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Mic design

You see them in music videos. You see them on album art and in classic photos of famous musicians recording in their studios. If you're lucky, you might also have a chance to use one while performing or engineering a performance yourself. I'm talking about classic microphones. Usually more than just museum pieces, these examples of fine electro acoustic design are highly prized and sought after by the people who make recordings.

But are they really better than today's mics? What makes the design of classic mics, such as the RCA 77 and the Neumann U47, so enduring? And, even more importantly, how do classic mics compare to those being made today? With modern design and manufacturing techniques, shouldn't today's mics be as good, if not better, than those designed and made decades ago? We asked experts in the field of mic design to help us find out.

One of the first things the experts pointed out is that you must keep in mind that mic evaluation is subjective. Specifications don't tell you the whole story. David Royer of Royer Labs says that if we were talking about modems or hard drives, we could use the specs and totally depend on science. But mics involve art as well as science. In the field of electro acoustics, there is a rule that you can't measure what is not there. That makes it difficult to provide numbers for some of the subtle differences in sound between microphones.

Oliver Archut (writing in the Neumann web forums) points out that after nearly 100 years of electro acoustics, we still use crude standards to measure and evaluate performance. We still measure audio as a static function and do not include the dynamic character of a recording. Dynamic range and intermodulation distortion are trying to place values on dynamic functions, but these measurements are still done static. Most experts agree that there is more to making an evaluation than just measurements. Royer says that music and tests tones are not the same, and it is quite easy to build equipment that sounds mediocre and that has superb measured performance.

So why do people keep coming back to the classic mics? Juergen Breitlow of Sennheiser believes that these classic designs have a very special character regarding their sound. They were used over the last decades in a lot of recordings with famous artists and have defined a special taste or preference in their sound. Why wouldn't you want to try to use the same tools that were used by these artists to reproduce the esthetics of these old recordings? Chris Currier, also of Sennheiser, says that there were some amazing things happening in the golden days of the Hollywood films and recording industry. Currier thinks that it is more than just a nostalgic memory; it is actual tangible history.

Royer admits that mic selection is partly nostalgia but that knowledge of mic performance still plays a large role. Performers know that, for instance, the U47 can generally be counted on to sound good on voices, and an RCA ribbon mic can be counted on to sound good on brass. If you are an experienced engineer, you are going to lean towards those mics for those situations because you know that they will work.

The old designs raised the bar for performance and were unique at the time, so they were easily recognized and remembered. Chad Wiggins, the category director of wired products for Shure, says that it makes sense that the tools and methods used to make legendary music are studied and emulated by today's performers and engineers. That's how art is advanced, after all. The next generation takes what is handed down from the previous one and expands on it.

Because early mic designers were basically starting from scratch, their products were made on the best technical level and materials (such as matching transformers) of that time. There were no marketing departments demanding that the company produce products that show the customer something new or better, so what you probably got was solid performance without some of the hype and gimmicks that you might be getting in today's microphone market.

Duplicating success

What can we do if we want to make new mics that perform as well as the classics? The task for present day designers is to use new technologies to make products that are equal to or better than the old ones, and that are more compact, versatile and reliable. Some things can't be improved on, though, which explains why most of the designers that responded to this article admit that many mic designs are basically copies of the old favorites, such as the U47 and SM58.

Thomas Stubics of AKG Harman states that modern production methods allow much lower production tolerances, higher quality and lower costs. You can set your goals on making a really good mic and keep the cost down because, for one thing, everything does not have to be assembled by hand as it did in the early days of microphones.

Changing mic design

Today's performers certainly have different demands of the product than earlier artists did. For instance, rock vocals as well as venues have changed since the 1950s, when mics such as the Shure 55 were initially designed.

There is no doubt that the state of the art in microphone design continues to advance. Wiggins states that audio performance has gotten better in terms of output level and self-noise. Of course, some mic designs are less rugged then others. A ribbon mic still needs to be treated with more care then a handheld dynamic. But advances in designs are making mics hold up better under stress and perform well under higher sound pressure levels than their predecessors.

Today's designers have several advantages over the people who took on this task years ago. Wiggins points out that the raw materials, manufacturing processes and measurement tools are “leaps ahead of what were available a few decades ago.” This allows manufacturers to produce mics that perform much more consistently than their forbears from unit to unit and year to year.

Size matters

Because modern design has made mics more rugged and compact, the look and profile for certain applications have changed. Today's mics combine size, shape and structural elements that not only determine styling, but also have an effect on sound performance. Wiggins cautions microphone buyers about styling and reminds them that styling should not be used just to get a look. Microphones that look radical often have radical performance — and not in a good way.

Breitlow says he sees two trends in the design of the outside of mics. One is smaller mics that allow a voice talent to see a screen or script on a stand, and larger mics trying to copy the old designs to give you some vintage feeling. He explains that the first microphones were quite big because the electronics were so huge. Now, the electronics can be made much smaller, but we still want to keep them a certain size. Especially for singers, if the mic gets too small, the singer does not feel like he or she is being recognized as a true talent. Can you imagine a rapper in the studio singing into a small stick mic?

Of course, the outside dimensions of a microphone affect its acoustics. Breitlow points out that most design elements have an influence on the sound. There is an interaction of the mic parts with the sound field as soon as the dimensions are comparable to the wavelength of the sound being recorded.

Going tubular

One trend you will see in looking over mic catalogs is the prevalence of vacuum tubes in microphones. Artists claim that tube microphones produce a pleasing and desirable sound. The theory is that saturation in well designed tube mics produces harmonics that sound warm and musical. (This is despite the fact that the circuits employed tend to have more total harmonic distortion.) Some people, however, might ask why use a mic in a situation that saturated the preamplifier.

How did tubes find their way into mics? The most famous examples of tube mics have traced their ancestry to Germany. According to Robin Stephenson of the Internet site eHow, American broadcasters intentionally employed limited bandwidth in the early days of radio. The primitive carbon mics of the time seemed to work well enough for this purpose. In Germany, however, broadcasting was state-run. The impeccable Germans insisted on the highest quality sound that they could broadcast. Better mics needed to be developed.

Condenser mics showed promise for better performance, but their high impedance and low output needed to be overcome with the use of a tube preamp built into the mic. The line of mics that came from this period is still among the most prized for use in recording, including the U47. According to one expert in the field of studio mics, up to the 1970s, the tube was a technical standard in that it filled the technical function for amplification that was described above. Because of the evolution of solid-state devices and circuits, the use of vacuum tubes to make a quiet and sensitive mic was no longer required. Now, says the expert, the tube is one of the “instruments” (like a musical instrument) used to create a special sound.

This is not to say that it is not a valid artistic choice (somewhat like choosing a particular guitar amp to achieve a sound). There is a technical issue here which is of concern to engineers. It can occur when the user of the tube mic also decides that the sound he or she wants requires a tube amplifier after the mic. The point was made by one mic expert that you are now combining two parts of a very complex nonlinear transfer function. There is no way to know how this is going to sound. You have lost the confidence in your final product that you thought you were going to achieve by using a well respected product.

The future of mics

Modern technology is moving mic design in new directions. Part of it is actually a new market. Mic designers admit that a new, large part of their business is to the large unwashed masses of mic buyers — that is, people who do not have a large, expensive studio or a lot of money to spend on equipment. The PC has allowed people to record music or webcasts at home. The latest equipment catalogs show plenty of mics that don't even have an analog output in favor of a USB connection that the user can connect directly to the PC. Some of them even include software to help you edit and publish your session to a podcast. Several well-known mic designs are now available in a USB model.

Udo Wagner of Microtech Gefell says that he expects to see more of the PC trend in mic designs of the future, along with smaller and smaller (micro, nano) designs that will probably include built-in DSP and computer aids to monitor audio levels, etc. He also contends that about half of the design efforts will be driven by the desire for “nostalgic old things” such as tubes. He admits that technological “toys” are finding their way into mic designs. LCD displays, LEDs and features from the mobile phone world are available on newer mics. This seems to make sense because, if you are marketing to the 30 something's, the best way to get their attention is to include something that looks like a cell phone.

In summary

Microphone design is an exciting combination of art and science. Future advancements will continue to bring us mics that serve the digital age, but the careful designs and work of an earlier time still give us a guideline for what to expect out of a microphone.

Kevin K. Ruppert, CPBE, CBNT, is the engineering maintenance supervisor for WISC-TV.