BRUEL & KJAER 1615 User guide

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. Instructions
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Octave and 1/3 Octave
Filter Sets 1614 and 1615
The Filter Sets are compact
instruments
of plug-in unit
construction. Types
1614 and 1615
filters conform to the IEC 225 and
ANSI Sl. II. standards and cover
the 2 Hz-160 kHz and
25 Hz-20 kHz
ranges respectively. "A", "B",
"C", "D" and "Linear" networks are
also included. Both the filters and
the networks can be automatically
scanned.

Octave and 1/3 Octave Filter Sets
Types 1614 and 1615
Reprint may 1970

CONTENTS
1. INTRODUCTION • • • • • • • • • • • • • • • • • . • • • • • . • • • • 3
2.
TECHNICAL DESCRIPTION • • • • • • • • • • • • • • • • • • • • • 5
Input Amplifier . . . . . . . . . . . . . . . . . . . . . . 5
1/3 Octave Filters . . . . . . . . . . . . . • . . . . . . . 5
Octave Filters ......... . .............. 10
Effective Bandwidth . . . . . . . . . . . . . . . . . . . 12
Phase Response ...................... 12
Filter Transient Response ............... 13
Weighting Networks .................... 14
Linear Ranges . . . . . . . .............. 14
Output Amplifier . . . . . .............. 14
Remote Control . . . . . . . . . . . . . • • • . . . . . . 14
3. CONTROLS •.•••••..••••.•....•••...••••.. 16
4. OPERATION ••••••.•..•••.•.•.••••••••.••• 19
General ...................•••..... 19
Conversion of 1615 to 1614 ............... 19
Use with Microphone Amplifier 2603/04 ..•..... 21
Use with Amplifier 2606 ..........•...... 23
Use with Frequency Analyzer 2107 ........... 25
Use with Precision Sound Level Meter 2203 and
Impulse Precision Sound Level Meter 2204 ..•... 27
Use with FM Tape Recorder 7001 ........... 28
Use with Random Noise Generator 1402 ........ 28
Use with Level Recorder 2305 • . . . • . • • • • . • . . 31

5. TYPICAL MEASUREMENT AND ANALYSIS SET -UPS USING
THE TYPES 1614/15 .....•.......... . ...... . .. 36
Direct analysis of sound
.... 36
Direct analysis of vibration . . . . . . . . . . . . . . 37
Bands
of Random Noise . . . . . . . . . . . . . . . 38
Analysis from Tape Recorder ...... . ....... 38
Low Frequency Analysis ............... . . 38
Analysis of Transients . . . . . . . . . . . 38
Recording
of Low Frequency Sound ........ . . 39
6. USEFUL FILTER INFORMATION AND DEFINITIONS ..... 41
Ideal Filter (Band-pass)
Effective Bandwidth
Octave
Filter Centre Frequency .. .. .. .
Filter Band-Edge Frequencies
Bandwidth
......... .
...... 41
...... 42
...... 42
. 43
. 43
. 43
Spectrum . . . . . . . . . . . . . . . . . . . . . . 43
Noise
............................. 44
7. SPECIFICATIONS ..........•................ 45

1. INTRODUCTION
The Filter Sets Types 1614 and 1615 are a development of the older design
(Type 1612).
The filter performance is generally improved and the Type
1614 includes extra filters at both low and high frequencies. Both 1614 and
1615 contain the sound weighting networks A, 8, C, and the more recently
introduced D network.
The Filter Sets are primarily designed for vibration and acoustic frequency
analysis, and have specifications and tolerances which conform
to the
following standards:
IEC 225 1966
ANSI S1.11-1966 (1/3octaveCiasslll, 1/1 octave Class II)
DIN
45652
The filters are band-pass filters, with 1/3 octave bandwidths. The filter
centre frequencies are spaced
1/3 octave apart, and filter selection is by a 50
-position switch on the front panel. In the octave mode, 3 adjacent 1/3
octave filters are connected such as to produce a 1/1 octave bandwidth.
Filter selection
is either manual or by remote control, enabling synchroniza-
tion with other equipment.
Linear ranges and
the A, 8, C, and D networks are also selected by the 50-
position switch.
The input and output to the filters can be connected to a wide range of
terminating impedances. For Field measurements provision is made for 12 V
DC operation.
Frequency analysis over a very wide frequency range can be accomplished
with
the Filter Set in conjunction with a 8 & K Sound and Vibration
Measuring amplifier
Type 2606 or Type 2603 or the 8 & K Sound Level
Meters. 1/3 octave or 1/1 octave bands of random noise may also be
produced by using
the Filter Set in conjunction with the 8 & K Random
Noise Generator
Type 1402. These and other typical uses of the Filter Set
are briefly mentioned in Chapter 4 of this Manual.
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Input
01 Bandwidth
1: 1/3 Oct.
2: 1/1 Oct.
02 Frequency Range
1: 25Hz-20kHz D-A-8-C-Lin
2: 2Hz-160kHz
03 50 Position Filter Switch
04 Scanning Selector
1: Manuel
2: Remote
05 Linear t8Hz-200kHz
• 1: On
2: Off
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2. TECHNICAL DESCRIPTION
The block diagram in Fig.2.1 shows the basic design of the instrument. The
signal is fed via an input amplifier to the filter inputs, which are connected
in parallel. The input amplifier has a high input impedance, and drives the
filters from a low output impedance. The filter outputs are selected by the
50 -position switch. When in the octave mode, the outputs of three
adjacent 1/3 octave filters are connected together (via resistors). The signal
from the filters is fed to two inputs of a buffer amplifier.
A subsidiary range of filters, from 25 Hz to 20 kHz with D, A, B, C and
Linear filters
can also be selected. This is also the only frequency range of
the 1615, which does not possess the low and high frequency filters.
The 50 position switch can be operated by actuating the electromagnetic
drive unit from the remote control socket.
The Filter set can be operated from normal mains supplies or from a 12 V
DC accumulator, for which purpose there is a DC- AC converter.
INPUT AMPLIFIER
The input amplifier provides the low impedance (rv0.8Q) drive required for
the filters. It has an input resistance of 125 KQ in parallel with 55 pF, and a
gain
of 0 dB. Its frequency response is flat from 1.8 Hz- 200kHz within
±0.1 dB.
1/3 OCTAVE FILTERS
The 1/3 octave filters are all 6-pole Butterworth networks and have the
centre frequencies and bandwidths given in Table 1.
The 2 - 200 Hz filters are active circuits consisting of 3 stagger tuned
Wien-bridge amplifiers, with an emitter follower output to reduce the out-
put impedance.
The other 1/3 octave filters are passive networks. Schematic diagrams for
both active and passive 1/3 octave filters are shown in Fig.2.2 and 2.3
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Centre
Centre
Frequency Bandwidth Frequency Bandwidth
Hz
Hz Hz Hz
2 0.46 630 145
2.5 0.58 800 183
3.15 0.73 1000 230
4 0.92 1250 290
5 1.16 1600 370
6.3 1.45 2000 460
8 1.83 2500 580
10 2.30 3150 730
12.5 2.90 4000 920
16 3.70 5000 1160
20 4.60 6300 1450
25
5.8 8000 1830
31.5 7.3 10000 2300
40 9.2 12500 2900
50 11.6 16000 3700
63 14.5 20000 4600
80 18.3 25000 5800
100
23
31500 7300
125
29
40000 9200
160
37
50000 11600
200 46 63000 14500
250
58
80000 18300
315
73
100.000 23000
400
92
125.000 29000
500
116
160.000 37000
Table I. Filter centre frequencies and bandwidths.
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