User manual PRISM SOUND FINEQC

[. . . ] CONTENTS How to get started. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . FINEQC calibration procedure. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1. 1 Output level. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1. 2 SPL Loopback calibration. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . [. . . ] This way the test will automatically repeat the specified number of times, and use the average for testing. Figure 8 ­ SPL Statistics with adjusted limits Note: When using soundcard - Keep the volume setting on your amplifier, and use the output Level (Fig. 7) to set the output voltage (Vrms). 20 4. 5 Measurement In this chapter I will show how an entire test setup is created. I select "New" from the menu and get the following window (Fig. 9), where I first specify the File name: Figure 9 ­ Full-range SPL Template I have selected the "Full-range" standard (Template) from the drop-down menu, which contains generic standard templates for the most used speakers. The 2. 5second sweep time is slow enough for the tester to listen for bad sounding drivers during normal testing. However the best is to find the Rub & Buzz using the new FINEBuzz feature, which can be set in "Edit QC Test". The limits can be specified in up to 8 bands; in this case the standard template is using 7 bands with +/-2dB from 100-1000 Hz, which is the stable mid-band region before break-up. The standard limits "Window" or "Mask" is opening up towards low and high frequencies, where we expect more deviation due to shifts in resonance frequency Fs and break-up at high frequencies. The user can change the limits any time if needed. Figure 10 ­ Full-range Impedance Template 21 After accepting the SPL limits the Impedance Template appears Fig. The deviation is here defined as a ratio because we are measuring impedance. The max and min ratios are 1. 2 (20%) and 0. 8 (80%) which I choose to use for now. After the sine sweep is played the next button down is "Set Window", which brings up the Time Domain window Fig. 11: Figure 11 - Time Window settings The impulse response is shown in the upper half and the windowed frequency response below. Most of the buttons in the upper half are automatically providing scaling of the impulse response. The time before the impulse is arriving is called the "Flying Time", which is the travel time (in air) from the speaker cone and until it reaches the microphone. The "Auto delay" button will find this time automatically and is on by default. Note: If you move the microphone closer to the speaker after saving the Setup file (*. fts), you may miss the initial impulse and the frequency response will look "strange". If you know that the microphone could move say 1cm closer, you should reduce the Initial Delay setting by 2 (1 gives appr. 0. 7cm). Therefore I only need to care about the end of the impulse, which is indicated in the lower right field: I have chosen 1000 samples or 20. 8mS corresponding to 50Hz (using the 1/f ratio) using a cosine/Hann window (Cos window Out). 20. 8mS is a long time, but is useable in this case because a large well damped test box was used with the microphone at ~20cm distance, which can be calculated from the initial delay of 562. 5uS, giving the actual distance of 19. 3cm. 22 The final windowed frequency response is useable from about 50Hz, showing good response from 150 Hz and almost up to 20 kHz. The acoustic phase response is shown as the dashed line and is well behaved and close to minimum phase. After OK the Z Mode button is pressed to enter the impedance limits screen Fig. First I pressed "Measure" to make sure the measured curve is the actual impedance. [. . . ] If you see the red "Overload" light, then select one step lower Input Attenuation and "Measure" again. The dashed curve is the acoustic phase response which will show less variation when the large pulse is close to 0mS c. Input a suitable number of samples in: (Cos Window Out / End (samples)) i. If you are using an anechoic room or really well damped box use ~10-20mS ii. [. . . ]