1605Chapter 46
Test and Measurement
by Pat Brown
46.1 Test and Measurement.................................................................. 1607
46.1.1 Why Test?......................................................................... 1607
46.2 Electrical Testing....................................................................... 1607
46.3 Acoustical Testing...................................................................... 1607
46.3.1 Sound Level Measurements........................................................... 1608
46.3.1.1 Conclusion..................................................................... 1610
46.3.2 Detailed Sound Measurements......................................................... 1611
46.3.2.1 Sound Persistence in Enclosed Spaces............................................... 1611
46.3.2.2 Amplitude versus Time........................................................... 1611
46.3.2.3 The Transfer Function............................................................ 1613
46.3.3 Measurement Systems................................................................ 1613
46.3.3.1 Alternate Perspectives............................................................ 1613
46.3.4 Testing Methods.................................................................... 1614
46.3.4.1 FFT Measurements.............................................................. 1615
46.3.4.2 Dual-Channel FFT............................................................... 1616
46.3.4.3 Maximum-Length Sequence....................................................... 1616
46.3.4.4 Time-Delay Spectrometry (TDS)................................................... 1616
46.3.5 Preparation......................................................................... 1617
46.3.5.1 Dissecting the Impulse Response................................................... 1618
46.3.5.2 The Envelope-Time Curve........................................................ 1618
46.3.5.3 A Global Look.................................................................. 1618
46.3.5.4 Time Window Length............................................................ 1618
46.3.5.5 Acoustic Wavelengths............................................................ 1619
46.3.5.6 Microphone Placement........................................................... 1619
46.3.5.7 Estimate the Critical Distance DC................................................... 1620
46.3.5.8 Common Factors to All Measurement Systems........................................ 1620
46.3.5.9 Data Windows.................................................................. 1622
46.3.5.10 A Methodical Approach......................................................... 1623
46.3.6 Human Perception................................................................... 1625
46.3.6.1 Percentage Articulation Loss of Consonants- (%Alcons)................................. 1625
46.3.6.2 Speech Transmission Index—(STI)................................................. 1627
46.3.7 Polarity........................................................................... 1627
46.3.7.1 The Battery Test................................................................ 1627
46.3.7.2 Polarity Testers................................................................. 1627
46.3.7.3 Impulse Response Tests........................................................... 1628
46.4 Conclusion............................................................................ 1628
References................................................................................ 1629
Bibliography............................................................................... 1629