SPL Meter - Is this right?

[Mavicator]

Forgive my lack of knowledge on this stuff, but by setting the channels + or -, aren't you essentially altering the power output for the channel in the same way as if there were seperate volume knobs for each channel? If this is true, then by lowering master volume from 0 to -10 and then raising a channel to +10, you're putting out the exact same power from the AVR to the speaker.

With that logic and assuming I'm not already making an idiot of myself, what would be the point of calibrating at -25 instead of calibrating at zero and just raising or lowering the volume to achieve your desired db level?

Of course I may have missed something in your post entirely.

[TheSoundBroker]

A few other points to consider...

Your 75db reference level should be set with your center channel as the master speaker at 0 DB. This way all the other speaker levels in the system key off the center. This is easier to do than chase things all over the place with the left and rights which often have uneven response due to acoustics. Set your center level to zero, turn the volume control up until it reaches 75db and then set the other speakers to 75db with that volume level as the master. Write down that volume control setting in case you ever need to duplicate things. Also, remember that if you have brand new speakers, you'll want to recheck your calibrations after about 100 hours when things are broken in...many speakers tend to get more efficient as the mechanical complience improves with some hours on the system.

If you have more than one seat in the room, you may want to take some measurements at the other seats to see what the levels are looking like. If you want one person performance, the single position test setting works great...but you may end up with imbalances at the other listening positions if your room doesn't have real even acoustics. This can be particularly true with the subwoofer and may lead you to play with positioning to get the smoothest and most even response at each seat (assuming there is more than one seat and you care ).

On your rear surrounds, do each one individually...but also try to do a combined response. Most of the time this entails unhooking the other speakers and running a test disc with pink noise thru the rears either by using a 5 channel "party mode" on the surround proc. or by physically hooking the rear channels into the front channels on the reciever (remember to change the crossover settings or you'll get false readings!). The reason to do this is because of cancellation effects...particularly with dipoles, and is one reason a lot of people set the rear channel levels...and then end up turning them up a few DB. Remember, you should see a few db more output with two speakers running so if the meter is reading 78db running two rears...you are good. Chances are you'll see less. You can also try this with the mains, but if you get *less* output with the lefts and rights running then you'll either want to check phase, check your speaker alignments, or seriously think about room treatment!

[DrWho]

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On 8/3/2005 3:03:22 PM Mavicator wrote:

Forgive my lack of knowledge on this stuff, but by setting the channels + or -, aren't you essentially altering the power output for the channel in the same way as if there were seperate volume knobs for each channel? If this is true, then by lowering master volume from 0 to -10 and then raising a channel to +10, you're putting out the exact same power from the AVR to the speaker.

With that logic and assuming I'm not already making an idiot of myself, what would be the point of calibrating at -25 instead of calibrating at zero and just raising or lowering the volume to achieve your desired db level?

Of course I may have missed something in your post entirely.

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I think this question is going to depend on the reciever in question and how the internals were constructed. In most cases the channel volume is controlling the preamp stage and then the master volume is controlling the voltage output of the power supply which is feeding the amps (kinda like a voltage controlled submaster for those of you that know what that is). So if you were to boost your preamp volume all the way, you run the risk of incurring clipping on that channel, which will then effectively cause your amp to clip as well. Running your input volume too low causes you to amplify the noise floor with the amp that is now turned up to compensate. It's best to find a happy medium somewhere in the middle where you aren't hearing any noise and where you aren't at risk of clipping.

I do it like Trey where I set the volume on the reciever to the value where I normally listen. Then I adjust the individual channels so that they all balance out, trying to keep the average as close to 0 as possible (ignoring the LFE channel setting). The reason I ignore that in my 0 average calculation is because there generally aren't any noise issues with a subwoofer (thanks to the crossover).

I have also noticed that my denon pink noise test tones don't correlate to any of the dvd's with tests on them...the biggest discrepancy is that the dvd tones require a 3dB boost for the center when compared to the reciever's tones. I don't understand the reason for this, but it doesn't matter to me because I tweak the center channel for every movie anyway because they're sometimes too loud or too quiet depending on the movie.

[MrMcGoo]

I am under the impression that the THX Ultra2 specification for subwoofers is that they must be able to hit 120.5 decibels at the listening position. Do not ask me why that extra .5 decibel is there in the specification.

I use full bandwidth pink noise from Avia to calibrate with the subwoofer off, but with the processor's crossover engaged. I calibrate to 75 db per channel with the processor volume set to -10.

If you have a receiver or amp that may clip, Trey's method is very good. If you have an amp that is highly unlikely to clip, then Trey's method may add distortion from clipping in the peramp. The bottom like is that you need to carefully pick the lesser of the two evils.

Bill