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Atlas Sound Tech Support Manager
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The Key Here Is That Power = Voltage x Current.
Example - I Want 100W Delivered to My House. Here Are Two Ways To Do This.
10V x 10A = 100W (Low Voltage x High Current)
Large Cable Needed Here To Carry The High Current!
Or, I Could Achieve The Same Result By…
100V x 1A = 100W (High Voltage x Low Current)
I Can Reduce The Wire Diameter And Still Get 100W To My House!
- 25V Systems Are Typically Found In Schools And Prisons. Considered Low Voltage, Conduit Typically Not Required.
- 70V Is The Most Common, May Or May Not Require Conduit For The Speaker Lines.
- 100V Is Used Where Very Long Speaker Runs Are Necessary, The Higher Voltage Results In Lower Current In The Speaker Line, Resulting In Smaller Gauge Wire Needed.
8 Ohm loudspeakers
This System Has 2 Speakers Connected, Usually Up To 4 Maximum
Assuming This Is A 100W Receiver And It Is Delivering Maximum Power, We Would “See” About 28VAC At The Speaker Terminals. Remember This Number.
A Typical Commercial BGM and Paging System
Commercial grade 70V ceiling speakers
CD Player-BGM Source
This Amplifier Is Rated At 120W. At Maximum Power, We See 70VAC At The Speaker Terminals.
Commercial Grade 70V Mixer Amplifier
By The Use Of Step Up And Step Down Transformers…………………
We “Step Up” The Voltage/Impedance (Audio Signal) Which Lowers The Current Coming Out Of The Amplifier, And “Step Down” The Voltage/Impedance (And Raise The Current Back Up) To The Loudspeakers!
Power Companies Do This Everyday, They Step Up The Voltage On The Power Lines For Distribution, Then Step It Back Down At Your Home!
Let’s Take A Closer Look At Transformers!
Typical 8W 70V step down transformer,
usually mounted on the loudspeaker
Low Voltage, High Current To Speaker
High Voltage, Low Current From 70V Amplifier
Taps Set The Amount Of Power The Speaker Will Draw From The Amp
Internal 25/70/100V Transformer
To 70V Loudspeakers
Now Let’s Take A Look At The Major Components In A 70V System….
70V Power Amps
Small Mixer Amps
Large Mixer Amps
Power Amps And Mixer Amps??
What’s The Difference?
4” Ceiling Speaker With Tweeter
High Power Ceiling Speaker
4” Ceiling Speaker
“Pendant” Type Speaker
Surface Mount Speaker
High Power Stadium Horn
Since We May Need A Way To Control The Loudness Of the Speakers, We Install Attenuators.
70V Attenuators Are Wired Into The Speaker Line, And Are Rated On How Much Power (Speaker Qty. x Tap Setting) They Can Deliver To The Speakers Connected!
Two Volume Controls
Paging Horns - Used Indoors And Out, Very Efficient, Voice Only
Surface Mount - Used Indoors, Voice & Music
Ceiling Mount - Used Indoors, Voice & Music
Coaxial Indoor/Outdoor Speaker - Voice & Music
We Have Chosen The Amplifier And The Loudspeaker, Now, How Many Will I Need?
Always Measure The Dimensions Of The Spaces Needing Audio.
- Room Length?
- Room Width?
- Room Height To Ceiling?
- Will Occupants Be Seated Or Standing?
Proper Speaker Spacing!
6” Speaker in a 10ft ceiling
r = (10-5) tan 110/2
Most Speaker Manufacturers Provide A Ceiling Speaker Calculator On Their Website!
Make Use Of It!
Each Type Has Its’ Own Pros And Cons
Let’s Start With……
Notice The Large Gaps In The Coverage?
-6dB Down Point For The Loudspeaker Or ¼ The Power
14’ On Center
See the overlap between adjacent speakers?
10’ on center
Our customers may not want a system with this much density, nor would they want to pay for it!
Lots Of Overlap Between Speakers
7’ On Center
This One Goes To “11”!
Typical 8” Ceiling Speakers Here, Tapped At ¼ to1W.
Paging Horns Required Here
Be Careful If SPL Is Above 100dB!
If You Are Unsure, Or Have An Install With Many Loudspeakers And Long Speaker Runs…
We Need To Determine The Wire Size For This Job. It’s Best To Calculate The Total Speaker Load That The Amplifier Will Be Required To Drive AND The Total Wire Length.
How Many Zones Will There Be?
Each Content Zone Requires A Separate Amplifier!
Each Volume Zone Requires A 70V Attenuator!
What Is It, And Why Is It Often Missing From Most Toolboxes?
The Impedance Bridge Is A Meter For Measuring The Impedance Of A 70V Speaker Line.
It Measures Impedance At A Specific Frequency Using An AC Signal.
Gives A Reading In Ohms Or Watts.
VOM’s Do Not Do This!
The Bridge Cannot Measure Voltage Or Current, And Is Typically Not Used Everyday By Installation People.
If One Calculates The Expected Impedance (Remember Taps X Speaker Count?) And Then Measures The Loudspeaker Line, The Numbers Should Be Close. If There Is A Big Difference, It’s Time To Figure Out Why.
The Impedance Bridge Connects To The (+) And (–) Connections Of The Speaker Line. It Measures The Impedance At One Or Several Frequencies, Much Different Than Using A Standard VOM Set For Resistance!
Let’s Go On A Service Call And Do Some Troubleshooting With Our Impedance Bridge.
We Have A Paging System That Was Working Well Until Yesterday. The System Has 8 Speakers Tapped At 1W, A 70V Mixer Amp and Paging Is Done With A Desktop Microphone. The Customer Says The Amp Is Running Hot And The paging Is Distorted.
We Check Out The Equipment And Wiring In The Rack And Everything Appears OK.
WeCalculate The Load…
8 Speakers X 1W Tap = 8W,
Impedance = 5000/8 = 625 Ohms.
We Disconnect The Speaker Line And Connect The Bridge. The Bridge Measures <8 Ohms, Where We Expected Around 625 Ohms!
What Could The Issue Be Here?
8 Speakers, All Tapped At 1W
120W Commercial Grade Mixer Amp
8 Speakers, All Tapped At 1W
Connect Bridge To Speaker Line
Someone Installed An 8 Ohm Speaker On The 70V Line!
You Have A Customer Who Wants To Upgrade Their Current System…Add More Speakers, Maybe Some Volume Controls In Each Room And They Are On A Budget….They Have A Consumer Grade Stereo Receiver That They Want To Re-Use!
How Can We Convert A Consumer OR Non 70.7V Amplifier To Run 70.7V????
-Available From Several Manufacturers
-Matches Loudspeaker Loads To Amplifier Outputs
-Step Up Or Step Down Voltage Or Impedance