Audio Video / Editorials
Distributed 70V Loudspeaker Systems Rick Kamlet, Sr. Director for Commercial Sound at JBL Professional
Distributed.speaker.systems.are.often.used.for.the.background.music.and.paging.systems.in.applications.such.as.retail.stores,. restaurants,.hotels,
.office.buildings.and.other.large.business.locations..In.the.US,
.these.systems.are.often.called.70-Volt.Systems. (
usually.printed.as.“70V”).
What is a 70V Distributed System?
In.a.70V.system,
.the.voltage.sent.down.the.loudspeaker.line.from.
the.power.amplifier.to.the.loudspeakers.is.high.(
as.high.as.70V.on. peaks)
.and.then.a.transformer.is.used.at.every.speaker.to.bring.the.
voltage.back.down.to.what.the.speaker.needs..The.diagram.to.the.
right.shows.a.typical.hookup.for.a.70V.distributed.speaker.system.
Why use a 70V Distributed System?
Distributed.systems.allow.driving.many.speakers.from.a.single.am-
plifier.channel.(
which.saves.money),
.allow.the.use.of.smaller.cable. sizes.(
which.also.saves.money),
.allow.for.each.speaker.to.be.set.at.a.
different.volume.without.affecting.the.other.speakers,
.and.makes.the.
calculations.for.choosing.the.amplifier.size.simple.and.straightforward.
In.70V.systems,
.amplifiers.are.designed.so.their.full.power.output
voltage.can.reach.as.high.as.70.volts.RMS,
.which.is.a.fairly.high
voltage..Then.the.power.that.each.speaker.takes.from.the.distributed.
speaker.line.is.set.via.a.tap.setting.on.the.speaker.
Connecting Many Speakers on an Amplifier Channel 8
With.low.impedance.speakers.(4-ohm.or.8-ohm.speakers),
.you.cannot.parallel.very.many.speakers.before.the.power.
amplifier.gets.loaded.with.too.low.of.an.impedance...In.distributed.systems,
.it.is.not.uncommon.to.have.dozens.or.even.
hundreds.of.speakers.driven.from.a.single.70V.power.amplifier.
Setting Speakers at Different Volumes
By.changing.the.tap.setting.of.the.70V.speaker,
.the.volume.of.the.speaker.can.be.adjusted.upward.or.downward,.
depending.on.what.volume.is.needed.from.that.speaker.
Wire Gauge
In.commercial-sound.projects,
.speaker.cables.are.frequently.quite.long,
.often.hundreds.of.feet..By.running.the.distributed.
speaker.signal.at.the.higher.voltage,
.the.current.going.through.the.wire.is.lower.so.you.can.use.smaller.gauge.cables..
Smaller.gauge.cables.can.save.the.installer.and.customer.a.substantial.amount.of.money.
How Powerful of an Amp to Use – Computing the Watts
All.the.loudspeakers.in.a.distributed.system.get.connected.across.the.two.wires.(
plus.and.minus)
.coming.from.the.power.amplifier,.
and.each.speaker.gets.tapped.as.needed..To.determine.the.amplifier.size,
.all.the.designer.has.to.do.is.count.Watts,
.adding.up.the.
sum.of.all.the.tap.settings.on.all.the.speakers..When.the.total.wattage.drawn.by.the.speakers.equals.the.power.output.rating.of.
the.amplifier,
.then.the.maximum.number.of.speakers.has.been.attached.to.the.amplifier’
s.output..In.practice,
.it.is.best.to.keep.the.
total.sum.of.the.speaker.taps.below.80%.of.the.power.amplifier.rating,
.giving.some.headroom.and.reducing.the.strain.on.the.power.
amplifier...Just.make.sure.that.the.amp.is.a.70V.commercial.amplifier,
.in.other.words.that.it.has.been.designed.to.be.utilized.in.a.
70V.distributed.speaker.system.
To.summarize,
.utilizing.a.70V.distributed.speaker.system.allows.for.fewer.power.amplifier.channels,
.uses.smaller.gauge. (ie,.less.expensive)
.speaker.cable,
.and.allows.for.volume.adjustments.without.affecting.other.speakers..Distributed.systems.
can.save.the.contractor.and.customer.a.lot.of.money.and.make.a.system.that.is.straightforward.to.design.and.install.
www.adiglobal.com
Basic 70V Distributed Speaker System
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