BEST PRACTICES FOR SELECTING CLASSROOM AMPLIFIERS

An audio amplifier is the heart of a sound reinforcement system in a classroom. The amplifier takes the line level signal produced by the source device, amplifies and distributes it to the speakers throughout the room. It is important to note that an amplifier will only be required for speakers that are not self amplified. Self amplified speakers will typically have line level audio inputs, such as RCA or 3.5mm. Speakers that require an audio amplifier will typically have speaker wire connection as inputs. Selecting the proper amplifier helps to ensure that the audio system performs to its maximum potential. There are many factors that must be considered when selecting the proper amplifier for an installation.

Size of Room
The size of the room is one of the most obvious considerations when selecting an amplifier. An amplifier that is designed for a typical classroom, typically 90ft2, would not be appropriate for an auditorium that is 900ft2. One of the main differences between the amplifiers for these different size rooms is the power output. For a typical classroom a power output of 40 to 50 watts is more than sufficient, whereas an amplifier with a power output of 500 to 1000 watts is better suited for an auditorium. While it is possible to use an amplifier that has more power than is needed within a classroom, this would incur an unnecessary expense.

Audio Inputs
The audio inputs on an amplifier are an important consideration because they impact the ease of installation. Many classrooms now integrate a microphone system for the teacher, in addition to a separate audio playback source such as a DVD or Blu-ray player. If an audio amplifier has only a single audio input, then a separate audio switch must be used to accommodate the extra device. This is not only an added expense, but also provides a potential point of failure in the audio system. The ideal solution is to have the same number of inputs on the amplifier as the audio source devices being used.

Connection style is another consideration. Some amplifiers accept standard audio connectors, such as 3.5mm or dual RCA, as an input. Other models are only able to accept bare wire connections as an input. There are advantages and disadvantages to both connection styles. Amplifiers that accept the audio connectors as an input provide the advantage of an easier installation and a lower probability of an electrical short. The disadvantage is that the connectors take up added space in a plenum box which will leave less space for additional equipment. The advantages to bare wire connection styles are a more secure connection and a smaller footprint within the installation location. The disadvantage of a bare wire connection style is a more difficult installation process and the increased likelihood of an electrical short because of the exposed conductor. This probability may be reduced by properly preparing the cable before making the connection to the amplifier. However, this preparation increases installation time and may increase cost.

Fire Rating
In many classroom installations the amplifier is installed within an environment such as a plenum air space. The National Electrical Code (NEC), as well as local building and fire codes, mandates that cables and devices installed within this environment meet fire ratings designed to protect the occupants of a building in the event of a fire. Amplifiers that meet these requirements are typically clearly marketed as "plenum rated". One important point to consider is that although the amplifier itself may be plenum rated, that does not mean that all components of the amplifier meet plenum requirements. As an example, power supplies are not typically plenum rated. Most manufacturers who produce a plenum rated amplifier provide a non-plenum rated power adapter. This means that the power adapter for the amplifier must either be installed within a plenum fire box, or outside of the plenum environment. Following these requirements when installing a plenum amplifier helps avoid the potential of serious injury or death in the event of a building fire. Consult local building codes and the NEC before installing an amplifier.

Features
Many classroom amplifiers offer additional features that provide cost savings or protection for the amplifier. An auto-shutdown capability allows the amplifier to power down when there is no audio signal detected. This allows for power savings when the amplifier is not in use and may extend the life of the amplifier. Many amplifiers also offer over current protection. This shuts down the amplifier before it is damaged in situations where the audio system pulls more current than the amplifier was designed to support. This feature can save an amplifier from irreparable damage and help prevent the possibility of a fire. These situation exist may exist if the speakers are wired incorrectly or during a power surge.

Selecting the appropriate amplifier helps avoid unnecessary expense, eases the installation process, and ensure that the building and fire codes required for the installation environment are met. Additional features provided by many amplifiers give the added benefit of cost savings and protect the amplifier from damage. These considerations will allow for the selection of an amplifier that will provide the best performance of the sound reinforcement system within the classroom and the best experience for both students and teachers.