KIRCHNER ATB 805 Handbook
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Contents
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28. CALIBRATING THE HIFI STEREO SYSTEM28.1 MICROPHONEThis chapter is for the loudspeaker developers out there! The ATB PC program offers thefunction continuous measurement with averages, a tool that no developer can miss. When usinga DVD player the measurement signal used is the PCM signal on the surround test DVD. If a CDplayer is the signal source then the CD plus signal is used on the auto test CD.The usual frequency characteristic measurements are carried out with a predefined microphoneposition on a certain axis and with a predefined angle. This enables the developer to optimisethe frequency characteristic for this position. To say that this diagram (results) is a lie would betoo hard a statement but the truth is that loudspeakers with almost identical frequencycharacteristics sound completely different with this method. A more satisfactory result is attainedwhen the reflected energy is measured. This corresponds to the audio impression heard with theear because indirect sound plays a larger role in living rooms. The sound waves that arereflected from floor, walls and ceiling must have a volume that is proportional in relation to themusic played. The professional journal “HiFi Vision” has not so long ago completed a series oftests with a rotating microphone and ascertained very satisfying results. Thanks to themeasuring program ATB PC the true frequency characteristic can be simply determined using apersonal computer. The continuous measurement function using averages is the key to correctresults. Whilst the measurement is being carried out the microphone is moved slowly, with adistance of 60 cm from source, in a circle with a radius of 60 cm. Practice shows that thefrequency characteristics are independent from this type of movement and thus enables thedetermination of a frequency characteristic error.The frequency characteristic of a loudspeaker measured with a predefined axis red and itsproper frequency characteristic green.The separate curvatures of a well-constructed loudspeaker will only differ in the drop whencoming towards the high tones, as depicted. A correct measurement is also well balanced. Thedrop in the high tone region is also an advantage in living quarters because the near wallsamplify high tones anyway.28.2 POSITIONING LOUDSPEAKERS AND THE SEATING POSITION92 |
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