Racks, enclosures, housings, whatever you call them they are the essential infrastructure component for any installation. They spend their lives behind doors labeled “authorized personnel only” and “danger high voltage.” Or, they remain anonymous behind an unmarked steel door in a dark corner of the basement. They stand side by side, often row after endless row, holding together the electronic components that make our systems function.
Without them, there would be no way to organize hardware, coordinate cabling, structure the signal flow of systems or perform a myriad of other often forgotten, but critical tasks. Racks also provide security, cooling, safety and increase serviceability.
An Introduction
In the A/V world, hardware designed to be placed in a rack is typically labeled as rack mountable, a rack mounted system, or a rack mount chassis. According to the EIA standard EIA-310-D, Cabinets, Racks, Panels, and Associated Equipment, the height of the electronic modules is standardized in multiples of 1.75 inches (44.45 mm) or one rack unit or U (less commonly RU). The industry standard rack cabinet is 42U (6.125 ft.) tall and 19 inches wide to accommodate most AV equipment.
Since the mid-1930’s, the ubiquitous 19-inch rack format has remained constant while the technology that is mounted within it has changed considerably. Typically, a piece of installed equipment has a front panel height 1⁄32 inch (0.031 inches or 0.787 millimeters) less than the allotted number of rack units. Thus, a 1U rack mounted device is not 1.75 inches (44.5 mm) tall, but 1.719 inches (43.7 mm) tall. 2U would be 3.469 inches (88.1 mm) instead of 3.5 inches (88.9 mm). This creates a tiny gap above and below an installed piece of equipment, allowing it to be removed without binding on the adjacent equipment.
The Standard 42U Rack
These simple steel frames often house mission critical AV components, but are habitually overlooked as an essential component of the overall system. As a result, the ordering and configuration of racks is usually left until very late in the project. Given the complex nature of today’s hardware and systems, that methodology is not efficient. Why? Because racks are the basic physical infrastructure of all AV systems and poor choices, or inadequate design, at this point will cause major headaches later on.
Today’s rack designs are made using fully computer controlled manufacturing, laser alignment and automated welding systems that produce a complete rack in one continuous process. This produces products that are identical (very important when there will be dozens of them side by side) and absolutely square, ensuring that all the components will fit properly and the rack itself will be solid and secure, as well as standardized to specific code requirements.
Basic racks are also available in what is commonly referred to as a “flat pack” option, where all the pieces have to be bolted and screwed together onsite. No matter how carefully this assembly process is done, such systems can never be as precisely square and solid as a welded structure, and in many jurisdictions, they will not meet code requirements. If the rack required is quite small (only 6 or so U high) and will only need to hold lightweight equipment, this may be a feasible alternative, but given the minor shipping cost differentials and increased labor costs, you will be far better off purchasing fully welded precision manufactured products.
The Half Height Rack
The second most commonly used rack format is often called the “half-height rack” wall mount design. These are popular in schools, auditoriums, gymnasiums and many hospital facilities. The half-rack designation comes from the fact that these enclosures are usually somewhere between 18 and 24U in height or about ½ the height of the standard 42U rack. These are especially useful for the deployment of smaller scale systems using a compact mixer, one or two modest sized amplifiers and perhaps some source/playback components. Usually supplied with a lockable door, half-racks can be attached easily to almost any wall that will support the weight. Be sure to calculate the actual weight of the fully loaded rack when making this choice.
As with the larger standard AV racks, the smaller products are offered in a variety of sizes, configurations, depths , etc. Today the swing away designs are quite common, allowing for easy and quick access for serving or maintenance. This style is available from most suppliers.
Three other principal categories for rack systems are designed for hazard areas such as earthquake zones, the racks that are specifically designed for increased half-rack width (that is the front panel of the device, regardless of the number of U high it is, is just under 9.5 inches wide allowing two units to fit side by side in 1 rack slot) and specific designs used for data, computer, server, router and telecom installs.
Johnathan Ivey, Senior Vice President Sales & Marketing Atlas Sound / Mitek Communications made the following points regarding both the hazard area racks and the emerging half-width rack configuration.
“While equipment racks are often the last piece added to any installation’s planning and purchasing process, it’s critical to understand that every rack is not produced to the same tolerances and manufacturing standards.”
Ivey explains this becomes especially important, “when different models of what would appear to be the same rack actually include different features that can make or break an installation based on the requirements”.
Increasingly, safety and fire codes are requiring that racks meet much stricter performance and mechanical/structural standards.
Ivey notes that “some cities, counties, or states have different requirements that must be adhered to for a project to be signed off on. One such requirement is a cabinet that features a seismic rating. Areas like California that frequently endure earthquakes and other seismic activity have requirements that equipment racks must be designed and manufactured to withstand up to a zone 4 level earthquake, which is comparable to Richter magnitude 8.0”
You also need to consider ventilation. Ivey suggests you ensure that any chosen rack “offers a solid design without punched vents to allow for a thermal air flow design that is precisely designed and maintained, ensuring that contaminants or other foreign objects are not introduced into the interior.”
Half Width Racks
Some applications call for an equipment rack, but a full size rack is too big or will not work in the desired install location. For example, classrooms with only one or two pieces of equipment or corner installations where a full size or swing out rack will not fit necessitate an alternative solution.
A number of manufacturers are now offering solutions for unique rack environments. Ivey points out that his company “now offers half width rack units in both on wall mount and in wall mount options that address these scenarios.”
Atlas Sound’s WMA model racks feature another approach, which uses a patent pending fold forward design that allows them to be placed in a corner installation and still allow access to the rear of the product for proper wiring and terminations. Additionally, the back box can be shipped to the install location separately from the rack so that the back box can be placed during construction while loading the rack offsite for installation post construction.
The half rack approach is now standardized with Extron, Middle Atlantic, Atlas (with it’s WMA models) as well as many other manufacturers.
Racks for Big Data, Small Data, IT and Telecommunications
The requirements for rack systems in data centers, for cloud servers, routers, and almost
