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Microphone Tech Specs

Microphone Tech Specs

Buying a microphone can be an ordeal. You have to balance features and price, and part of that is having to wade through the many technical specifications.

Buying a microphone can be an ordeal. You have to balance features and price, and part of that is having to wade through the many technical specifications.

If you've ever had to buy a mic and try to determine your needs by the specs, you know the challenge. No two manufacturers offer the same set of information, reference points are different and there aren't any real standards for comparison. So how do you navigate the sea of information? After reading through several dozen spec sheets, we've created an essential list of specification categories and their meanings. With this information as a guide, you're armed with the essentials to choose any type of microphone, from lapel to shotgun.

Transducer Type

For the most part, you have to worry about only two different types of microphone transducers: dynamic and condenser. Dynamic microphones are durable and virtually impervious to temperature and humidity. The trade-off is larger size, reduced sensitivity and slightly limited frequency response. By contrast, condenser mics offer extended sensitivity and range but fare worse in weather extremes. They also require a power source of some kind, either battery or phantom power. From time to time, you may encounter a ribbon or crystal microphone. These are typically reserved for specialized recording and live-sound applications.

Frequency Response

Experts say that human hearing typically reaches from 20Hz to 20,000Hz. Generic microphone frequency responses usually fall within that range, a little shy of the extremes of the scale. While a rated frequency response is nice, you'll learn more about how the mic sounds by viewing a graph or chart of the response. As you're looking, watch for unevenness in the curve and how quickly it drops off at the top and bottom of the scale. In either case, smoother is usually better. A frequency-response chart often includes additional traces indicating the effects of various pads and low cut switches.

Polar Pattern

Standard video production microphones have a directional or a non-directional pickup pattern. Directional patterns come in several flavors, starting with cardioid. A cardioid pattern picks up sound primarily from the front of the mic, with some pickup on the sides and none at the rear. Super- and hyper-cardioids are simply tighter pickup patterns that help focus the sound and minimize other noises. By contrast, the non-directional pattern picks up sound from every direction, hence the name omni-directional. Some studio microphones also include a figure-8 pattern with equal pickup in front and back and no pickup on the sides - not too useful on a video shoot, but handy in the studio.

Output

Microphone outputs are important, as they determine how you'll attach the mics to your equipment. The standard professional connector is the 3-pin XLR. This offers a balanced output that stays interference-free for hundreds of feet. Of course, not every camcorder has balanced inputs. Several microphones offer consumer-type 1/8" plugs, which match smaller cameras. These connections are typically unbalanced and are prone to interference, so don't try to extend them. You may also see output impedance rated in ohms. Balanced microphones range from 150-600 ohms. Unbalanced mics run up to 10,000 ohms.

Sensitivity

Microphone sensitivity ratings are confusing. It seems that every manufacturer uses a different scale or measurement method. On close examination, you'll find terms like Pascal and Dyne, along with abbreviations such as dBV and SPL.

Let's simplify things a bit. The number you're looking for is negative and may be listed as something like -54.5 dBV/Pa. In general, greater numbers mean microphones that are more sensitive. Keep in mind, higher sensitivity doesn't automatically mean a better mic; it just means that it's more sensitive to a given volume level. In some cases - loud instruments, for example - a lower sensitivity means less chance for signal overload.

Power Supply

Earlier we mentioned that condenser microphones require power. Depending on the make and model, that power can come from something as simple as an AA battery. In fact, many shotgun microphones use this as a power source, which is handy for cameras without power options.

Phantom power is the industry standard for condenser microphones and comes from balanced input jacks on mixers and cameras. A little switch supplies the mic with 48 volts, but there's no risk of shock. Although the voltage is fairly high, there's not enough current to give you even a tingle.

Maximum SPL

There's only so much volume a microphone can take. Don't worry: it won't blow up, but it can sound pretty bad. Several factors determine the maximum volume level - the diaphragm and electronics are at the top of the list. Years ago, a loud blast could permanently damage a ribbon or condenser microphone. Today's models are much more durable. The maximum SPL number simply indicates the loudest sound the mic can reproduce cleanly. Anything above that risks distortion.

Size & Weight

There's no mystery to this information, but it's important anyway. Consider how you will use the microphone and the impact of size and weight in your production. For instance, when you are choosing a shotgun mic, the length can be critical if you mount it to the camera. While a longer microphone may provide more audio focus, you also run the risk of a drooping mic in the top of your frame. Using a zeppelin and/or furry windsock amplifies this potential. With lapel mics, smaller is usually better, but only when balanced against sound quality.

Supplied Accessories

Some manufacturers are a bit skimpy when it comes to accessories. While most microphones come with some sort of mounting clip, it may not be the one you want or need. This can contribute significantly to the purchase price. Look closely for windscreens, shock mounts or adapters that may be necessary for your setup.

Everything you need is out there somewhere - maybe in a bundled package. Just don't assume it's included unless you see it written in the literature.

Conclusion

It's easy to get buried in the details when shopping for a microphone. The final decision is a delicate balance of price, performance, sound quality and suitability. There is no perfect microphone, and the right one for your production may be completely wrong for my style. The good news is that high-quality microphones are available at virtually every price point today. Now that you know how to read the spec sheets, there's nothing to stop you finding that magic balance of price and quality.

Contributing Editor Hal Robertson is a digital media producer and technology consultant.

Side Bar: Stuff They Don't Publish

Several items just don't translate to a spec sheet - the way a given microphone fits in your hand or works with your equipment, for example. Another item is handling noise. While some mics are deathly silent when handled, others rattle and bang like there's something loose inside. Finally, there is the sound. Regardless of how good the mic looks on paper, the sound seals the deal. The temptation is to find the lowest price and order online. But, whenever possible, audition potential microphones with your own gear. This way, you'll find the perfect fit and minimize surprises.

Tags:  December 2008
Hal
Robertson
Mon, 12/01/2008 - 12:00am