how to aim SPL

SPL..........Sound Pressure Level
SPL Meter ....Measures SPL from usually a fixed position, usually in our needs from the sweet spot.
Not all speakers are created equal...Or....are from the the same distance from their location to your ear. Like setting a delay....helps ensure you are getting similar volume..or pressure levels from each speaker reaching your ear all at the same time.
That's my meager understanding of the whole gig...anyone want to add...
Peace StuffMD

Just curious, how accurate is the little Rat Shack analog meter?

Cheers,
Russ

I have both the Rat Shack meter, and a professional grade Bruel & Kjaer meter with the calibration test tone generator. The B&K is factory certified accurate, and I calibrate it regularly.

Russ - the Rat Shack meter is actually pretty accurate above about 50 Hz. Below that, it's pretty whacked.

Add the following dB at the noted frequencies to get the actual output.

16Hz/11dB

20Hz/7.5dB

25Hz/5.5dB

31Hz/3.5dB

40Hz/2.0dB

So, Schumach - to answer your question - the meter reads about 2 dB LOW on the typical sub test tone (around 40 Hz), so 75 dB on the meter is actually 77 dB.

Liv4Fam - a tripod is better than standing. It has better repeatability, and it allows you to not block the rear surrounds with your body. Experts actually recommend crouching next to the meter (or lying on the couch) while it is mounted on the tripod.

Test tones on the receiver are good, and a calibration DVD, like Avia or Video Essentials is even better since it processes the signal through the DVD player. ALL channels (including LFE) should be set to the SAME volume.

Many prefer the sub a tad hot (i.e., a bit louder than the other channels) for moderate volume HT playback and that's fine - I run mine about 2 dB hot. At very high volume HT playback, this can overstress the sub, though, so be careful.

In addition to properly calibrating your system, the Avia or VE DVD also allows you to determine what master volume setting will provide you actual reference level playback in your HT room.

As defined by Dolby Labs, "Reference Level" is 105 dB peaks from any surround channel and 115 dB peaks from the LFE channel. If you set your speaks to small, this becomes 121 dB peaks from the LFE channel.

The Avia disc is mastered 20 dB below reference, so at the correct master volume level, the test tones will be 85 dB at the listening position. The VE disc is mastered 30 dB below reference, so at the correct master volume level, the test tones will be 75 dB at the listening position.

Be aware that most (nearly all) systems cannot safely play back at the true reference master volume setting, so don't try it. I recommend 10-15 clicks below the reference master volume setting for actual comfortable playback that won't ruin your ears or your sub.

Doc