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14
Here is a handy chart that pulls together horn selection along with distance and power settings in typical commercial
applications:
Step 3 Select the Correct Amount Of Power
Inthissectionwewillseehowtoselecttheappropriatesizepowersupply(selfamplied24voltsystem)or
amplier(centralamplied70voltsystem).
Self amplied
Central Amplier
For central amplier 70 volt systems, the sum of the selected speaker wattage taps will determine the size of the amplier
— in other words, add up the wattage taps. Forty speakers tapped at 1 watt represent a total wattage demand of 40
watts.Then,sizetheampliersothatthesumofthewattagetapsdoesnotexceed85%oftheamplier’sratedpower.
This will ensure headroom and reserve power.
Horn Loudspeaker Selection Guide
Noise
Level
Typical Area
Wheelock Self
Amplied Horn
Effective
Forward
Coverage
Wheelock
Central
Amplied
25/70/100
Volt Horn
Wattage Tap/Effective
Forward Coverage
Quietto
Moderate
50-75dB
Shipping
Warehouse
SA-H5 128 feet ST-H15B 3.8 watts/128 feet
Noisy
75-85dB
Print Shop,
Factory
SA-H5
SA-H15
64 feet
96feet
ST-H15B 7.5 watts/64 feet 15.0
watts/96feet
Very Noisy
86-96dB
Machine
Shop, Factory
SA-H15 32 feet ST-H15B
ST-H30
15.0 watts/32 feet 30.0
watts/48 feet
Selfamplied(24VDC)systemsare4-wiresystems.ApairofwiresfortheaudioandapairfortheDCvoltagenecessary
topowereachspeaker’samplier.
A very important consideration then is the maximum total current draw, in
milliamps of all speakers to be connected on the same power supply. Thus a single Wheelock RPS-2406 power
supply, which provides 600mA, may be sufcient to power multiple speakers. Actually this approach is somewhat
conservative;itisseldomnecessarytooperatethesespeakersatfullvolumeandpower.Athalfvolumeselfamplied
speakers draw considerably less current and still deliver plenty of sound for most environments. Power supplies can
be run in tandem...that is, paralleled with positive poles and negative poles connected together to yield double the
available current. Forexample,apairof600mARPS-2406powersuppliescanbetiedtogethertoyield1200mA(1.2
amps).Formorepower,Wheelockalsoprovidesthe4ampRPS-244024VDCpowersupply,andthe8-output,20.8
amp PSC-2420-B 24VDC power supply. The PSC-2420-B features a battery charging circuit with automatic switchover
tobackupbatteries.Checkthespecicationsofthepowersupplytobeusedinordertostaywithinitsoperatingrange.
Usingself-ampliedspeakersandother24VDCproductswithapowersupplywithbatterybackupwillallowacompletely
battery backed telephone paging system.
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