SPL Meters

SPL stands for sound pressure levels, a term that represents the local ambient pressure caused by a sound wave. In the home theater manner of speaking, the SPL becomes the immediate sound pressure level from the local atmospheric pressure which is caused by a sound wave at a fixed location on a certain instant of time. The underlying principle behind the SPL might sound vague if you don’t have a background on engineering, but you will definitely feel the SPL in front of a full volume speaker, or the bass thumping in a car audio subwoofer.

Very lately, home theater is sparking large interest in the DiY world. Many DiY enthusiasts scrapped a lot of projects to entertain the newest rage, having their very own home theater. Not only DiYers though, as home theater has become among the latest quirks in real estate planning and selling. The release of inexpensive system (still expensive by the way, but at least more affordable) had also helped propel home theater into the masses’ homes.

Though it is a very complicated venture, Do-it-yourself home theater installation is very feasible. The only thing that complicates home theater installation is the SPL configuration. And hopefully, this article will jump start you with some ideas.

Regardless of what you will be building, whether a dedicated theater with component systems or simple theater-in-a-box, you still have to configure SPL levels to achieve the best audio outputs. One important way to achieve the optimal SPL is to have the exact positioning of the speakers. This is in itself, a complicated task and needs a lot of explanation so I suggest you look another of my article that explains correct speaker placement. But in brief, the first thing to do is identify the probable location of the audience(s). Then have the following:

Put the center speaker facing the listener, but slightly above the ear level.

Put the two main speakers on the opposite corners of the back wall facing the listener, still slightly above the ear level.

The surround speakers are placed on the sides relative to the listener, still slightly above ear level.

Search for for the best location of the subwoofer. Subwoofers usually don’t have a fixed location since every room presents different acoustics.

After doing this correctly (and I mean checking my other guide about speaker installation), each of the audience locations are then tested to see if it gets the same amount of SPL, using SPL meters. The science of SPL calibration ensures that every location gets the same SPL intensity from each of the speakers. In a flawed setting, the audience may be unable to hear subtle details in the surround channels, or that some parts of the sound, like the dialogue, may be overwhelmed by others.

The THX Reference for movie theaters sets the average SPL around 85 dB. Take note that 85 dB in a non theater setting might be too loud, since the relative distance between components to the listener is quite near. My personal SPL preference would be 75 to 80 dB and an intermittent peak of 85 dB. This is my setting by the way, and everyone has different tolerances to sound levels.

The most indispensable tool you need for sound pressure level measurement is an SPL meter. What SPL meters do is measure the level of a sound pressure produced by a source, an example is your audio system. Typical SPL meters have an adjustable sensitivity range from 50 dB to 126 dB, with a choice between Weighted A or C scale. The most familiar brand is the Radioshack SPL Meter; you might find it on your local electronics store.

Sound engineering using SPL meter for your DiY project might be hard, but doable. Remember, most successful sound engineers lack formal engineering degree, though it draws heavily from several disciplines, particularly electrical engineering, music and acoustics. Experience is the key.