June 2, 2005 - Podcast #10

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This weeks show

Today we will cover the news, answer listener emails, discuss how to set speaker levels, and ask for your help with a survey at TechPodcasts.com. Also, starting with next week's show our RSS feed will simply contain the audio enclosure. We will no longer copy the text you see here.

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Calibrating speakers

To calibrate the speakers, you will need a sound meter. These are available at your local Radio Shack store and cost less than $50.

Put a test tone in the left speaker (see your manual) and adjust the volume until the sound meter reads 75dB (85 dB for large rooms). Next, put the tone in the center speaker and read the sound meter. If it does not read 75dB, increase or decrease the level (for that speaker only) until it the sound meter reads 75 dB.

Do this for all the speakers in your home theater. Unless there is furniture blocking the speakers, the adjustments should be small, ± 2 dB.

Notes:
Using efficient speakers requires less power to achieve higher sound pressure levels. Your receiver will last longer too! Sound pressure is measured in decibels (dB). The following table lists some common sounds and their average SPL.

Common Sounds
Noise Level in dB
Comments
Rocket launching pad
180
Permanent hearing loss
Aircraft carrier deck
140
Pain
Jet takeoff (200 feet)
120
Loudest human
Firecracker
100
Very loud
Alarm clock
80
Annoying
Vacuum cleaner
70
Conversation difficult
Clothes dryer
60
Noticeable
Bedroom at night
40
Quiet
Library
30
Quiet

Finally, a human's perception of sound is not linear. Simply put, a 10dB increase in SPL is perceived to be twice as loud (70dB is twice as loud as 60dB). Doubling the power of an amplifier increases the sound by 3 dB at the speakers. Conclusion: Don't let a salesman convince you to upgrade from a 50-watt receiver to a 75-watt receiver. You won't be able to tell the difference.

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