Dynaudio Air Series manual Rear wall cancellation

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ACOUSTICS - BACKGROUND INFO

Rear wall cancellation

When the monitor is set up at some distance in front of a wall, reflections from the wall may occur and influence the perceived frequency response. This could result in comb filtering if all frequencies produced by the monitor were radiated in all directions. But the monitors are typically only omni-directional at low frequencies.

The result of the reflection is a single or few dips in the frequency response perceived in front of the monitor.

This frequency is cancelled because of the oppositely phased reflection

The frequency response may look like this: one cancellation at the frequency that has a wave length of four times the distance to the rear wall.

The dip - or cancellation frequency - is dependent on the distance to the wall. If the distance is 1 m, the first dip frequency will occur at a frequency with a wavelength of 4 m.

l = c / f where

l = wavelength [m] (or ft.)

c = speed of sound [m/sec] (or ft./sec.) f = frequency [Hz]

Hence

4 = 344 / f f = 86 Hz

A closer position will result in a cancellation at a higher frequency. This is then limited by the frequency where the monitor becomes directional and does rot radiate sound to the rear.

A farther position will result in cancellation at a lower frequency. This is limited by the distance being so long, that the reflected sound is attenuated due to the long extra path travel.

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Contents Page Page Voltage Line plug according to standard Important Safety InstructionsPage Table of Contents Quick Setup Reference Quick Setup Reference Main Display Operational OverviewStereo Setup SetupsStereo Setup with mono Subs Stereo Setup with stereo SubsAnalog Setup Digital SetupThis illustration shows how to connect a 5.1 digital setup This illustration shows how to connect a 5.1 analog setupThis illustration shows how to connect a 5.3 Analog setup This illustration shows how to connect a 5.3 Digital setupDig/6 Master This illustration shows how to connect a 6.1 Analog setupOther Chained Setups Stereo Setup With Chains on L & RAnalog/Digital setup Analog connectionsDigital 192 kHz Digital Setup This Manual IntroductionBreak Product ConceptCommon Features Remote ControlMaster Unit Slave & Sub UnitsMaster Unit Analog I/O Rear Panel Description MasterSlave/Sub Optional Digital I/O cardOverload Indication AIR DisplayEnter key Cursor UP/DOWN keys Overload Indication LEDParameter Description Press Enter to access the Select ModeBasic operation in all menus Main DisplaySetup Setup MenuSet Monitor Task External ClockStore LFE channel noteRecall Overview Placing the MonitorsOther situations Close to wall / WallOn the bridge / Console Phase checking Checking the placementChecking by ear when listening to the signals In phase EvaluationNext EqualizingInterchannel calibration Calibrating Main Monitors CurvesAcoustic level calibration CurvePlacing the Subwoofer Evaluation Low frequency sweepsTo Calibrate Checking summing phase cancellationControlling standing waves Checking the CrosspointPhase Introduction PhaseLFE Gain PolarityReverberation time AcousticsGood acoustics Sabines formula Diffusers AbsorbersMembrane absorbers Absorbtion or diffusion ? Resonance absorbersStanding Waves Background Info AcousticsAxial Tangential Radial Room modesHow does the standing waves influence the sound field? How to prohibit standing wavesAcoustics Background Info Comb Filtering Dip frequencies Or +Rear wall cancellation Subwoofer Subwoofer Background InfoLFE Channel Subwoofer & LFE Channel Background InfoCross-overs Low Pass LFE GainCinema setup Delaying Monitors LINE-UP & CalibrationAcoustic summation of audio signals Calibration of 5.1 in an ITU-775 arrangement How to measure the sound pressure?LINE-UP & Calibration Background Info Introduction Remote Control FeaturesAIR Remote Volume potentiometer Preset 1/3 and 2/4 keysREF Level 1-3 keys Shift keyNavigating AIR Soft AIR SoftTools MainNetwork Preset ListSystem Setup Chained monitors Calibrate AIR-BaseMiscellaneous Reset ProceduresGlobal Parameters Local ParametersTC Link Standard Cat-5 cables CablesAES/EBU Standard cables Serial to Cat-5 cableAIR 20 & AIR 25 Master and Slave AIR 6 & AIR 15 Master and SlaveAIR Base AIR-Base-1 & AIR-Base-2AIR Remote specs Room & DistanceGeneral for all Products Error messages etc Delay in System & Error Messages ETCAIR AIR-Base Certificate of ConformityCertificate Of Conformity # Name Preset List