Question on Avia disc and Sound Level Meter

[tjkahn]

Forgive me for posting this here, as I already posted it on the Speaker Positioning Forum, but that one doesn't seem to get a lot of looks.
I've been meaning to ask this for a while, and I know this is the right place to get it answered. I actually have 2 quesitons:

1) On the Avia disk, they say to calibrate to 85db, or lower if that's too loud. My question is, why does that even matter? Isn't the only important thing to have the same db reading for all speakers, and then you can listen to whatever overall volume you want by adjusting the master volume when watching a film or listening to music. Am I missing something here?

2) For my five main speakers (which are JBL's that I'm upgrading to Axiom's), it's very easy to get the needle to hold steady in the same place for all five speakers, but the needle tends to bounce around a little more on the subwoofer (M&K MX-125). I assume that this is normal because the lower frequency causes more vibrations and the needle is reacting to the vibrations on the wall/hardwood floor caused by the subwoofer? I'm taking a guess here. Input from someone who actually knows what they are talking about would be greatly appreciated.

Thanks!!
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[Audioholics]

Good questions:

1) You want it much louder than any potential ambient noise. I use 75dB pretty consistently.

2) Pink noise through a subwoofer will wreak havok with your room so you will see alot of play with the needle, though usually only around 3dB. I try to shoot for the middle. 74-77 dB if I'm calibrating to 75dB, with a tendency to err a bit higher if at all. You can also help by setting the response time to slow so it doesnt jump around as fast.

 

[Unregistered]

1) On the Avia disk, they say to calibrate to 85db, or lower if that's too loud. My question is, why does that even matter? Isn't the only important thing to have the same db reading for all speakers, and then you can listen to whatever overall volume you want by adjusting the master volume when watching a film or listening to music.

85dB is Dolby 'reference' level. When the test pink noise is at a level of -20dBFS (20dB below 'full scale'), you adjust the meter to read 85dB. With a full scale signal, your peaks will reach 105dB (85+20). The test tones on Avia are at the required -20dB level and they are just telling you to adjust your channel trims so the meter reads 85dB to match Dolby reference standards. They suggest using 75dB in some cases simply because 85dB is quite loud and peaks that reach 105dB are *extremely* loud.

Note that Digital Video Essentials (DVE) tones are at -30dbFS which is why they tell you to calibrate to 75dB. Calibrating using DVE to 75dB will result in the same settings as using Avia calibrated to 85dB [85+20=105, 75+30=105]. Test tones on THX certified receivers follow the -20dBFS requirement; non-THX units may or may not.

You are correct that all that really matters is that all of the channels are equal - you can set your idea of 'reference' to anything you want. The idea is simply to have a mark on the dial that represents the maximum you would ever want to listen at. For Dolby standards, that is 0dB on the volume scale (for receviers with relative volume displays) and at that level the SPL is 85dB (as described above).
For receivers with only absolute volume displays (like 0-100), they usually don't tell you which number to use for 'reference' - you can choose any number you like (within reason, obviously you cannot achieve such a high output level at at a low number on the scale when the channel trims have a limited range, usually +/-12dB). A good rule of thumb is somewhere around 75-80% of the range of the scale.

You are also correct that you will likely NEVER listen to music or movies at that level - you will always adjust the volume dial to somewhere below reference level that is comfortable for your ears - but having a reference is still valuable. By definition, a reference is simply a point from which everything else is relative. So if you calibrate to Dolby reference level (the way it 'should' be in the theater) and you like to listen at -20, then you can say that you prefer to listen at 20dB below reference. But, you can only compare your listening levels to others if you all use the same test tone and calibrate to the same SPL. That is why the reference level is specified - so we can all be on the same page when discussing levels.

2) For my five main speakers (which are JBL's that I'm upgrading to Axiom's), it's very easy to get the needle to hold steady in the same place for all five speakers, but the needle tends to bounce around a little more on the subwoofer (M&K MX-125).

The RS meter is less accurate at low frequencies; you can find charts of correction factors by searching on the internet. There is also some controversy over how accurate the tones on the test discs are for the subwoofer - many suggest just using your receivers tones for the sub.

Just try to match the sub as close as possible to the mains. Note that the Dolby ref standard allows the LFE channel to be up to +10dB hotter (so peaks of 115dB). If you use the RS meter for the sub, it will already be a little hotter than the mains, so probably best to just get it close and then tweak by ear.

 

[tjkahn]

Quote:

"85dB is Dolby 'reference' level. When the test pink noise is at a level of -20dBFS (20dB below 'full scale'), you adjust the meter to read 85dB. With a full scale signal, your peaks will reach 105dB (85+20). The test tones on Avia are at the required -20dB level and they are just telling you to adjust your channel trims so the meter reads 85dB to match Dolby reference standards.

You are correct that all that really matters is that all of the channels are equal - you can set your idea of 'reference' to anything you want. The idea is simply to have a mark on the dial that represents the maximum you would ever want to listen at. For Dolby standards, that is 0dB on the volume scale (for receviers with relative volume displays) and at that level the SPL is 85dB (as described above)."

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Ok, I think I get it. This is pretty interesting stuff. So what you're saying is that if I set my Denon 3802's volume to 0dB and play the test tones out of the avia disk, then I would calibrate the individual channel volumes to 85dB for 'reference' level sound. I think what the Avia disk fails to mention is that YOUR RECEIVER'S VOLUME SHOULD BE AT 0dB! and at that level, I would start with all of my channels at -12 dB, the lowest possible setting, and work up, because pink noise at 85dB, IMHO, is very hard to listen to (especially if the wife is home)! Then, if you want to listen to 10 dB below reference, I would just set the volume to -10. It takes the guesswork out of where to set your master volume when you want to watch a movie at reference, reference -10, etc. I'm sure this is old stuff to most, but just understanding it now is pretty cool (at least I think I understand it).

Thank you, and also thanks for the comments on the sub. It pretty much confirms what I thought, and when everything is calibrated you need to use your ears to be a final judge.

 

[tjkahn]

2) Pink noise through a subwoofer will wreak havok with your room so you will see alot of play with the needle, though usually only around 3dB. I try to shoot for the middle. 74-77 dB if I'm calibrating to 75dB, with a tendency to err a bit higher if at all. You can also help by setting the response time to slow so it doesnt jump around as fast.

That's what I thought (or was hoping), and I am within about 3dB (using the slow setting). They seem to indicate on the Avia disk that it's easy to calibrate all of the speakers precisely. For the speakers, it was pretty easy to keep the meter fairly still, but there was noticably more play from the sub, however not outside the acceptable range you mention above.

Thanks!! BTW, I enjoyed your review of the Epic 80 home theater, and I'm auditioning it with the M22's up front instead of the 80's (I'll eventually get the 60's or 80's when I have more room for floorstanders, assuming I like the speakers during the audition period).

 

[Unregistered]

I think what the Avia disk fails to mention is that YOUR RECEIVER'S VOLUME SHOULD BE AT 0dB!

You should set it at 0dB only if you want to use 0 as the reference volume setting. That is the 'standard', but you can choose any number you like. In a small room, with a reasonably powerful receiver you may not be able to get 85dB with the volume dial at 0 simply because the channel trims don't have much range - if that is the case, set it at -10 and go again.

Here's an example from calibrating one of my receivers: (uses absolute scale of 0-79)

Volume dial=60, channel trim(fronts)=-11, SPL=85dB
Volume dial=50, channel trims(fronts)=-3, SPL=85dB

So you can see that there is some leeway to setting the level that is dependent on the range of the trims. I left mine calibrated with 50=85dB. So 'reference' volume setting for this receiver is 50 and at that setting it matches Dolby reference level because I calibrated it to 85db SPL. If I happen to listen at a volume setting of 40, then I am listening at 'reference' - 10. If you calibrate to 0=85dB, then -10 = 'reference' - 10. If you calibrate to -10=85db, then -20 = 'reference' -10.

It can be confusing, as evidenced by the large number of questions on the topic I have seen on many forums, but once you do it a few times, it becomes clear. If you think 85dB is way too loud (I would agree!), then by all means choose 75dB.

 

[tjkahn]

You should set it at 0dB only if you want to use 0 as the reference volume setting. That is the 'standard', but you can choose any number you like. In a small room, with a reasonably powerful receiver you may not be able to get 85dB with the volume dial at 0 simply because the channel trims don't have much range - if that is the case, set it at -10 and go again.

If you think 85dB is way too loud (I would agree!), then by all means choose 75dB.

Although I haven't recalibrated yet, you make an excellent point - I doubt with my average size room (perhaps a bit smaller), and the Denon 3802's master volume set to 0dB, that the channel trims would be able to go low enough to produce an output as "quiet" as 85dB. So my reference point will likely be below 0dB on the maser volume, regardless of whether I calibrate to 75dB or 85dB.

Perhaps I misspoke when I said that the Avia disk fails to tell you to set your master volume to 0dB. What is clear to me now, and wasn't clear to me from watching the disk (although I will have to watch it again to see if I missed anything), is that you should set the master volume to the point at which you want to listen to movies at your calibrated levels. It really doesn't matter if it's 0 on a dB scale, or 50 on an absolute scale. Then, having that number memorized, you will always be able to listen at YOUR calibrated levels (whether it's 75dB, 85dB, etc.), or at a relative point higher or lower by adjusting your master volume accordingly. This has become much less confusing.

 

[Unregistered]

It really doesn't matter if it's 0 on a dB scale, or 50 on an absolute scale. Then, having that number memorized, you will always be able to listen at YOUR calibrated levels (whether it's 75dB, 85dB, etc.), or at a relative point higher or lower by adjusting your master volume accordingly. This has become much less confusing.

Exactly! Now help spread the word as there are still many audio enthusiasts that haven't quite got it figured out yet.