Radioshack Analog Sound Level Meter

How does a sound level meter work?
This Radioshack SPL meter is equipped with a omni directional microphone that is used to measure sound levels in the range of 50-126dB. It uses an analog display that ranges from -10dB to +6dB and a setting that allows you to select one of seven ranges centered at 60dB, 70dB, 80dB, 90dB, 100dB, 110dB and 120dB. For example, at the lowest setting with the dial set to 60dB, the display will show readings in the range of 50 dB through 66 dB. At the highest setting with the dial set to 120dB, the display will show readings in the range of 110 dB through 126 dB. The dial also has a setting that can be used to test the meter's 9V battery.

Aside from a dial for range selection and an analog display, the meter consists of a switch for changing the meter's frequency response (also called the "weighting") and a switch to change speed of its response to changes in sound levels. The weighting switch allows for switching between the standard 'A' and 'C' weightings. Choosing the 'C' weighting will make the meter respond uniformly over the frequency range from 32 - 10,000 Hz, and the 'A' weighting will make the meter more sensitive to frequencies in the range 500-10,000 Hz. The response switch allows for changing the speed of the meter's response from 'SLOW' to 'FAST'. A 'SLOW' response setting will make the meter less sensitive to rapid changes in sound level and should be used for measuring average sound levels. The 'FAST' setting is more useful when you are trying to measure peak sound levels, since the meter will respond to very rapid changes in sound levels.

Although the meter should not require any calibration before being ready to use, there is an input labeled 'CAL' that would allow recalibration if necessary. Finally, the meter is equipped with a phono type output jack for connection to other measuring equipment and a standard mounting socket for tripod mounting.

My Use of the Radioshack Analog Sound Level Meter
As I stated in the introduction, I have owned this SPL meter for quite a long time and have used it extensively in optimizing my 5.1 home theater. I had a couple of DVDs that I used for testing, with the primary one being the Avia Guide to Home Theater Setup. The Avia Guide has a number of test tones and test patterns that make it easy to measure the sound level across the frequency range.

My use of this SPL meter came after I had already chosen the location of my couch and HDTV. From there, I followed the basic setup guidelines for 5.1 speaker placement. I had also already adjusted both the speaker volume levels and the speaker placement of my 5.1 set up using my best guess from listening to some CDs. Normally, you would first choose your primary listening position (most likely the center seat of your couch) and work backward from that point. But, with the size of my TV and the size of my couch, there was really only one arrangement in my basement that would work well and I had to adjust the speakers to fit that arrangement.

After installing the required 9V battery (not included in the box), the first step was making sure I had the right SPL meter settings. Since I wanted to measure the average level of sound and not the peak level, I set the weighting to 'C' and the response to 'SLOW'. Next, I positioned the meter in the location where my head would be if I were seated on the couch watching a movie. It is important to stand to the side of the meter so that you form a right angle between the meter and the sound source - this reduces reflections from your body that might impact the resulting measurements. It is also important to hold the meter steady as you are taking measurements, since any bouncing around can also impact the results.

After getting the meter and myself into the right position, I set my receiver to the normal volume level that I use to watch DVDs. I then began playing the test tones and test tracks from the Avia DVD and writing down the resulting SPL measurements. It took a few guesses as to which dB setting on the SPL meter I should use, but I finally settled on the 70 dB setting. After running through the first test using "pink noise" , I found that my center speaker was producing 4-5 dB more sound than all other speakers, my right front speaker was producing 3-4 dB less than the left front speaker, and the right and left rear surround speakers were both producing 5-6 dB less than the other speakers. After adjusting the receiver settings to boost the level to some speakers and to reduce the level to others, I was able to achieve a relatively smooth result of within 1-2 dB across the left-front, center, left-right, surround-left and surround-right speakers. Next came the same test with "pink noise" , but now it included a signal to the subwoofer. I like to really be able to feel the bass when I watch movies, so I was not surprised when the test showed that my subwoofer was producing 8-10 dB more sound than my other speakers. I dialed back the volume level on my subwoofer a bit and repeated the test a few times, and now my subwoofer is only about 4-5 dB louder than my other speakers in this "pink noise" test. Although this may not be considered optimal by technical standards, my personal preference is to have a bit more low-end when watching movies. Keep in mind that these types of objective tests should never overrule your personal taste when listening to music or movies. You are the one who will be doing the listening, and improving your enjoyment of that experience is the whole goal of this exercise.

Next: Radioshack SPL Meter - Conclusion