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Twenty Questions Toward a Correct Home Theater Room

by Jeff Hedback December 08, 2007

Let’s get right to it. You love audio, are passionate about your system and are always searching for a better experience, a more accurate response. You’ve heard the term “room correction”. You’ve heard speakers in various rooms, you are aware of acoustical treatments and active room correction systems (ARC). You know that your dedicated audio system is not in a purpose built room. You would like to make the room as “correct” as possible; however you have no clear idea what approach is best for your room.

What is a correct room? Depends…on the use of the space and how the listener perceives sound.. A pro studio has a completely different purpose than a home theater. A home theater that is primarily for movies verse one geared toward listening has different needs in terms of room correction. It should be pointed out that each person perceives sound in a unique manner. So there is no definitive “correct” room, only rooms where the compromises are known and addressed appropriately.

You certainly can get fooled by the frequency response data of speakers. You certainly can get confused by what types of audio/acoustical measurements can be gathered and interpreted. This article is intended to highlight the primary room correction options with enough background to help you select the best way to correct your room.

To do this, I created a version of the childhood game Twenty Questions. Yes, the game where one person selects a target and then compels others to guess this target using a series of questions- Is it...? Our target is Room Correction. There are a great variety of Active Room Correction Systems (ARC) today; more every year as technology rapidly opens new possibilities. When combined with a growing availability of quality acoustical control materials, I suggest it is difficult for a theater-phile to know how and where to start a room correction effort. I enlisted the help of pros across the board. The "guessers" are from different sides of this enticing topic: acoustics, active room correction, custom integration, musical content, and audio engineering.

Summary definitions for our purpose:

Active Room Correction (ARC) happens before the event using digital filters. These systems have the ability to address frequency response, time domain issues, spatial response (how the room sounds at various locations), impulse response issues, and phase response of the speaker itself. The room data is gathered by an acoustical mic/analysis process (each manufacturer typically offers their own system), and the DSP makes adjustments to the signal before it is transmitted by the speaker. The results are minimized room coloration of the content.

Acoustical treatments “work” at the boundaries and address issues by “absorbing” sound energy and/or scattering reflections. Devices include bass traps, absorption panels and diffusion panels. The type and placement of acoustical treatment will determine the frequency response, time domain and spatial response results.

In both cases, there are layers of complexity based on distances between source/surfaces/listeners and the physics of how sound behaves at different frequencies.

Let's get on with the Game!

Each of the participants was given the qualifiers and questions below:

Select one answer per question. Please answer in relation to your day to day efforts.

1- little/none
2- Minimal
3- Take it/leave it
4- Helpful
5- Crucial

The Questions-

1. Room design including sound isolation, room dimensions, and surface finishes?
2. Use of acoustical reflection control devices such as absorption and diffusion panels?
3. Use of acoustical low frequency control devices either passive or tuned?
4. Acoustical measurements of the room actual or predicted?
5. Acoustical coupling of speakers to surfaces, i.e mounting options (stands, in-wall, shelves, etc.)?
6. Speaker positioning?
7. Spatial response, meaning how the room responds at various positions not just a single location.
8. Crossover adjustments.
9. Phase response of speakers including subwoofer(s).
10. DSP design: number of filter points, measurement points, etc…
11. Aesthetics including surface finishes, furnishings and lighting?
12. Consumer demand for innovative acoustical treatment products?
13. Consumer demand for innovative active room correction products?
14. Use of specially trained room calibration specialists?
15. Video Quality?
16. End user expectation is similar to control room environment?
17. End user expectation is similar to a commercial cinema?
18. Dynamic range of content
19. Changes in musical composition and sound effect elements in relation to the advances in residential theaters?
20. Changes in surround mix techniques due to advances in residential theaters?

and now on to the feedback from the various industry folk that I polled on these questions....


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Recent Forum Posts:

gullfo posts on December 17, 2007 22:53
i'd have to side on the folks rating the room as one of the most important aspects. as Russ Berger points out, right or wrong, it all interacts as a system. you need a good room, good electronics, and good setup to get the maximum benefit from your system. tweaking via EQ and time/phase effects should be a final step with the understanding that time/phase effect ARC systems will be point solutions rather than a broad treatment.
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