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RESEARCH DEPARTMENT 



The Neumann Microphone Type U 47 



Report No. H.020 
Serial Mo. 195*/ 23 



THE BRITISH BROADCASTING CORPORATION 
ENGINEERING DIVISION 



RESEARCH DEPARTMENT 

THE NEUMANN MICROPHONE TYPE U U7 

Report No. M.OZO 
Serial No. 1954/2 3 



HoD. Harwood, B. Sc, 

RoJo Packer (W. Proctor Wi 1 son) 



Report No. M.080 



THE NEUMANN MICROPHONE TYPE U 47 



Section Title Page 

SDMMABY 1 

1 INTRODUCTION . 1 

2 DESCRIPTION OF MICROPHONE 1 

2. 1. General ,. 1 

2.2. Weight . 4 

3 PERPORMANCl ... 4 

3.1. Methods of Measurements. .... 4 

3.2. Frequency Characteristics 4 

3.3. Sensitivity 4 

3.4. Noise 4 

3.4.1. General 4 

3.4.2. Interference from Magnetic Fields 5 

4 LISTENING TESTS • B 

5 CONCLUSIONS • 5 

APPENDIX . ............. i: 



OONPIDMTIAL 



Report No. M.020 
June 1954 

Serial No. 1954/23 



THE NEUMANN MICEOPHONE TYPE U 47 



SUMMARY 

A new directional electrostatic microphone, tjfpe U.47, produced by the firm 
of Neumann in Berlin, incorporates the capsule originally designed for the type M 49 
microphone but uses a cheaper form of head amplifier. The U 47 microphone is designed 
to give either cardioid or omnidirectional polar response. Frequency characteristics, 
sensitivity aad noise have been measured on a sitigle specimen for both conditions. 

The response of the microphone capsule in the cardioid condition is very 
good, but' the overall performance is spoilt by the obstacle effect of the large head 
amplifier. The signal-to-noise ratio is unusually high. 

In the omnidirectional condition the microphone is of no special interest. 



1. INTRODUCTION. 

The U 47 is a recent addition to the series of directional : electrostatic 
microphones manufactured by Messrs. Neumann in Berlin and has lately been described in 
the technical press*. Omnidirectional or cardioid polar characteristics can be 
selected by a switch mo\inted on the head amplifier. The microphone is stated by the 
manufacturers to be a less costly version of the M 49, using the same capsule with a 
different amplifier sind mains unit. The quality of reproduction compares very 
favourably with that obtained with other electrostatic microphones. A specimen has 
been in use for several months and performance tests on this instrument were under- 
taken at the request of S.S.E., H. S.B. 

The price of the microphone complete with cables and mains unit is £100. 



2. DBSCEIPTION OP MICROPHONE. 

2.1. General. 

Fig. 1 shows the appearance and dimensions of theinstr^ument, together with 
the location of the main components in the head amplifier. The microphone casing is 
plated; the central portion surrounding the amplifier has a matt finish, the remain— 

Bauch, "New high-grade eondenser microphones". Tireless Torld, No. 69, Uarcb 1853, pp. 111-14. 



50 mesh with 
to mesh covering 






Fig. I. Neumann condenser microphone type U.47 



II5.V. 



Switch open for cardiod 
characteristic, closed for 
omnidirectional characteristic. 





t-T 



400 400 Ik Ik Ik 

I — t-^W^T-C2^2>T-^AA^-^AAA^-t-^AA^ 



40 



^ 



40 



40 



c^' 



t— " 



(b). Power supply unit. 









^ — Power and 
signol socket 



Output 






socket 



Fi c. 2. Ci rcu i t di egram. 



der being polished. The circuit diagram, Pig. 2, shows two unusual features. The 
valve used has a high-voltage heater, the current for which is taken. from the H.T. 
supply through a voltage dropping resistance. The heater current, amotmting to some 
40 mA, returns, to earth through a 89 ohm resistor included in the. cathode circuit and 
thus provides the necessary, biasj no by— pass condenser. is necessary since the cathode 
resistance is too small to produce appreciable feedback or noise. 

The. microphone capsule is attached to the top of the amplifier by a rubber 
stalk which provides a certain degree of insulation against vibration. Mechanical 
protection and electrical screening are afforded by an. outer case of 50 mesh wire 
gauze sandwiched between two layers of 10 mesh gauze. By modern standards the head 
amplifier is unnecessarily large. Even though no miniature components are used the 
size could easily have been reduced. 



X 4 in. 



The microphone is connected by a 6 pin plug and cable to a mains unit, .4 in. 
X 84 in. (102 mm x 102 mm x 216 mm) long. The audio-frequency output is 



taken from the mains unit through a 3 pin plug; the nominal output impedance is 
200 ohms. 

2, 2. Weight. 

The weight of the microphone is 1° 5 Ih (0°68 Kg), and of the mains unit, 
6° 2 lb (2° 8 Kg). 



3. PERFORM ANCl. 

3, 1« Methods of Measiirement. 

The frequency characteristics were measured by comparison with a pressure 
standard in a dead room except in the oardioid condition at frequencies below 200. c/s, 
for viioh the measurements were made in a plane-wawe duct. The accuracy of comparison 
with the standard was in general ± § db, except for catrdioid operation at angles of 
incidence greater than ± 90 , in which case errors up to ± 1 db would be possible. 
The chareicteristics of the standard are known to within ±4 db. 

3.2, Frequency Characteristics, 

Figs, 3, 4 and 5 show the open— circuit frequency characteristics of the 
microphone in the omnidirectional condition for sound incident at various angles in 
the horizontal and vertical planes. Figs, 6, 7 and 8 show corresponding plane-wave 
characteristics for the microphone in the cardioid condition. In Figs, 4 and 7 the 
irregular nature of the curves at frequencies above -2 kc/s for sound incident at 90 
is due to interference between the direct wave and the wave reflected from the head 
amplifier. 

Throughout the audio— frequency band the impedance of the microphone is so 
close to the nominal -SX) ohms that the on— load frequency characteristics do not differ 
significantly from those shown. 

Figs. 9(a) and 9(b) show the manufacturers' curves for the omnidirectional 
and cardioid conditions respectively, 

3. 3, Sensitivity, 

In the mid-bamd region the open-circuit sensitivity of the microphone is 
- 57 db relative to 1 volt/ dyne/ onl^ for the omnidirectional and - 51 db for the cardioid 
condition; these values agree closely with those given by the makers. If an ideal 
transformer were used to raise the output impedance to 300 ohjnsj the sensitivity 
measured at the output terminals would be - 55 db and - 49 db relative to 1 volt/dyne/ 
crt^ respectively. The corresponding figure for the type AXBT microphone is — 71 db. 

3.4, Noise, 

3.4.1. General; In the absence of interference the noise output of the 
microphone is a combination of flicker effect in the valve and thermal agitation in 
the resistive component of the grid circuit impedance. In the present case both 



sources have a similar spectrum, the noise having roughly constant power per octave 
throughout the audio-frequency band. 

Per the omnidirectional and cardioid conditions the open-circuit noise 
levels, vhen weighted by an aural sensitivity network ASN/3, are respectively - 110 db 
and - 108 db relative to 1 volt. The mid-band sound pressures required to give the 
same output levels are + 20 db and + 16 db relative to 0-0002 dyne/crt^. ffor compari- 
son, the corresponding sound pressure for the AXBT microphone is + 18 db. For the 
U 47 microphone the makers claim an equivalent noise figure of less than 18."phons"; 
it is not stated whether this figure refers to the omnidirectional or -cardioid 
condition and no indication is given of the type of weighting used. 

3.4.2. Interference from Magnetic Fields: The open-circuit pick-up in the 
microphone generated by a uniform magnetic field was measured at 50 c/s, l.kc/s and 
10 kc/s. The table shows the pick-up for the orientation which gives the maximum 
output at each frequency, together with the sound level in the mid-band, region 
necessary to give an equivalent output. For compatrison, corresponding figures for a 
typical AXBT microphone are also included. 



4. LISTENING TESTS. 

Speech tests were carried out using male voices in acoustically dead 
surroundings. In the omnidirectional condition the accentuation of high frequencies 
caused by the rise in response in the region of 8 kc/s to 10 kc/s was clearly audible 
and the effect was possibly increased by the fall in response for frequencies between 
4 kc/s and 6 kc/s. In the cardioid condition a slight bass loss was noticeable but 
the peak at 10 kc/s was not prominent. The signal-to— noise ratio was extremely good. 

Further listening tests, using orchestral music, were carried out by S.S.E. , 
H.S.B. 's Department; the results of these tests are given in the Appendix. 



5. CONCLUSIONS. 

The signal-to-noise ratio of the microphone is very good, especially in the 
cardioid condition. The falling off in the low-frequency response in this condition 
is noticeable on speech from a non-reverberant room although it seems, from the 
comments of S.S.E. , H.S.B. 's Department, that the bass response in reverberant 
surroundings is adequate; in viewof the poor directional properties in this frequency 
band it is not certain that equalisation would bring about an improvement in quadity. 
The polar characteristics are good in the mid-bajid region but deteriorate at high 
frequencies, particularly for angles in the vertical plane, and the response at 
frequencies between 9 kc/s and 12 kc/s could with advanteige be reduced. 

In the omnidirectional condition the frequency response is good apart from a 
shajrp rise in the 8 kc/s to 10 kc/s region. 

The interference caused by extrsaieous magnetic fields is extremely low and 
should not give rise to any trouble. 



In the cardioid condition the microphone capsule is one of the hest of its 
type tested. It is therefore regrettable that the response has been degraded by the 
use of such a bulky head amplifier. In the omnidirectional condition the microphone 
does not appear to have any specially commendable properties. 



TABLE 1 



TABLE 2 



OPEN-CIRCOIT VOLTAGE AT 300 OHM OUTPUT 
FRSaUlNCT DUE TO MAGNETIC PICK-UP IN A fflELD OP 

ONE MILLIGAUSS 



SOUND LEVEL IN MID-BAND REGION 

TO GIVE OPEN-CIRCUIT OUTPUT SHOWN 

IN TABLE 1 







Zero = 


= 1 volt 






(a) 




(b) 


(c) 




U 47 
omnidirectii 


onal* 


U 47 
cardioid* 


AXBT" 


c/s 


db 




db 


db. 


BO 


•=126 




-126 


-133 


1,000 


-124 




-124 


-121 


10,000 


-110 




-110 


-107 



ero = 2 X 10 ■ 


* dyne/ciil^ 


(a) 


(b) (c) 


U 47 

' J.£ T* _. 


„"5.;. "BTt 



omnidirectional* cardioid* 



db 

+3 

+5 

+ 19 



db 

-3 

-1 
+ 13 



db 

+ 12 
+ 24 
+38 



At terniinals of ideal 200' I 300 ohm transformer 
jPigures given represent a typical microphone* 




-48 



-50 



-52 



-54 



-58 



-60 



-62 



-64 



■66 



J-SB 



Fig. 3. Frequency characteristics in horizontal plane. Omnidirectional conditioif * 




Fig. If. Frequency characteristics in vertical plane above axis. 

Omnidirectional condition. 









... 

St 


1 — ] 

■lal Mo 


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IV 




































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0' 




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^ 


/ 


f 


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-y 


















r 


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45' 
































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S 5 



Fig. 5. 



o o oo 
o o oo 

^ CO o>o 



i/f >o jO 



o o o o 
o o o o 
o oo o 

"of o 



-48 
•50 
■52 

■54 
-56 

■58 
-60 
-62 

-64 

-66 



Frequency in cycles per second. 

Frequency characteristics in vertical plane below axis. 
Omnidirectional condition. 




Fig. 6. Frequency characteristics in horizontal plane, Cardioid condition 




4-6 % 



48 o 



o o o o o o 
O o o o o o 

I/* *o !*• OB ^ O 



O O o o oo 
o o o o o o 

o o o o '^ o 



rrzquency in cycles per second. 



Fig. 7. Frequency characteristics in vertical plane above axis. Cardioid condition. 







T T 

Serial H>.il97 
















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_,^^ 


,. . 




-" 


-45' 


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/- 


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-135 l-90' 

1 A . , 



-46 
-48 

-50 
-52 

-54 

-56 

■58 

--60 

--62 

-64 

--66 

-68 



Fig. 8. Freauency characteristics In vertical piane oelow axis. Cardioid conditi 



S?a -5 




•54 g- 

-56 5 

-58 $, 

-fio £ 

-61 B 

-64 g 

1. 

-66 t 



-SB S 

"i 



-48 



Fig. 9(a). frequency cnaracteri sties in horizontal piane plotted from mal«er's 

data. Omnidirectional condition. 































^^^ 


^'^S..^ 




^ 






















0* 







K 




\ 




















































■ 






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180° 




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I35» 








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i'L.. 



o 00000 
o 00000 
m ^ ^- 80 o»o 



o 000000 
o 000000 
o o o o o o o 



-iO 
52 
S4 
56 
58 
60 
62 
64 
66 
68 
70 

-72 



Frequency in cycles per second. 

Fig. 9(b). Frequency characteristics in horizontal plane plotted from matter's 

data. Cardioid condition. 



10 



APPENDIX 

The following comments are taken from a memorandum, dated 9th September, 
1953, from Mr. Qundi^ to S.S.B. , H.S.B., desorihing a test, carried out with orchestral 
music, in which the U 47 was compared with other types of microphone. The instrument 
referred to as "the Philips condenser microphone" is the Philips type EL 3921/00, 

" In the omnidirectional condition this [the U 47 microphone]" was 

compared with the Philips condenser microphone. It was definitely preferred to the 
Philips, having negligible colouration at very high frequencies and being otherwise at 
least as good. Further comparison with the P6D ribbon microphone showed that in 
general the tonal quality of these two was almost identical, though the extreme bass 
seemed slightly better defined on the U 47, The U 47 was then switched to cardioid 
polar diagram. Again, tonally it differed little from the PGD, but the. slight 
superiority in bass definition persisted. These tests confirmed the impression 
gained when using the U 47 that it gives the best tonal quality of any condenser 
microphone we have yet tested, and is markedly preferable to that obtained from the 
three M 49 specimens in our possession. Moreover, it has sufficient bass output 
without equalisation. Ho tests have been carried out on its front— to— back ratio as a 
cardioid at low frequencies, where the M 49 is unsatisfactory. 

In all the above tests the condenser microphones were used without correc- 
tion; the PGD had approximately 3° 5 db top lift at 10,000 c/s. All microphones were 
side by side, regardless of polar diagram and at about the normal working distance for 
a ribbon microphone 

The U 47 microphone is an excellent microphone of simple construc- 
tion, the mains unit containing no valves, though the valve in the head-amplifier is a 
special Telefiinken type. However, it is considerably larger than the Philips, and 
Telefunken omnidirectional microphones, and therefore not suitable for certain 
purposes, such as the Royal Festival Hall "