Real time analyzers
Several readers have been asking how we measured the response of the speakers in the sound room. As well, others have asked if there is a good test for determining if your ears are working well. I'll share with you what we did and do. To measure your loudspeaker's response you will need two things: a real time analyzer (RTA) and a pink noise source. Using the two will give you a close approximation of the output your speaker is producing in terms of both volume and frequency. Here is what a plot like that looks like: I just grabbed this as an example and it is not a measurement of anything in particular. Getting a picture to use on these posts from our RTA in the lab is a challenge. What this graph shows you is loudness of the speaker at specific frequencies. Each of the blue lines represents a slice of frequency, the highest frequencies are on the right, the lower bass notes on the left. The height of each slice displays volume; taller equals louder. For a source, there are many available choices. For my application I prefer to use a simple CD with a pink noise track. It's also easy to download the same thing. Here is a link to a free download of pink noise. The easiest do-it-yourself method for making a quick measurement is using one of the fine mobile apps. There is an Apple iPhone app here, and an Android app here. Each work quite well for what you want this for. They both use the built in microphone, equalized for flat response, on the mobile device and include a pink noise source as well. Neither is good enough to design a loudspeaker, but for checking to see how your system is working, they are perfectly fine. The real trick to using an RTA is where to point the microphone. That's rather tricky and I am not a great teacher for this. I will tell you what I know. Try and get an average, standing perhaps a meter or two away from your speaker. Don't get too far back because you'll get much of the room interactions in the measurements. If you get too close to the speaker you will get a measurement more of the individual drivers rather than the speaker as a whole. If nothing else it's a handy low cost tool to play with. Tomorrow I'll give you the secret to a personal audio test.
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