376:) 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.
283:
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
334:
164:
287:; 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.
175:
201:
190:
391:
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
274:, 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.
314:
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
282:
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
356:
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
390:
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
262:
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
425:
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
242:
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.
602:
1140:, 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.”
319:, 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.
1101:
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
785:
155:. 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.
263:
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
1124:
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
485:
979:
234:
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.
291:
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
1085:
365:) 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.
344:
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.
841:
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.
361:) 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
372:. 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 (
695:
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
976:
815:
701:
151:
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
685:
211:
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
477:
665:
645:
625:
426:
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.
181:
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
1089:
1119:
597:{\displaystyle Z_{0}={\frac {1}{\pi }}{\sqrt {\frac {\mu }{\epsilon }}}\ln \left({\frac {l}{R}}+{\sqrt {\left({\frac {l}{R}}\right)^{2}-1}}~\right),}
144:
Circuits driving balanced lines must themselves be balanced to maintain the benefits of balance. This may be achieved by transformer coupling (
1065:
1032:
963:
904:
867:
933:
999:
837:
transmission are referred to as a balanced line since the instantaneous sum of the three line voltages is nominally zero. However,
1173:
688:
307:
479:
of a transmission line is an important parameter at higher frequencies of operation. For a parallel 2-wire transmission line,
395:
provide symmetric signals. Symmetric differential signals concern headroom and are not necessary for interference rejection.
1153:
1055:
212:
76:
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227:
to ensure that each conductor is equally exposed to any external magnetic fields that could induce unwanted noise.
450:
255:
216:
113:, used for traditional telephone, professional audio, or for data communications. They are to be contrasted to
31:
849:
373:
231:
152:
80:
196:
Balanced line in DM quad format. This line is intended for use with 4-wire circuits or two 2-wire circuits.
247:
126:
88:
818:
207:
Balanced line in twin lead format. This line is intended for use with RF circuits, particularly aerials.
310:
carrier systems, are usually 4-wire circuits rather than 2-wire circuits (or at least they were before
852:, two conductors are used to carry in-phase and out-of-phase voltages such that the line is balanced.
259:
220:
122:
68:
64:
60:
793:
780:{\displaystyle Z_{0}={\frac {120~\Omega }{\sqrt {\epsilon _{r}}}}\ln \left({\frac {2l}{R}}\right),}
223:
to ground minimizes differential pickup due to stray electric fields. The conductors are sometimes
858:
lines at which each pole is operated with the same voltage toward ground are also balanced lines.
877:
441:
antenna input could only be connected to a coaxial cable from a cable TV system through a balun.
296:
182:
134:
72:
56:
44:
40:
1029:
71:, and to other circuits. The primary advantage of the balanced line format is good rejection of
1016:
670:
333:
1061:
929:
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418:
352:
to a mixer in professional systems. Classically, both dynamic and condenser microphones used
422:
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130:
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430:
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signals over coaxial cable (which is unbalanced) through 300 feet (91 m) of balanced
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341:
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239:
114:
95:
170:
Balanced line in twisted pair format. This line is intended for use with 2-wire circuits.
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106:
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Typical professional audio sources, such as microphones, have three-pin
295:, the lines that connect each subscriber's premises to their respective
17:
1154:
Balanced Lines, Phantom
Powering, Grounding, and Other Arcane Mysteries
200:
174:
1157:
899:
894:
189:
410:
404:
332:
251:
138:
315:
and return circuits themselves. The most common cable format is
121:, which is designed to have its return conductor connected to
125:, or circuits whose return conductor actually is ground (see
977:
Evaluating
Microphone Cable Performance & Specifications
953:, Fifth Edition, Taylor & Francis, 2015, p. 1267–1268.
148:) or by merely balancing the impedance in each conductor.
109:, used for radio frequency communications. Also common is
27:
Electrical circuit with two conductors of equal impedance
796:
704:
673:
653:
633:
613:
488:
458:
409:
Interfacing balanced and unbalanced lines requires a
98:
and reproduction, balanced lines are referred to as
809:
779:
679:
659:
639:
619:
596:
471:
348:An example of balanced lines is the connection of
627:is half the distance between the wire centres,
30:"Balanced" redirects here. For other uses, see
433:balun was found at the antenna terminals of a
8:
964:The Importance of Star-Quad Microphone Cable
1057:The Worldwide History of Telecommunications
1049:
1047:
1045:
63:of the same type, both of which have equal
413:. For example, baluns can be used to send
137:can be interfaced using a device called a
1120:International Electrotechnical Commission
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1122:. 2000. p. 111. IEC 602689-3:2001.
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188:
173:
162:
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437:receiver. Typically a 300-ohm balanced
1017:What's Special About Star-Quad Cable?
945:
943:
941:
926:The Penguin Dictionary of Electronics
7:
357:cable (or a pair-derivative such as
238:Some balanced lines use 4-conductor
905:Low-voltage differential signalling
727:
105:A common form of balanced line is
25:
1054:Huurdeman, Anton A. (July 2003).
833:, the three conductors used for
884:Balanced transmission standards
429:A once common application of a
308:frequency division multiplexing
230:Some balanced lines also have
219:on the line, and the balanced
1:
810:{\displaystyle \epsilon _{r}}
254:on a connection by rejecting
1138:Handbook for Sound Engineers
951:Handbook for Sound Engineers
846:single-phase electric power
831:electric power transmission
821:of the surrounding medium.
1190:
1118:(Third ed.). Geneva:
890:Ethernet over twisted pair
402:
383:
326:
258:. The lines have the same
29:
680:{\displaystyle \epsilon }
380:Balanced and differential
340:Microphones connected to
246:A balanced line allows a
1086:"Audio Balancing Issues"
844:For the transmission of
451:characteristic impedance
445:Characteristic impedance
256:common-mode interference
67:along their lengths, to
32:Balance (disambiguation)
850:railway electrification
647:is the wire radius and
374:differential signalling
232:electrostatic shielding
153:differential signalling
1174:Communication circuits
1116:Sound system equipment
1114:"Part 3: Amplifiers".
811:
781:
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661:
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208:
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186:
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127:earth-return telegraph
89:differential amplifier
819:relative permittivity
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687:are respectively the
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662:
642:
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599:
474:
472:{\displaystyle Z_{0}}
336:
248:differential receiver
203:
192:
177:
166:
1060:. Wiley-IEEE Press.
825:Electric power lines
794:
702:
671:
660:{\displaystyle \mu }
651:
631:
611:
486:
456:
53:balanced signal pair
997:The Star Quad Story
135:unbalanced circuits
1035:2016-11-12 at the
1030:How Starquad Works
1002:2016-12-23 at the
982:2016-05-09 at the
878:Twisted-pair cable
807:
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217:common mode signal
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183:professional audio
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59:consisting of two
57:electrical circuit
45:professional audio
41:telecommunications
1067:978-0-471-20505-0
873:Twinaxial cabling
868:Differential pair
835:three-phase power
768:
743:
742:
726:
640:{\displaystyle R}
620:{\displaystyle l}
585:
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563:
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419:E-carrier level 1
306:, and especially
278:Telephone systems
83:device such as a
73:common-mode noise
16:(Redirected from
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1141:
1134:
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1088:. Archived from
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423:category 5 cable
386:Balanced circuit
272:unbalanced lines
265:category 5 cable
225:twisted together
115:unbalanced lines
94:As prevalent in
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240:star quad cable
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146:repeating coils
96:sound recording
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403:Main article:
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370:XLR connectors
363:mixing console
329:Balanced audio
327:Main article:
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250:to reduce the
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100:balanced audio
79:when fed to a
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1100:
1094:. Retrieved
1090:the original
1082:Graham Blyth
1076:
1056:
1028:
1024:
1015:
1011:
995:
991:
975:
971:
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856:Bipolar HVDC
854:
848:as used for
843:
838:
828:
789:
693:permittivity
689:permeability
606:
448:
428:
408:
392:
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367:
354:transformers
347:
337:
301:
285:twisted pair
281:
270:Compared to
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193:
178:
167:
150:
143:
111:twisted pair
104:
93:
81:differential
77:interference
52:
48:
38:
36:
1136:G. Ballou,
949:G. Ballou,
350:microphones
312:fibre-optic
304:trunk lines
293:local loops
159:Explanation
85:transformer
1096:2014-10-27
924:Young EC,
912:References
435:television
415:line level
302:Telephone
221:impedances
117:, such as
65:impedances
61:conductors
799:ϵ
749:
734:ϵ
728:Ω
675:ϵ
655:μ
576:−
528:
519:ϵ
516:μ
508:π
439:twin lead
417:audio or
359:star quad
317:star quad
260:impedance
107:twin-lead
1168:Category
1033:Archived
1000:Archived
980:Archived
928:, 1988,
862:See also
297:exchange
131:Balanced
18:Balanced
1125:signal.
839:balance
817:is the
338:Fig. 5.
215:only a
205:Fig. 4.
194:Fig. 3.
179:Fig. 2.
168:Fig. 1.
1158:Mackie
1064:
932:
907:(LVDS)
900:RS-485
895:RS-422
790:where
725:
607:where
584:
399:Baluns
213:induce
123:ground
69:ground
55:is an
411:balun
405:Balun
252:noise
139:balun
1062:ISBN
930:ISBN
691:and
449:The
133:and
75:and
47:, a
43:and
829:In
722:120
393:not
129:).
87:or
51:or
39:In
1170::
1099:.
1084:.
1044:^
940:^
746:ln
667:,
525:ln
299:.
267:.
141:.
102:.
91:.
1160:;
1070:.
803:r
775:,
771:)
766:R
762:l
759:2
753:(
738:r
716:=
711:0
707:Z
635:R
615:l
592:,
588:)
579:1
571:2
566:)
561:R
558:l
553:(
546:+
541:R
538:l
532:(
505:1
500:=
495:0
491:Z
465:0
461:Z
185:.
34:.
20:)
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