TOOLS FOR CALIBRATE

OVERVIEW

How much money you have to spent on the diagnose tools. I am sure that you dislike to spent a lot (like me to).  I using a PC minimum Pentium 233MMX. Next thing is a compatible sound card that have full duplex or half duplex should be ok (I use Creative AWE64). Next is only a few software to install  and a files to download. I hope this will give and idea to calibrate your system.

The software you need to install is Sound Forge version 5.0 by Sonic Foundry. If you cannot find the software you still can use Microsoft recording. Another software to be install is Win amp well I think this is easy many of the pc have this player. The hardware is a dynamic microphone. I hope you buy a moderate price of dynamic microphone due to expensive is more accurate. Next thing is the resource for the testing unit. You have to download a few wav files, the 20Hz to 10kHz , 20Hz to 280Hz and 300Hz to 4kHz sine frequency sweep.

DOWNLOADS

Wave Category	File Name
20Hz to 280Hz Sine Frequency Sweep	Sound1
300Hz to 4kHz Sine Frequency Sweep	Sound2
20Hz to 10Khz Sine Frequency Sweep	Sound3

INSTRUCTIONS

1. Install sound forge and Win Amp. Then plug in the dynamic microphone. Be sure you have muting the microphone section in the volume properties of your PC.
2. Then deselect the mute under microphone and start to self test by using your voice. Make sure the microphone is online. Then you set it back to mute mode.
3. Start the Win Amp and please off the equalizer and set the output sound by setting it under Preferences -Plug-ins and select the Nullsoft direct Sound plug-in and close.
4. Play the file name sound1 and you now can hear the sine sweep sound. Adjust the volume to normal level.
5. Place your microphone in the center of the loudspeaker. The microphone must not to far then the loudspeaker.  Do not use your hand to hold it. Lift the microphone by placing on anything that can support it.
6. Open the Sound Forge and click on record button (the Japan red symbol). Then select new and choose mono, 44100 sample rate and 16bit recording then close. Select the box that stated as monitor.
7. Then started recoding by click the red button icon. Now shift to Win Amp and play the sine file.
8. The recording process now running. Wait until Win Amp finished play the sound. Then you shift back to the Sound Forge and click the stop icon. You now can see and output file created. You now started edit the output respond. If there are nothing you see maybe the recording are low in gain. So you must louder the volume using the menu process to select normalize and under normalize select to -10dB for speech. Now you can see and hear the output respond of your system. The best system is the flat respond of every frequency.
9. If you using a Microsoft Audio Recorder you have to  follow the step from  3 to 5. Then you open the Microsoft Audio Recorder and set the recording source to microphone. And started to record.
10. Next play the Sound1 file and wait until it finished and then close the recording session at the Audio recorder. 
11. When the recording process is complete you have to edit the output respond by increase the volume until you hear the sound1 files clearly.
12. Now to get the data. The analysis of the output respond using a simple mathematic. If the source of the file is 15 sec long and sweep from 20Hz to 280Hz that mean every 1 sec the frequency will times to 18.7Hz. 20-280/20sec. The calculation will show you respond frequency (Hz) against time (sec) . Please use the real time starting and ending of the source file. To do this you must firstly check the starting of the recording same as the starting point of the source. You can easily cut unwanted starting time using Sound Forge to get a same starting recording time.

I hope this article will bring you an idea to calibrate your system. I using this method to check my system. It is not an acuarate way. The better is to use a SPL unit. At my country the SPL is around RM500 (USD $ 125) and I cannot afford it. Enjoy..

nanhifi november 2002