Common Confusion in Home Theater: Part 8

3d1In the previous blog post, we discussed how the room in which you place your home theater (or two-channel audio system) can greatly affect the quality of the sound produced. In this post, let’s explore room correction and room dynamics (the size and shape of the room and the nature of the stuff in it).

  • Part 1: Volume and zero dB, updating firmware, disadvantages of Blu-ray
  • Part 2: Speaker resistance and analog vs. digital amps in AV receivers
  • Part 3: PCM vs. bitstream and Blu-ray player upscaling/upconversion
  • Part 4: THX certification, DLNA network access, and distortion and THD
  • Part 5: HDMI (including cable length and controversial expensive cables)
  • Part 6: Closed-back vs. open-back around-ear headphones
  • Part 7: Understanding your room and room dynamics
  • Part 9: Ethernet, separates, and broadband internet routers


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Curt Robbins

Room Correction

Many AV receiver models, especially those manufactured within the past five to eight years, feature something called room correction (also called auto-calibration or automatic EQ). In a nutshell, room correction, as its name implies, makes small adjustments to the speaker outputs of the receiver based on your particular room layout in an effort to improve your sound—with a focus on surround sound and the combined effect of all of your speakers.

The task of room correction involves a small microphone that plugs into your AV receiver. The receiver produces a series of test tones from each individual speaker that are “heard” by the calibration microphone, which provides feedback to the receiver. The receiver uses this information in two ways. First, it adjusts the relative loudness of your speakers so they’re all producing sound at the same level (based on the position of the microphone during testing). Second, it attempts to determine how your specific room acoustics are affecting and harming the quality of the output of your speakers and applies equalization (EQ) to try to improve the situation.

Don’t downplay the importance of good room correction. “I didn’t realize how much better [music] could sound until I finally took the 30 minutes to run the [room correction] program. Wowza, what an experience! The surround channels seemed to come to life, and the bass response throughout the room was much more consistent and pleasing to the ears,” said David Vaughn in a receiver review for Sound & Vision magazine.

If your receiver doesn’t feature built-in room correction (many don’t, especially entry-level models), you can use a supplemental tune-up disc (a good example is Sound & Vision Home Theater Tune-Up, available for about $15 from resellers like Amazon). Most products of this type offer a comprehensive set of tests and tools to adjust and enhance both your audio and video, including speaker placement, sound levels, and other audio settings. Another, albeit more expensive, option is hiring a certified technician to calibrate your home theater (installers often offer this service).

Speaker Position & Room Dynamics

As you learned in the A Word About Your Room section of the Components chapter, it’s important to realize that the room in which your speakers reside has a dramatic effect on the quality of the sound produced by them. This includes the volume, clarity, and dynamic range perceived by you and your listeners. Rooms that provide too much sound wave reflection, or, conversely, too much sound absorption, will color the audio produced by any speaker. The shape of the room also heavily influences the path traveled by sound waves before they reach your ears, significantly influencing your perception of the sound.

The position of speakers is also critical and applies to both two-channel systems as well as 5.1 and larger surround configurations. Not only is the position of speakers relative to each other significant, but also their locations relative to the room and walls. Is your home theater environment fully enclosed? Partially open? Mostly open? What is the nature of the surfaces of the walls? The ceiling? Is the floor highly reflective ceramic tile, or a deep-pile sound-absorbing carpet? How dense is the furniture and decor in the room? These are all important considerations that go beyond the inherent quality of the speakers themselves.

Curt Robbins is author of the following books from Amazon Kindle:

You can follow him on Twitter at @CurtARobbins, read his AV-related blog posts at rAVe Publications, and view his photos on Flickr.