Steps Ahead A Guide to Loudspeaker Paging and Telephone Systems Interface
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Contents Step 1 Select the Correct System...............................................................................................................................3 24vdc Self Amplified System 70v Central Amplified System 25v And 100v Central Amplified Systems Step 2 System Design and Layout..............................................................................................................................
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Step 1 - Select the Correct System 24 volt self amplified or 70 volt central amplified. Which is best? The answer is that either system is right for certain applications. Here are a few guidelines: For small systems involving 6-8 speakers, 24VDC self amplified systems offer the advantages of low cost, easy installation using telephone (quad) wire, individual volume control and built-in redundancy (if one fails, the rest keep working).
Amplified Paging Speakers and Horns SA-Series Amplified Speakers and Horns The SA-Series Amplified Speaker Horns provide clear, audible, output for voice paging, background music, and tone alerting. The two models offered are 5 watt and 15 watt weatherproof horns. Each model features a built-in amplifier and individual tamper resistant volume control. The horns are provided with a conduit interface adapter and a clear plastic shield.
Step 2 - System Design and Layout It’s easier than it may first appear, and once you master some basics, it will become routine. Armed with these basics and a good dose of common sense, you can design a system that will work well, every time.
Distance and the 6 dB rule Simply put, doubling the distance from the speaker means you lose 6 dB SPL, cut the distance in half, and you gain 6 dB. This means that each time you double or half the distance you lose or gain 6 dB. In the above example, an appliance delivers 90 dB @ 64 feet with 3.8 watts of applied power. Double the distance to 128 feet and the SPL drops 6 dB to 84 dB. Doubling once again to 256 feet means 78 dB, and so forth.
Ceiling Mount Speakers Speaker spacing For ceiling mount installation in most offices, stores, schools, etc., recessed ceiling mount speakers can be used. Space the speakers at twice the ceiling height. If the ceiling is 12 feet high, space the speakers 24 feet apart. This will provide uniform coverage. Ceiling Speaker Spacing and Coverage Ceiling Height Spacing 20 ft 40 ft 12 ft 24 ft 10 ft 20 ft 8 ft 16 ft How many speakers? First, find the coverage given by one speaker in square feet.
Wheelock Speaker System Calculator Much of the information contained in this book has been condensed into a simple and easy to use sliderule calculator available from your local Wheelock sales representative. This powerful tool calculates the required number of ceiling speakers or horns, power requirements, wire size, etc., for a given size area, ceiling height and background noise level. The calculator is designed for both self amplified (24VDC) and central amplified (25/70/100 volt) systems.
The choice of wattage tap in this situation can simply depend on the number of speakers required. In other words, more speakers tapped at 1/4 watt could be put on the line than speakers tapped at 1/2 watt. It’s just that you have to crank up the amplifier a little more and sacrifice some headroom. In any case, as we will also see a bit later, the amplifier size is determined by the sum total of the wattage taps, not the number of speakers.
Wall Speaker Layout Speakers Mounted on One Wall and Pillars Wall Speaker Layout Speakers Mounted on Opposing Wall Horns Horns are used in large, open areas or very high noise areas mainly because of their efficiency. They put out a lot of sound! Typical applications are factories, warehouses, loading docks, school yards, military applications, parking lots, etc. Typical Horn Installation www.coopernotification.
Spacing and forward projection Experience has shown that the most effective side to side spacing of a typical horn is about 40 feet. This is determined by the flare rate and dispersion pattern, which are fixed and constant. The front-to-rear spacing requires a little more thought, because we are actually dealing with the forward projection of the horn.
Remember, we need 91 dB for an effective page. From the table, we can see that at 64 feet the selection of wattage taps gives us the SPL range we need. At the 7.5 watt setting the horn will give 93 dB which is certainly adequate. Note that at 128 feet there is a range of 84 dB to 90 dB (not quite good enough) and that at 32 feet the range is 90 dB to 102 dB — probably too much, and spacing the horns at 32 feet instead of 64 feet means twice the quantity of horns and twice the money.
Application of Horns in a Noisy Production and Warehouse Facility PRODUCTION AREA (23,040 SQUARE FEET TOTAL 120’ 64’ WAREHOUSE WITH STORAGE RACKS 192’ 64’ 64’ 128’ 64’ 64’ 40’ EACH AILSLE TREATED AS A SEPERATE LONG NARROW ROOM 40’ 240’
Here is a handy chart that pulls together horn selection along with distance and power settings in typical commercial applications: Horn Loudspeaker Selection Guide Wheelock Central Amplified 25/70/100 Volt Horn Typical Area Wheelock Self Amplified Horn Effective Forward Coverage Quiet to 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 96 feet ST-H15B 7.5 watts/64 feet 15.
Power Supplies A RPS-2406: Fully Regulated and Filtered, 24 VDC, 600 mA. Current limited, short circuit and overload protected with auto shutdown and reset. Wall mounting with 6 ft. AC power cord. RPS-2440-A: 24 VDC, dual output. Either two 2 A, or one 4A. Fully regulated and filtered. Each output with independent power on LED, current limiting overload and short circuit protection, auto shutdown and reset. AC circuit breaker for input protection.
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 efficiency 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 flow is vital. Wire that is sized too small acts like a resistor in the circuit and can restrict the flow.
In self amplified speakers, the small amplifiers behind each speaker are powered with 24 VDC, and these amplifiers have a definite current draw, which means that a specific length of run and wire size (which in turn create a certain resistance) will have an impact on the amount of current, measured in amperes, or milliamps, that the amplifiers will actually receive. By imposing a larger current draw than the wiring can handle, the system will “see” a drop in voltage and current flow.
What about the audio pair? As mentioned previously, self-amplified speakers use a 4-wire hook-up: A pair for the 24 VDC power and a pair for the paging audio. What about the audio pair? Shouldn’t we worry about correct wire size for the audio wiring as well? Pre-amplified paging audio is a very low power, low impedance (usually 600 ohms or less) electrical signal. For this reason, small gauge wire of #22-24 AWG works well, even for very long cable runs.
Centrex systems work very much like PBX systems with one important difference: Instead of being located on premise, the switching gear is located at the telephone company’s central office (CO). The extension lines come back from CO like telephone lines coming into your home — with 90-130 volt ringing voltage. Centrex lines cannot be directly connected to amplifier inputs. An telephone paging interface must be used to connect a ring voltage line to a paging system.
Single Zone CO Port Paging Applications Talk battery can be provided with a filtered and regulated 24 VDC power supply as illustrated by the following diagram 2 WIRE CABLE 2 WIRE CABLE TELEPHONE SYSTEM UNUSED CO PORT TELEPHONE INPUT (+) (-) SPARE POWER SUPPLY Note: This diagram shows the output of the telephone system feeding the input of a typical Wheelock amplifier for distribution on a 70 volt system.
ORDERING INFORMATION Item A Input Output 50-130 V, 20-30 Hz Ringing Voltage or Contact Closure B Application Model No. Monitor up to 3 tip & ring lines (one zone) CA-312-1 Monitor up to 6 tip & ring lines (two zones) CA-622-1 NOTES: 1. Both models UL 1459 Listed, FCC Registered.
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