Hack #63 from Home Theater Hacks by Brett McLaughlin (O’Reilly Media).
Although the on-screen instructions on calibration DVDs [Hack #62] are clearly written, sometimes questions arise as to how to calibrate the audio portion of the system using the test patterns included on these discs. This hack deals with that process in detail, adding additional detail that is left off of many discs’ instructions.
Figure 8-2. Speaker levels being modified
It also is a good idea to set all treble and bass controls to 0 as well.
Set your meter to “slow” response and the weighting to the setting suggested by the calibration test you’re using (both VE and Avia offer on-screen instructions on proper meter settings). Most calibration tests suggest a “C” weighting (as seen in Figure 8-3).
Figure 8-3. SPL meter weighting and response settings
Positioning the SPL Meter
Place the SPL meter at your main listening position, approximately at the height of your nose while seated, and point it forward, angled upward at about 40°; a decent rule of thumb is aiming it at the point where the ceiling meets the front wall. You also should crouch down (behind a couch if possible) so that you aren’t in between the meter and any speakers. Standing up while taking sound levels results in an inaccurate reading, unless, of course, you prefer to stand through a three-hour showing of The Return of the King!
It is helpful to place the meter on a camera tripod; the RadioShack SPL meter even has a nice tripod mount on its back. This will help make sure you keep the meter in one spot. You’ll find it is a bit tough to hold the meter, read the meter, and make receiver adjustments on the remote. You also can recruit a “calibration buddy” to help you in lieu of a tripod.
Don’t move the meter during the tests. You don’t need to point the meter at each speaker during the tones; in fact, you should avoid doing this. Leave the meter fixed at ear level, pointing forward and angled slightly upward.
Testing the First Speaker
Insert your test tone disc and begin the audio test for speaker calibration. Both Avia and VE have these tests, and they should be reasonably easy to find. The majority of discs start with the left speaker tone. While the left speaker tone is playing, increase the master volume on your receiver or processor until you reach a reading of 75dB on your meter.
The Avia disc has some tones that are intended to be calibrated to 75dB, while others are intended for a reading of 85dB. Be sure to read the instructions carefully to ensure which test tones are which.
Determining the sound level is simple: set the meter’s dial on a number, such as 70. When the dial is set to 70, the needle is displaying sound pressure measurement relative to 70. When the needle hits the middle 0 position, the SPL of the sound you’re measuring is 70dB. If it reads -4, that means it is 4 under 70, or 66dB. To measure 75dB output, set the dial on the meter to 70 and then adjust the speaker volume until the little needle hits the +5 mark on the meter display. To measure 85dB output, set the dial on the meter to 80 and then adjust the speaker volume until the little needle hits the +5 spot on the meter display.
That Stupid Tone Is Moving Too Fast!
The various calibration discs usually play a tone for a few seconds, and then move to the next speaker. This can be a bit frustrating, as that brief tone often doesn’t provide you with enough time to get a good reading, make level adjustments, and prepare for the next speaker. However, the discs tend to put each speaker’s test tone on a different DVD chapter; this allows you to play the tone you want, and quickly press the Repeat button on your DVD player or remote. The tone will continue to play, stop, and then, instead of moving to the next speaker, repeat. Once you’ve got the level locked in, you can move to the next speaker.
At this point, the first speaker should be set so that it is outputting 75dB of sound, with no level correction (the speaker level is at 0dB). This effectively determines the reference level of your receiver [Hack #64]. Once you’ve reached this level of volume, you are done with your master volume.
Testing the Remaining Speakers
As the tone cycles to each of the other speakers, adjust the individual speaker level in the receiver menu so that each speaker measures the proper level on the meter.
Don’t continue to change the master volume on your receiver or preamplifier because this will change the output level from the first speaker tested, skewing your setup.
It might take a couple of times around the room to get everything right. Keep working at it, and be sure to leave the meter in the same place. By the time you are finished, all the channels should measure the same on your SPL meter. It’s a good idea to go around the room one final time to ensure that everything is set properly. Once all speakers output the same level, you’ve got a well-calibrated home theater speaker setup. –Vince Maskeeper-Tennant, Brett McLaughlin
This material has been adapted from Home Theater Hacks by Brett McLaughlin, published by O’Reilly Media, Inc. Copyright O’Reilly Media, Inc., 2005. All rights reserved.
A smart collection of insider tips and tricks, Home Theater Hacks covers home theater installation from start to finish, purchase to experience. Just imagine: no frustrating trial and error process and better yet, no expensive appointments with installation experts. Home Theater Hacks prevents both by imparting down-and-dirty technique not found anywhere else.