Wheelock MX-8 Mixer Specifications download pdf (Page 18)

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Correct Wire Size for Central Ampliﬁed System Speaker Lines and

Ampliﬁed Speaker System 24 VDC Power Lines

Inanyelectricalinstallation,soundorotherwise,properwiresizeisimportantifyouwantmaximumefciencyfromthe

system, not to mention safety and reliability.

Wire conducts the audio and electrical signals in your system. Like arteries and veins in the human body, good unobstructed

owisvital.Wirethatissizedtoosmallactslikearesistorinthecircuitandcanrestricttheow.Ifthewireistoosmall

(ortheruntoolong)forthespeakerload,alotofamplierpowerwillneverreachthespeaker.Thiselectricalenergy

simply becomes heat in the wires, and will result in volume loss.

So, bigger is better. The less restriction in the wire, the better the path for your audio and electrical signals. It’s like

the difference between sending your signal down a dirt road or the interstate. However, if you have more wire size than

you need you’re wasting money. So, it’s important to know what size wire to use for a given power load and how far you

can run this particular size wire with this power load.

Cable lengths for 70 volt speaker lines

Table#1shouldproveusefulfor100volt,70volt,25voltorlowimpedance(8ohm)speakerlines.Asanexample,let’s

sayyourinstallationcallsfora60wattloadandyouhavetorunthecableabout900feet.Lookingatthechart,the

correct wire size is #14. Or, let’s say it’s an older installation and you want to use the existing wire — 600 feet of #22.

Again, looking at the chart, you must limit the connected load to 15 watts, which could be 15 speakers tapped at 1 watt,

30speakerstappedat1/2wattorasinglehorntappedat15watts.Theseguresaremeanttobeguidelines.Itisnot

thatthesystemwouldnotworkatallifyouusedsmallerwireorlongerrunsthanspecied,itisjustthatthevolumeloss

wouldbegreater,andtheefciencyofthesystemreduced.

Table #1

2 WIRE COPPER CABLE LENGTHS FOR SPEAKER LINES AT 0.5 dB

LOSS IN SPL (12.5% POWER LOSS IN WATTS)

Cable Lengths for 24 VDC Power Lines

Wiringforselfampliedsystems,orsystemsusinglowvoltageDCtopowerselfcontainedampliedspeakers,can

present a different problem, and that is voltage drop. With 70 volt speaker systems, the audio signal is distributed at a

higher voltage and then stepped down at each speaker via a transformer much the same way utility companies bring

powertoyourhome—highvoltagetransmissionthatissteppeddownateachlocation.Thisisaveryefcientmethod

thatworksbecauseofthenatureofACvoltages(audioisanACvoltage)andtransformers(voltagescanbesteppedup

ordown).DCvoltagecannotbesteppedupordownwithtransformers,sothevoltagethatisavailablefromthesource

(thepowersupply)isthesamevoltagethatthedevicereceives.Ifthedevicethatmustbepoweredbythisvoltageis

some distance away, careful attention must be paid to current draw, length of run and wire size.

AWG Max Low Impedance 70 Volt Speaker Line AWG

Size Power Speaker Line Nominal Power in the Load Length in Feet Size

AWG 8 Ohms 10W 15W 20W 40W 60W 100W 125W 200W 250W 400W 500W

10 Per NEC 240

15,0009,900 7,500 3,750 2,500 1,500 1,180 730 590 370 290

12 Per NEC 150

9,100 6,200 4,680 2,340 1,560 940 730 460 370 230 180

 14 1,060W 95

5,600 3,800 2,880 1,440 960 600 450 280 220 140 110

16 420 W 60

3,600 2,400 1,870 930 620 370 290 180 140 90 —

18 210 W 40

2,300 1,500 1,150 570 380 230 180 110 — — —

20 70 W 25

1,400 960 730 360 240 — — — — — —

22 35 W 15

900 600 460 — — — — — — — —

NOTE: 1. For 25 V line divide all 70.7 lengths by 8. 2. For 100 V line multiply all 70.7 lengths by 2.0. 3. To allow for future expansion and distribution

cablelineloss,itisrecommendedthatthetotalsystemwattageshouldnotexceed85%oftheamplier’sratedoutput.4.Thetotalsystemwattage

requirementisthesummationofthewattagetapselectionsofallsystemspeakersandhorns.

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Wheelock MX-8 Mixer Specifications Page 18

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