Mis à jour le 15 March 2019.
For home hi-fi installations, a low impedance wiring system using high quality speaker cables is used to connect each speaker to the amplifier. However, audio systems for public spaces, such as shopping malls, stores, offices or any other buildings, require multiple speakers and long lengths of wires. A regular configuration just isn’t suitable, as it would overload the amplifier and cause it to cut out. A 100 volt distributed system is therefore the best solution to power several speakers efficiently with one amplifier.
Why set up a 100 volt system?
When installing an audio system in a building, the distance between the speakers and the amplifier often exceeds dozens or even hundreds of meters. Such lengths lead to a great amount of power loss and voltage drops in the wires. Unless heavy gauge wires are used, which would raise the cost of the installation, using a low impedance system isn’t efficient enough to compensate for the power loss over the line.
Also, for the sound to cover the entire area of the building, it is generally necessary to use multiple speakers that are far apart. Because it is essential to respect the amplifier’s impedance and maximum output power, using a regular low impedance system complicates the wiring. For example, if you need to connect eight 4 Ohm speakers in parallel, the total impedance will be 0.5 Ohms. No amplifier can withstand such a load: it could blow out or damage the speakers. Consequently, the wiring must be done by combining both series and parallel circuits in order to comply with the amplifier’s minimal impedance. However, this type of wiring can rapidly become rather complicated, expensive and time-consuming. Such setups also require identical speakers to be used and don’t allow a different volume in each room. Moreover, if one of the speakers is damaged, none of the other speakers will be powered. Therefore, a classic low impedance system is highly unsuitable for powering a large number of speakers.
In this case, using a 100 volt distributed speaker system offers many advantages, starting with lower voltage drops. This permits the use of thinner gauge wires (0.77 mm or more) at a lower cost. In addition, when using multiple speakers, the entire load isn’t calculated according to their impedance, but is based instead on the total of each speaker’s power handling capacity in watts. Parallel wiring is no longer a problem and it is also possible to use speakers with different power ratings. The only requirement is that the total power of the installation must be lower than the amplifier’s maximum output power. For example, to create an audio system for a hotel, you could use four 10 watt speakers in the hall, ten 5 watt speakers in the corridors, two 10 watt speakers for the bar and four 15 watt speakers in the gym. The total power would be 145 watts. Then all you have to do is choose a hi-fi stereo amp that has a maximum output power slightly superior to the one just calculated. In our example, it would be possible to use the 2×150 W Atoll IN200 Signature amp. If the speakers’ power rating appears high, then a preamplifier and power amplifier will be necessary.
How does a 100 volt distributed speaker system work?
In a 100 volt distributed speaker system (also called public-address or PA), a transformer is placed at the amplifier’s output to increase the line voltage. Next, each connected speaker is fitted with a second transformer dedicated to converting the incoming 100 volt voltage back into a modulation signal and isolating the speaker’s impedance load from the amplifier. This transformer usually allows the power allocated to the speaker to be modified: each speaker then only takes the necessary amount of power from the line. It is therefore possible to use multiple speakers with different power ratings in the same 100V circuit. Consequently, the power and volume of each speaker can be adjusted separately.
Mono or stereo 100V system?
Technically, there’s nothing stopping you from creating a stereo system in 100 volts. That said, most 100V installations are done in mono as this makes the wiring a lot easier to do because you avoid wiring two separate lines. More importantly, a mono configuration ensures optimal musicality, regardless of listener’s position in the room. For a stereoscopic effect to be successful, the user must be positioned in a defined area between the left channel speaker and right channel speaker. Outside this area, the stereo effect won’t work, and the listener won’t hear the music in its entirety. Therefore, in a mall or other space in which the user is constantly moving, using a mono 100V system is more appropriate.
How to create a 100V system
Creating a 100 volt public-address system requires using speakers and drivers that are specifically made to withstand a voltage of 100 volts. The choice of speakers then depends on the layout of the room. For example, in a building with a high ceiling, using in-ceiling or hanging speakers is the most suitable solution. These types of speakers are often used for meeting areas to ensure a 360° sound restitution, so that each visitor can benefit from optimal sound quality without the sound being obstructed by furniture or people standing in front of the speakers. The speakers in the Elipson Bell range are designed for this use, in a classic low impedance system or a 100 volt public-address installation.
To bring sound to an outdoor space or a humid room such as an indoor swimming pool or changing rooms, it is essential to choose tropicalized speakers that are weatherproof and resistant to humidity. In this category, the Monitor Audio Climate Garden System CLG140 speakers are ideal for a discreet garden installation.
Once you have determined the type of speakers you would like to use, you will need to calculate how many it will take to successfully restitute sound throughout the whole area. This number can be easily determined by dividing the floor area by the area covered by a single speaker. For the sound restitution to be consistent, the adjacent listening zones must overlap slightly.
A hi-fi amplifier with a power output that is 10 to 15% higher than the total power of the installation should then be used to avoid overloading or damaging the speakers. The amp must be paired with an output transformer to raise the voltage to 100 volts. There are many different models available, from basic devices to more elaborate equipment. If you are thinking of setting up a 100V distributed speaker system or any other professional hi-fi or home theater installation, the Son-Vidéo.com/pro service provides offers and discounts tailored specially for your business that take into account your VAT rate and specific needs.
Lastly, when installing or handling a 100V system, always make sure that you follow electrical safety regulations. An amplifier used at full power combined with a 100V transformer can deliver dangerous voltage levels. It is therefore imperative to always disconnect the amplifier and transformer from the power supply before handling them to avoid any risk of electrocution.