PMC was founded in the belief that there were many ways in which loudspeaker design could be improved. Through innovation, attention to detail and working with music creators we develop new technologies and pr
When designing a loudspeaker, it is vitally important that we can completely characterise the acoustic behaviour of each individual component, as well as the system as a whole. To do this as accurately as possible, we need to ensure that our acoustic measurements are capturing only the sound produced by the part we are testing, and not any unwanted reflected sounds or reverberant sounds that could otherwise alter the measurement results and prevent us from getting a true picture of the performance of the speaker.
The ideal situation to achieve this goal would be to have the speaker and measurement microphone both floating in mid-air with an infinite distance to any reflective surface on all sides and absolutely no background noise. This would ensure that any sounds the microphone records during the measurement could only come directly from the speaker. This situation can be approximated by placing the speaker on top of a very tall pillar outside, but this can be incredibly impractical, and the measurement will still need to be processed to exclude the sound reflected from the ground (this will cut the measurement accuracy at low frequencies – the taller the pillar, the lower frequencies that can be accurately measured).
A far more practical method to achieve accurate measurements is to measure inside an anechoic chamber – specially designed room where as much sound as possible is absorbed at all of the room’s surfaces, with the goal being that no sound at all is reflected from the walls. As with the pillar method, there is a low-frequency limit to any anechoic chamber’s accuracy, determined by the depth and specification of the absorption used on the room’s surfaces. A good anechoic chamber however can have almost perfect anechoic performance down to below 80Hz, and only slightly worse performance below this point. This allows for very quick and accurate measurements to be taken of a loudspeaker.
It is important to note that a single measurement microphone can only sample the acoustic output from a speaker at a single point in space. In reality, any speaker will radiate different levels of sound at different frequencies in all directions. To fully characterise this behaviour, it is necessary to take measurements at many different points in a sphere around the speaker under test to build up a complete picture of how it performs. It is possible to use motorised turntables and robotic control systems to automate the process of taking very large numbers of measurements in an anechoic chamber to speed up this process, which is incredibly useful when making iterative design changes as it lets us rapidly determine what effect the latest design iteration of a part is having on the performance of the product as a whole.
