SPS - Week 4

This week’s blog post comes from an article from DPAmicrophones talking about the process and specifications of measuring microphones.  Although the concept is fairly simple to go about taking measurements from a microphone, there are some discrepancies in how the measurements are taken, the accuracy of the data, and even how the measurements are listed according to the manufacturer.  

When charting a frequency response graph, manufacturers can actually use two methods to show better performance from their microphones than what a given actual product may be able to replicate.  Deception may evolve from two places: in measurement and in data representation.  There are two methods by which measurements can be taken: point-by-point and continuous sweep.  The point-by-point method measures a pure sine wave at several select frequencies and a graph is formed by the collected points.  Unless 20,000 measurements are taken, the accuracy of the chart is less than perfect, but peaks and valleys of the response are more detailed as opposed to the continuous sweep.  When measuring using a continuous sweep method, a sweeping sinusoidal wave through the audible spectrum is captured by the microphone.  The output is analyzed against the input and the resulting graph is printed in real time.  This method may seem more accurate, however it is required that a manufacturer lists the speed at which this method was performed on the resulting graph.  If the sweep moves too quickly, it is highly likely that a flatter response will be recorded since the diaphragm of the microphone does not have time to fully capture individual frequencies.  Deception may also come by the frequency response graph itself as manufacturers may show the actual measured frequency response, or a “typical” (averaged) response with a tolerance field (quality control).

The measurement standard for a microphone involves four things: The accuracy of the measurement equipment, the calibration of the measurement equipment, the laboratory’s acoustical environment, and the quality and calibration of the reference microphone.  However, finding a standard form of referencing measurements of different microphones has definitely been one major problem.  Different areas of the world adhere to different sets of rules and regulations set forth by their specific standards committee; the top three being the International Electrotechnical Commission (IEC), the Deutsche Industri Norm (German DIN), and the Audio Engineering Society (AES).  Right here from the get-go we can see a possible area for measurement discrepancy.  Some of the larger named microphone manufacturer’s are German and might be more likely to adhere to the DIN standard, while some other manufacturers from other countries might follow the regulations of the IEC.  Of course, this is just speculation, but nonetheless, defining an international ultimatum of standards is something that is still in the works.

It seems that there are still areas of questionable uncertainty when it comes to comparing the standards of multiple manufacturers.  For most of the measurement techniques, the results rely heavily on the comparison to a reference microphone, the measurement equipment, and most importantly: the anechoic room.  Setting aside the microphone preamps, power supplies, computers, analyzers, and etcetera, two very crucial problems remain: the reference microphone and the anechoic room.  No two microphones are exactly congruent, even if multiple manufacturers use the same make and model.  More importantly than that, however, is unless measurements are taken in a vacuum – which would defeat the purpose of measuring sound – all rooms are subject to noise of some kind.  Even the minutest sound would still be present in a measurement, which is still less than perfection.  Aside from nit picking, there are many uncertainties that still remain.  Perhaps either an ultimate international standard, or a single measurement company is the solution for ensuring that you get what you pay for.