The 70-volt line system has become the dominant wiring method in the commercial sound field due to its simplicity and flexibility. However, as a result of the use of less-expensive line transformers, the potential sound quality available from most amplifiers and loudspeakers is severely restricted. 

dB
	Frequency

The above graph shows the loss in the important low frequencies. Attempts to offset this deficiency by increasing the amplifier's volume and bass controls can easily cause amplifier failure. (The impedance in a transformer declines at the lower and higher frequencies.) Unfortunately, the characteristics of a transformer cannot be determined solely by physical inspection since the quality of the metal used, as well as the overall size and weight, must be considered.