Recording - November 2014 - 18

Mikkel Nymand
How does placement
impact what and how you
hear in a situation like this?
An awful lot! [laughs]
Sometimes even musicians
understand this better than engineers. Let me
put up this analogy. If you play the violin,
you know that the high frequencies project
more in a certain direction than in another
direction. The bite of the high frequencies is
only heard in a certain angle. Now, you
know something about how instruments project their sound, but you also need to know
how microphones pick them up; you have to
be able to work with these two parameters
at the same time. If the violin sounds too dull,
have you placed the mic where higher frequencies are not projected at all, or perhaps
angled it in a wrong way?

adjust your gain according
to that, it's completely different from being even just a
few feet away from the voice.
You set your gain some 15 to
20 dB lower, which will draw
in less of the surroundings.
I was not aware that a human voice
could get as loud as 150 dB! People
think of 150 dB as like a jet engine, but
of course that's a jet engine from a
safe distance away.
That is amazing, isn't it? We've measured quite a few professional singers
over the years and the record is 154 dB.
This is of course a peak level, but it's still
a real measured SPL.
Let's talk a little bit about the second
test in the Echo Room, a room at DPA
headquarters which was specifically
designed for terrible acoustics.

For a headset, how does that interaction with the human voice work?
People tend to think that you have to
always have the microphone right in front of
the mouth. It's not necessary. If it's an omni
microphone, you can get acceptable fullbandwidth level of the voice, even with the
element back on the cheek. That's why we
experience such amazing sound quality with
our omni headsets. But the cardioid headset,
put on the cheek, gives trouble unless you
push it a little in front of the mouth or to the
corner of the mouth.

That is something in fact I don't think
we ever talk about.
When you listen to the audio files from
the echo room, pay special attention to the
low-frequency content of the background
noise, because it's gone on the cardioid
track. The proximity effect is the most isolating factor; the DPA cardioid headset mic
will not react to any frequencies below
500 Hz if they're over 3 feet away.

And of course, that raises the issue of
the air that is coming out of the mouth
and it makes you more susceptible to
things like plosives?
Right, which is quite annoying. This
heavy air turbulence will become a problem for any mic.
Now when you move to something like
a lavalier or the necklace microphone,
things like plosives become less of an
issue, but then you have the situation
where you now have quite some distance from the mouth, with environmental sounds competing with the voice.
You have to be more aware of the
acoustical environment-have low background noise and so on. In controlled environments like a good broadcast studio, the
lavalier and necklace mics will be perfect.
People scratch their heads over the idea
of an omni headset... if it picks up
everything from everywhere, how come
it works so well in a live music situation? Why is it that an omni mic on the
cheek can do this great job without
interference from outside sounds?
I think the key word to this is gain structure. The voice can reproduce a lot of
SPL-up to 150 dB if you're a trained
singer. If you're so close to the voice and
18

RECORDING November 2014

as the speaker was disciplined enough to
point herself towards the mic, no problem.
When moving into the Echo Room, we
move from something close to perfect to
something as close to imperfect as possible. What we can conclude is that the
more you go towards uncontrolled
acoustics, the more you should consider a
directional headset. And in the case of
the Echo Room, especially with the diffuse
pink noise background, it's not a question
of acoustically perfect timbre, it's a question of "Can you at all hear what is being
said?" A cardioid mic rejects a lot of the
background noise that the omni mic
reproduces from that reverberant room.
And here comes another point that I
want to make, which is understanding the
proximity effect. The proximity effect
works like what I usually call a "distance
low cut." Most people have experienced
that when you go closer to a pressure gradient microphone, you'll have this low frequency boost, but a lot of people forget
that the opposite also takes place-when
you are far from the sound source it will
actually dip the lower frequencies.

We had an acoustician to design it as
bad as possible! It is tiny, about 4 meters by
2 meters, maybe 3.5 meters to the ceiling.
We had some flutter echo between ceiling
and floor, but those are the only two parallel surfaces in there. The walls are not parallel, and there is nothing absorbing on
them, so the sound energy is kept alive. We
ended up with a 4 second reverb time,
which is not far from a cathedral!
It was fun being a guinea pig in there!
I wore two headset mics-one omni,
one cardioid. I read a news article
from Wikipedia, first with just the bad
characteristics of the room and then
with a pink noise source right behind
me, a big speaker on a chair. This is the
opposite of a good clean studio! How
does directionality benefit us now?
In the controlled acoustics of our studio, I
think we all agreed that the table microphone sounded the best. It had the richness
to it, the most natural sound quality-as long

Now that's a nice number to be able to
give our readers.
It is true for that headset model and will be
different for others. Here we come into the
details of designing a cardioid microphone.
If it's a headset, OK, we know we are
always close to the sound source. So we can
make it linear within, like, an inch, and then
have a very fast rolloff of the low frequencies. And on top of that comes the directionality at the higher frequencies to reject noise
not rejected already by proximity effect.
Fantastic. Any other small points about
directionality that might have been on
your mind that you'd like to add here?
I want to come back to polar patterns
once more. When you look at polar patterns, you may see some manufacturers
show you the patterns at different frequencies. Ask yourself: "Is it the same all the
way around, is it symmetrical? Is the shape
recognizable? What are the differences
between the frequencies on that polar pattern? How much is actually attenuated to
the rear?" And so on and so forth... I could
say a lot of things here!
Learn more about DPA Microphones at
www.dpamicrophones.com/en

http://www.dpamicrophones.com/en

Recording - November 2014

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