Groove Tubes: Microphone Manufacturing Standards

There are quite a number of condenser microphones to choose from on the market today. Many look professional on the outside and, indeed, most will give you acceptable sound. But much of the difference comes down to manufacturing standards.

The Story Behind Affordable Matched Pairs For Stereo Miking

One of the factors making the difference between amateur and professional recordings is the use of stereo miking techniques. Pro engineers have long relied on matched pairs of microphones in attaining optimal results from stereo recording methods. Why a matched pair? You wouldn’t consider monitoring with a mismatched pair of speakers, right? Similarly, you want the left and right mics “hearing” exactly the same way in order to achieve a balanced sound.

From a technical standpoint, that means that the two mics need to be as identical as possible in frequency response. A “flat” frequency response implies that there is no deviation in the output level versus the input level at any and all frequencies across the audible spectrum. While a flat frequency response is theoretically ideal, it is rarely completely achieved in any audio component. A mic might exhibit, say, a 1dB boost at 1kHz and start rolling off at 3dB per octave at 14kHz. The perfect matched pair would exhibit those exact same characteristics in both mics. Here again, such an exacting match is rare. Therefore manufacturers each establish their own window of acceptable deviation that they will certify as a being a “matched pair” (there is no industry standard). Note that we’re actually talking about two different variables that are subject to interpretation and little disclosure—the deviation between two “matched” microphones of the same model, as well as their deviation from the given manufacturer’s standard reference mic for that model.

Even the most famous of classic microphones have exhibited disparities in frequency response of 6dB or more from unit to unit. Manufacturers would then go into a batch of mics and select a pair of mics that were closer together in response—on the order of 2dB up or down for a total window of about 4dB. Such matched pairs have typically been a special order and required paying as much as a 20 percent surcharge. Not so with Groove Tubes. In order to pass inspection, all mics in our redesigned Groove Tubes line must be within +/-1dB of not only each other, but of our “golden reference” mic for that model—the one we wouldn’t sell for anything. Furthermore, there’s no special order or additional charge because all Groove Tubes mics now ship in matched pairs.

Higher Standards

Groove Tubes is able to offer such high quality and tight tolerances at affordable prices for several reasons. For openers, highly skilled technicians use the latest computer-controlled equipment for manufacturing and testing.

The reality of today’s marketplace is that most companies manufacture their products offshore in order to be profitable. The fact is that many microphones on the market today are made in China or other countries where labor is cheap—even the ones that say that they are made elsewhere. At Groove Tubes, manufacturing is a hybrid operation. The designs all start in the USA, as do the manufacturing of all critical path elements like transformers, capacitors, resistors, our renowned tubes and custom diaphragm material. We then complete the machining and assembly in our own facility in Beijing. In this way we attain the best of both worlds—quality and affordable pricing.

While we’re on the subject of standards, let’s talk about the frequency response graphs that are often included with microphones. These graphs illustrate the deviation between input and output across the frequency spectrum. The ideal is to have as flat a line as possible indicating as little deviation as possible. Such graphs can be misleading because the industry has no universally accepted measurement standards that factor in distance from the mic, volume, angle relative to axes, and so forth. Moreover, there is no standard for rendering these graphs. Major deviations apparent on a graph calibrated vertically at +/-10dB look much more like a flat line if displayed on a graph calibrated at +/-100dB. So in a world where everybody draws nice looking graphs because they feel they must in order to be competitive, we simply decline to play the game until such time that standards exist that level the playing field. As stated earlier, all Groove Tubes mics are manufactured to within +/-1dB of each other and our golden reference standard. We’re confident that your ears will tell you everything else you need to know.

This story is excerpted from our free Record Now: Choosing and Using Microphones guide, which covers microphone technology and techniques. It’s available either via download or at your local M-Audio dealer.

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