Achieving Efficiency: Rent Com Inc: Audio Visual, Video, Projection, Presentation Rental AV Equipment

Achieving Efficiency

Efficiency is a measure of how much acoustic power results from an application of electrical power. In the early days of audio, transducer efficiency was a prime consideration, mainly because the largest amplifiers were able to produce only a few watts of power. High efficiency meant that most of this power could be converted into sound. With the advent of solid state electronics, amplifier power became quite economical. These days, amplifiers in the thousands of watts are readily available and (at least compared to the old days) inexpensive. So why would we continue to be concerned about efficiency? The answer lies in what a transducer does with the electrical power that it receives. Each watt drawn by the transducer is converted into one of two types of energy: sound or heat. While sound is what we are after, it is inevitable that heat will also be produced, and heat is a main culprit for many transducer failures in high-level systems.

While a frequency response specification is useful, it may be misleading at high frequencies due to high-frequency beaming, a phenomenon that occurs as the wavelength being reproduced by a driver becomes small when compared to the diameter of the driver. Even though the on-axis response is flat, the pattern has narrowed and there is less off-axis coverage. Power response is best measured on a constant-directivity horn or plane wave tube, which gives a better representation of these two parameters. Simply stated, a highly efficient transducer produces more sound and less heat. Efficiency in a transducer is proportional to the amount of magnetic flux that can be concentrated into a magnetic field gap. This magnetic field gap should be made as narrow as possible, yet not so narrow as to allow the voice coil to rub as it moves through the gap.

The M4 achieves a highly concentrated magnetic field by using a unique focused geometry and an added flux stabilizing ring. This combination helps keep the magnetic field from varying under high power inputs. This voice coil and magnetic assembly, when combined with other design features, result in an amazing 43% efficiency rating for the M4. This means that 43% of the incoming electrical energy is actually converted into acoustical energy, and only 57% is converted into heat. The following chart shows the typical efficiency ratings for various types of transducers. The high efficiency of the M4 means that it will be less prone to heat related problems, such as power compression, and therefore much more reliable than other devices.

Power compression results from the tendency of voice coil impedance to rise as temperature increases. This causes less power to be drawn from the amplifier, and hence a reduction in acoustic output. The power compression in many devices can be several dB. Due to the M4's efficiency, virtually no power compression occurs.