Brüel & Kjær 4131 User guide
Quarter-inch Condenser Microphones
Microphone Cartridges Type
4135/36
and associated cathode follower.
Precision
condenser
microphones
for
laboratory
measurement
purpose.
Each
microphone
is
in-
dividually
calibrated
.
Frequency
range
of
cali-
bration:
20
Hz
-200 kHz.
Dynamic
range
up
to
180
dB.
BRUEL&KJ£H
Nrerum.
Denmark
.
eyr;
80
05
00
•
,;:;:'
BRUKJA,
Copenhagen
.
Telex:
5316
BB
4185
/
86
Quarter-inch
Condenser
Microphones
FEBRUARY
1966
Contents
0. Introduction
Purpose
of
the
Quarter-inch
Microphones
. . . . . . . . . . . . . . . . . . . . . . . . 3
Principle
of
the
Condenser
Microphone
. . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
Definitions
of
Free-field
and
Pressure
Response
. . . . . . . . . . . . . . . . . . . . 5
Random
Incidence
Response
(Diffuse
Field
Response)
. . . . . . . . . . . . . . 6
1.
Description
General
Description
of
the
Equipment
. . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
Quarter-inch
Condenser
Microphone
Cartridges
. . . . . . . . . . . . . . . . . . . . 8
Cleansing
of
the
Microphone
Diaphragm
. . . . . . . . . . . . . . . . . . . . . . . . . .
11
Associated
Cathode
Follower
Type
2615 +
UA
0035
................
11
Characteristics
of
the
Quarter
-
inch
Microphones
. . . . . . . . . . . . . . . . . .
15
1.
Sensitivity
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
2.
Frequency
Response
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
3.
Pha
se
Characteristics
and
Pulse
Responses
. . . . . . . . . . . . . . . . . . . . 17
4.
Free
Field
Corrections
........................................
19
5.
Directional
Characteristics
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
22
6.
Dynamic
Range
(
Noise
and
Distortion)
. . . . . . . . . . . . . . . . . . . . . . . . 22
7.
Equivalent
Air
Volume
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
22
8.
Influence
of
the
Polarization
Voltage
. . . . . . . . . . . . . . . . . . . . . . . . . . 23
9.
Temperature
Characteristics
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
10.
Influence
of
Ambient
Pressure
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
11.
Influence
of
Humidity
.......................................
26
12.
Influence
of
Vibrations
..........
......
.
.....
....
.
....
.....
..
26
13.
Sensitivity
to
Magnetic
Fields
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
14.
Spurious
Microphonics
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
2.
Accessories
Nose
Cone
UA 0053 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
Flexible
Adaptors
UA 0122
and
UA
0123
....
.
.......
. .
..
.
........
...
28
Microphone
Stand
UA 0049
.........
.
...........
.
...........
.. ..
...
31
Extension
Cables AO 0027-28
-2
9, AR 0001 . . . . . . . . . . . . . . . . . . . . . . . . 31
Mechanical
Adaptor
DB 0264 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
Probe
Microphone
Kit
UA 0040
........
...............
.
..........
32
Two-Channel
Selector
4408 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
Microphone
Power
Supply
2801 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
Appendix
Microphone
Calibration
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36
Pi
sto
nphon
e 4220 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
Electrostatic
Actuator
UA 0033
..
.
...
..
..............
.
.............
38
The
Range
of
B & K
Condenser
Microphones
. . . . . . . . . . . . . . . . . . . . . . 39
Specifications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43
0.
Introduction
Purpose
of
the Quarter-inch Microphones.
The
B & K
Quarter-inch
Condenser
Microphones
are
designed
for
precision
sound
pressure
measurements.
Because
of
their
small
dimensions,
they
leave
the
sound
fields
undisturbed
at
audible
frequencies
and
their
first
res
·
onance
frequency
is
far
above
the
audible
range.
They
have
consequently
very
flat
frequency
responses
and
excellent
responses
to
sharp
pulses
as
illustrated
m
the
Appendix.
In
addition,
they
allow
measurements
without
distortion
of
very
high
sound
pressure
levels
(up
to
180 dB)
as
missile
exhaust
noise
etc.
On
the
other
hand
they
are
not
suited
for
low
sound
level
measurements
(below
70
dB,
see
Appendix
Fig.
A.4).
Their
most
outstanding
feature
is
excellent
long-term
stability
under
a
great
range
of
environmental
conditions
and
especially
their
insensitivity
to
temperature
variations.
They
are
therefore
well
suited
for
field
measure-
ments,
though
the
accuracy
of
calibration
matches
laboratory
standard
re-
quirements.
Principle
of
the Condenser Microphone.
A
condenser
microphone
consists
essentially
of
a
thin
metallic
diaphragm
mounted
in
close
proximity
to
a
rigid
back
plate
.
Diaphragm
and
back
plate
are
electrically
insulated
from
each
other
and
constitute
the
electrodes
of
a
capacitor.
See
Fig.
0.1.
Housing
and
insulator
form
with
the
diaphragm
Insulator
Back Housing
Hole for
static
pressure
equalization
Fig. 0.1.
Schematic
construction
of
a
condenser
microphone
cartridge.
4135
• 4136- INTRODUCTION
a
closed
chamber,
which
is
only
in
communication
with
the
outside
for
slow
static
ambient
pressure
variations.
When
the
microphone
is
exposed
to a
sound
pressure,
the
diaphragm
is
submitted
to
an
alternating
force
proportional
to
the
pressure
and
the
diaphragm
area.
The
consequent
move-
ment
of
the
diaphragm
varies
the
capacity,
and
these
variations
are
trans-
duced
into
an
AC
voltage
component
if
a
constant
charge
is
present
between
the
electrodes.
The
charge
is
obtained
by
means
of
a
stabilized
DC
polari-
zation
voltage,
and
it
remains
constant
as
long
as
the
charging
time
constant
of
the
circuit
is
much
longer
than
the
period
of
the
sound
pressure
variations.
It
is
possible
by
careful
design
to
maintain
the
proportionality
of
the
AC
output
voltage
to
the
sound
pressure
within
a
wide
frequency
range
and
an
extended
dynamic
range.
The
widest
linear
frequency
range
for
the
pressure
response
is
obtained
if
the
resonance
of
the
mechanical
system
(diaphragm)
is
critically
damped.
This
damping,
which
is
due
to
the
back-and
-
forth
movement
of
the
air
contained
between
diaphragm
and
back
plate,
is
determined
by
the
shape
of
the
back
plate,
the
mechanical
tension
of
the
diaphragm
,
and
the
spacing
between
plate
and
diaphragm.
The
low
frequency
limit
of
the
linear
range
is
set
by
the
"cut-off"
(or
time
Cartridge
Cathode Follower
Mechanical I
Electrical
Elasticity
C+LlC
~-~
Mechanical Damping
Eo
R~
· /
-~
Polarization
Circuit
C =
Polarized
cartridge
capacity
llC = Variation of
capacity
producing
the
signal
Cs =
Stray
capacity
of
connection
to
cathode
follower
R;.C;
=Input
impedance
of
cathode
follower
1621
61
Fig. 0.2.
Simplified
diagram
of
the
condenser
microphone.
(The
electrical
leakage
in
the
cartridge is neglected).
4
4135
•
4136
-
INTRODUCTION
constant)
of
the
microphone
cartridge
circuit.
Referring
to
the
schematic
diagram
of
Fig.
0.2
the
cut-off
frequency
is:
fo
=
--------------------------
2 :n
(C
+ C +C ) Rt
Re
8 1 Rt +
Re
Since
the
sensitivity
of
the
microphone
is
determined
by
the
relative
variation
of
capacity
Ll
C!(C +
Cs
+ Ct),
the
total
parallel
capacity
should
be
made
as
small
as
possible.
The
first
amplifier
stage
is
therefore
built
in
the
same
housing
as
the
microphone.
A
cathode
follower
stage
providing
a
very
great
input
impedance
is
employed,
because
small
parallel
capacity
requires
high
Rt
and
Re
in
order
to
obtain
a
satisfactory
low
limiting
frequency.
Definitions.
Free-field
and
Pressure
Response.
T:he
Free-field
Response
of
a
microphone
is
the
ratio
of
the
r.m.s.
output
voltage
to
the
r.m.s.
sound
pressure
existing
in
the
free
field
at
the
micro-
phone
location
with
the
microphone
removed
from
the
sound
field.
The
Pressure
Response
of
a
microphone
is
the
ratio
of
the
r.m.s.
output
voltage
to
the
r.m.s.
sound
pressure,
uniformly
applied
over
the
diaphragm.
The
two
definitions
coincide
for
a
microphone
having
negligible
dimensions
with
respect
to
the
sound
wavelength.
In
the
case
of
the
B & K
quarter
inch
microphones
this
is
practically
fulfilled
up
to
about
5300
Hz,
*)
where
the
wavelength
equals
ten
times
the
diameter
of
the
microphone
(i.e. 63.5
mm).
The
difference
in
response
is
then
less
than
one
decibel.
Free-Field Response=
~o
Pressure
Response=
_!L
p,
vo~ts
------lrv
L__M_icroph-one
__f":::tZ:::::::::=--~
-~~
·
Wavelength
Sound
pressure
p
0
____________
___
_
0°
incidence
(62(60
Fig. 0.3.
Definitions
of
Free-field
and
Pressure response.
*)
Hz
international
c/s
used
in
United
Kingdom
and
U.S.A.
5
4135
· 4136- INTRODUCTION
At
higher
frequencies
the
diffractions
of
the
sound
waves
on
the
microphone
produce
an
appreciable
change
in
the
resulting
sound
pressure
acting
on
the
microphone
diaphragm
as
illustrated
in
Fig.
0.3.
The
difference
Pl
-po,
called
free-field
correction,
depends
on
the
orientation
of
the
microphone
with
respect
to
the
direction
of
propagation
of
the
sound
and
on
the
external
dimensions
of
the
microphone
(
in
particular
those
of
the
front
and
of
fitted
protective
grids
or
"
nose
cones").
The
free-field
behaviour
of
a
microphone
is
thus
described
by
means
of
a
s
et
of
free
-
field
correction
curves
for
various
incidences,
which
should
be
added
to
the
pressure
frequency
curve
of
the
microphone
in
each
particular
case.
See
Figs.
1.14-1.16.
For
microphones
intended
for
free-field
work
it
is
possible
to
give
the
diaphragm
resonance
such
a
damping
that
the
normal
incidence
free-field
c
orrections
are
compensated
for
up
to
frequencies
well
above
the
resonance
frequency,
in
order
to
ob
t
ain
the
flatt
e
st
possible
frequency
response.
Random
Incidence
Response
(Diffuse
Field
Response).
The
random
incidence
response
of
a
microphone
for
a
given
frequency
is
the
root-mean-
s
quare
value
of
the
free
field
sensitivity
for
all
angles
of
inciclence
of
the
s
ound
wave.
It
corresponds
to
the
diffuse
field
sensitivity
of
I
he
microphone,
the
diffuse
field
being
a
sound
field
in
which
the
souncl
e
nergy
density
is
uniform
and
the
mean
acoustic
power
per
unit
area
is
the
same
in
all
directions.
The
International
Electrotechnical
Commission
(
publication
no.
123, § 8.2)
ha
s
given
a
practical
rule
for
the
calculation
of
the
random
incidence
sensitivity
from
the
free
-
field
sensitivities
at
definite
angles,
with
coefficients
proportional
to
the
relative
solid
angles
.*)
Fi
gs. 1.3
and
2.2
show
the
random
incidence
frequen
cy
r
es
pon
se
of
the
different
B & K
quarter-inch
microphone
combinations.
The
se
curves
should
be
taken
into
consideration
in
the
case
of
measur
e
ments
in
highly
reverberant
rooms
giving
rather
diffuse
field
condition
s.
Wh
en
the
spectral
distribution
of
the
sound
varies
with
the
angle
of
incidence,
correct
integration
is
only
possible
in
the
range
where
the
micro-
phone
is
both
lin
e
ar
and
omnidirectional
(practically
up
to
2(}
kHz
with
the
quarter-inch
microphones).
Omnidirectional
microphones
are
also
necessary
in
the
case
of
rapidly
mo
v
ing
sound
sources
(
aeroplanes,
motorcars,
etc.).
*) So, Sso, S6o, - - - - S1so
being
the
sensitivity
of
the
microphone
at
angles
of
incidence
of
0°,
30°, £0°, - - - - 180°,
the
random
incidence
(diffuse field)
response
S is given by
the
formula:
S2
= o.018 (So2 + S1so2) + o.129 (Sso2 +
S1
5
o2
) + o.
224
(S6o2 + S12o2) + o.258
Sgo2
6
1.
Description
General Description
of
the Equipment.
A
complete
microphone
consists
of
a
microphone
cartridge
and
a
cathode
follower
for
impedance
conversion,
allowing
long
cables
and
relatively
low
input
impedance
amplifiers
to
be
used
between
the
microphone
and
the
measuring
instrument.
The
microphone
cartridge
is
screwed
onto
the
housing
of
the
cathode
follower
by
means
of
an
adaptor
making
a
small,
rugged
unit.
Fig.
1.1.
Cable
Fig. 1.1.
Quarter-inch
microphone
with
outer
dimensions
in
mm
(1
mm
= o.03937
inch).
The
microphone
may
be
directly
connected
to
the
different
B & K
measuring
instruments
which
are
provided
with
a
"Condenser
Microphone"
input
socket
fitting
the
microphone
connecting
plug.
Stabilized
plate
and
heater
voltages
for
the
cathode
follower
and
polarization
voltage
for
the
cartridge
are
avail-
able
on
this
seven-pin
socket.
The
microphones
may
also
be
used
with
other
equipment
when
operated
from
a
Microphone
Power
Supply
Type
2801
which
provides
the
necessary
voltages
in
the
same
conditions
as
the
B & K
measuring
instruments
(see Accessories).
For
free-field
and
room-acoustic
measurements,
the
microphones
should
be
placed
remote
from
the
measuring
instruments,
since
these
would
often
disturb
the
sound
field
because
of
their
non-negligible
dimensions.
Different
types
of
microphone
stands
and
extension
cables
are
available
for
this
purpose,
see
Accessories.
The
length
of
cable,
however,
has
a
significant
influence
on
the
response
above
40
kHz
as
will
be
seen
in
the
description
of
the
cathode
follower.
7
1135
·
4136
-
DESCRIPTION
Microphone
Amplifier
Fig. 1.2.
Typical
B ,& K
measuring
equipment.
Both
amplifier
and
level re-
corder are linear
up
to
200
kHz.
A filter
set
(Type
1612) is also available for
automatic
plotting
of
spectrograms
in
the
range 22
Hz-45
kHz.
Quarte·r-inch Condenser Microphone Cartridges.
Two
different
types
are
available:
1.
The
Microphone
Cartridge
Type
4135,
with
a
sensitivity
of
o.2 mV/,ubar,
featuring
a
free-field
frequency
characteristic
which
is
flat
up
to 100
kHz
and
a
dynamic
range
going
up
to
174 dB.
2.
The
Microphone
Cartridge
Type
4136,
with
a
sensitivity
of
o.l
mV/,ubar
,
having
a
pressure
frequency
characteristic
which
is
flat
up
to
70
kHz
and
a
dynamic
range
going
up
to
180 dB.
The
difference
in
characteristics
is
illustrated
in
Fig. 1.3.
The
two
cartridges
have
the
same
mechanical
construction
(Fig. 1.4)
differing
only
in
the
diaphragm
which
is 2
,u
(80 tt")
thick
in
the
case
of
the
4135
and
6
,u
(240 ,u")
thick
for
the
4136.
The
latter
thickness
and
the
shape
of
the
back
plate
have
been
determined
in
order
to
achieve
the
critical
damping
of
the
diaphragm
resonance
of
the
4136.
In
this
way
the
widest
possible
flat
frequency
range
of
the
pressure
response
is
obtained.
To
the
thinner
diaphragm
of
the
4135
corresponds
a
higher
damping
factor
and
thus
a
fall
of
the
pressure
response.
The
thickness
of
2
,u
has
been
chosen
in
order
to
obtain,
a
fall
in
pressure
response
which
compensates
exactly
the
free-field
pressure
increase
at
normal
incidence
for
the
cartridge
without
protecting
grid.
The
pressure
increase
with
grid
is
appreciably
higher
and,
above
50
kHz,
it
is
rather
dependent
on
how
tight
the
grid
is
screwed
on
the
cartridge.
Measure-
8
4135
• 4136- DESCRIPTION
"
00
Type
4135+UA 0035+2615 --
-R
1d8
p_±
F
90°
00
=
~
Type
4136+UA0035+2615
R
"
1d8
.,
90°
50 100 500 1000
10
50 100
20
200Hz
2000
20kHz
200
162567
Fig. 1.3. Most
significant
frequency
characteristics
of
the
quarter-inch
micro-
phones
90°
=free-field
response
at
90° (grazing
incidence)
0° = free-field response
at
0°
(normal
incidence)
R =
random
incidence
(diffuse-field)
response
full line:
without
grid
dashed
line:
with
grid
P = pressure response
(towards
the
higher
frequencies,
the
slope is
about
-12
dB/octave).
ments
involving
ultrasonic
frequencies
should
therefore
be
carried
out
with
the
grid
removed.
However,
the
random
incidence
pressure
increase
with
grid
appears
to
be
practically
equal
up
to
40
kHz
to
the
normal
incidence
pressure
increase
without
grid,
and
it
is
therefore
advantageous
to
keep
the
grid
on
in
the
particular
case
of
diffuse
field
measurements
with
the
4135.
Towards
the
low
frequencies
the
response
of
the
cartridges
is
only
affected
by
the
influence
of
the
pressure
equalizing
arrangement.
This
arrangement
consists
of
a
capillary
leakage
hole
through
which
the
equalization
of
the
static
air
pressure
on
both
sides
of
the
diaphragm
is
obtained
at
a
suitable
rate.
The
influence
of
ambient
pressure
(or
altitude)
variations
on
the
microphone
sensitivity
has
been
practically
eliminated
by
proper
design
of
the
pressure
equalization
hole.
The
time
constant
of
the
pressure
equalization
of
the
quarter-inch
cartridges
corresponds
to
a - 3 dB
cut-off
frequency
between
o.5
and
5
Hz
and
will
not
influence
the
measurements,
since
the
- 3
dB
low
frequency
cut-off
of
the
complete
microphone
is
20
Hz.
The
mechanical
construction
of
the
cartridges
is
shown
in
Fig.
1.4.
The
choice
of
the
materials
and
Ihe
de
sign
of
the
suspensions
of
the
different
parts
are
made
principally
with
a vie\\ to
obtaining
the
best
possible
long-term
stability
and
temperature
independeney
of
the
sensitivity
.
9
4135
• 4136- DESCRIPTION
In
particular,
the
diaphragm
is
not
damped
but
electro-deposited
onto
the
tensioning
ring,
forming
one
mechanical
piece.
The
tension
of
the
diaphragm
is
thereby
unaffected
by
temperature
variations.
The
cartridges
are
also
subjected
to
a
complete
artificial
aging
process
during
manufacture
consist-
ing
of
controlled
temperature
variations
over
at
least
two
weeks.
The
basic
parts
are
made
of
high
nickel
alloy
(K-Monel).
The
insulator
used
is
silicone
treated
quartz
and
for
guaranteeing
a
disturbance-free
connection
to
the
cathode
follower,
gold-plated
contacts
are
used.
The
diaphragm
is
mounted
at
a
distance
of
18
p,
from
the
back
plate.
The
10
tote
ao.ck
p
{62f79
Fig. 1.4.
Exploded
view
of
a 1/4"
microphone
cartridge.
6.3S"t0.03mm
0.25±0.
0012..
~
--
-
E~
ELf')
Ol~
0
/ 6
~
s70
E
E :
L/')
~
d~
~
0
Fig. 1.5.
Dimensions
of
the
1/ ,
{'
microphone
cartridges
Type
4135-4136.
4135
~
4136- DESCRIPTION
polarized cartridge capacity,
which
is
of
the
order
of
6
pF,
is
measured
individually
for
each
cartridge
(see
the
calibration
chart).
The
insulation
is
verified
as
higher
than
105
M.Q.
Cleansing
of
the Microphone Diaphragm.
CAUTION.
On
no
account
should
the
diaphragm
com
e
into
contact
with
fingers
or
other
objects.
Th
e
protecting
grid
should
only
be
removed
when
absolutely
necessary.
Should
the
diaphragm
become
contaminated
by
liquids
or
dust
it
may
be dried
off
with
cottonwool
or
a
very
soft
paint-brush
, using
great care,
and
if
necessary
a
proper
solvent.
The
diaphragm
will
not
normally
corrode,
but
any
appreciable
added
mass
will
change
the
frequency
response.
Associated Cathode
Follower
Type
2615 +
UA
0035.
The
quarter-inch
microphone
cartridges
Type
4135-4136
are
intended
to
be
used
with
the
cathode
follower
Type
2615
provided
with
an
adaptor
Type
UA
0035.
The
"goose-neck"
cathode
follower
Type
2614
may
be
used
instead
of
the
2615
but
it
is
then
necessary
in
order
to
obtain
identical
results
above
40
kHz
to
load
the
output
of
the
2614
with
a
capacitance
of
600
pF
(e
.g.
the
10
m
long
cable
Type
AO
0028).
A
photograph
of
the
2615 is
seen
in
Fig.
1.6
and
the
basic
diagram
is
given
in
Fig.
1.7.
The
electrical
components
have
been
divided
into
two
groups.
Those
belonging
to
the
high
impedance
input
circuit
are
mounted
in
the
main
housing
containing
the
vacuum
tube,
while
all
parts
on
the
low
impedance
side
are
located
in
the
connecting
plug.
A
two-meter
long
multi-
core
cable
is
inserted
between
housing
and
plug.
The
dimensions
of
the
housing
are
thus
reduced
to
a
minimum:
diameter
12.7
mm
(%"),
length
Fig. 1.6.
The
Cathode
Followers
Type
2614
and
2615
with
included
input
adaptor
JJ
2614.
11
4135
• 4136-
DESCRIPTION
Components
in
7-
poled plug
Coble
L------
---
-----
---
--
---
--1
r-----
-
---
--
-~~~sj~L
__
.J
f6oso'T
Fig. 1.7. Basic diagram
of
the
cathode-follower
showing
the
principle
of
the
guard ring
system.
SmV
O.BmV
o.
oamv
§
Shock
0
I=
-----.
I=
__.
I=
-------.
. 1
100
200
max
.
allowable
:
level
:
40db
--
40
time
:
1.6sec
.
db
t--
1sec
.
20
10
--
senes
A s erte_s_t!_
f6216
7
2615 .
130
d8
acoustic
test
c=
=
.100
1000
~
<5!1"
.1000
1
0000
200
1000 cfs 10000N
0$0
.9
Fig.1.8.
(a)
Test
of
a
tube
EF
731. Microphonics are excited
by
means
of
two
series
of
lateral
shocks
and
recorded
whereby
the
amplitude
and
duration
of
transi-
ents
are closely checked.
(b)
Recording
of
the
output
from
a 1
/2"
cathode
follower
loaded
by
a 6
pF
dummy
cartridge,
exposed
to a
sound
field
of
130
dB
at
varying
frequency.
12
4135
• 4136- DESCRIPTION
approx.
7
em
(2
3
/l')
. See
also
Fig
. 1.1.
The
components,
which
are
compactly
mounted
on
a
teflon
base,
have
been
carefully
selected
in
order
to
ensure
high
operating
stability
under
the
most
severe
environments.
Before
mounting
each
tube
is
tested
for
sensitivity
to
shock
according
to
the
Mil-EIC
specifications
.
In
addition,
during
the
final
test
the
cathode
followers
are
exposed
to
a
sound
pressure
of
130 dB
where
their
microphonics
is
checked
to
be
smaller
than
8 mV
throughout
the
frequency
range
20-20ooo
Hz
(Fig. 1.8).
The
input
circuitry
is
internally
screened
by
means
of
a "
guard
ring"
which
is
connected
to
the
cathode
of
the
tube.
In
this
way
the
input
capacity
is
reduced
to
an
absolute
minimum.
The
guard
ring
is
extended
to
the
top
of
the
cathode
follower
which
allows
the
use
of
low
capacity
extension
con
-
nectors
such
as
UA
0035
between
microphone
cartridge
and
cathode
follower
.
The
capacitive
load
due
to
the
three
signal
conductors
of
the
multi-core
cable
causes
through
the
guard
ring
circuit
the
input
capacity
to
increase
with
frequency.
This
is
shown
in
Fig.
1.9
together
with
the
consecutive
loss
of
sensitivity
of
the
complete
microphone
in
a
typical
case.
When
adjusting
the
frequency
response
of
the
cartridge
this
loss
is
taken
into
account
in
order
to
provide
a
flat
frequency
response
of
the
complete
micro-
phone.
The
power
supplies
necessary
to
operate
the
cathode
followers
are
provided
by
the
B & K
measuring
amplifiers,
or
the
Microphone
Power
Supply
Type
2801,
via
the
multipin-socket
at
the
front
panel
as
shown
in
Fi
g.
1.11.
12
10
C;
9
pF
0.2
- -
0.5
d8
~
~
,..v-
,....,--
v-::::
_..-
~-;;::
p~;:,
-......-
2615
with
UA
0035-------..,
"'
,..,
........
,.""
2615
without
UA
0035
-
.n
,,."""""
h-
v/
10~
v'
//
~
.....
C
1
:30~
30
/
1~
0
.....
£'
~
/''~
/',..,-
v
.....
/
.........--
"'
~-
....
~
....
-
"::::""-
........
__.-;;----
~
........
·-
-
r--·
--
--
----
cllc]
2615
I:
Ct~
~
I I
~
/
US
ll
10
20
50
100
200
Fig.
1.9.
Variation
of
the equivalent
input
capacitance C,
of
the cathode
follower 2615 as a function
of
frequency for different external capacitive
output
loads.
The
corresponding loss in microphone sensitivity is equal to
C + 3·
25
C b · h 1 · d
"d
. . . F h
C + C, , ezng t e po arzze cartrz
ge
capaczty
gwen
zn
p on t e
individual calibration chart. This loss is given in dB on
the
right scale in
the case where C = 6 pF.
13
4135
• 4136- DESCRIPTION
0.2
0.5 2
10
20
kc/s
50
100
200
Fig. 1.10. Upper
limit
of
the
dynamic
range
of
the
cathode
follower.
The
limit
given
by
this
graph
is
the
peak
output
voltage
corresponding
to a distortion
of
4%
as a
function
of
frequency
and
loading.
The
dashed
lines
show
the
cor-
responding
input
voltage
(minus
o.9 dB).
Ground
Polarization
Voltage
200V
D.C.
Cathode
'--v----J
Filament
6.3V
D.C
200mA
(max. ripple 2mVolt)
Plate
150V
D.C
2mA
(max. ripple 60
j-JVolt)
Connection
tor
4408
f59
i?
f6
Fig. 1.11.
Plug
connection
of
the
cathode
follower
(viewed
from
outside).
The
cathode
followers
can
be
used
separately
whenever
a
high
invnt
impe-
dance
amplifier
is
needed
for
voltage
measurements
at
the
output
of
small
transducers
etc.
An
input
adaptor
JJ
2614 is
supplied
for
this
purpose
with
each
cathode
follower,
as
seen
in
Fig. 1.6.
This
adaptor
can
be
screwed
onto
the
cathode
follower
housing
instead
of
the
UA
0035
and
contains
a
capacitor
of
a
few
thousand
pF
for
blocking
the
200 V DC
polarization
14
GENERAL CHARACTERISTICS
voltage.
The
adaptor
provides
a
standard
14
mm
coaxial
socket
fitting
the
B & K
JP
0018
plug.
Specifications.
Input
Impedance: 700
M.Q
in
parallel
with
3 ± o.5
pF.
(Below
10
Hz
and
above
2
Hz:
more
than
200 MD
in
parallel
with
3 ± o.5
pF).
Output Impedance:
Approximately
750
.Q.
Transmission Loss: Voltage
gain
= - o.9 dB .± o.2 dB.
Self-generated Noise Level:
Approximately
80
fi-V
at
cathode
follower
output,
with
the
input
loaded
by
a
capacitor
of
8
pF
(20
Hz-200
kHz).
Distortion: 4 :%
distortion
occurs
with
input
voltages
higher
than
20 volts
r.m.s.
at
1 kHz. (See Fig. 1.10
for
higher
frequencies).
Tube: 5899
(EF31),
specially
tested
for
low
microphonics.
Characteristics of the Quarter-Inch Microphones.
The
fO'llowing
characteristics
of
the
quarter-inch
condenser
microphone
(Type
4135/36 +
UA
0035 + 2615)
are
described
below:
1.
Sensitivity.
1.
Sensitivity
2.
Frequency
response
3.
Phase
characteristics
4.
Free-field
corrections
5.
Directional
patterns
6.
Dynamic
range
(Noise
and
Distortion)
7.
Equivalent
air
volume
8.
Polarization
voltage
U.
Temperature
10.
Static
pressure
11.
Humidity
12.
Vibrations
13.
Magnetic
fields
14.
Spurious
microphonics
The
nominal
sensitivity
of
the
quarter-inch
microphone
is o.2
mVIJA-bar
(-74
dB
re
1
V/JA-bar)
when
equipped
with
a 4135
cartridge
and
o.1 mV/,ubar
(-80
dB
re
1 V/,ubar)
with
a 4136
cartridge.
However,
the
cartridges
are
individually
calibrated
and
the
actual
sensitivities
may
lie
between
± 3 dB
of
the
nominal
values.
On
the
calibration
chart
(Fig. 1.12)
which
is
delivered
with
each
cartridge
is
also
given
the
cartridge
open
circuit
sensitivity
(about
4 dB
higher
than
the
sensitivity
of
the
complete
microphone
depending
on
the
cartridge
capacity)
and
a
factor
K
equal
to
the
difference
between
the
microphone
11
4135
• 4136-
DESCRIPTION
0
0
0
0
0
0
0
0!
0 •
0 )
0
0
0
[]
[]
[]
[]
[]!
[]
.
[]
J
0
[]
[]
0
[]
[]
[]
[]
[]
[]
[]
!
[]
.
<I
.h
~
jl
+·o I g
I
~~
"'
~~
u
[]
[]
0
[]
[]
0
0
[]
0
~~
"'
•Cl-
~
·~
~~······-·,....
[]
•
lol-l-l++l+H++++-I+l-l+l++ll++l++++-l+l-l+l++l+H++++-1+~
0 )
lol-+i+H+++-H+1+H+++-H+1H+++++-H+1++++++-H+1+++-f-H-j
0
0
[]
0
0
t +0
Fig. 1.12. Calibration charts
supplied
with
each
microphone
cartridge.
The
pressure response is
automatically
plotted
by
a process
having
an
accuracy
of
± o.2
dB
up
to
10
kHz
and
± o.5
dB
up
to
200
kHz.
After
publication
of
this
manual,
the
dotted
open-circuit response curve
will
not
be
included
since
it
can
be easily
computed
from
Fig. 1.9.
16
..,
()
"'
GENERAL CHARACTERISTICS
sensitivity
to
which
the
sound
level
graduation
of
the
B & K
instruments
is
referred
and
the
particular
microphone
sensitivity.
2.
Frequency
Response.
Each
cartridge
is
upon
delivery
provided
with
an
individually
plotted
fre-
quency
response
chart
(Fig. 1.12).
Three
curves
are
given
for
the
4135:
(a)
The
pressure
response
(with
a
cathode
follower
2615 +
UA
0035).
(b)
The
normal
incidence
free-field
response
of
the
complete
microphone
without
protecting
grid.
(c)
The
random
incidence
diffuse
field
response
of
the
microphone
with
protecting
grid
(only
defined
up
to
50
kHz
).
Only
the
curve
(a)
is
actually
measured
on
each
cartridge.
The
other
curves
differ
from
(a)
by
an
amount
which
is
equal
to
the
respective
correction
and
has
been
determined
once
for
all.
For
further
details,
see
item
4:
"Free-field
corrections".
With
the
cartridge
Type
4136,
only
curve
(a) is
given.
If
the
open-circuit
frequency
characteristics
of
the
cartridges
have
to
be
considered,
they
can
be
deduced
from
the
given
curves
by
applying
a
correction
as
d~scribed
in
Fig.
1.9
(curve
0).
3.
Phase
Characteristics
and
Pulse
Responses.
Typical
pressure
response
phase
angle
characteristics
of
the
quarter-inch
microphones
are
shown
in
Fig.
1.13.
The
fundamental
resonance
of
the
V(
I
"'
r I
0
1/4"
cartridges
4135
phose
characteristics
41.:1b
t3:_
rl
0
0 I I
L
140
120
100
20
0 I J
0
)/I
.
d_"
~
0
/
~
v
0
l---:::::
----
V"
0
---
1635 ' ?
80
60
40
0
0.2 0.5 2 5 10 20
kcfs
50
100 200
Fig. 1.13.
Typical
pressure-response phase-angle characteristics
of
the
quarter-
inch
micro
phone
cartridges.
17
4135
• 4136-
DESCRIPTION
10
j
_I
.1
I I ! I
........
.....Pt
1---
Free
f1eld
corrections
/
~
r--
for
Type 4135 I J I
/~
~
N_Oo
-I'.
f-----
Without protecting grid
//
1\.
1'-f..-/'
1'--
//
!'....
dB
5
/.
v ___.JOo
1\
~
I'-
1'\.
~
........-.::::ol'\
-~
1/
~~~f-
..
__
"'
~
--
90° '
0
~-
_
...
-
',\
\
18~ioo"
1
\\
150~"""-
~
~
" " I\ I\
~
~~~00
' \
{0
\.
~
\
~J
]50°\\
' \
C'
( (
-.
.,
t 0°•lncidence'120 \ \'
~
_\
l J J
~
~
'
1\
~goj
_
\
1
-5
db
/ '
1\,
180°\
1
-10
1
\\
"~
\ \
2 ko/s 3 4 5 7
10
15
20
30
40
50
70
100
ko/s
150
200
162291.
Fig. 1.14. Free field corrections
for
the
quarter-inch
microphone
equipped
with
a cartridge
Type
4135
without
grid.
10
-
I I I I I I
1----
Free field
corrections
1----
for
Type 4136 I I I
dB
t---
without
protecting grid
5
0 -
-5
ea-~
( ( I
db
I
-10
2
Ko/s
3 4 . 5 7
""""
r-t
l
/
30~
v/
~
""'\j '
/ v
""
r-f-"""'...
t-./
//
I 1
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180° 1\,
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10
15
20 30
40
50
70
100Ko/s
150
200
162295
Fig. 1.15. Free field corrections for
the
quarter-inch
microphone
equipped
with
a cartridge TrJpe 4136
without
grid.
18
This manual suits for next models
5
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