18 | Chapter 1: Crown Amplifiers In-Depth |
level to drive the speaker, and are connected across the wires (see Figure 1.26). The combination of transformer and speaker line presents a much higher impedance to the amplifi er than would the speaker itself, making it possible to add many speakers to a single home run.
In distributed speaker systems, as the ratio of voltage to current become greater, less power is lost on the home run. This makes it possible to use much smaller gauge wire for home runs than would otherwise be possible.
What is Constant Voltage?
“Constant-voltage” amplifi ers do not, in fact, supply a con- stant output voltage. The audio is represented with varying voltage just as with a low-impedance amplifi er. The term “constant-voltage” was arrived at for two reasons. First, con- stant-voltage amplifi ers produce their maximum power when the output voltage reaches the specified value. For example, an amplifi er rated at 200 watts, when set to 70V output, will produce 200 watts when the output voltage reaches 70V. Second, the output voltage of an amplifier driving a con- stant-voltage (distributed) speaker run remains constant across a wide range of impedances.
Using Low-Impedance
You can use amps without constant-volt- age settings on distributed speaker sys- tems if the power output is high enough. For example, an amplifier rated for 78 watts output into 8 ohms will directly drive a 25-volt line. To calculate the necessary power for driving a specifi c voltage line use the following formula:
where P equals the necessary power output,
V equals the voltage of the distributed speaker system, and R equals the imped- ance of the amplifi er for the power specifi -
Transformer Saturation
It’s important to know that transformers can easily become “saturated” at low-frequencies. Transformer saturation occurs when the magnetic fi eld created by the signal content becomes too much for the core of the transformer to handle. This condition can be dangerous to the amplifi er, and can also cause distortion.
An effective way to prevent step-down transformer saturation is to fi lter the very low-frequency content from the audio. Your amplifi er may provide high-pass fi lters for this purpose (see your Operation Manual). If not, see Sec- tion 1.2.2 for filter suggestions.
1.4Multi-way Systems
(with Expansion Modules)
This section shows how multi-way systems can be effectively designed using optional expansion modules that feature active crossover networks. Example systems are shown for single and multiple amp two-way systems and three-way systems.
The range of frequencies present in full-range music is wider than most any single speaker component can accu- rately reproduce. Because of this, most professional speaker systems employ two or more speaker components to do the job. Crossover networks (or crossovers) are electrical circuits that divide an incoming signal into two or more separate frequency bands. The separate bands are then routed to speakers designed to reproduce the range of frequencies they are being fed.
1.4.1 Active vs. Passive Crossover Networks
There are two types of crossovers: active and passive. Passive crossover networks are located in the signal chain between the amplifier and speakers. The networks built into speaker cabinets are typically passive. The primary advantage to passive crossovers is that they use fewer amplifi ed channels. The primary disadvantage is that they work with amplifi ed or high-voltage signals because of being located after the amplifi er in the signal chain, causing them to waste much of the power before it gets to the speakers. They also have lower dynamic range.
Active crossovers are typically located before the amplifier in the signal chain. They work with lower “line-level” signals, meaning they waste much less power.
Amplifier Application Guide
