Rode NTG8
REVIEW
Shotgun roundup
Looking down the barrel of Sennheiser’s MKH8060 and MKH8070,
Shure’s VP82 and three lengths of VP89, and Rode’s NTG8,
PATRICK MORVLYTH checks out the latest audio weaponry among
shotgun and rifle microphones.
I
’ll challenge anyone to be able to distinguish a hypocardioid from a
hypercardioid microphone at three paces, and only the sharp-eyed can
separate those two from a pressure omni, but almost anyone can recognise
the gun-barrel of an ‘interference tube’ microphone — revolver-like in the
case of a ‘short-rifle’; closer to a 12-bore for the ‘shotgun’. You will rarely find
them in studios but they are the mainstay of TV and film location work, and also
frequently used in theatres where their extended pick-up range is valuable.
They are something of a Johnny-come-lately to the microphone family, with
the first one appearing barely 50 years ago. First-order directional microphones —
that’s the basic range of cardioid variants — were fine for music and radio work,
but film and particularly TV (which had no time for dialogue replacement) wanted
microphones well out of the picture. That meant that the microphone had to be
further away than ideal, and recordists soon found they needed what is delightfully
(and indelicately) termed more ‘suck’.
The simple phase cancellation technique used with a cardioid-style pressuregradient capsule can only yield a maximum Directivity Index of 6dB (an omni is
0dB). That is for a hypercardioid (defined as having a rear null at 110°), or 5.7dB
for a supercardioid (rear null at 126°). In everyday language these microphones
allow you to double the pick-up distance and still get approximately the same level
of forward sound as you would with an omni. To move further away and get a
reasonable balance between direct sound and ambience needs something cleverer.
There have been some interesting developments using digital techniques such
as the early Audio-Technica AT895 and the more recent Schoeps Super CMIT,
but by far the most usual method is the interference tube, which was originally
conceived as an array of different length pipes, or as a single pipe with a series of
holes down it, but is now simplified to a tube with multiple slot openings along
its length. Sound from directly in front (0°) goes straight down the tube to the
capsule at the far end. Off-axis sound hits each slot at an angle with a slightly
different timing and thus experiences a degree of cancellation on its way down the
tube. This is totally dependent on the angle of incidence and the wavelength of
the sound, so the results vary greatly across the audio spectrum. Above the critical
length where the tube can have any useful effect the Directivity Index increases
by about 3dB/octave. For practical microphones the DI can reach as high as
15dB, but only for very high frequencies. Interference tubes are most often
added to a hyper- or super-cardioid capsule with its underlying DI of ~6dB so a
200mm tube doesn’t have any useful effect until >2500Hz, and even a massive
800mm one doesn’t do much below 1kHz. Thus Directivity Indexes in the speech
range only improve to 7-9dBs at best — useful but not as startling as some
would imagine.
There are also, inevitably, downsides too. Since the cancellation effects
are extremely sensitive to frequency and angle of incidence the off-axis high
frequency response of the microphone can be messy. A polar plot usually shows
a number of narrow ‘starfish’ lobes around the main frontal one, and these vary
depending upon frequency. Another way of describing that is ‘colouration’ —
interference tube microphones may produce sweet sound on axis but the ambience
can be significantly coloured, and this can change very obviously when moving
the microphone [see sidebar]. A short-rifle held on a boom in the open can sound
good but moving that scene indoors and adding a low ceiling may produce strange,
honky results from the reflected sound.
Long tube microphones tend to display the colouration effects at lower
frequencies and their characteristic sound is sometimes more obvious as a result,
though that isn’t a universal rule. They are also unwieldy so they have become
less widely used than they once were. However, short-rifles have increased in
popularity with the democratisation of video. At the top-end of the range of both
successful efforts have been made to smooth the polar response.
Since interference tube microphones are used in awkward locations, and
are frequently waved on poles or fitted to wobbling video cameras, they need
protection from wind and handling noise to function successfully. Indeed they can
be virtually worthless unless proper provision is made. Many manufacturers are
aware of this and now include, or at least offer, bespoke accessories beyond simple
stand clips and generic foam hats. n
Shure VP82
Sennheiser MKH8060, MKH8070
Sennheiser MKH8060, MKH8070
Sennheiser has had a very long association with
shotgun microphones. The MKH416 has been by
far the most widely used short rifle microphone in
history, and being not far off 40 has lived longer
than most workhorses. The MKH8060 could well
be construed as its replacement. It follows in the
tradition of being an RF capacitor microphone, which
uses the capsule in a low impedance mode. The
great benefit of this, for location recordists, is an
inherent immunity to humidity — an environmental
headache that DC capacitor microphones can never
quite avoid. Unlike the 416 the 8060 also makes use
of Sennheiser’s symmetrical capsule design, which
places the diaphragm between two backplates — a
technique that minimises distortion. The MKH8070
is essentially the same, but with a much longer
interference tube to give greater directionality.
Both microphones are fitted with MZX8000
XLR adapters, which screw onto the body of the
microphone, but these can be swapped for remote
cable adapters, MZD digital output sections, or allow
the insertion of an MZF filter unit.
The MKH8060 is very short — a mere 178mm
even with the XLR adapter — and slim (19mm)
but quite weighty at 112g. That’s significantly more
than the 89g of the 251mm Schoeps CMIT or
the 71g of the 210mm DPA 4015, both plausible
22
competitors. For use on a boom pole — mass
multiplied by extension equals arm ache. The slotted
length is 115mm, which leaves just 60mm to hold
the microphone by if you want to be able to slide
the foam windshield on. Modern suspension systems
such as Rycote’s lyres can just cope with that, but
even they would be floored by the MKH8070 with its
total length of 465mm. Holding 332g by the tail-end
60mm can only be done using a beefy, rigid clamp,
which Sennheiser does provide. For shockmounting
the only option is a clip suspension that holds the
tube part way down its length, together with a full
basket windshield.
Both microphones sound excellent on-axis, as one
would expect. At 180° the 8060 has noticeably less
rejection than the 8070 but at intermediate angles
is somewhat sweeter, without undue colouration.
However, for sheer suck the 8070 is most impressive
with an extremely narrow pick-up angle and good
gain. Both microphones have excellently low selfnoise (11dB A) but both are very hot mics in terms
of sensitivity. The 8060 is 63mV/Pa and the 8070 is
112mV/Pa — coupled to a max SPL of 129dB and
124dB respectively that means that these mics can
generate >+13dBu maximum output. You might well
need the 10dB pad in the (optional) MZF8000 filter
to tame these beasts. P48 current consumption to
provide all this power is 3.3mA.
resolution Shure is best known for its live-sound microphones but
has also made several interference tube microphones
for location work. The VP82 is a permanently charged
(electret) short rifle with an aluminium body. At 22mm
diameter and 195mm long it is light (76g) and small.
Shure provides various Rycote lyre mount options
to support the microphone on poles, pistol grips,
hot-shoes or camera adapters. These give excellent
isolation against handling noise, which
makes it a little strange that the microphone
has been rolled-off (12dB/oct) from 150Hz.
This undoubtedly gives it insensitivity to
handling noise and also to wind but does
leave the microphone sounding a little thin.
The polar diagram suggests that off-axis
sound is evenly controlled up to 2.5kHz
but becomes a little ragged above that —
listening tests do reveal some colouration
— but this is a microphone designed for
down-and-dirty location work. As such
these compromises are reasonable, as is the
powering marked as P48 (which it needs for
full spec performance), it will deliver sound
across the P12-48 powering range.
Sensitivity is on the low side for an
electret (2.11mV/Pa) but there is no risk of
the microphone overloading the inputs of
video cameras possessed of underwhelming
preamplifiers. Self-noise is a respectable
15dBA.
April 2012
REVIEW
Shure VP89
The technical specifications for the VP89 follow
those of the VP82 in respect of sensitivity, noise and
powering, but the design concept is very different.
Instead of being a one-piece microphone it is a
modular one with three different length interference
tubes incorporating integrated capsules, and if you
use the optional A89U it can even be ‘folded’ in half.
The preamplifier section is 90mm long (excluding
its screw connector), 22mm in diameter, and has
a biro-tip switchable 12dB/oct high pass filter. The
nominal knee frequency is 200Hz but the actual
response is modified by the interference tube/capsule
it is attached to. With the shortest version (VP89S –
which makes a 227mm, 117g microphone) the flat
LF rolls off almost as steeply as the VP82, being 3dB
down at 140Hz, and it has a slight presence lift. The
medium length (330mm, 138g) VP89M extends the
lift further into the HF region and rolls the
LF off below 100Hz. The longest version,
the VP89L (475mm, 174g) drops the LF
roll-off to 60Hz. The VP89 is solidly built,
the screw joint of the capsule feels secure
and reliable, and Shure has wisely provided
a comprehensive suite of windshields and
suspension systems that should cover every
style of use.
To my ears the short version is a little
anorexic at the lower end, with a bass
response that is lighter than ideal, and I can’t
think of many occasions when you would
want to add the additional HPF into circuit.
But by the time you get to the long VP89L
tube the response has improved greatly, with
the roll-off beginning to be effective at the
point where suspension isolation
often becomes less reliable. Here
the HPF makes much more sense.
However, the upside of a restricted
LF response is that infrasonic
noise from wind or camera
vibration has little effect — these
microphones are easy to keep
quiet in adverse conditions. As
electrets they should be relatively
free of humidity problems,
and freezing them to promote
condensation displayed
no ill effects (So, can
cook from frozen. Ed).
The VP89L, contrary
to expectation, has the
least colouration, but the
VP89S and its shorter
VP82 cousin will be of
greater interest to the
video world. The A89U
is a fascinating (and
unique) approach to
making
microphones
ever more compact for
videographers. It is a
U-adapter that reduces
the length of the VP89S
to a mere 155mm (and
ups the mass to 155g)
— shorter even than the
VP82. With the VP89M
it reduces the microphone
length to 257mm, which
could well make it possible
to fit many cameras to
give better performance at
a distance.
April 2012
Response — A surface plot to show the response
of a microphone is unusual but can allow you to
see colouration effects that are not visible in polar
diagrams. This example is a real-world measurement
of a well-designed short-rifle microphone.
At low frequencies the classic hypercardioid
response with a rear null of ~120° is easy to see.
Above about 2500Hz the response starts to narrow
as the interference tube becomes active, until the
pick-up is <40° at 20kHz. However, at the same time,
the off-axis response ceases to be the relatively
smooth hypercardioid one and grows a family of
hillocks and crags (far right in Figure 1). These are
the starfish lobes of a polar plot.
Figure 1.
Rotating the plot so that you look down on it from
above (Figure 2) you can see that the off-axis HF
response forms curved grooves. As you turn the
microphone to follow on-axis sound the different
frequencies of off-axis sound passes through these
response grooves at different moments, producing
the typical colouration effects of interference tube
microphones
Røde NTG8
A few years ago Røde introduced the NTG3, a short
rifle using the RF capacitor technique that has been
Sennheiser’s realm for so many years. The NTG8 is
the long shotgun sibling — half a metre (560mm)
of slim 19mm pipe in an exotic aluminium storage
tube. The microphone weighs in at a considerable
345g. This needs a substantial isolation mount and
the SM8 provided is a doubled-up rubber cage version
that adds another (somewhat unwelcome) 215g.
This makes a secure and solid arrangement, but one
that is perhaps more suited for static set-ups unless
you hate your boom-op. The NTG8 has a good LF
response that doesn’t start to roll off till 80Hz, though
you will have to tailor the bass bandwidth externally
to prevent infrasonic overloads. A 50Hz HPF is ideal,
leaving excellent clean bass, but if the SM8 mount
is being used you’ll need to lift that to nearer 150Hz
since the LF isolation is ineffective below 100Hz.
If the NTG8 is a heavyweight physically it is also
powerful on performance. It is very quiet (–8dBA is
claimed) but also on the hot side in terms of sensitivity
at 97.5mV/Pa. The maximum output is 8.2dBu,
resolution
Figure 2.
which would risk overloading most mic preamps
unless fitted with input pads. As a microphone it
sounds sweet, with a gentle HF lift centred around
10kHz, characteristic of the classic shotguns. It will
inevitably be compared with the obsolete (but still
popular) Sennheiser MKH816 and I think it sounds
cleaner and less coloured off-axis. On-axis pickup is
very narrow at +/- 15°. Røde now uses the laudable
technique of swaged-pin grounding to improve RF
immunity. This continues the metal case across the
floor of the XLR connector, with pin 1 directly fixed
into it and the audio pins 2 & 3 poking though
insulated ports. This reduces to a minimum the risk
of RF interference being coupled into (or out of) the
microphone. n
Contact
Sennheiser, Germany:
Web: www.sennheiser.com
Shure, US:
Web: www.shure.co.uk
RØde, Australia:
Web: www.rodemic.com
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