Exclusive distribution agreement signed between Ligra DS and Zero-Ohm Systems

Zero-Ohm Systems is a Canadian company that has developed a somewhat revolutionary passive device that allows any amplifier to be interconnected to several loudspeakers without worrying about load impedances and cable lengths.

This device allows users to connect 20, 30, 40 or more loudspeakers in parallel to a single amplifier channel without the use of transformers, typical of 100 V systems. Until now, this possibility was conditioned by the possibility of running the amplifier at a very low load impedance for reasons we will explain in a moment. Although there are power amplifiers capable of operating safely at 4 ohms and 2 ohms, going below a threshold value results in the failure of the device (if not adequately protected) and consequent interruption of service.

Zero-Ohm, on the other hand, solves the problem at the source and for this reason is suitable for all installations in arenas and stadiums, amusement parks, bars, cinemas and theatres, reception halls, airports, cruise ships, hotels, outdoor shopping centres, restaurants, water parks and more.

Ligra DS has seized the opportunity of being able to distribute, exclusively for the Italian market, a device like this to installers and system integrators, which offers, among other things, a fundamental advantage: for the same number of loudspeakers, it considerably reduces the number of amplifiers required and consequently the costs.

The problem of load impedance

The laws of electrical engineering teach us that by connecting two identical loudspeakers in parallel, therefore with the same impedance, to the channel of an amplifier, the total impedance is halved. For example, using a pair of speakers with a nominal impedance of 8 ohms, the output stage of the amplifier sees a load of 4 ohms at its terminals. If the speakers are now changed from two to four, the resulting impedance becomes 1/4 of that of the single speaker, in this case 2 ohms. However, the output stage of the amplifier cannot continue to supply current when the load becomes too low, as the impedance it sees at the terminals comes dangerously close to short-circuiting. This reasoning leads us to understand how there is a maximum number of speakers that can be connected to a single amplifier. 

In order to prevent the circuits from burning out, almost all amplifiers are equipped with more or less sophisticated protection circuits that 'disconnect' the device when the load seen falls dangerously below a certain threshold or reaches a certain temperature. The problem is that the amplifier stops working.

100 V systems and their limits

100 V, or distributed loudspeaker systems, are an alternative to the parallel connection just described (also known as 'low impedance') and are widely used where multiple loudspeakers are required. At the basis of these systems is a power distribution method similar to that adopted for the distribution of electricity in our homes, i.e. high voltage, 100 V (or 70 V) precisely. The amplifier has a built-in step-up transformer, i.e. it raises the voltage and causes the signal to be transmitted over an even very long line with negligible losses. Each loudspeaker/speaker then has its own step-down transformer to convert the signal back to low voltage/high current:
Beyond the technical aspects, these systems have one big advantage: to connect several loudspeakers, we simply put them all in parallel and add up the total powers. If, for example, we have an amplifier with 100 W @ 100 V, we can connect 20 speakers with 5 W each (20 x 5 = 100 W) or 10 speakers with 10 W each (10 x 10 = 100 W) or even combine speakers with different powers. Distributed loudspeaker systems are commonly used in airports, shopping centres, schools, churches, clubs, offices, car parks, sports grounds and wherever many loudspeakers are required with a small number of amplifiers. However, they have a number of drawbacks, the most important of which is the fact that each speaker requires its own transformer and these heavily influence the sound quality (loss of low frequencies etc.) to such an extent that they can only be used for the reproduction of speech and low-level background music.

The Zero-Ohm solution/revolution

Until now, a choice had to be made at the design level between prioritising audio quality at the expense of the maximum number of speakers that could be connected to each individual amplifier or the number of speakers at the expense of quality. Until Zero-Ohm patented its system, which translates into a unit to be interposed between the power amplifier and speakers to connect dozens of speakers in the conventional low-impedance mode, i.e. in parallel, offering the following advantages
  • No transformer required
  • Several speakers can be connected in parallel (more than 40) without load impedance problems
  • Possibility of using loudspeakers with any nominal impedance: 2, 4, 8, 16 ohm
  • Uniform power distribution over long cable runs
  • Unlimited frequency response in the audio band
  • Cost reduction due to fewer amplifiers

There are four Zero-Ohm products currently available that are totally passive and belong to the Disruptor and Renegade series:


These devices have one pair, or four, inputs and two outputs A and B to drive the loudspeakers.

The connection is made using cables with Speakon connectors, so that - on the outputs - once the first speaker is connected, the relay is sent to the second and so on until the whole series is completed.