Recording - July 2015 - 58

ike
By M

s

River

Part 3: Sensitivity-It's Like Gain, Only Different
The concept of gain is fairly straightforward, but in order to measure or calculate gain, you need to have the same thing coming out
as what went in-volts in and volts out, amps in, amps out, dollars
in, dollars out. However, with many audio devices, what comes out
is in a different form than what went in, even though in some (but
not all) cases, both the input and output are electrical. A device that
converts one form of energy to another is called a transducer.
Microphones convert air pressure to voltage. Loudspeakers
do the opposite, using electrical power to move air. An A/D or
D/A converter converts between volts and bits. A power amplifier converts volts to watts. So how do we express the relationship between a transducer's input and output in a way that's as
meaningful and handy as gain? It's called sensitivity. Let's look
at a few devices where it applies.
Microphones
A microphone's sensitivity is specified in terms of its output
voltage for a given sound pressure level (SPL). Modern microphone manufacturers usually specify SPL in pascals (Pa), the SI
(metric) unit of pressure. It's like pounds per square inch in your
tires, but a more conveniently-sized unit for dealing with small
changes in pressure. 1 pascal is equivalent to 94 dB SPL, about
the volume level of a tolerably loud concert.
A microphone's output is usually measured in millivolts RMS,
unloaded (open circuit), though in the spec sheet it's often
expressed as dBV or dBu. In real life, with the mic loaded by a
mic preamp's typical input impedance of around 2000 ohms, its
output level will drop about 1 dB from the lab measurement. The
measurement is made in an anechoic chamber or free field environment (no nearby reflective surfaces), with the source on axis
to the mic. Directional mics are usually measured at 1 kHz while
omni mics are sometimes measured at 250 Hz.
Modern mics specify sensitivity as dBV or mV per Pa, though
when perusing vintage mic specs, you might find SPL in dynes/cm2
(dynes per square centimeter) or µbars (microbars, from "barometric pressure"). 1 dyne/cm2 = 1 µbar = 1/10 Pa = 74 dB SPL.
The sensitivity spec for the popular Shure SM57 is: "-56 dBV/Pa (1.6
mV)." The classic RCA 77DX is specified as "Uni-directional: -50 dBm"
with a footnote that the reference SPL is 10 dynes/cm2. Since it states
that the output is unloaded, hence a negligible amount of power,
I'm guessing that "dBm" is what we now call dBu (2.4 mV). The
address http://is.gd/MicSensitivityConverter leads to a handy online calculator will help you to compare mics with sensitivities specified in different units.
58

RECORDING July 2015

A mic with high sensitivity isn't necessarily better than a low
sensitivity one. Sensitivity is a characteristic that gives us guidance as to how the mic is best used, and how much gain we'll
need in order to make it work in a given application.
Loudspeakers-passive and active
Loudspeakers, which convert electrical energy to sound pressure,
have a sensitivity specification similar to that of microphones, only in
reverse. Loudspeaker sensitivity is usually specified as SPL for a given
power, measured on axis at a distance of 1 meter or 1 foot. The specification is usually written as (for example) "91 dB, 1 W, 1 meter." SPL
is usually measured at a single frequency, typically 1 kHz for a fullrange speaker, with more appropriate frequencies used when measuring limited-range speakers such as super-tweeters or subwoofers.
Two speakers that have similar sensitivity, driven by the same
amplifier and playing the same program material, can differ
considerably in subjective loudness. Two factors that influence
this are the speaker's directivity and how its impedance varies
with frequency ("8 ohms" is only nominal).
In a powered (active) speaker system, the input is to an amplifier rather than a loudspeaker, so the sensitivity is specified as
input voltage (dBu) for a given SPL. Powered speakers usually
have an input sensitivity control to accommodate a range of
inputs, so sensitivity is often specified at the maximum setting or
at one of the de facto standard nominal operating levels of +4
dBu or -10 dBV. Another important specification is SPL with the
amplifier(s) delivering their maximum power, which is usually
limited to avoid damage to the amplifier or speakers. A typical
powered speaker's spec might read:
Input sensitivity: +4 dBu, 94 dB SPL @ 1m
Maximum continuous SPL: 106 dB @ 1m
Peak SPL: 112 dB @ 1m
This tells you that with the input sensitivity control (if there's one)
set for +4 dBu (there's often a detent at that position) it'll reach its
rated SPL at an input level of +16 dBu [ = +4 dBu + (106 - 94)
dB] and can tolerate occasional input peaks of +22 dBu [ =
+16 dBu + (112 - 106) dB]. However, if your mixer's maximum
output is +24 dBu (and we all run them up to the red line sometimes), backing off the speaker's input sensitivity control by a couple of dB will keep all of your mixer's headroom.
This analysis can be extended to power amplifiers, which are usually specified as maximum power into a specified impedance, as
well as how many volts at the input are required for a given amount
of power. Do the math and set up your system accordingly.


http://www.is.gd/MicSensitivityConverter

Table of Contents for the Digital Edition of Recording - July 2015

Contents
Recording - July 2015 - Cover1
Recording - July 2015 - Cover2
Recording - July 2015 - 1
Recording - July 2015 - 2
Recording - July 2015 - 3
Recording - July 2015 - 4
Recording - July 2015 - 5
Recording - July 2015 - Contents
Recording - July 2015 - 7
Recording - July 2015 - 8
Recording - July 2015 - 9
Recording - July 2015 - 10
Recording - July 2015 - 11
Recording - July 2015 - 12
Recording - July 2015 - 13
Recording - July 2015 - 14
Recording - July 2015 - 15
Recording - July 2015 - 16
Recording - July 2015 - 17
Recording - July 2015 - 18
Recording - July 2015 - 19
Recording - July 2015 - 20
Recording - July 2015 - 21
Recording - July 2015 - 22
Recording - July 2015 - 23
Recording - July 2015 - 24
Recording - July 2015 - 25
Recording - July 2015 - 26
Recording - July 2015 - 27
Recording - July 2015 - 28
Recording - July 2015 - 29
Recording - July 2015 - 30
Recording - July 2015 - 31
Recording - July 2015 - 32
Recording - July 2015 - 33
Recording - July 2015 - 34
Recording - July 2015 - 35
Recording - July 2015 - 36
Recording - July 2015 - 37
Recording - July 2015 - 38
Recording - July 2015 - 39
Recording - July 2015 - 40
Recording - July 2015 - 41
Recording - July 2015 - 42
Recording - July 2015 - 43
Recording - July 2015 - 44
Recording - July 2015 - 45
Recording - July 2015 - 46
Recording - July 2015 - 47
Recording - July 2015 - 48
Recording - July 2015 - 49
Recording - July 2015 - 50
Recording - July 2015 - 51
Recording - July 2015 - 52
Recording - July 2015 - 53
Recording - July 2015 - 54
Recording - July 2015 - 55
Recording - July 2015 - 56
Recording - July 2015 - 57
Recording - July 2015 - 58
Recording - July 2015 - 59
Recording - July 2015 - 60
Recording - July 2015 - 61
Recording - July 2015 - 62
Recording - July 2015 - 63
Recording - July 2015 - 64
Recording - July 2015 - 65
Recording - July 2015 - 66
Recording - July 2015 - 67
Recording - July 2015 - 68
Recording - July 2015 - 69
Recording - July 2015 - 70
Recording - July 2015 - 71
Recording - July 2015 - 72
Recording - July 2015 - Cover3
Recording - July 2015 - Cover4
https://www.nxtbook.com/musicmaker/musicmaker/recording_202404
https://www.nxtbook.com/musicmaker/musicmaker/recording_202403
https://www.nxtbook.com/musicmaker/musicmaker/recording_202402
https://www.nxtbook.com/musicmaker/musicmaker/recording_202401
https://www.nxtbook.com/musicmaker/musicmaker/recording_202312
https://www.nxtbook.com/musicmaker/musicmaker/recording-november-2023
https://www.nxtbook.com/musicmaker/musicmaker/recording_202310
https://www.nxtbook.com/musicmaker/musicmaker/recording_202309
https://www.nxtbook.com/musicmaker/musicmaker/recording_202308
https://www.nxtbook.com/musicmaker/musicmaker/recording_202307
https://www.nxtbook.com/musicmaker/musicmaker/recording_202306
https://www.nxtbook.com/musicmaker/musicmaker/recording_202305
https://www.nxtbook.com/musicmaker/musicmaker/recording_202304
https://www.nxtbook.com/musicmaker/musicmaker/recording_202303
https://www.nxtbook.com/musicmaker/musicmaker/recording_202302
https://www.nxtbook.com/musicmaker/musicmaker/recording_202301
https://www.nxtbook.com/musicmaker/musicmaker/recording_202212
https://www.nxtbook.com/musicmaker/musicmaker/recording_202211
https://www.nxtbook.com/musicmaker/musicmaker/recording_202210
https://www.nxtbook.com/musicmaker/musicmaker/recording_202209
https://www.nxtbook.com/musicmaker/musicmaker/recording_202208
https://www.nxtbook.com/musicmaker/musicmaker/recording_202207
https://www.nxtbook.com/musicmaker/musicmaker/recording_202206
https://www.nxtbook.com/musicmaker/musicmaker/recording_202205
https://www.nxtbook.com/musicmaker/musicmaker/recording_202204
https://www.nxtbook.com/musicmaker/musicmaker/recording_202203
https://www.nxtbook.com/musicmaker/musicmaker/recording_202202
https://www.nxtbook.com/musicmaker/musicmaker/recording_202201
https://www.nxtbook.com/musicmaker/musicmaker/recording_202112
https://www.nxtbook.com/musicmaker/musicmaker/recording_202111
https://www.nxtbook.com/musicmaker/musicmaker/recording_202110
https://www.nxtbook.com/musicmaker/musicmaker/recording_202109
https://www.nxtbook.com/musicmaker/musicmaker/recording_202108
https://www.nxtbook.com/musicmaker/musicmaker/recording_202107
https://www.nxtbook.com/musicmaker/musicmaker/recording_202106
https://www.nxtbook.com/musicmaker/musicmaker/recording_202105
https://www.nxtbook.com/musicmaker/musicmaker/recording_202104
https://www.nxtbook.com/musicmaker/musicmaker/recording_202103
https://www.nxtbook.com/musicmaker/musicmaker/recording_202102
https://www.nxtbook.com/musicmaker/musicmaker/recording_202101
https://www.nxtbook.com/musicmaker/musicmaker/recording_202012
https://www.nxtbook.com/musicmaker/musicmaker/recording_202011
https://www.nxtbook.com/musicmaker/musicmaker/recording_202010
https://www.nxtbook.com/musicmaker/musicmaker/recording_202009
https://www.nxtbook.com/musicmaker/musicmaker/recording_202008
https://www.nxtbook.com/musicmaker/musicmaker/recording_202007
https://www.nxtbook.com/musicmaker/musicmaker/recording_202006
https://www.nxtbook.com/musicmaker/musicmaker/recording_20205
https://www.nxtbook.com/musicmaker/musicmaker/recording_202004
https://www.nxtbook.com/musicmaker/musicmaker/recording_202003
https://www.nxtbook.com/musicmaker/musicmaker/recording_202002
https://www.nxtbook.com/musicmaker/musicmaker/recording_202001
https://www.nxtbook.com/musicmaker/musicmaker/recording_201912
https://www.nxtbook.com/musicmaker/musicmaker/recording_201911
https://www.nxtbook.com/musicmaker/musicmaker/recording_201910
https://www.nxtbook.com/musicmaker/musicmaker/recording_201909
https://www.nxtbook.com/musicmaker/musicmaker/recording_201908
https://www.nxtbook.com/musicmaker/musicmaker/recording_201907
https://www.nxtbook.com/musicmaker/musicmaker/recording_201906
https://www.nxtbook.com/musicmaker/musicmaker/recording_201905
https://www.nxtbook.com/musicmaker/musicmaker/recording_201904
https://www.nxtbook.com/musicmaker/musicmaker/recording_201903
https://www.nxtbook.com/musicmaker/musicmaker/recording_201902
https://www.nxtbook.com/musicmaker/musicmaker/recording_201901
https://www.nxtbook.com/musicmaker/musicmaker/recording_201812
https://www.nxtbook.com/musicmaker/musicmaker/recording_201811
https://www.nxtbook.com/musicmaker/musicmaker/recording_201810
https://www.nxtbook.com/musicmaker/musicmaker/recording_201809
https://www.nxtbook.com/nxtbooks/musicmaker/recording_201808
https://www.nxtbook.com/nxtbooks/musicmaker/recording_201807
https://www.nxtbook.com/nxtbooks/musicmaker/recording_201806
https://www.nxtbook.com/nxtbooks/musicmaker/recording_201805
https://www.nxtbook.com/nxtbooks/musicmaker/recording_201804
https://www.nxtbook.com/nxtbooks/musicmaker/recording_201803
https://www.nxtbook.com/nxtbooks/musicmaker/recording_201802
https://www.nxtbook.com/nxtbooks/musicmaker/recording_201801
https://www.nxtbook.com/nxtbooks/musicmaker/recording_201712
https://www.nxtbook.com/nxtbooks/musicmaker/recording_201711
https://www.nxtbook.com/nxtbooks/musicmaker/recording_201710
https://www.nxtbook.com/nxtbooks/musicmaker/recording_201709
https://www.nxtbook.com/nxtbooks/musicmaker/recording_201708
https://www.nxtbook.com/nxtbooks/musicmaker/recording_201707
https://www.nxtbook.com/nxtbooks/musicmaker/recording_201706
https://www.nxtbook.com/nxtbooks/musicmaker/recording_201705
https://www.nxtbook.com/nxtbooks/musicmaker/recording_201704
https://www.nxtbook.com/nxtbooks/musicmaker/recording_201703
https://www.nxtbook.com/nxtbooks/musicmaker/recording_201702
https://www.nxtbook.com/nxtbooks/musicmaker/recording_201701
https://www.nxtbook.com/nxtbooks/musicmaker/recording_201612
https://www.nxtbook.com/nxtbooks/musicmaker/recording_201611
https://www.nxtbook.com/nxtbooks/musicmaker/recording_201610
https://www.nxtbook.com/nxtbooks/musicmaker/recording_201609
https://www.nxtbook.com/nxtbooks/musicmaker/recording_201608
https://www.nxtbook.com/nxtbooks/musicmaker/recording_201607
https://www.nxtbook.com/nxtbooks/musicmaker/recording_201606
https://www.nxtbook.com/nxtbooks/musicmaker/recording_201605
https://www.nxtbook.com/nxtbooks/musicmaker/recording_201604
https://www.nxtbook.com/nxtbooks/musicmaker/recording_201603
https://www.nxtbook.com/nxtbooks/musicmaker/recording_201602
https://www.nxtbook.com/nxtbooks/musicmaker/recording_201601
https://www.nxtbook.com/nxtbooks/musicmaker/recording_201512
https://www.nxtbook.com/nxtbooks/musicmaker/recording_201511
https://www.nxtbook.com/nxtbooks/musicmaker/recording_201510
https://www.nxtbook.com/nxtbooks/musicmaker/recording_201509
https://www.nxtbook.com/nxtbooks/musicmaker/recording_201508
https://www.nxtbook.com/nxtbooks/musicmaker/recording_201507
https://www.nxtbook.com/nxtbooks/musicmaker/recording_201506
https://www.nxtbook.com/nxtbooks/musicmaker/recording_201505
https://www.nxtbook.com/nxtbooks/musicmaker/recording_201504
https://www.nxtbook.com/nxtbooks/musicmaker/recording_201503
https://www.nxtbook.com/nxtbooks/musicmaker/recording_201502
https://www.nxtbook.com/nxtbooks/musicmaker/recording_201501
https://www.nxtbook.com/nxtbooks/musicmaker/recording_201412
https://www.nxtbook.com/nxtbooks/musicmaker/recording_201411
https://www.nxtbook.com/nxtbooks/musicmaker/recording_201410
https://www.nxtbook.com/nxtbooks/musicmaker/recording_201409
https://www.nxtbook.com/nxtbooks/musicmaker/recording_201408
https://www.nxtbook.com/nxtbooks/musicmaker/recording_201407
https://www.nxtbook.com/nxtbooks/musicmaker/recording_201406
https://www.nxtbook.com/nxtbooks/musicmaker/recording_201405
https://www.nxtbook.com/nxtbooks/musicmaker/recording_201404
https://www.nxtbook.com/nxtbooks/musicmaker/recording_201403
https://www.nxtbook.com/nxtbooks/musicmaker/recording_201402
https://www.nxtbook.com/nxtbooks/musicmaker/recording_201401
https://www.nxtbook.com/nxtbooks/musicmaker/recording_201312
https://www.nxtbook.com/nxtbooks/musicmaker/recording_201311
https://www.nxtbook.com/nxtbooks/musicmaker/recording_201310
https://www.nxtbook.com/nxtbooks/musicmaker/recording_201309
https://www.nxtbook.com/nxtbooks/musicmaker/recording_201308
https://www.nxtbook.com/nxtbooks/musicmaker/recording_201307
https://www.nxtbook.com/nxtbooks/musicmaker/recording_201306
https://www.nxtbook.com/nxtbooks/musicmaker/recording_201305
https://www.nxtbook.com/nxtbooks/musicmaker/recording_201304
https://www.nxtbook.com/nxtbooks/musicmaker/recording_201303
https://www.nxtbook.com/nxtbooks/musicmaker/recording_201302
https://www.nxtbook.com/nxtbooks/musicmaker/recording_201301
https://www.nxtbook.com/nxtbooks/musicmaker/recording_201212
https://www.nxtbook.com/nxtbooks/musicmaker/recording_201211
https://www.nxtbook.com/nxtbooks/musicmaker/recording_201210
https://www.nxtbook.com/nxtbooks/musicmaker/recording_201209
https://www.nxtbook.com/nxtbooks/musicmaker/recording_201208
https://www.nxtbook.com/nxtbooks/musicmaker/recording_201207
https://www.nxtbook.com/nxtbooks/musicmaker/recording_201206
https://www.nxtbook.com/nxtbooks/musicmaker/recording_201205
https://www.nxtbook.com/nxtbooks/musicmaker/recording_201204
https://www.nxtbook.com/nxtbooks/musicmaker/recording_201203
https://www.nxtbook.com/nxtbooks/musicmaker/recording_201202
https://www.nxtbook.com/nxtbooks/musicmaker/recording_201201
https://www.nxtbook.com/nxtbooks/musicmaker/recording_201112
https://www.nxtbook.com/nxtbooks/musicmaker/recording_201111
https://www.nxtbook.com/nxtbooks/musicmaker/recording_201110
https://www.nxtbook.com/nxtbooks/musicmaker/recording_201109
https://www.nxtbook.com/nxtbooks/musicmaker/recording_201108
https://www.nxtbook.com/nxtbooks/musicmaker/recording_201107
https://www.nxtbook.com/nxtbooks/musicmaker/recording_201106
https://www.nxtbook.com/nxtbooks/musicmaker/recording_201105
https://www.nxtbook.com/nxtbooks/musicmaker/recording_201104
https://www.nxtbook.com/nxtbooks/musicmaker/recording_201103
https://www.nxtbook.com/nxtbooks/musicmaker/recording_201102
https://www.nxtbook.com/nxtbooks/musicmaker/recording_201101
https://www.nxtbook.com/nxtbooks/musicmaker/recording_201012
https://www.nxtbook.com/nxtbooks/musicmaker/recording_201011
https://www.nxtbook.com/nxtbooks/musicmaker/recording_201010
https://www.nxtbook.com/nxtbooks/musicmaker/recording_201009
https://www.nxtbook.com/nxtbooks/musicmaker/recording_201008
https://www.nxtbook.com/nxtbooks/musicmaker/recording_201007
https://www.nxtbook.com/nxtbooks/musicmaker/recording_201006
https://www.nxtbook.com/nxtbooks/musicmaker/recording_201005
https://www.nxtbook.com/nxtbooks/musicmaker/recording_201004
https://www.nxtbook.com/nxtbooks/musicmaker/recording_201003
https://www.nxtbook.com/nxtbooks/musicmaker/recording_201002
https://www.nxtbook.com/nxtbooks/musicmaker/recording_201001
https://www.nxtbook.com/nxtbooks/musicmaker/recording_200912
https://www.nxtbook.com/nxtbooks/musicmaker/recording_200911
https://www.nxtbook.com/nxtbooks/musicmaker/recording_200910
https://www.nxtbook.com/nxtbooks/musicmaker/nxtd
https://www.nxtbookmedia.com