Effects of cable loss in passive loudspeakers
The graph shows the degradation in response of a generic 4 Ohm passive loudspeaker system connected to the amplifier using different lengths of cable with a conductor size of 2,5 mm². The lower red curve represents impedance vs frequency of the loudspeaker system. Cable loss is unavoidable, so cables have to be as short as possible in order to minimize loss.
MB audiosystems integrate processing modules, power amplifiers and transducers. Power cables are therefore extremely short and cable loss is practically negligible.
Effects of cable loss are significant when the resistance of the loudspeaker cable is more than 4-5% of the nominal load impedance, which is normally the case for most of installed and touring systems configurations.
The resistance of the loudspeaker cable causes a voltage drop along the conductors and a consequent loss in SPL level. This loss in SPL level depends on the impedance of the loudspeaker, which varies with frequency. As a consequence the SPL level loss will also depend on the frequency, resulting in a deterioreted frequency response. Lower the impedance, greater the loss due to the cable. For full range systems this may considerably affect tonal balance.
Cable loss also has non linear effects on frequency responce curve and SPL level, since loudspeaker impedance curve changes dynamically while the system is in operation. This is mainly related to voice coil temperature and cone excursion, and therefore depends on the operating level of the system.
Each loudspeaker cable also has a specific impedance curve, since the resistance of the cable varies with frequency. More in detail resistance increases at higher frequencies, due to the inductance of the cable. Therefore cable inductance causes an added voltage drop at high and very high frequencies. The effect of cable inductance is not represented in the graph, to have simplified presentation.