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How To Calibrate Your Surround Sytem Using an SPL Meter (Page 1 of 2)

In movie theaters and professional studios, audio systems are calibrated using sophisticated measuring equipment to make sure the sound is being replicated in a precise manner. One of the calibrations they do involves balancing the volume output of every channel in the system. Today's home theater receivers give you one of the tools necessary to do the same for your home theater system.

What you need:

  1. A home theater receiver with a pink noise (or test tone) generator.
  2. An SPL (sound pressure level) meter.

Why is SPL calibration important?

Recorded sound material is mixed to certain standards. During the mastering process, a Sound Engineer adjusts the sound level of every sound that goes into the recording. When played back on a home audio system, the sound pressure levels of those same sounds will vary from how they were heard by the Sound Engineer due to many factors.

For example: A Sound Engineer may sit at a distance of 5 feet from each speaker during recording. The studio audio system is setup to make sure that the volume level of each channel is the same for every speaker at the position of the Sound Engineer. In your living room, you may sit 5 feet from the surrounds, 10 feet from the center, 9 feet from the front left and right, and 6 feet from the subwoofer. Since the speakers are at different distances from you, all of the speakers will have different volume levels relative to your position when sound is played back through them.

Proper calibration ensures that you hear everything with the same intensity as the Sound Engineer when he recorded the audio material. Without proper calibration, you may not hear subtle details in the surround channels that you should, or some details may be overwhelmingly exaggerated if the levels are too high. You also may be hearing more volume from the left speaker than the right. Worst of all, the center channel may become difficult to hear because the fronts are set so high that the center can't overcome them. In other words, improper calibration destroys the vision that the Sound Engineers had while recording, and you're not experiencing the sound as it was intended.

The SPL meter

Although calibrating the channel levels on your receiver is actually pretty easy, you'll first need to have a general idea of how an SPL meter works.

SPL meters come in two varieties. There are models with an analog meter and ones with a digital display. Most experts recommend the analog version because it's easier to work with. There are several places you can obtain a SPL meter. For most, a model from Radio Shack is usually good enough for home use. There are other models available that may take more accurate measurements, but they are usually much more expensive. There are five major components on a SPL meter. Depending on the model you own, your meter may have more functions than what's listed below.

SPL Meter Features Explained

  • Microphone - there is a sensitive microphone at the top of the SPL meter.

  • Range - This indicates the range of sensitivity for the microphone, which has corresponding values usually from 60db to 120db.

  • Weighting - The weighting affects how sensitive the microphone will be over a given frequency range. For calibrating an audio system, you will use the C-weighting setting.

  • Speed - This adjusts how quickly the needle will respond to changes in sound pressure level. The "slow" setting averages the changes in pressure. You will want to use the "slow" setting for calibrating a home theater receiver.

  • Readout - The readout on analog meters contain some markings and a little needle, similar to what you saw on amplifiers years ago. The markings will vary in meaning depending on the range of the dial. The 0 marking will mean 80 if the dial is set to 80. If the dial is set to 90, the -4 marking will mean 86, and the +4 marking will mean 94. Digital meters will have an LCD display that indicates the sound pressure level in db.

Setting up, positioning, and holding your SPL meter

With your speakers in their permanent locations, move to your primary listening position. If you frequently sit in multiple locations, find an average location between your listening positions. For example: If you will be sitting on both the left and right sides of a sofa, the middle will be the average position. Hold the meter in a position close to what your ears would be. In other words, don't calibrate your system while standing unless you're standing when you listen to your speakers.

There is mixed advice about how to hold your SPL meter to take measurements. Some will tell you to aim the SPL meter's microphone at the speaker you're measuring. If you consistently do it like this for every speaker, you'll be fine. Others will tell you to hold the meter straight up for every channel. Most enthusiasts feel that holding the meter straight up provides more consistent results between channels. (Think about it. Your ears are not directly aimed at your speakers when you listen to them).

Check the battery on your SPL meter. A weak battery will skew your results, so replace it if it's low. Set the range on the SPL meter to 70, C-weighting, and slow response.

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