BRUEL & KJAER 4409 User guide

Response Test Unit Type 4409
Test Records Types QR 2007-08-09
The test unit and r ecordings have been designed
to aid the accurate investigat i ons of the frequency
re sponse of sound reproducing equipment i.e.
record ~Iayersl tape & film recorders etc.
BRUEL & KJ.N..H
N",rum, Denmark. I!E 800500 . .;:>" BRUKJA, Cop enhagen. Telex: 5316
Be 440Q

Response Test Unit
Type 4409
Test Records
Types OR 2007 -~09
FEBRUARY 1964

Contents
1. Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 3
Purpose of the Equ ipm ent . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 3
Description of the Test Records ... . ... ..... . ............. . ......... 4
General. . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 4
Recording Characteristics ........... ... ...... .. . .. . . .. . .. . . . ..... .. 9
Recorded Level Tolerances ............. . .. ..... . ..... . .. ......... . 11
Response Test Unit Type 4409 .. ...... .... .... . ...... .. . ...... .... .. 13
Channel Selector ....... ........... .... ....... .... ...... .. ....... . . 14
Equalizing Filter ........ .... . .. .................... . .. . ........... 14
Synchro -Starter ............... .. ......... .. ... . .. .. .. . ............ 14
General Description ...... .... . .. . .... .. . . .................. . ....... 14
Functioning . ...... ... . . . .. ..... ................................... 16
2. Operation ................ ...... .. . ................ . ... .. ......... 17
Practical Hints for Use of the Test-Records ..... . . .. . .. ... ...... ... .. 17
Aut omatic Frequency Response Plotting ... . ... . ..... .. . ...... . . .... 17
Automatic Gliding Frequency Cross-Ta lk Measurements . ............. 19
General . .......................................................... 19
Operating Procedure ........ . ... . . .... .. . ...................... ... 20
Synchronous Filtering Adjustment . ... ... ... .. ... . . ........ . .... . .. . 22
Automatic Distortion Measurements ............. .. ........ . ........ 25
Examples of Practical Results ..... ... .... . ...... . .. .. . . . ... ... . .... 26
Use of th e Te st Record QR 2008 . ..... .. .... ..... . .... .. ......... . .. 28
Spot Frequencies ... .... ..... .. . ......... .......... ................ 28
1 Kc/s Reference Tones . .... .. . .................................... 28
100 C/S Tracking Test ................ . ..... . .. .. ..... . .. ...... . .... 28
Tone Arm Resonance ..... . ... .. .. ...... .... . ... . ... ... ..... .. ..... 29
Test of Tape Recorders etc. .... ... ......... . .... .. . .. . ........ . .. .. 30
Synchro-Start of a Continuous Recording ... ........ .. .. . ............ 33
Specifications . ............ .... . ...... . ..... . ............ ........... .. 34

1. DESCRIPTION
1. Description
Purpose of the Equipment.
Th e Response Test U nit Type 4409 is int ended for use with the B & K a ut o-
ma ti c fre qu en cy res pon se plotting e quipm e nt wh en investigating th e fre qu ency
r
espo nse of so un d re pr o du cing e quipm ent.
Fi
g. 1. 1 shows an example in whi ch the 44 09 a nd a test record are in vol ve d in
th e testing of a stereo ph onic record player.
Le vel recor de r
Fi g. 1.1. Meas uring se t-up for a ut om a ti c plo ttin g of th e frequen cy r espo nse
of a stereopilOnic reco
rd play er.
The 4409 fulfils thr ee differe nt fun ct io ns:
(a) cha
nn el sel ec ti on in th e case of stereo ph onic equipme nt either man ually,
wh en o nl y one cha nn el is inves ti gat ed , or a ut omatically at a recur ing fr e-
quen cy of 1. 2 cis for a ut omatic cross-ta lk or co mp arison meas ur eme nt s.
(b) e qnali zation, by differe nt RC filters, of th e recording cha r acter istic of the
test
reco rd.
(c) sync hr onization of th e pape r-driv e of th e Level Recorder Type 23 05 with
th e reference r ec ord ings (reco rd or tap e) und er re pr o du ct ion.
It is thu s possible to a ut omatically pl ot th e frequency response of the sound
re produ cing eq uipm ent. A typical expe rim e nt al result is shown in Fi g. 1.2.

1. DESCRI PT ION
Wh ere th e recorder is int egrated with th e re produc er, as in th e case of tap e
reco
rd er s, motion pictur e systems etc., refere nc e reco rdin gs are taken from
th e consta nt voltage output of a generator, but in the cas e of phonogr a ph
testing, accurate refere nc e disc r ec ordin gs are ne eded.
The Gliding Frequency Reco rdin gs Type QR 2007 a nd 2009 are especially
designed
for th e purpo se of fr e qu e nc y res pons e investiga tion . They provide
OOODOODaOODDOOOODOOO OOO OOODODOO aOOOQOO OOOOoooooooo
"':!!'.' ." ~ ............ ......,..... ..... . ..... 1(1 :IS
........ - -- ..
StereophoniC
piCk. up type «I Z
Ortof on SPII.G
No 1
Fil ter l in"
OR 2007 Mod1
~ ----
~~- -- .,
LUoo.r., __ _
,... lOdS
::..s,.,~ .
~f_s.. ... ,- O OIO
QP 1123 10
Fi g. 1.2. Typical ex perimental result obtained by means of ti le se t-up of Fig.
1.1.
(Test of a high qllality stereophonic head pr esenting a certain unbalance).
The total duration of one plot is 35 sec. between th e instant wh en the pick-up
is put d ow n on th e record QR 2007 and th e ins tant wh en th e set-up is r ea dy
to start a new plot.
co ntinuou s frequency sweeps fr om 20 cis to 20 kc l s, with late ral mod ul a ti on
on
the QR 2007 and left, rig ht , late ral , ve rtical modul ations on th e QR 2009.
The Pickup Test Reco rd Typ e QR 2008 i s, on th e ot her ha nd , designed for
meas ur eme nt s at fixed frequencies and for ton e a rm res on ance investigation s.
It is int e nd ed for pick-Up design work , and also for general purpo se chec ks in
com bin a ti on with the gliding fr e qu e ncy reco rds wh en c ur ve plotting e quipm e nt
is not ava ilable.
Description of the Tcst Records.
General.
The B & K referenc e recordings are delivered in box es containing five ide ntical
vinylite reco rds and one instruction manu al (Fig. 1.3).
Both sides of eac h record being id en tical, a total of ten sides are ava ilabl e,
a large enough qu a ntit y to g uar a nt ee a great numb er of pl ay ings without
4

1. DESCRIPTION
alteration of the characteristics. This number, however, is greatly dependent
on th e care exercised in th e use of the records. By conserving one side as a
reference, it is possible to
check on th e service lif e of each record in use.
Fig. 1.3. Gliding Frequency Recordings Type QR 2007.
The cutting process and th e dimensions are in accordance with the Recor.:-
me
ndation of th e Int erna tional Electrotechnical Commission ( lEC 98/98-1)
recogniz
ed by most countries.
The detailed specifications are given at the end of this manual.
The reproduction of th e label of the QR 2007 (Fig. 1.4) and the photograpb
of a section of th e record, illuminat ed by a grazing light beam (Fig. 1.5),
s
how th e exact composition of the recordings .
The QR 2008 a nd QR 2009 are desc rib ed in the same way by figures 1.6
through 1.9.
The original sinusoidal signal used for recording th e disc tracks was obtained
from a B & K B eat Frequency Oscillator with especially low distortion. For the
r ecor din g of th e gliding frequency bands the frequ e ncy of the signal was vari ed
according to a fun ction of time which was purely logarithmic within± 2.2 %
± 1.3 cis.
This tolerance is e qual to th e tolerance on the de termination of the recorded
frequency when using the Gliding Frequ e ncy Records at th e exact specified
rot a tion speed (45 rpm ) and assuming a logarithmic sweep.
5

1. DESCRIPTION
All rights res erv8a
Briiel & Kjan
Copenhage n Denmark
Monophonic
Gliding Frequency Record
20-20000 cIs
Type OR 2007
o
45 r.p.m. 6
Frequency Sweeps: logarithmic 20 cIs to 20 kc/s in 15 seco nds
Start Marking (20 cIs point): Cease of the 1 kc/s si gnal preceeding each ba nd
Recording Characteristic: lE e Standard No.3 without treble emphasis
(constant velocity above 1 kcfs) .
Recorded Velocity at 1 kc /s: 3.16 em!s r. m.s.
Bands 1 to 10: lateral cut
/63695
Fi g. 1.4. La bel of th e QR 2007.
10
QR 2007
Bands 1 to 10 : A B
20 cis 20 kc /s
8/9 octave per re v.
Fi g. 1. 5. Section of tile QR 2 00 7 sh ow ing tile succession of glidin g fre qu ency
ba
nd s pr eceded by a 1 kc/s sta rt a nd reference signal.

AU r igh ts reserved
Briiel & Kjmr
Copenhagen Denmark
Pick-up Test Record
Section 1
ve r~~i~~ 1~: e ,~~~~j~~ ~s~Oc ~ . ~~s~ i~2:i5 ~ ~~d k ul~t io n .
Sand 1: 45 ° l eft modulation (A). Sand 2: 45 ° right modulation (B).
Section 2 0 Section 3
Reference Tones, 1 kcls, 4 x 60 sec . ' Lateral Tracking Test,
Velocity level : 2.24 cm/ sec. rm s (45 0) 100 cIs (A+ B), 5 x 15 sec .
(3 . 16 cmls lateral or vertical) Sand 1: 0. 00 1 cm peak amplitude
::~~ ~ ~ :~~ ~ ff~t ( ~~) ::~~ ~~ g : ~ : " ..
Sand 3: l atera~ (A+B) Sand 4: 0.004 ..
Sand 4: vertical (A-B) SlInd 5: 0.005 ..
Sect ion 4
Vertical Tracking Test , as section 3 but wi th vertical (A- B) modulation.
Section 5
Logarithmic Frequency
Sweep s 10 cIs -100 cIs in 161 /J sec .
Start Marking (10 cIs point): cessation of the 1 kcls sig nal
R
ecorded lever~~~~~~~t ~~~ l i~~d~·0.OO 113 em peak.
Sand 1: 45° left (A) Sand 3: lateral (A+ B)
Sand 2: 45° right (B) Sand 4: vertical (A - B)
Sect ion 6
as se ction 1, but wit h sma ll groove spe ed
~.cord . ",.~\ (63696
tJd on ORTO FON e.o.U \~
Fig. 1. 6. Label 0/ th e QR 20 0 8.
5sot freguencies
2 -16-12.5-10 kc/s
(0 .6 cm/sec rms)
·1kc/s reference
tone
(3.16 cm/secl
(compliance) A+B
Tracking test 1
100 CIS bands of
increasing amp!. A ~ B
0. 001 to 0.005 cm
10-100 cIS SWl!ePS } A
constant amplitud B
(0.00113 cm peak) A+B
for tone arm A-8
reSonance
as first section } ~
QR 2008
2
3
4
5
6
(33h rpm)
+61~2
1. DESCRIPTION
Fig. 1.7. Section 0/ th e QR 2008 sh ow ing the succession 0/ bands.
7

1. DESCRIPTION
. ~::- ~
/ ~ ."
I Briiel &
Kjcer
Copenhagen Denmark
Stereophonic
Gliding Frequency Record
20-20000 cis
Type OR 2009
o
45 r.p.m. ,6.
Frequency Sweeps: Logarithmic 20 cIs to 20 k c/s in 50 secon ds
Start Marking (20 cIs p oi nt ): Cease of the 1 kc/s signal preceeding each band
Recording Characteristic: IEC Standard N o.3 without treble emphasis
(constant vel ocity above 1 kc/s)
Recorded Velocily.t 1 kc /s: 2.24 em!s r. rn .s. in 45 ° modulation
(3.16
em /s in lateral and vertica l m odulat ions)
Bands 1 and 5: 45 ° left m odulatio n (A)
Bands 2 and 6: 45 ° right modulation (9 )
Bands 3 and 7: lateral modulation (A+ B)
Bands 4 and 8: vertica l modulation (A - B)
Fig. 1. B. Label of th e QR 2009.
A
-V-
S
~
AtS
~
A
S
A+S
A-S
Fig. 1.9. Section of the QR 2009 showing the succession of gliding frequen cy
bands preceded by a 1 kc/s start and reference signal.
8

1. DESCRIPTION
Recording Characteristics.
Pick-ups should be tested with reference to the internationally recognized
characteristics if th ey are int en ded to give co nstant output as a function of
frequ ency. Gliding frequency records s hould in general be cut according to
the recording character istics shown in Fig. 1.10-bottom . In the case of the
B & K Gliding Frequency Records , a charact e ristic as shown on top of Fig. 1.10,
which is converted by an e qualizing filter in th e measuring chain to th e
appropriate characteristics has been adopted. The reaso n for the high fre-
quency level limitation on the record is that if tru e reproduction is intended,
th e radius of curvature of the modulated groove wall must re main apprec ia bly
larger than th e stylus tip radius .
The wave-length be ing de termined by the chosen groove speed, and th e stylus
tip radius being norm alized to 15- 18 fl for stereophonic pick-ups , this sets a
db
IIII I I I I II
HttIT 11 11 1
:: 0
"g
~ / Recording Characteristic
0
".....
Gliding Frequency Records ClR 2007 & ClR 2009
II IIII I I I I II IIII I
r
: -20
20
f.- 50
100 200 500 1000 2000 10000 20000
20
r--
Type 1,409 Equilizing Filters Characteristics /
db IN
Filter Switch pas: I.E .C. Curve 2, "
10
.. " ":I.E.C . Curve 3
II I I r>-
Filter StitCh pas.: Lin.
.1:-::=':'
-
0 II
III I I
~ ~ _~ 50 100 200 500
1000 2000 10000 20000
+::: :: :1 :1:111 :1 :: =::1 : :::::=:: : ::=::
TotaL Characteristics I
-
(TfiS , f~12001/19+4t09I H++t +-+-f- H+Ht w ,,"-llri
+10 f- H--f-jf++ ++- + +- +-+++++++--++-++ w!+.l1If-H
Fi lter Switch pas. : lin .
~ O f---- H+H+++-++-~ I ~\++~~~~--++~~_+H
~
.
~ _10f---- H + H+ tl-+9-V -t-+ -tFilter . SwitchP05 .: I.E.G. curve~ J
/' I .. II "I I " : 1.~ . Ci ~ u ll e l ~
-20 t==T-+-t-ttttl I--t--t--++-t-t+lttt-III I -++-+-++ I H+ 11 1tt--H II
III I I IIII I
20 50 100 200 500 1000 2000 10000 20000
{.6 Z32~
Fig. 1.10. Recording characteristics available when using the Gliding Frequency
Recordings
in connection with the Response Test Unit Type 4409. The curve
no. 3 is specified by the International Electrotechnical Commission in its
publication
no. 98-1 for steI'Cophonic recordings.
9

1. DESCRIPTION
maximum limit to th e am plitud e of modulation at high frequencies. The
co ndition s obtained on th e B & K Gliding Frequency Records, wher e th e
re
corded velocity is limit ed at 20 kc/s to 3.5 cm /s pe ak in eac h channel, are
illustr at ed in Fig. 1.11.
Bond 1
Bond 8
Pig. 1.11. Views in th e plane 0/ modulation showing the relative dimensions
0/ th e maximum allowed tip radius and the minimum radius of curvature
(! on the record QR 2009's outer and inner bands presenting a diamet er of
28.2 and 12.6 cm respec tiv e ly at 20 kc/s. Note that e is proportional to the
square 0/ the diameter D (or 01 the groove speed). The speed of rotation being
45 r.p.m., i.e. 0.75 r.p.s., the expression for e is
_ n(0.75 D)2 _ 88 ~
e-2 I v - o. f v
where / is the frequency and v the peak channel velocity (3.5 em Is).
Th e advantage of th e standardized recording characteristic is to give the
optimum signal-to-noise ratio by incr e asing the reco rd ed a mplitude at low fre-
qu encies, where th e rumbl es a nd vibrations of th e turntabl e are important ,
a
nd th e reco rd ed velocity at hi gh fr e qu encies wh e re th e surface noise increases
r api dly. Using any other charact e ristic will result in a decr ease of the overall
sig nal-to-noi se ratio after correction of the characteristic by an equalizing
filter. In th e case of th e B & K Gliding Frequ e ncy Records th e signal-to-noise
ratio is d ec r ease d by about 6 dB aft er e qualization , but this does not affect the
measuring possibilities.
In addition, the correction of th e reco rding characteristics can eas ily be made
by m ea ns of a simple RC filt er. Using diff e rent filters enables th e selection of
different characteristics. This is of interest since there are diff ere nc es between
the various national standards. Using a suitable filter, a constant recorded
ve locity reference can also be obtained for testing electrodynamic pick-ups
without th e ir associate eq ualize rs . Thre e different characteristics are thus
10

1. DESCRIPTION
provided by the B & K me asuring equipment. See Fig . 1.10. The determination
of the correcting filt ers re sults immediat e ly from the mathematical definition
of the standard c har ac te risti cs:
1 1
10 log (1 +w2 t12) -10 log (1 + - ~ - 2 - ) + 10 log (1 +- 2- 2- )
w
-t 2 w t3
wh e re w is th e an g ular fr e quency and
t1 = 50 fls (c urv e 2) or 75 fls (curve 3), t2 = 318 fls, t3 = 3180 fis.
Th e reco rding characteristics of the B & K tcst r ec ords co rr es ponds to
t1 = 0, t2 = 318 fls, t3 = 3180 fis.
As seen on th e figur es, eac h glidinG fr e qu en cy ba nd is pr ece ded by a 1 kc/s
start and refer ence signal lasting a few se conds. The starting point of the
logarithmic sweep coincides with th e en d of th e 1 kc/s modulation. Th e
purpo se of this 1 kc /s signal is, in addition to th e de termination of th e fr e-
qu encies in th e results as de scribed be low (sync hr oniza tion of te st signal and
reco rding paper ) to allow a quick a dju s tm e nt of th e m eas uring chain sen-
sitivity to be mad e be for e actual m eas ur eme nts are taken. On all reco rds the
1 kc /s start signal is modul ated lat e rall y (A +B) or ve rtically (A - B) wh en
pr ece ding a vertical (A- B) band .
Recorded Level Tolerances.
The ac curac y in a mplitude of th e reference recordings is determin ed to within
0.5 dB in a limited fr e qu e ncy ran ge by th e optical me thod of th e " Filtered
B-line lig ht patt e rn " refe rr ed to in th e American Standards. Over th e whol e
frequ e ncy rang e, th e accuracy is checked by m ea ns of a professional ele ctro-
dynamic pick - up espec ially selected for this purpose. The check is carried out
at two diff ere nt rotation s pe eds in ord er to distinguish th e non-linearities of
th e pick-up from thos e of th e record its e lf: a change in rotation speed
accompanied by a corresponding change of th e tim e constant of th e e qualizing
filter , produc es a fr e qu e ncy tr a nslation of th e record defects, while th e fre-
qu e ncy res pons e of th e pick-up is unchang ed. The inv estiga tion is ca rri ed out
both on th e nick el "m aste r" and on th e vinylite reco rds.
Th e flatn ess in fr e qu e nc y char ac teris ti c obtained in serial production is be tt er
than ± 0.5 dB from 100 cis to 10 kc /s and ± 1 dB from 20 cis to 16 kc / s.
Be tw een 16 kc ls and 20 kc /s a dip in the fr e quen cy res ponse which is du e to a
s
purious resonan ce in th e di sc recorder mi g ht be pr ese nt and th e tole rances
are th ere for e e nlar ged as shown on Fig . 1.12.
Anoth er important characteristic of th e stereophonic test records is th e upper
limit of th e r ec orded cross-talk on th e unmodulated groove walls of bands
A and B. This co rresponds to th e separation of th e disc re cord er since it is
practically unaffect ed by disc copying op e rations . Th e determination of th e
s
purious cross-talk in th e pick-up employed for checking th e record ed cross-
11

1. DESCRIPTION
talk can also be mad e by comparison between two tests of different rotation
speeds, giving a frequency translation of the characteristic for th e record
only . The re cord ed cross-talk, express ed in dB with refe rence to the modulation
level, is th e se par ation between c hann el of th e re cording . The minimum
se paration of th e QR 2009 is shown on Fig. 1.13.
Th e toleranc es of th e Te st Re cordings Typ e QR 2008 ar e given on p. 5.
+4
db
o
-1
-4
UR 2009
·
OR 2007
-Logarithmic sweep
accurac~ :
. . ~
~
~
20
100
OR 200~ ~
OR 2007 -=:
-
E ±2 .5% ±1c/s
~ -
-
..
-
1000
- -
10 000 20000
""62332
Fig. 1.12. Curves showing tIze manufacturing tolerances Wllicil include both
th e record itself and tlIe equalizing filter characteristics. Th e accuracy is best
for lateral
modu lation and tlIe tolerances are th ere/ore narrow er for th e
o
db
-10
-20
-30
-40
EE
» .
20
R ec ord QR 2007.
A= modulated groove wall
A=
8 =unmoduloted wall
(upper limit of the:
reco rds crosstalk,
measured in 1/3 octave
_ filhrs)
a ~ ~
-
..
1 00 1 000
8
-
-
- -
10 000 20000
~~2333
Fig. 1.13. Limit of cross-talk on tIle stere ophonic recordings of Type QR 2009,
bands 1- 2 and 5- 6, measured in dB witlI respect to 'tlIe recording level
(i.e.:
maximum mea surable clIannel separation).
N.B. Valid
only wIz en tlIe playing angle does not deviate muclI from tlIe
cutting angle (100 ± 5°).
12

1. DESCRIPTION
Response Test Unit Type 4409.
The Unit Type 4409 groups, in the same cabinet, thr ee independent sections
which are connected as shown in Fig. 1.15. The left hand knob (Fig. 1.14)
relates to the channel selector and the right hand one to the filter section. The
synchro-starter is fully automatic .
The unit is transistorized and the pow er supply is tak en from the 24 Volt DC
circuit of the Level Re cord er Type 2305 via the multi-pin plug.
Fig. 1.14. Response Test Unit Type 4409.
4409
#62335
Fig. 1.15. Block diagram of the 4409. (The synchro-starter is only connected
to
the filter-input terminal when a DC power supply of 24 V is applied between
pins 1 and 4
of the multipin plug).
13

1. DESCRIPTION
Clwnnel-selector.
The two-channel-selector consists of a low noise relay driven by the output
of a bi-stable multivibrator. The ' multivibrator may be blocked in one of the
other positions by setting the CHANNEL SELECTOR switch in "left" or
" right " positions. In the "left-right" position, an automatic switching is
obtained at a recuring frequency of 1.2 ci s. In other words , each channel is
connected during a pe riod of 0.4 seconds. Transients and switching times are
shorter than 0.02 seconds.
Equalizing Filter Section.
Fig. 1.10 shows th e three different equalization characteristics provided by this
section.
They are selected by mea ns of the FILTER SWITCH which also ha s
a fourth position marked "D irect " wh ere the filter section is short-circuited as
needed wh en testing sound reproducers other than record players (e.g. tap e
reco
rd ers).
The filters are of the RC type a nd are designed to be us ed as external filters
on th e B & l{ ampl ifiers such as the Microphone Amplifier Type 2603. The
standard characteristics are obtained only if th e test r ecor ds are rotat ed at th e
specified speed.
Synchro-startcr Section.
General Description.
The purpos e of this section is to command the paper drive st art of the Level
Recorder Type 2305 at th e e nd of the 1 kc ls start signals reco rded on the test
records,
thus automatically e nsuring synchronism between the instantaneous
test frequ e ncy on th e reco rd and the fr e quency calibration of the recording
paper.
Level Record er
Gear
PoPe!' drive
r-il~;W~~~r-~g
C)
f---i
~ tLl
Automatic 113 octave
filter switch
4-623&3
Fig. 1.16. Block diagram of the equipment for automatic frequency re-sponse
I and separation measurements.
14

1. DESCRIPTION
An important point for th e practical f eas ibility of this synchronization is that
the time delay of the pap er drive start should be negligible. The clutch of the
Level Recorder Type 2305, as schematically outlined in Fig. 1.16, is engaged
when no current passes through it and disengaged wh en exc ited. It is a non-
slip device and, since the coupling of the paper driv e system to the continu-
ously rotating synchronous motor introduces a negligible variation of kinetic
ene rgy in the system, the start of the paper drive occurs practically instantane-
ously when the current is cut. The command is thus mad e from the signal
recorded on th e test disc , by simply actuating a relay device cutting the clutch
circuit at the e nd of the start signal. This is perform ed by the synchro-
starter whose block diagram is sketched in Fig. 1.17.
Type 2305 Type
H09
Filter input
Fig. 1.17. Block diagram of the automatic start/stop arrangement (Synchro-
starter of 4409 + clutch circuit of the 2305).
The scanning speeds of both th e disc turn-table and the Level Recorder paper
drive are tied by the mains frequency and no mechanical connection is
needed.
This allows the turn-tabl e to be installed freely on an anti vibration
support which is an important point for pr ecise measurement.
The starting signal is applied to the "F ilter Input" terminal of the 4409, and
should have the following characteristics for operating the starter:
Frequency:
Voltage:
Duration:
1000 cIs ± 100 cIs.
from 0.1 to 32 V r.m.s. (at 1 kc/s).
at least 0.1 second.
Not e: By means of a relay connected in parallel with the clutch of the Level
Recorder, the syncho-starter is only connected to "Filter Input" when the
connection to the recorder is made and when the paper drive is stopped.
15

1. DESCRIPTION
Detailed Functioning of the Relay Arrangement.
The synchronous motor of the 2305 is running continuously and, as can be
seen
from Fig. 1.16 the start of the paper-drive is obtained by disconnecting
the 24 V supply across the clutch coil. Since the relay 01 is connected in
parallel with the clutch coil, the synchro-starter is only connected to "Filter
Input" when the paper drive is stopped. The relay circuits for 01, 02 and 03
are all sketched in Fig. 1.17. The relays are shown in their released position.
Before
connecting the 4409 the Level Recorder should be started by setting
the controls as shown on Fig. 2' .1 and 2.2. When connecting the 4409 to the
2305, the relay 03 then short-circuits the single chart push button which
otherwise should have been lifted up to obtain the automatic stop. The
paper-drive stops as soon as the automatic stop switch is closed by the cam
and the 24 V supply is applied to the crutch.
When the 1000 cis start signal arrives through the Filter Input, the relay 02
is energized which in turn causes 03 to be energized whilst "Single chart"
is stilI short circuited, but now by 02.
When the 1000 cis start signal ceases, 02 is released, but 03 is still energized
since its coil has a much larger resistance than the clutch coil which is fed
in series
with it from the 24 V supply.
The short-circuit across "Single chart" is therefore interupted and the clutch
is released, starting the paper drive.
03 is finally released by the cam releasing the automatic stop switch.
16

Operation
Practical Hints for Usc of th e Test Records.
General Instructions.
2. OPERATION
The test r ecords should be handl ed with th e same care as commercial high
fidelity LP records . The numb er of playings which can be mad e without
alteration of th e characteristics is greatly dependent on th e care exercis ed in
the use of the records. By conserving one r ecord side as a reference, it will
be
possible to check on the service life of eac h record in use.
H is of course of prim e importance to ch eck th e reproducing stylus tip and th e
tracking weight befor e eac h reco rd play in g. The tip radius should be between
12 and 18 ft (0.0005 and 0.0007 inch .) or 26 It (0.001 inch .) in the case of
lateral bands, with an included angle of 40° to 50 °.
The records are cut in acco rdance with the Recommendations of the IEC
which are recognized by mo st coun tries. All modulations are sinusoidal with
negligible distortion.
Finally, th e r ecor ds should be carefully protected from dust. Th e use of
"antistatic" cleaners is reco mmend ed.
Turn-table.
When re producing heads are to be tested separately, a good professional turn-
table should be selected, especially with r egar ds to investigations at low
frequenci es, wher e the influence of wow and rumble is predominant. The
rotating speed must be adjusted with great care by stroboscopic comparison
with the mains frequency. Finally, it is recommend ed to isolate the turn-table
and possibly also th e preamplifier from external vibrations. This may be done
very efficiently by suspending the tabl e supporting the two devices from the
ceiling by means of four rubber tub es. (Ano th er possibility is the use of
el ectrical high - pass filters).
Use 01 rotating speeds otller tllan nominals.
Since the test frequ e ncy and velocity levels are proportional to th e rotating
speed, it is possible to extend the frequency range of the tests by using different
rotating speeds. How ever, it is then necessary to modify th e RC equalizing
filters e
mploy ed according ly, by mea ns of a proportional change of the
capacitors.
Automatic Frequency Rcsponse Plotting.
In the following, an example of operating procedure for au t omatic frequency
respons e plotting by means of the B & K In s trum en ts Type 2603, 4409 and
2305 is given.
17

2. OPERATION
It is esse ntial, however , that th e instruction manual of eac h instrument be
r ea d carefully before using th e equipment.
1) Pl ace th e reco rd player on a vibration free tabl e. Connect and set the
apparatus as shown in Fig. 2.1. Select th e des ired reco rding characteristic*)
Pick- up
under t est
Cont.
Record .
o 0
100
10
fig. 2.1. Set-up for automatic frequency response plotting with a QR 200,
reco rd. When using a QR 2008 or 2009 the adjustments are the same witll
aception of the settings of th e Level Recorder, which then should be a.
mown on Fig. 2.2. A single lead is reco mm e nded between Amplifier ana
Hecorder since
the ground connection is already made by th e synchro-starte,
conn ection.
by means of the 4409's FILTER SWITCH. Th e pap er drive controls of the
2305 are set to " on", "start", " forward ".
2) Pre liminary Adjustments. It is convenient, in order to ensure that the correct
automatic stop position is a ttain ed, to pl ay a record band before actual
m eas ur e ments are taken. In addition it wil! be possible , during this pr e paratory
playing, to adjust the sensitivity of the measuring instruments. Proceed as
follows:
a)
Place the pick - up on a l ead- in groove for playing th e selected band.
b) If the automatic synchro-starter does not operate after a few seconds
playing, check that th e speed of rotation is 45 r.p.m. and switch METER
RANGE on the 2603 to 10 mY. Also check that the pick-up und er test
is in normal condition .
*) Th e recording c hara c tcristic should be selected in order to o bt ain a constant reference
level..
With amplitude sensitive pick-ups such as piezoelectric devices or other types
with built in equalizers, th e positions "lEC Curve 2 or Curve 3" should be used. (The
lEC specifics Curve 3 for stereophonic recordings). With velocity sensitive pick-ups such
as e lectr odynamic devices, the position "Lin." which gives constant recorded velocity
conditions should be used.
18

2. OPERATION
c) Whil e playing the frequ e ncy sweep, set METER RANGE to the position
giving normal point er deflection on th e meter throughout the frequency
sweep. Then give th e Level Reco rd er writing stylus a convenient de-
flection by means of the INPUT ATTENUATOR a nd INPUT POTENTIO-
METER knobs.
d)
Finally, when the paper driv e is s topp ed, shift the paper by means of
the Finger Whe el Z (see the 2305 Manual) until th e writing stylus rests
on the 20 cis line. Approach the re quired position in the reverse'
direction.
3) Before starting th e a utomatic fr eq u ency response plot, check that the
rotation speed of th e r ecord player is exac tly 45 r.p.m. when load ed by th e
pick-up to be tested, e.g. when tracking a groove.
4) Engage th e pick-up on the lead-in groove of th e band which has been
selected
for the test. During th e first few seco nds (playing of the start signal)
it will be possible to fine adjust th e 1 kc/s deflection if necessary. The plotting
of th e fr e qu ency respons e tak es place automatically when the 1 kc /s s tart
signal ceases, and wh en the paper drive stops on th e 20 c/s line of the next
chart , th e set-up is ready for another plotting without any further a djustment.
Note: Use of 25 or 10 dB Potentiometer for detail ed fr e qu e ncy respons e in-
vestigations. The only modification to be mad e in this case is that the
POTENTIOMETER RANGE knob of the Level Recorder has to be shifted from
"50" to "25" or "10" respectively.
Play-back Losses.
At high frequencies, the accele ration which is communicated to th e re producing
stylUS attains a few hundr ed g (gravity). Consequently, even if the stylus mass
has been reduced to a minimum, th e reaction of the stylus on the record may
cause non-n egligible elastic deformations of the groove walls. This phenomenon
which, in most cases corresponds to a reduction of amplitude and velocity of
the stylus movement, is commonly called "Play back loss".
The play back losses are gre atly depe nd e nt on the construction of the re pro-
ducing pick-up. They ma y be negativ e as well as positive and cannot be
determined without accurate knowledg e of th e m ec hanical constants involved.
A theor etical investigation of th e phenomenon*) shows that play back losses
(or gains) increase
rapidly with fr eq u ency in all cases. Practically, play back
losses attaining a few dB at 20 kc /s are observed when tracing the inner bands
of the Gliding Frequency Records with commercial pick-ups of good quality.
Automatic Selective Cross-talk Measurements.
General.
Gliding frequency cross-talk meas urem e nts are carried out by means of the
record QR 2009 and the set-up of Fig. 2.2.
When testing good quality pick-Ups, it will be noticed that the inherent surface
*) See B & ]{ Technical Review No 3- 1962 , Appendix A.
19