70V Line Speaker Wiring: Difference between revisions
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This method of getting audio from amplifiers to speakers is similar in principle to power transmission methods used to distribute electrical power. The power company puts power on a line that carries it a long distance with thousands of Volts. The voltage is stepped down to hundreds of Volts at the building where the power is used. Because lower currents are required at high voltage, the resistance of the line does not cause a loss of power because of heat, and smaller diameter wires can be used. | This method of getting audio from amplifiers to speakers is similar in principle to power transmission methods used to distribute electrical power. The power company puts power on a line that carries it a long distance with thousands of Volts. The voltage is stepped down to hundreds of Volts at the building where the power is used. Because lower currents are required at high voltage, the resistance of the line does not cause a loss of power because of heat, and smaller diameter wires can be used. | ||
Similarly, we can apply a high voltage audio signal to a speaker line as long as there is a transformer at the speaker end to reduce the voltage to appropriate values for the drivers. Usually this system is used to distribute audio to a large venue with many speakers. In some cases, a constant | Similarly, we can apply a high voltage audio signal to a speaker line as long as there is a transformer at the speaker end to reduce the voltage to appropriate values for the drivers. Usually this system is used to distribute audio to a large venue with many speakers. In some cases, a constant voltage system is used to save money on speaker wire. | ||
The reason the North American audio industry settled on 70 Volts is so all audio wiring can be installed without conduit. Many electrical codes of the time stipulated that voltages of 100 or more Volts must be installed in conduit. Modern codes break audio and signaling voltages into various classes. Class 2 covers typical speaker wiring installations. The main implication is that primary wiring and Class 2 wiring must never be placed in the same conduit or junction box. Note that the voltage is not ''constant,'' as its name seems to imply, but does actually fluctuate with the audio signal. The tapped transformer Power to the speaker voice coil reaches its rating when the speaker line Voltage reaches 70. | |||
== Loudspeaker connection == | == Loudspeaker connection == | ||
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=== Low Impedance Speakers === | === Low Impedance Speakers === | ||
Use of low impedance speakers connected directly to the outputs of a modern solid state amplifier generally provides the best sound quality. The length and size of the speaker cable must be carefully determined. For our typical 400 Watt systems, 14 AWG wire is generally suitable up to 100 feet. For longer lengths consider using 12 AWG. Always used '''stranded''' wire for audio. | Use of low impedance speakers connected directly to the outputs of a modern solid state amplifier generally provides the best sound quality. The length and size of the speaker cable must be carefully determined. For our typical 400 Watt systems, 14 AWG wire is generally suitable [[InSpire_audio_connections#What_size_wire_should_I_use.3F|up to 100 feet]]. For longer lengths consider using 12 AWG or larger. Always used '''stranded''' wire for audio. | ||
=== Locate the amplifier near the speakers === | === Locate the amplifier near the speakers === | ||
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*Cost: The addition of transformers increases the cost of these speakers | *Cost: The addition of transformers increases the cost of these speakers | ||
*Frequency Response: Inexpensive transformers may have poor low and high frequency reproduction. | *Frequency Response: Inexpensive transformers may have poor low and high frequency reproduction. Primary applications for constant voltage systems are low fidelity paging and background music systems. | ||
*Insertion Loss: As much as 20% of the amplifier's power is wasted through the transformers. This figure should be accounted for and compared to when calculating the losses encountered through various sizes of low impedance wiring. | *Insertion Loss: As much as 20% of the amplifier's power is wasted through the transformers. This figure should be accounted for and compared to when calculating the losses encountered through various sizes of low impedance wiring. | ||
*Capacitance: To handle higher powers, transformers have to be scaled up in size. The added capacitance begins to attenuate high frequencies. | *Capacitance: To handle higher powers, transformers have to be scaled up in size. The added capacitance begins to attenuate high frequencies. | ||
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== Transformers == | == Transformers == | ||
=== Atlas 70 Transformer wiring === | === Atlas PD-60AT 70 Volt Transformer wiring === | ||
Internally mounted transformers | [[File:PD60ATDrivers.jpg|400px|thumb|PD60AT Drivers]] | ||
Internally mounted transformers Atlas PD-60AT drivers have the following color code: | |||
Red - Voice Coil Negative | Red - Voice Coil Negative | ||
White - Voice Coil Positive | White - Voice Coil Positive | ||
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Brown - 2.5W input terminal | Brown - 2.5W input terminal | ||
=== San Ming 70 Transformer wiring === | === San Ming 70 Volt Transformer wiring === | ||
Internally mounted transformers in San Ming drivers have the following color code: | Internally mounted transformers in San Ming drivers have the following color code: | ||
Top terminals - Voice Coil | Top terminals - Voice Coil | ||