Symptoms of Inadequate Home Theater Acoustics

By Terry Montlick Laboratories LLC

Symptom:

I have to raise the volume control to clearly hear dialog, then lower it for loud music and effects.

Diagnosis:

Low dialog intelligibility. This is a common problem with home theaters that do not have adequate acoustical treatment. A number of factors contribute to poor dialog intelligibility. Long reverberation time (room is too “live”) is the usual culprit. A high background noise level can also effect intelligibility. The room should have an acoustical analysis done to determine where the problem frequencies are, and the right amount of absorption added at the correct frequencies.

Symptom:

I had an installer equalize my audio system so that the frequency response is nice and flat. But my system still doesn't sound good.

Diagnosis:

Inadequate analysis.

Spectrum analyzers work only in the frequency domain, not in the time domain, where major of room acoustics problems occur. Time domain analysis is necessary to diagnose reverberation and early reflection problems. Time domain analysis is harder, and has in the past required an acoustician for interpretation.

Symptom:

The front sounds don’t seem to come from definite spots, or they come from far outside the screen area.

Diagnosis:

Assuming your front speakers aren't too far apart and are properly connected, this is due to early reflections (also called "first reflections"). These come from the screen wall, side walls, floor, and/or ceiling, and appear within the first 15 milliseconds after the arrival of the direct sound. During this time, your ear combines the sounds into one, causing the sound source to shift or become indistinct.

Symptom:

The high frequencies seem weak, but low frequencies are loud and boomy.

Diagnosis:

Assuming you don't have equalizer settings badly skewed, this is due to uneven absorption, with too much in the middle to high frequencies.

Symptom:

Loud music and other sounds are indistinct. The sounds seem to smear together.

Diagnosis:

Inadequate absorption over the full audio spectrum.

In order for the sounds to be “tight,” there must not be too much reverberation in any of the audible frequencies.

So how do I fix my home theater?

Call a professional acoustician!