365:) but need not do so. They are often termed "hot" and "cold," and the AES14-1992(r2004) Standard suggest that the pin that carries the positive signal that results from a positive air pressure on a transducer will be deemed 'hot'. Pin 2 has been designated as the 'hot' pin, and that designation serves useful for keeping a consistent polarity in the rest of the system. Since these conductors travel the same path from source to destination, the assumption is that any interference is induced upon both conductors equally. The appliance receiving the signals compares the difference between the two signals (often with disregard to electrical ground) allowing the appliance to ignore any induced electrical noise. Any induced noise would be present in equal amounts and in identical polarity on each of the balanced signal conductors, so the two signals’ difference from each other would be unchanged. The successful rejection of induced noise from the desired signal depends in part on the balanced signal conductors receiving the same amount and type of interference. This typically leads to twisted, braided, or co-jacketed cables for use in balanced signal transmission.
272:
pair. This proved insufficient, however, with the growth of electric power transmission which tended to use the same routes. A telephone line running alongside a power line for many miles will inevitably have more interference induced in one leg than the other since one of them will be nearer to the power line. This issue was addressed by swapping the positions of the two legs every few hundred yards with a cross-over, thus ensuring that both legs had equal interference induced and allowing common-mode rejection to do its work. As the telephone system grew, it became preferable to use cable rather than open wires to save space, and also to avoid poor performance during bad weather. The cable construction used for balanced telephone cables was
323:
153:
276:; however, this did not become widespread until repeater amplifiers became available. For an unamplified telephone line, a twisted pair cable could only manage a maximum distance of 30 km. Open wires, on the other hand, with their lower capacitance, had been used for enormous distances—the longest was the 1500 km from New York to Chicago built in 1893.
164:
190:
179:
380:
the two conductors in the driver, line and receiver (impedance balancing). These conditions ensure that external noise affects each leg of the line equally and thus appears as a common mode signal that is rejected by the receiver. There are balanced drive circuits that have excellent common-mode impedance balancing between the legs but do
263:, balanced lines reduce the amount of noise per distance, allowing a longer cable run to be practical. This is because electromagnetic interference will affect both signals the same way. Similarities between the two signals are automatically removed at the end of the transmission path when one signal is subtracted from the other.
303:
became widespread) and require a different kind of cable. This format requires the conductors to be arranged in two pairs, one pair for the sending (go) signal and the other for the return signal. The greatest source of interference on this kind of transmission is usually the crosstalk between the go
271:
The first application for balanced lines was for telephone lines. Interference that was of little consequence on a telegraph system (which is in essence digital) could be very disturbing for a telephone user. The initial format was to take two single-wire unbalanced telegraph lines and use them as a
345:
to provide a differential-mode signal. While transformers are still used in the large majority of modern dynamic microphones, more recent condenser microphones are more likely to use electronic drive circuitry. Each leg, irrespective of any signal, should have an identical impedance to ground. Pair
379:
Many explanations of balanced lines assume symmetric signals (i.e. signals equal in magnitude but of opposite polarity) but this can lead to confusion of the two concepts—signal symmetry and balanced lines are quite independent of each other. Essential in a balanced line is identical impedances in
251:
to ground, so the interfering fields or currents induce the same voltage in both wires. Since the receiver responds only to the difference between the wires, it is not influenced by the induced noise voltage. If a balanced line is used in an unbalanced circuit, with different impedances from each
414:
by using a pair of baluns at each end of the CAT5 run. As the signal travels through the balanced line, noise is induced and added to the signal. As the CAT5 line is carefully impedance balanced, the noise induces equal (common-mode) voltages in both conductors. At the receiving end, the balun
231:
to provide immunity to magnetic fields. The geometry of the cable ensures that magnetic fields will cause equal interference of both legs of the balanced circuit. This balanced interference is a common-mode signal that can easily be removed by a transformer or balanced differential receiver.
591:
1129:, Fifth Edition, Taylor & Francis, 2015, p. 1267. “Two signal voltages have symmetry when they have equal magnitudes but opposite polarities. Symmetry of the desired signal has advantages, but they concern head room and crosstalk, not noise or interference rejection.”
308:, where the diagonally opposite conductors form the pairs. This geometry gives maximum common mode rejection between the two pairs. An alternative format is DM (Dieselhorst-Martin) quad which consists of two twisted pairs with the twisting at different pitches.
1090:
Let's be clear from the start here: if the source impedance of each of these signals was not identical i.e. balanced, the method would fail completely, the matching of the differential audio signals being irrelevant, though desirable for headroom
774:
144:. Balanced lines and differential signalling are often used together, but they are not the same thing. Differential signalling does not make a line balanced, nor does noise rejection in balanced cables require differential signalling.
252:
conductor to ground, currents induced in the separate conductors will cause different voltage drops to ground, thus creating a voltage differential, making the line more susceptible to noise. Examples of twisted pairs include
1113:
Only the common-mode impedance balance of the driver, line, and receiver play a role in noise or interference rejection. This noise or interference rejection property is independent of the presence of a desired differential
474:
968:
223:
to reduce the amount of noise introduced. The cable is often wrapped in foil, copper wire, or a copper braid. This shield provides immunity to RF interference but does not provide immunity to magnetic fields.
280:
were used to improve the distance achievable with cable but the problem was not finally overcome until amplifiers started to be installed in 1912. Twisted pair balanced lines are still widely used for
1074:
354:) does not disturb the line balance, and is able to ignore common-mode (noise) signals, and can extract differential ones, then the system will have excellent immunity to induced interference.
333:
join together diametrically opposite conductors to maintain balance. This is different from the usage on 4-wire circuits. The colours in this diagram correspond with the colouring in figure 2.
830:
in this field is referring to the symmetry of the source and load: it has nothing to do with the impedance balance of the line itself, the sense of the meaning in telecommunications.
350:) is used to maintain the balanced impedances and close twisting of the cores ensures that any interference is common to both conductors. Providing that the receiving end (usually a
361:. One connects to the shield or chassis ground, while the other two are for the signal conductors. The signal wires can carry two copies of the same signal with opposite polarity (
684:
of the surrounding medium. A commonly used approximation that is valid when the wire separation is much larger than the wire radius and in the absence of magnetic materials is
965:
804:
690:
140:
Lines carrying symmetric signals (those with equal amplitudes but opposite polarities on each leg) are often incorrectly referred to as "balanced", but this is actually
674:
200:
Transmission of a signal over a balanced line reduces the influence of noise or interference due to external stray electric fields. Any external signal sources tend to
466:
654:
634:
614:
415:
responds only to the difference in voltage between the two conductors, thus rejecting the noise picked up along the way and leaving the original signal intact.
170:
Balanced line in star quad format. This line is intended for use with 4-wire circuits or two 2-wire circuits. It is also used with microphone signals in
1078:
1108:
586:{\displaystyle Z_{0}={\frac {1}{\pi }}{\sqrt {\frac {\mu }{\epsilon }}}\ln \left({\frac {l}{R}}+{\sqrt {\left({\frac {l}{R}}\right)^{2}-1}}~\right),}
133:
Circuits driving balanced lines must themselves be balanced to maintain the benefits of balance. This may be achieved by transformer coupling (
1054:
1021:
952:
893:
856:
922:
988:
826:
transmission are referred to as a balanced line since the instantaneous sum of the three line voltages is nominally zero. However,
1162:
677:
296:
468:
of a transmission line is an important parameter at higher frequencies of operation. For a parallel 2-wire transmission line,
384:
provide symmetric signals. Symmetric differential signals concern headroom and are not necessary for interference rejection.
1142:
1044:
201:
65:
844:
834:
819:
878:
823:
216:
to ensure that each conductor is equally exposed to any external magnetic fields that could induce unwanted noise.
439:
244:
205:
102:, used for traditional telephone, professional audio, or for data communications. They are to be contrasted to
20:
838:
362:
220:
141:
69:
185:
Balanced line in DM quad format. This line is intended for use with 4-wire circuits or two 2-wire circuits.
236:
115:
77:
807:
196:
Balanced line in twin lead format. This line is intended for use with RF circuits, particularly aerials.
299:
carrier systems, are usually 4-wire circuits rather than 2-wire circuits (or at least they were before
841:, two conductors are used to carry in-phase and out-of-phase voltages such that the line is balanced.
248:
209:
111:
57:
53:
49:
782:
769:{\displaystyle Z_{0}={\frac {120~\Omega }{\sqrt {\epsilon _{r}}}}\ln \left({\frac {2l}{R}}\right),}
212:
to ground minimizes differential pickup due to stray electric fields. The conductors are sometimes
847:
lines at which each pole is operated with the same voltage toward ground are also balanced lines.
866:
430:
antenna input could only be connected to a coaxial cable from a cable TV system through a balun.
285:
171:
123:
61:
45:
33:
29:
1018:
60:, and to other circuits. The primary advantage of the balanced line format is good rejection of
1005:
659:
322:
1050:
918:
861:
407:
341:
to a mixer in professional systems. Classically, both dynamic and condenser microphones used
411:
374:
253:
119:
444:
1025:
992:
972:
639:
419:
410:
signals over coaxial cable (which is unbalanced) through 300 feet (91 m) of balanced
347:
330:
260:
228:
103:
84:
159:
Balanced line in twisted pair format. This line is intended for use with 2-wire circuits.
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619:
599:
351:
317:
134:
88:
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358:
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107:
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99:
342:
300:
73:
423:
403:
338:
292:
281:
427:
305:
95:
152:
357:
Typical professional audio sources, such as microphones, have three-pin
284:, the lines that connect each subscriber's premises to their respective
1143:
Balanced Lines, Phantom
Powering, Grounding, and Other Arcane Mysteries
189:
163:
1146:
888:
883:
178:
399:
393:
321:
240:
127:
304:
and return circuits themselves. The most common cable format is
110:, which is designed to have its return conductor connected to
114:, or circuits whose return conductor actually is ground (see
966:
Evaluating
Microphone Cable Performance & Specifications
942:, Fifth Edition, Taylor & Francis, 2015, p. 1267–1268.
137:) or by merely balancing the impedance in each conductor.
98:, used for radio frequency communications. Also common is
16:
Electrical circuit with two conductors of equal impedance
785:
693:
662:
642:
622:
602:
477:
447:
398:
Interfacing balanced and unbalanced lines requires a
87:
and reproduction, balanced lines are referred to as
798:
768:
668:
648:
628:
608:
585:
460:
337:An example of balanced lines is the connection of
616:is half the distance between the wire centres,
19:"Balanced" redirects here. For other uses, see
422:balun was found at the antenna terminals of a
8:
953:The Importance of Star-Quad Microphone Cable
1046:The Worldwide History of Telecommunications
1038:
1036:
1034:
52:of the same type, both of which have equal
402:. For example, baluns can be used to send
126:can be interfaced using a device called a
1109:International Electrotechnical Commission
790:
784:
744:
725:
707:
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476:
452:
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1111:. 2000. p. 111. IEC 602689-3:2001.
188:
177:
162:
151:
906:
426:receiver. Typically a 300-ohm balanced
1006:What's Special About Star-Quad Cable?
934:
932:
930:
915:The Penguin Dictionary of Electronics
7:
346:cable (or a pair-derivative such as
227:Some balanced lines use 4-conductor
894:Low-voltage differential signalling
716:
94:A common form of balanced line is
14:
1043:Huurdeman, Anton A. (July 2003).
822:, the three conductors used for
873:Balanced transmission standards
418:A once common application of a
297:frequency division multiplexing
219:Some balanced lines also have
208:on the line, and the balanced
1:
799:{\displaystyle \epsilon _{r}}
243:on a connection by rejecting
1127:Handbook for Sound Engineers
940:Handbook for Sound Engineers
835:single-phase electric power
820:electric power transmission
810:of the surrounding medium.
1179:
1107:(Third ed.). Geneva:
879:Ethernet over twisted pair
391:
372:
315:
247:. The lines have the same
18:
669:{\displaystyle \epsilon }
369:Balanced and differential
329:Microphones connected to
235:A balanced line allows a
1075:"Audio Balancing Issues"
833:For the transmission of
440:characteristic impedance
434:Characteristic impedance
245:common-mode interference
56:along their lengths, to
21:Balance (disambiguation)
839:railway electrification
636:is the wire radius and
363:differential signalling
221:electrostatic shielding
142:differential signalling
1163:Communication circuits
1105:Sound system equipment
1103:"Part 3: Amplifiers".
800:
770:
670:
650:
630:
610:
587:
462:
334:
197:
186:
175:
160:
116:earth-return telegraph
78:differential amplifier
808:relative permittivity
801:
771:
676:are respectively the
671:
651:
631:
611:
588:
463:
461:{\displaystyle Z_{0}}
325:
237:differential receiver
192:
181:
166:
155:
1049:. Wiley-IEEE Press.
814:Electric power lines
783:
691:
660:
649:{\displaystyle \mu }
640:
620:
600:
475:
445:
42:balanced signal pair
986:The Star Quad Story
124:unbalanced circuits
1024:2016-11-12 at the
1019:How Starquad Works
991:2016-12-23 at the
971:2016-05-09 at the
867:Twisted-pair cable
796:
766:
666:
646:
626:
606:
583:
458:
335:
206:common mode signal
198:
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176:
172:professional audio
161:
48:consisting of two
46:electrical circuit
34:professional audio
30:telecommunications
1056:978-0-471-20505-0
862:Twinaxial cabling
857:Differential pair
824:three-phase power
757:
732:
731:
715:
629:{\displaystyle R}
609:{\displaystyle l}
574:
570:
552:
532:
511:
510:
499:
408:E-carrier level 1
295:, and especially
267:Telephone systems
72:device such as a
62:common-mode noise
1170:
1130:
1123:
1117:
1116:
1100:
1094:
1093:
1087:
1086:
1077:. Archived from
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996:
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412:category 5 cable
375:Balanced circuit
261:unbalanced lines
254:category 5 cable
214:twisted together
104:unbalanced lines
83:As prevalent in
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1172:
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1168:
1167:
1153:
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1091:considerations.
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1026:Wayback Machine
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420:radio frequency
396:
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377:
371:
331:star quad cable
320:
314:
269:
229:star quad cable
150:
135:repeating coils
85:sound recording
24:
17:
12:
11:
5:
1176:
1174:
1166:
1165:
1155:
1154:
1151:
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1138:
1137:External links
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392:Main article:
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373:Main article:
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359:XLR connectors
352:mixing console
318:Balanced audio
316:Main article:
313:
310:
268:
265:
239:to reduce the
149:
146:
89:balanced audio
68:when fed to a
15:
13:
10:
9:
6:
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3:
2:
1175:
1164:
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1145:– from
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1081:on 2016-10-24
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108:coaxial cable
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39:
38:balanced line
35:
31:
26:
22:
1126:
1121:
1112:
1104:
1098:
1089:
1083:. Retrieved
1079:the original
1071:Graham Blyth
1065:
1045:
1017:
1013:
1004:
1000:
984:
980:
964:
960:
951:
947:
939:
914:
909:
845:Bipolar HVDC
843:
837:as used for
832:
827:
817:
778:
682:permittivity
678:permeability
595:
437:
417:
397:
381:
378:
356:
343:transformers
336:
326:
290:
274:twisted pair
270:
259:Compared to
258:
234:
226:
218:
199:
193:
182:
167:
156:
139:
132:
100:twisted pair
93:
82:
70:differential
66:interference
41:
37:
27:
25:
1125:G. Ballou,
938:G. Ballou,
339:microphones
301:fibre-optic
293:trunk lines
282:local loops
148:Explanation
74:transformer
1085:2014-10-27
913:Young EC,
901:References
424:television
404:line level
291:Telephone
210:impedances
106:, such as
54:impedances
50:conductors
788:ϵ
738:
723:ϵ
717:Ω
664:ϵ
644:μ
565:−
517:
508:ϵ
505:μ
497:π
428:twin lead
406:audio or
348:star quad
306:star quad
249:impedance
96:twin-lead
1157:Category
1022:Archived
989:Archived
969:Archived
917:, 1988,
851:See also
286:exchange
120:Balanced
1114:signal.
828:balance
806:is the
327:Fig. 5.
204:only a
194:Fig. 4.
183:Fig. 3.
168:Fig. 2.
157:Fig. 1.
1147:Mackie
1053:
921:
896:(LVDS)
889:RS-485
884:RS-422
779:where
714:
596:where
573:
388:Baluns
202:induce
112:ground
58:ground
44:is an
400:balun
394:Balun
241:noise
128:balun
1051:ISBN
919:ISBN
680:and
438:The
122:and
64:and
36:, a
32:and
818:In
711:120
382:not
118:).
76:or
40:or
28:In
1159::
1088:.
1073:.
1033:^
929:^
735:ln
656:,
514:ln
288:.
256:.
130:.
91:.
80:.
1149:;
1059:.
792:r
764:,
760:)
755:R
751:l
748:2
742:(
727:r
705:=
700:0
696:Z
624:R
604:l
581:,
577:)
568:1
560:2
555:)
550:R
547:l
542:(
535:+
530:R
527:l
521:(
494:1
489:=
484:0
480:Z
454:0
450:Z
174:.
23:.
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