition, the fan should be a low noise type.
Typical Noise Criteria for broadcast facilities are as follows:
All sound rated partitions, ceilings, and floors must be sealed airtight including all penetrations.
Install resilient isolation board the perimeters of floating floors.
Provide mineral wool or fiber glass batt insulation in all sound-rated wall stud cavities and above sound-rated ceiling assemblies. Provide R-11 in 4-inch studs, R-19 in 6-inch studs, an R-19 above gypsum board ceilings. Provide R-30 mineral wool in attics. Wrap all piping in sound-rated walls or passing above sound-rated ceilings with batt insulation and enclose in an insulated and sealed gypsum board soffit.
Use acoustical sealant to seal gypsum board at the head and sill of sound rated partitions. Use acoustical sealant at the perimeter of resiliently suspended ceilings. Use backer rod as required where gaps to be sealed exceed 3/8-inch. Seal duct, pipe, and conduit penetrations in sound-rated partitions.
Use sheet caulking covering the back and sides of all recessed junction boxes in soundrated construction.
Provide back-to-back structural studs for 4 x 6’s as rough framing around all sound-rated door openings. Doors can be either steel STC 49 with dual magnetic head and jamb gaskets and cam-lift hinges or, STC 42, 2-1/4-inch thick wood doors with Pemko 350 CSR gaskets at head jambs and Pemko 434 AR at fully mortised automatic door bottom.
Use 3/8-inch thick anti-static cut pile carpeting with pad in the Announce Booth, and any other area where control of ESD is important.
All technical equipment rooms should be kept free of dust and lint fiber. The ‘air filtration’ quality specification for the SIC audio/video system is 65%. (65% filtration quality is based upon a compromise between data and film environments as recommended by the ASHRAE 1995 applications handbook.)