How to Get the Best Sound from Your Musical Instrument
by Using the Right Microphone Placement - Part 2 -

The Inverse Square Law

Doubling the distance of a mic from the sound source can halve the output (-6 dB), and four times the distance can decrease the output by as much as 12 dB. However, the amount of leakage or bleed that is picked up by the mic will be just the opposite. Twice as close (half the distance) may equal half the amount of bleed (or room noise pickup). That’s a lot of “cans” and “mays,” but I have run into comb filtering problems that were caused by reflections off of music stands. The science (art) of correct mic placement is never completely predictable.

Concave surfaces are a nightmare because they focus or reflect beams to specific areas. These exact locations are unpredictable because they depend on the location of the sound source. If a microphone happens to be located in one of these “hot spots,” its signal output will be severely affected.

Hint: Adding a few dispersion panels to the sides of amphitheater band shells has proven to not only remedy this focusing problem, but also to facilitate a more balanced and even blend of the stage sound from the musician’s perspective.

Want to know about the studio’s acoustics? Put on a pair of cans, hook up an omni directional microphone, and walk around the room snapping your fingers or use castanets (they work better). What you hear is what you have to work with, unless variable acoustics are accessible.

The Studio Microphone Placement Dilemma

At one point in my career, I went at this problem head on. Not because I was any kind of crusading “correct all things audio” fanatic, but because I was afforded the luxury of having plenty of studio time and the equipment to attempt to find a way to make my job of microphone placement a lot easier.

Okay, back in the 1980s my time was divided equally between engineering, teaching, writing, and maintenance work. To perform preventative maintenance (my technical specialty) wherein you are repairing problems before they cause breakdowns, you need to have a lot of off-hour control room/studio time.

Reviewing professional audio equipment meant having a test bench at the ready. Since my reviews (as well as tutorial articles) contained a good deal of practical user information, the review equipment had to be placed into professional studios.

This was just fine with the studio owners I knew and they were more than willing to provide me with ample studio time to run the equipment through its paces myself. Most often I’d also gather several engineers and musicians together to get their input. All found no problem with this as it gave the engineers a chance to check out some of the newest equipment available first hand, and the musicians knew they would walk away with a great sounding demo tape.

It also afforded me the opportunity to experiment with different micing techniques while being scrutinized by the most critical of onlookers: fellow recording engineers. The task of repeated microphone repositioning, monitor level adjustment, and multiple subjective evaluation note-taking was eased by my class full of assistants during teaching hours.

Finally, the majority of my engineering work during this period came from other engineers who were overbooked. They were often involved with several projects at the same time so their being present at every recording “date” was not possible. This is how staff assistant engineers pick up their first full-fledged engineering work. I was overdubbing all kinds of instruments.

Recording overdubs are easier than basic sessions as there’s a lot less setup involved. The atmosphere is more relaxed, there’s less pressure from time constraints, and you’re usually working with well-maintained instruments played by ace musicians.

Once I had matched the new part to the old sound, and laid all the punch points into the multi-track’s memory, I was pretty much free to listen to the results of all the other microphone positions I had set up. Their positions were based on the theories that I had been experimenting with during my maintenance, teaching, and reviewing hours.

Musicians are not shy about letting engineers know how they feel about the sound of their performance. If the overdubbed sound doesn’t cut it, there will be no additional session work from that same engineer. If there was enough real estate on the multi-track tape, I would also record my “experimental” mics to a separate track.

I’d include a note to the engineer/producer to ask them for their opinion and possibly suggest that they try blending in some of “my” sound to augment the overdub track. Almost everyone appreciated this and quite often my tracks were the ones used during mix down. This was especially true when I recorded solos. It was a nice life.

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