Constant Voltage Speaker System - Disadvantages

Disadvantages

• Frequency Response: Inexpensive transformers may have poor reproduction of low and high frequencies.
• Distortion: 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 loss: 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.
• Capacitance: 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.