![]() ![]() ![]() In this series of measurements we are using closed loop tests because amplifiers have inputs and outputs that can be connected directly to the test equipment.īenchmark Media's AHB2 is a power amplifier with very low THD and very low noise. Another method is an open-loop measurement in which the DUT input is not connected to the measuring equipment, such as a smartphone, or MP3 player. Measuring methods include closed loop measurement, in which digital or analog signals are input to the DUT, such as DACs, power amplifiers, and headphone amplifiers, and the DUT output is connected to the measurement equipment to form a complete loop. The measurement equipment evaluates the DUT (Device Under Test) by comparing the input waveform to the output waveform. Since it is only necessary to compare the characteristics of an output signal to an input signal, the evaluation of the result is relatively easy. Unlike complex acoustical measurements, which often require the use of an anechoic chamber and a microphone array to measure three-dimensional acoustic properties, electrical measurements are a one-dimensional phenomenon in which the path of a signal travels along a signal line. Measurement of electrical performance is easier and clearer in some respects than measurement and evaluation of acoustical performance. When the Audio Precision and Audio Graph products are combined, it is easy to measure the amplifier's performance at various angles, and these test results should be more readily available in the near future.Īudio Precision APx555 with an AudioGraph Active LoadBox Electrical vs. Over the years, audio measurement equipment has improved and new devices have been introduced. This may have been because some manufacturers did not want to advertise the shortcomings of their amplifiers, or it may be that they lacked the proper measuring equipment. To do this we need a speaker simulation device such an AudioGraph Active Loadbox which can precisely simulate the speaker R, L, and C components of a speaker load. Unfortunately, few manufacturers have provided such measurements until now. To accurately measure the performance of a power amplifier, it must be measured at various impedances and with varying phase angles between current and voltage. It may sound a bit complicated, but this means that an 8 ohm speaker will behave differently than an 8 ohm dummy resistor when driven by a power amplifier.Ī speaker is always a more difficult load than a resistor of the same impedance. Speaker manufacturers usually talk only about impedances in terms of ohms, but the capacitive and inductive components of speaker impedance create a phase angle between current and voltage. In fact, speakers used in conjunction with power amplifiers have all the elements of resistance, capacitance, and inductance that are fundamental to electrical circuits. This has been expressed in vague terms such as 'driving power' and 'reaction force' which are almost the same as the realm of superstition. However, if two power amplifiers have identical specifications, there may still be audible differences when listening to music. In the case of power amplifiers, the price is often determined solely by the amp's power output, THD, and brand. Numerical superiority is often recognized as a sign of a good device and this tends to lead to higher prices. ![]() The measured performance of an audio amplifier can be quantified with common measurements such as THD+N, dynamic range, frequency response, and output power. The following is a translation of the original report: Introduction
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