Home THX Equalization Manual Rev. 1.5 Home THX Audio System Room Equalization Manual Rev. 1.
Home THX Equalization Manual Rev. 1.5 Table of Contents Introduction and Background: Why Room Equalization? ..................................... 3 Test Equipment Requirements ........................................................................... 4-5 The Home THX Equalizer ....................................................................................... 5 Equalization Procedures ...................................................................................
Home THX Equalization Manual Rev. 1.5 Introduction and Background: The goal of the Home THX Audio Program is to reproduce in the home the film sound experience exactly as the director heard it on the film dubbing stage. Even with all the elements of a Home THX Audio System correctly installed, one challenge remains to our ability to perfectly “close the loop” connecting the dubbing stage to the home environment. That challenge is the almost infinite variability of room acoustics.
Home THX Equalization Manual Rev. 1.5 Test Equipment Requirements The use of a single RTA, a large number of multiple measurements, and the averaging of these measurements is a time consuming 1.) Real Time Analyzer process and can be subject to a high degree of operator error. It is therefore highly recomThis procedure requires the use of a realmended that R-2 be employed whenever time (spectrum) analyzer and a pink noise source. possible. The analyzer approved for use is theR-2 THX Audio Analyzer.
Home THX Equalization Manual Rev. 1.5 Equalization Procedure peak level meter or some RTAs you will notice peaks far above the average. This is more noticeable through a Subwoofer than through an LCR speaker. This is because a random bass peak can last for a longer time (lower frequency = longer period) than most RTAs or SPL meters average for. Higher frequency peaks last for a shorter period.
Home THX Equalization Manual Rev. 1.5 SECTION 1: Room Analysis Using the R-2 Analyzer 1.1) Define The Listening Area: The first step in correctly equalizing a Home THX Audio System is to identify the listening area. The equalized response of the system will be averaged over this area to provide a balanced sound field for all listeners. Equalizing for a single position can result in poor performance at other points in the listening area.
Home THX Equalization Manual Rev. 1.5 • Choose four positions that represent prime listening positions spaced equally throughout the listening area (Fig. 1). • Position your analyzer’s microphones at seated ear height (38" to 48" off finished floor). Place the microphone(s) on a stand. • Do not attach any microphone directly to the analyzer or hold it in your hand. Your body is an acoustical object large enough to influence what is supposed to be a room measurement.
Home THX Equalization Manual Rev. 1.5 1.3) Home Theatre and Test Equipment Set-Up Home Theatre Equipment: • Switch your Home THX Controller to the “Dolby Pro Logic Surround” mode. The Home THX Cinema mode must be switched off for this procedure. Note: For Controllers featuring Dolby AC-3 Decoders, there is no easy method to insert broad band pink noise into this signal path. Equalization should be done through the Dolby Pro Logic mode on these controllers as well.
Home THX Equalization Manual Rev. 1.5 Set the measurement time to aminimum of 20 seconds. F-4 , F-2 Begin the multiplexing operation. F-1 1.4) , F-5 Real-Time Analysis: • Begin with the Center Channel • Start your pink noise source. F-7 If using “Wow!” Chapters 9, put the appropriate track on A-B repeat so that it conveniently cycles automatically.
Home THX Equalization Manual Rev. 1.5 1.5) Equalize: The resulting spatial average will approximate the inverse of the correct EQ curve. As a starting point, assume that a dip of -3 dB on the analyzer calls for an increase at the appropriate EQ frequency of +3 dB. Remember the scale on the analyzer is 2 dB per division. Since we will re-measure a number of times, any over correction or under correction will be caught.
Home THX Equalization Manual Rev. 1.5 You will have achieved a correct EQ curve when successive measurements show the same flat response. Repeat this procedure for each remaining screen channel and the subwoofer. Use the appropriate track on “Wow!” or your pink noise source, and remember to connect only the speaker that you are testing. Your front channels are now equalized. 1.
Home THX Equalization Manual Rev. 1.5 When equalizing the Subwoofer Channel, you should concentrate on reducing the serious peaks. You may find that because of the depth of the room modes a ruler flat response is not within the range of the equalizer. This not a major concern since a response within ± 3 or 4 dB is very acceptable. One tip; a reduction of energy in the 20-30 Hz range will enable the subwoofer to play louder without before encountering excursion problems. 1.
Home THX Equalization Manual Rev. 1.5 nel splices to the Subwoofer channel by using your Left and Right Channel EQs. Remember, if the relative levels are off, use your Home THX Controller to adjust the levels.Use only the Left, Center, or Right EQ controls to adjust for uneven frequency response at the Subwoofer splice point. WARNING! If a dip remains at the Subwoofer splice point even after drastic EQ, check for correct loudspeaker polarity.
Home THX Equalization Manual Rev. 1.5 SECTION 2: Room Analysis with a Conventional RTA This method of room analysis was written tomimic the spatial and temporal averaging of the R-2 THX Audio Analyzer. The procedures for choosing microphone positions and the techniques for equalization are identical with both types of instruments. 2.1) Define The Listening Area: The first step in correctly equalizing a Home THX Audio System is to identify the listening area.
Home THX Equalization Manual Rev. 1.5 • Choose four positions that represent prime listening positions spaced equally throughout the listening area (Fig. 8). • Position your analyzer’s microphone(s) at seated ear height (38" to 48" off finished floor). Place the microphone(s) on a stand. • Do not attach any microphone directly to the analyzer or hold it in your hand. Your body is an acoustical object large enough to influence what is supposed to be a room measurement.
Home THX Equalization Manual Rev. 1.5 2.3) Home Theatre and Test Equipment Set-Up Home Theatre Equipment: • Switch your Home THX Controller to the “Dolby Pro Logic Surround” mode. The Home THX Cinema mode must be switched off for this procedure. • Disconnect or disable the Subwoofer and the channels you are not measuring. You want to analyze each channel individually and disconnecting unused channels helps prevent assignment errors.
Home THX Equalization Manual Rev. 1.5 NOTE: CHECK THE OVERALL SPLs AT EACH MICROPHONE LOCATION. IF THESE VARY BY MORE THAN ± 1 dB, ADJUST THE MASTER VOLUME ON THE CONTROLLER TO COMPENSATE THE SPL AT EACH LOCATION TO APPROXIMATE THE SPL AT THE REFERENCE POSITION (Microphone 1). FAILURE TO DO SO MAY RESULT IN SKEWED SPATIAL AVERAGES. With the four positions stored in memory, now average to obtain the spatial response for the entire listening area.
Home THX Equalization Manual Rev. 1.5 2.6) Re-analyze: After applying the corrections to the appropriate channel frequency centers, re-run the above procedure to verify the corrections. You will find that you will have to measure and correct several times to achieve a balanced and repeatable response. NOTE: ABOVE 1 kHz, IN TYPICAL ROOM ENVIRONMENTS, THE SOUND FROM HOME THX LCR SPEAKERS IS DIRECT FIELD DOMINATED AND THE FREQUENCY RESPONSE MAY BE POSITION DEPENDENT. AVOID DRAMATIC EQ CHANGES ABOVE1 kHz.
Home THX Equalization Manual Rev. 1.5 2.7) Subwoofer Equalization: All Subwoofer measurements should be done using the Center Channel Pink Noise band on “Wow!” (Chap. 9) or with your pink noise source into the Left and Right inputs of the decoder. Disable or disconnect the LCR speakers.
Home THX Equalization Manual Rev. 1.5 2.8) Confirm the Subwoofer Splice: Center Channel The next step is to activate the internal test signals present in your Home THX Controller and readjust all SPL’s to their correct 75 dB C weighted levels. This will even out any level variations introduced by equalization. After level check, return to your “Wow!” Center Channel pink noise; Chapter 9. Observe on your RTA the relative levels of the Subwoofer and the Center Channel.
Home THX Equalization Manual Rev. 1.5 WARNING! If a dip remains at the Subwoofer splice point even after drastic EQ, check for correct loudspeaker polarity. Subwoofers or LCR speakers connected out of phase may cause a “suck-out” at the crossover point. Subwoofers offset from the LCR plane by a large distance or multiple Subwoofers can do the same. If you are using a single Subwoofer and have a large offset, reverse the polarity of the Subwoofer signal.
Home THX Equalization Manual Rev. 1.5 Equalization Checklist: Set-UP • Set Up Home THX Audio System • Aim L, C, R loudspeakers using pink noise on “Wow!” disc • Calibrate individual channel levels with controller’s internal test signals • Set Up Microphone positions • Set RTA weighting for Flat • Set Up Scale Range and Divisions With R-2 Audio Analyzer only • Set Measurement interval for 20 sec.
Home THX Equalization Manual Rev. 1.5 Appendix: “WOW!”— A User’s Guide Chapter 2: The Home THX Audio System; Tomlinson Holman discusses the elements of the Home THX Audio System and what sets it The “WOW!” laser disc was created by apart from more conventional home theatre Lucasfilm for use with Home THX Audio systems. systems. “WOW!” consists of exciting demonstration, educational, and testing material to help you best Chapter 3: Mode Selections; appreciate the Home THX Audio System.
Home THX Equalization Manual Rev. 1.5 Chapter 7: Pink Noise, Circulating L-C-R-S, -10 dB; This signal is comprised of broad band noise and can be used to calibrate all the individual output level controls after the input level controls have been calibrated. Set the level to read 75 dB SPL on a sound level meter, C-weighted, Slow mode in each channel in turn, measured from the primary listening position.
