Constant voltage speaker system
Encyclopedia
Constant voltage speaker systems refer to networks of loudspeaker
s which are connected to an audio
amplifier
using step-up and step-down transformer
s to simplify impedance
calculations and to minimize power loss over the speaker cables
. They are more appropriately called high-voltage audio distribution systems. The voltage is constant only in the sense that at full power the voltage in the system does not depend on the number of speakers driven (as long the amplifier's maximum power isn't exceeded). Constant voltage speaker systems are also commonly referred to as 25-, 70-, 70.7-, or 100-volt speaker systems; distributed speaker systems; or high-impedance speaker systems. In the US, they are most commonly referred to as 70-volt speaker systems. In Europe, the 100V system is the most widespread, with amplifier and speaker products being simply labeled with 100V.
Constant voltage speaker systems are analogous to electrical power transmission methods employed by power companies to transmit electrical power over long distances. Typically, a power company will step up the voltage
of the power being transmitted, which correspondingly reduces the current
and therefore also reduces the power
loss during transmission. The voltage is stepped back down at the destination. Similarly, in a constant voltage speaker system the amplifier uses a transformer to step up the voltage of the audio signal to reduce power loss over the speaker cable, allowing more power to be transmitted over a given wire diameter. Each speaker in the system has a step-down transformer to convert the voltage back to a usable level.
. All of the loudspeaker step-down transformer primaries are connected in parallel to the constant voltage line.
introduced the DC300 amplifier, which is capable of directly driving 70-volt lines, as well as traditional speaker loads, thanks to its overall power of 500W. In 1987, Crown introduced the Macrotech 2400, capable of driving 100-volt lines directly. Since that time, further developments in high-power amplifier technology have widened the choices; many manufacturers make amplifiers capable of direct connection to a high impedance constant voltage speaker line. High-voltage audio amplifiers have almost become a one chip solution. For example, National Semiconductor
's LME49810 (and similar products LME49811 and LME49830) can output 100V peak to peak signals, but have relatively low current output, so a standard circuit includes a Darlington or FET discrete output stage.
and the Indianapolis Motor Speedway
prior to its redesign in 2003. Safety considerations involved with such high voltages require speaker line installation within conduit
in most of the world.
Another alternative are loudspeakers with an amplifier built in to the speaker enclosure (also known as self-powered loudspeakers). Since the amplifier is at the same location as the speaker, the speaker requires only a line level
audio signal as an input. Line level signals are typically around 1-2 volts, and can be transmitted over much smaller cable (typically 20-26 AWG). The main disadvantage of powered loudspeakers is that they have the additional requirement of being locally powered, whereas passive speakers do not require a local power receptacle.
Loudspeaker
A loudspeaker is an electroacoustic transducer that produces sound in response to an electrical audio signal input. Non-electrical loudspeakers were developed as accessories to telephone systems, but electronic amplification by vacuum tube made loudspeakers more generally useful...
s which are connected to an audio
Sound
Sound is a mechanical wave that is an oscillation of pressure transmitted through a solid, liquid, or gas, composed of frequencies within the range of hearing and of a level sufficiently strong to be heard, or the sensation stimulated in organs of hearing by such vibrations.-Propagation of...
amplifier
Amplifier
Generally, an amplifier or simply amp, is a device for increasing the power of a signal.In popular use, the term usually describes an electronic amplifier, in which the input "signal" is usually a voltage or a current. In audio applications, amplifiers drive the loudspeakers used in PA systems to...
using step-up and step-down transformer
Transformer
A transformer is a device that transfers electrical energy from one circuit to another through inductively coupled conductors—the transformer's coils. A varying current in the first or primary winding creates a varying magnetic flux in the transformer's core and thus a varying magnetic field...
s to simplify impedance
Electrical impedance
Electrical impedance, or simply impedance, is the measure of the opposition that an electrical circuit presents to the passage of a current when a voltage is applied. In quantitative terms, it is the complex ratio of the voltage to the current in an alternating current circuit...
calculations and to minimize power loss over the speaker cables
Speaker wire
Speaker wire is used to make the electrical connection between loudspeakers and audio amplifiers. Modern speaker wire consists of two or more electrical conductors individually insulated by plastic such as PVC, PE or Teflon. The two wires are electrically identical, but are marked Speaker wire is...
. They are more appropriately called high-voltage audio distribution systems. The voltage is constant only in the sense that at full power the voltage in the system does not depend on the number of speakers driven (as long the amplifier's maximum power isn't exceeded). Constant voltage speaker systems are also commonly referred to as 25-, 70-, 70.7-, or 100-volt speaker systems; distributed speaker systems; or high-impedance speaker systems. In the US, they are most commonly referred to as 70-volt speaker systems. In Europe, the 100V system is the most widespread, with amplifier and speaker products being simply labeled with 100V.
Constant voltage speaker systems are analogous to electrical power transmission methods employed by power companies to transmit electrical power over long distances. Typically, a power company will step up the voltage
Voltage
Voltage, otherwise known as electrical potential difference or electric tension is the difference in electric potential between two points — or the difference in electric potential energy per unit charge between two points...
of the power being transmitted, which correspondingly reduces the current
Electric current
Electric current is a flow of electric charge through a medium.This charge is typically carried by moving electrons in a conductor such as wire...
and therefore also reduces the power
Electric power
Electric power is the rate at which electric energy is transferred by an electric circuit. The SI unit of power is the watt.-Circuits:Electric power, like mechanical power, is represented by the letter P in electrical equations...
loss during transmission. The voltage is stepped back down at the destination. Similarly, in a constant voltage speaker system the amplifier uses a transformer to step up the voltage of the audio signal to reduce power loss over the speaker cable, allowing more power to be transmitted over a given wire diameter. Each speaker in the system has a step-down transformer to convert the voltage back to a usable level.
Loudspeaker connection
In a constant voltage speaker system, each loudspeaker's step-down transformer can be designed for a single power level or it can have multiple taps, one of which is selected to match the desired power level to be applied to the loudspeaker. Transformers with various taps allow the installer to adjust the sound pressure level up or down at an individual loudspeaker. To minimize power losses, the wires connecting the loudspeaker to the step-down transformer are kept as short as possible. Purpose-built models are available that have the transformer contained within the loudspeaker enclosureLoudspeaker enclosure
A loudspeaker enclosure is a purpose-engineered cabinet in which speaker drivers and associated electronic hardware, such as crossover circuits and amplifiers, are mounted...
. All of the loudspeaker step-down transformer primaries are connected in parallel to the constant voltage line.
Amplifier connection
There are three different ways to connect constant voltage lines to an amplifier:- External step-up transformer
- Internal step-up transformer
- High voltage, transformerless output
External step-up transformer
This topology allows the contractor to choose a general-purpose amplifier with typical low-impedance output by connecting its output to the primary of an external step-up transformer. It also allows the contractor to specify special-purpose transformers to tailor the system design to the project's target power levels. Multiple amplifiers can be hitched together via transformers to yield higher voltage and higher current capacity lines. For instance, three 70-volt amplifiers have been used to make a 210-volt line by connecting them to a special-purpose external output transformer that has three primaries and a single secondary.Internal step-up transformer
Amplifiers with built-in 70-volt output transformers are available with low impedance and high impedance output connections, the latter typically labeled "25v" and "70v." These are robust, purpose-built amplifiers with many application-specific design features such as overcurrent protection and aggressive high-pass filtering for flyback voltage protection. Some models can be configured so that one channel drives one or two low impedance 8-ohm speakers while the other drives a constant voltage string of speakers.High voltage transformerless
With advances in power semiconductors, it became possible to output high voltage directly from the output stage of the amplifier. For example, in 1967, Crown InternationalCrown International
Crown International, or Crown Audio, is a manufacturer of audio electronics, and is a subsidiary of Harman International Industries. Today the company is known primarily for its power amplifiers, but has also manufactured microphones, a line of commercial audio products as well as digital audio...
introduced the DC300 amplifier, which is capable of directly driving 70-volt lines, as well as traditional speaker loads, thanks to its overall power of 500W. In 1987, Crown introduced the Macrotech 2400, capable of driving 100-volt lines directly. Since that time, further developments in high-power amplifier technology have widened the choices; many manufacturers make amplifiers capable of direct connection to a high impedance constant voltage speaker line. High-voltage audio amplifiers have almost become a one chip solution. For example, National Semiconductor
National Semiconductor
National Semiconductor was an American semiconductor manufacturer, that specialized in analog devices and subsystems,formerly headquartered in Santa Clara, California, USA. The products of National Semiconductor included power management circuits, display drivers, audio and operational amplifiers,...
's LME49810 (and similar products LME49811 and LME49830) can output 100V peak to peak signals, but have relatively low current output, so a standard circuit includes a Darlington or FET discrete output stage.
High voltage
High voltage constant voltage systems can be designed to use 140-, 200- and 210-volt lines, depending on the transformers selected and the amplifier connection topology. Such high voltage systems have been used in locations where small diameter wire is already in place, where long distance wire runs are involved and at especially loud installations such as Daytona International SpeedwayDaytona International Speedway
Daytona International Speedway is a race track in Daytona Beach, Florida, United States. Since opening in 1959, it has been the home of the Daytona 500, one of the most prestigious races in NASCAR. In addition to NASCAR, the track also hosts races of ARCA, AMA Superbike, Grand-Am and Motocross...
and the Indianapolis Motor Speedway
Indianapolis Motor Speedway
The Indianapolis Motor Speedway, located in Speedway, Indiana in the United States, is the home of the Indianapolis 500-Mile Race and the Brickyard 400....
prior to its redesign in 2003. Safety considerations involved with such high voltages require speaker line installation within conduit
Electrical conduit
An electrical conduit is an electrical piping system used for protection and routing of electrical wiring. Electrical conduit may be made of metal, plastic, fiber, or fired clay. Flexible conduit is available for special purposes....
in most of the world.
High current
600 watt transformers are widely available for contractors needing high power loudspeakers in constant voltage installations. Special purpose transformers capable of handling 1250 watts down as low as 50 Hz are available. One problem with high power, high current transformers is that fewer can be used on a single constant voltage line. Larger diameter speaker wire is recommended. Larger transformers needed for high power handling have reduced high frequency response.Alternatives
The traditional alternative to constant voltage speaker systems are low impedance speaker systems (commonly referred to as "8-ohm speaker systems" in spite of the fact that their impedance may not be 8 ohms), in which the amplifier and speaker are directly coupled without the use of transformers. The disadvantages relative to constant voltage systems are that speaker cables need to be shorter or larger diameter and that more amplifiers are needed if different listening levels are desired at different locations.Another alternative are loudspeakers with an amplifier built in to the speaker enclosure (also known as self-powered loudspeakers). Since the amplifier is at the same location as the speaker, the speaker requires only a line level
Line level
Line level is a term used to denote the strength of an audio signal used to transmit analog sound between audio components such as CD and DVD players, TVs, audio amplifiers, and mixing consoles, and sometimes MP3 players....
audio signal as an input. Line level signals are typically around 1-2 volts, and can be transmitted over much smaller cable (typically 20-26 AWG). The main disadvantage of powered loudspeakers is that they have the additional requirement of being locally powered, whereas passive speakers do not require a local power receptacle.
Advantages
The main advantages of using a constant voltage speaker system over a conventional low impedance speaker system are:- Multiple loudspeakers: Many loudspeakers can be driven by a single amplifier without complex series/parallelSeries and parallel circuitsComponents of an electrical circuit or electronic circuit can be connected in many different ways. The two simplest of these are called series and parallel and occur very frequently. Components connected in series are connected along a single path, so the same current flows through all of the...
connection schemes. - Multiple power levels: Different sound pressure level targets can be achieved at different listening areas while still using a single amplifier.
- Less expensive: Since the voltage of the signal has been stepped up and the current is relatively low, lighter, less expensive cable can be used without incurring additional power loss. Where a typical 8-ohm speaker system might require 12 gaugeAmerican wire gaugeAmerican wire gauge , also known as the Brown & Sharpe wire gauge, is a standardized wire gauge system used since 1857 predominantly in the United States and Canada for the diameters of round, solid, nonferrous, electrically conducting wire...
cable, a 70-volt system could use 18 gauge or smaller cable.
Disadvantages
- Frequency ResponseFrequency responseFrequency response is the quantitative measure of the output spectrum of a system or device in response to a stimulus, and is used to characterize the dynamics of the system. It is a measure of magnitude and phase of the output as a function of frequency, in comparison to the input...
: Inexpensive transformers may have poor reproduction of low and high frequencies. - DistortionDistortionA distortion is the alteration of the original shape of an object, image, sound, waveform or other form of information or representation. Distortion is usually unwanted, and often many methods are employed to minimize it in practice...
: Overdriven transformers can add ringing distortion to the audio signal. Low cost transformers are prone to distortion at higher power levels, especially with regard to low frequency response. Low level signals can fail to energize a poorly designed transformer core enough to prevent higher than normal amounts of harmonic distortion. - Variation: Unit-to-unit variation can be observed in poorly made transformers.
- Delay: More distant speakers on the same constant voltage line cannot be delayed to match the speed of sound in air so that the impulses from a string of loudspeakers arrive at the same time from the point of view of a distant listener.
- Insertion lossInsertion lossIn telecommunications, insertion loss is the loss of signal power resulting from the insertion of a device in a transmission line or optical fiber and is usually expressed in decibels ....
: The transformers themselves commonly reduce total power applied to the loudspeakers, requiring the amplifier to be some ten to twenty percent more powerful than the total power that is intended to be applied to the loudspeakers. Typical transformer insertion loss measurements are taken at 1,000 Hz in order to make the transformer's specifications appear as good as possible. Using this method, typical insertion losses are about 1 dB, a 20% power loss. Unfortunately, most of the power in voice-application audio systems is below 400 Hz, meaning that insertion loss at lower frequencies would be greater. The best transformers reduce mid-band frequencies by 0.5 dB (approximately 10% power loss) or less, resulting in a ten watt loudspeaker drawing 11.1 watts from the amplifier. - CapacitanceCapacitanceIn electromagnetism and electronics, capacitance is the ability of a capacitor to store energy in an electric field. Capacitance is also a measure of the amount of electric potential energy stored for a given electric potential. A common form of energy storage device is a parallel-plate capacitor...
: To achieve higher power levels, transformers must be physically larger. Large transformers (above 200 watts) begin to suffer from high frequency attenuation due to self-capacitance. - More expensive: If high-power loudspeakers are used with an emphasis on low frequency response, the required transformers will be much larger and will add significant cost to the project. Additionally, in some areas, local building and electrical code requires 70-volt cabling to be carried within conduit, increasing the overall project cost.
- More sensitive: Since constant voltage systems operate at relatively high impedances, they are more sensitive to small amounts of leakage current and partial short circuits. Running 70-volt speaker lines in conduit that may collect water can result in crackling sounds heard in the system.