Wheelock MX-8 Mixer Specifications download pdf (Page 7)

Step 2 - System Design and Layout

It’seasierthanitmayrst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.

Creating a uniform sound eld

In order to be effectively heard, a paging system simply has to be loud enough to be heard above the noise level of the

environment, and intelligible,whichmeansthesystemshouldproduceclear,audiblesoundwithoutbeingmufedor

distorted.“Sounds”simple,right?Nowlet’slookalittlecloser.

An important point to remember is that effective

coverage in a room depends more upon speaker

placement and spacing than upon volume of the

speaker themselves.

For example, a garden hose has a certain spray pattern. Increasing the water pressure will not give you much greater

coverageforyourgardenbutaddinganothernozzlecertainlywill.Inasimilarfashion,multiplepagingspeakers“spray”

sound evenly to all areas and create a uniform sound eld.Achievingsufcientloudnessandintelligibilityisnotsimply

amatterofturningupthevolume.Manypoorpagingsystemsaretheresultoftryingtocompensateforaninsufcient

amountofspeakerswithtoomuchvolume.Atoneendoftheroompeopleareasking“Whatdidhesay?”...whilethe

peoplenearthespeakeraregetting“knockedoutoftheirsocks”.

SPL & dB — WHAAAA???

Here come two more intimidating terms. But, once you master their meaning and application, they will become two of

the best tools you could possibly have. Your customers will also be impressed with your expertise, which will enhance

yourimageasaknowledgableinstaller.Weshouldrstdiscuss“soundpressurelevel”(SPL)whichyourearsinterpret

as“loudness”or“volume”.SPLisexpressedindecibels,abbreviateddB.dB’saretossedaroundalot,withoutmuch

understanding. When you talk dB’s, you are always talking the difference between two sound levels. For example, “100

dBSPL”meansasoundpressurelevel100dBaboveazeropointsetatthelowestsoundpressureleveldiscernible

by the average human ear.

You are also talking differences when you say one sound is 3 dB louder than another sound. A 3 dB difference can be

heardbymostpeople,butitcertainlywon’t“knockyoursocksoff”.Ittakessomethinglikea10dBdifferenceinaverage

SPLtobeperceivedasadoublingofloudness.Asweshallseeinthenextsection,doublingamplierpowergivesonly

a3dBincreaseinaspeaker’soutput.Thesameresult,orbetter,canbeobtainedbyusingamoreefcientspeaker.

Forexample,aceilingspeakermightspecify92dBSPL@1meterdistancefromthespeakerwith1wattofapplied

power.Yet,adifferentspeakermayyield95dBSPL@1meter@1watt.That’s3“free”dB,orabout30%morevolume,

becauseofthedifferenceinspeakerefciency.

Power and distance

Okay,nowthatit’ssafetotalkaboutdB’sandSPL,let’scontinue—Apagingspeaker’sloudness(SPL)isaffectedby

two unchanging laws of physics: The power(inwatts)appliedtothespeakerandthedistance between the listener

and the speaker itself.

Power and the 3dB rule

As previously stated, if you double the power to a speaker, you gain 3 dB. Cut the power in half and you lose 3

dB.Forexample,ifyouhaveanappliancethatproduces90dBatadistanceof64feetusingthe3.8watttap,then

doublingthepowerbyusingthe7.5watttapwillgiveyou93dB.Amodestgainatbest,andsomethingtoreallyconsider

sincedoublingthepowercanmeandoubletheampliercost.Amoreefcientspeakerormoreeffectiveplacement

couldgiveyouthatextra3dBwithouthavingtodoubletheamplierpower.HMM...seemslikewe’vementionedthis

before, but let’s go on.

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Wheelock MX-8 Mixer Specifications Page 7

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