Calibrating front stage

I picked up an SPL meter to calibrate my fronts (and sub) tonight and wanted to run the numbers by you guys.

Currently running 340 classics for left and right, 340se for center and a PSB 6i sub.

Using a meter to calibrate to 70db, my receiver was on -24.5db, left 0db, center -3db, right +1db, sub +4 (but that needs a lot of work, havent played with room position, etc etc yet)

Does that sound anywhere near right? I was using the test tone out of my Harman Kardon AVR 247.

Crossover set at the receiver is 60hz for the left right and center
Seating position is 10ft from l/c/r, room size is about 17ft front to back, 5 ft from left speaker to left wall, right side of room is open

While those number sound okay, what are you using to generate the tones?

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Originally Posted by AndrewM

Using a meter to calibrate to 70db, my receiver was on -24.5db, left 0db, center -3db, right +1db, sub +4 (but that needs a lot of work, havent played with room position, etc etc yet)

Does that sound anywhere near right? I was using the test tone out of my Harman Kardon AVR 247.

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The left, center, and right channel settings look fine, although I prefer to use all negative values (cuts instead of boosts). As for the subwoofer level, I'd suggest using a much lower value on virtually any receiver: -5 or -6 as opposed to +4 (turn up the volume control on your sub to compensate). This is to help ensure that the subwoofer pre-out is not overloaded by the combination of the LFE channel and bass management.

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Originally Posted by AndrewM

Crossover set at the receiver is 60hz for the left right and center

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You might want to consider crossing over at 80 Hz instead.

I got this from SVSOUND's FAQ and I'm confused:

"Keep the receiver's subwoofer output control to about 25% up or lower than "0 dB" (or say -6dB given a typical receiver channel limits of –12 dB to +12 dB) . This will allow your amp to work with the cleanest signal possible from your receiver, while still leaving plenty of downward adjustment you can use from your viewing position (using the remote)."

My receiver sub level goes from 1-20. Does this mean that I should put it at 5 or 15 before calibrating by adjusting the sub amp?

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Originally Posted by Grayson73

My receiver sub level goes from 1-20. Does this mean that I should put it at 5 or 15 before calibrating by adjusting the sub amp?

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For standard calibration using test signals and an SPL meter, on your specific receiver, you should set the sub level at 5 to begin with, make a couple of attempts to set the volume control on the sub to get fairly close to the intended value on the meter at the primary listening position, and then have a seat and tweak the sub level setting on the receiver once again to fine-tune your sub's calibration.

However, note that as I pointed out in another thread, because of unpredictable room interactions (that nonetheless share some general characteristics), the calibration might be skewed--potentially by quite a bit (pink noise calibration seems to work a lot better at higher frequencies). So while this might make for a better starting point than no measurement at all, feel free to adjust your sub's volume control over time as you play an increasingly diverse collection of material in order to find the compromise that is most acceptable to you. Now, if you want to achieve a significant degree of control over the situation, then read the following pages:

http://www.hometheatershack.com/roomeq
http://www.hometheatershack.com/forums/bfdguide

Sounds like their advise is after calibrating everything knock the sub down about 6dB. Find Dread Pirate's post about the set-up discs being hot for the sub.

Interesting. I calibrated using 15 because I found that the sub would stay in standby mode sometimes when playing at lower volumes.

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Originally Posted by Quinn

Sounds like their advise is after calibrating everything knock the sub down about 6dB. Find Dread Pirate's post about the set-up discs being hot for the sub.

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I think I just said that some of the subwoofer calibration signals on both of the major calibration DVDs are wrong. I probably should have been more specific.

Digital Video Essentials' subwoofer signal is encoded in the LFE channel only, and is apparently recorded 10 dB louder than it is supposed to be--in other words, they probably just used the very same signal they had used for the other channels. According to the instructions, you should match the levels at 75 dB on your SPL meter, but because the decoder turns up the LFE channel by 10 dB just like it is supposed to, you're going to end up turning the subwoofer's volume down 10 dB too low for playing movies. :( The obvious solution would be to calibrate your subwoofer 10 dB higher than the main channels on your meter. One additional complication for which I currently have no confirmation is that supposedly newer pressings of this DVD have been corrected. It looks as though DVE owners will have to experiment a little to find out what's on their copy. :rolleyes:

Avia has at least one (I believe it's the only one) incorrect subwoofer test signal: the LFE portion of the six-channel pan is recorded too low, and should be ignored entirely. The actual subwoofer calibration signals are correct, as far as I know, but they absolutely require that you set all of your speakers to "Small" to let bass management route the bass to the subwoofer; in contrast to DVE, there is no signal in the LFE channel whatsoever. While I would've liked for them to have included some LFE-specific signals to enable additional tests, Avia's method should result in a superior calibration to that of DVE.

The reasons for setting the subwoofer pre-out level to about 25% of the way up from the lowest available value really have nothing directly to do with the calibration DVDs or the errors therein. The subwoofer pre-out is basically a tiny amplifier itself, which bears the burden of combining the LFE signal hyped up by 10 dB with all of the low-passed bass from up to seven main channels. Using as low a setting as you can helps ensure that this little amp is not overloaded into clipping or other distortion before it's even able to get its signal to the subwoofer's amp. Those who use parametric equalizers (PEQs) to flatten their subwoofers' frequency response must also take into account the range of signals that their PEQs can accept, which is critical. In addition, you wouldn't want to set the subwoofer level too low or else electronic noise might become more of an issue than it should, and you won't have any room to tweak the level lower if you have to for some reason. As it turns out, in real world use, for most receivers in most situations, setting the subwoofer level at 25% will usually get you pretty close to the ideal balance between all of these factors, and also allows you, in most cases, to use reasonable values for the levels of the rest of your speakers as well as the sub's volume control--it's just a good "rule of thumb" based on experience (albeit not always the ideal value).

One additional note is that most people who calibrate their subs using pink noise tend to deliberately run them hot by a few dBs because it just sounds better to them in practice. There are at least a couple of potential reasons why this is so (besides simply preferring exaggerated bass response, which is hardly becoming of Ascend owners in particular). The first is that most rooms tend to greatly reinforce certain limited bass frequency ranges (most commonly centered near 40 Hz, 60 Hz, or both) to the point of driving down the overall calibrated level enough that the resulting audio is seriously deficient in both the highest and lowest bass regions. This very often has a negative effect near the common subwoofer crossover regions, which can spoil the integration with the other speakers. Obviously, turning the overall sub volume a bit higher than the calibrated level can help ameliorate this integration issue (although it does nothing for the bloated bass). The other reason is that our hearing decreases in sensitivity more rapidly in the bass (and high treble) region with reduced volume than it does in other regions of the audio spectrum (Fletcher-Munson curves). In a nutshell, this means that any given sub calibration is only valid for one volume level, and if you often listen at a lower volume, as most people do most of the time, then you'll actually get a more accurate presentation of movie soundtracks by running your sub a bit hot (this is far from a perfect solution, but virtually nothing about HT is perfect anyway). The best solution, in my opinion, would be to dial in a carefully shaped "house curve" with a PEQ, which has worked out really well for my situation, for instance (although I still listen to music using a flat frequency response).

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Originally Posted by Grayson73

Interesting. I calibrated using 15 because I found that the sub would stay in standby mode sometimes when playing at lower volumes.

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Using a higher sub pre-out value would definitely help with waking the sub from standby mode, and for all I know, this setting might work perfectly for your equipment and your viewing preferences. That said, it's certainly not a conservative practice, generally speaking. The only way to know for sure whether you're safe, I guess, would be to run tests using an oscilloscope to check what's coming out. As long as you don't hear anything obviously wrong, though, you're probably OK.

In my case, for comparison, I have to set the sub pre-out level to -9 dB (nearly all the way down) to avoid clipping the signal on my PEQ while playing the most intense bass scenes I have. As you probably suspect, I don't even bother with the "Auto" setting on the sub because it rarely works right with my settings--I just leave it on while I'm home and turn it off when I leave. I probably should get one of those "Smart Strip" thingies so that my sub will turn on and off automatically with my receiver.