# SPL calibration after applying house curve...?



## Vader (Jul 8, 2006)

Hi all,

When calibrating SPL levels via pink noise (band limited, 40 to 80Hz), what exactly am I measuring? My layman's understanding is that pink noise is composed of all inclusive frequencies at equal SPL levels (is this somewhat accurate?). That being the case, if I were to calibrate the sub SPL level _after_ applying my house curve (about 12dB/ovtave, 32Hz - 80Hz), wouldn't I be setting the sub trim relative to the highest SPL in the curve (in this case, 40Hz), and everything above that (up to 80Hz) would be lower than it should be? Should I calibrate the SPL flat first, then apply the house curve, effectively running up to 10dB hot near 40Hz? Everything sounds great when calibrating against the house curve, but if I am doing something wrong...


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## Mark Seaton (Jun 22, 2006)

12dB/oct house curve? This would mean your response is >12dB stronger at 32Hz than 80Hz?  That might appear true when looking at the subwoofer alone, with the low pass and without the mains, but if you have that much lift to the bottom end, I can't imagine it not sounding a bit bloated or overly "fat" at all but the lowest listening levels.

There is a lot of confusion about the "proper" setting for subwoofer levels, and rightfully so. Properly recorded test signals account for proper C-Weighting of most SPL meters. They also assume flat frequency response from both your main speakers and your subwoofer. Good luck on that one. 

I prefer to look at a full range signal passed through the center channel and look at the frequency response. Make your level determinations based on the combined response you get after smoothing the subwoofer's response. Of course then you get into the quandry of the level having effects on the response through the crossover. How the sub and mains interact, will determine what adjustments make sense. In the real world, the subwoofer LFE test signals should give you a baseline indication from which you will make adjustments based on listening and/or full range measurements.

Sorry, I know everyone want's us to tell them that a simple meter and level adjustment does the trick, but that's really just the starting point if you're interested in experiencing all that your system is capable of.


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## Wayne A. Pflughaupt (Apr 13, 2006)

> When calibrating SPL levels via pink noise (band limited, 40 to 80Hz), what exactly am I measuring?


Well, with the meter set to “A” weighting, it only “sees” response down to 500 Hz or so. Change to “C” weighting and the bass frequencies are added. “C” weighting starts to roll out about 30 Hz or so, IIR.

So – considering that in most systems the bass frequencies will be at a higher level than the mid and upper frequencies, with pink noise and meter set to “C”, the reading you get on the display will essentially be the _hottest bass frequency_. That’s “exactly what you are measuring.”



> That being the case, if I were to calibrate the sub SPL level I]after[/I] applying my house curve (about 12dB/ovtave, 32Hz - 80Hz), wouldn't I be setting the sub trim relative to the highest SPL in the curve (in this case, 40Hz)...


Yes, (assuming you’ve EQ’d out all the peaks), but that’s okay. You have to keep in mind that while the house curve _measures_ hot at the lower frequencies, it _sounds_ flat all the way through to the top of the sub range. If you haven’t already, you might want to take a look at the house curve sticky thread over at our REW / BFD Forum.



> ...and everything above that (up to 80Hz) would be lower than it should be?


Lower, yes, but that’s not necessarily “lower than it should be.” If the upper bass frequencies sound weak, you’ll need to re-calibrate your house curve.

Basically, the routine is to EQ the sub with the house curve, then calibrate as you would normally. All you’ve done with the house curve is assured the sub will sound flat, so using a calibration disc should nail it. (I say “should,” because I’ve never used a calibration disc.) If you feel the sub level needs to be tweaked from that point, feel free. Many (myself included) prefer the sub level to be a bit hotter for movies than for music.

Regards,
Wayne


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## Vader (Jul 8, 2006)

> 12dB/oct house curve? This would mean your response is >12dB stronger at 32Hz than 80Hz?


Hi Mark,

I determined the perceived curve following the "House Curve Sticky" here on HTS. Basically, I listened to an 80Hz tone, followed by a 32Hz tone, and adjusted upwards until I perceived the volume to be the same. It came out to be about 11.3 dB (actually, there was a lot of wiggle room, I'm sure; since I could not play the tones directly back to back as I had to switch volume while giving the VC a cool down).



> ...but that's really just the starting point if you're interested in experiencing all that your system is capable of


Yea, I know.... before I started with the sub stuff, I thought all that was needed was to pick a good spot to put the sub and crank it.... sometimes ignorance really is bliss (but I am loving learning and tinkering)....

Wayne,

My sub is EQ'd to the house curve, and I calibrated using the tones on DVE (75 dB for satellites, and 85dB for LFE) with the BFD filters in place. So I'm not so far off base? To my untrained ears, it sounds great (entirely due to all the help and patience you guys have afforded me!)


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## Wayne A. Pflughaupt (Apr 13, 2006)

> To my untrained ears, it sounds great...


Well, let’s see: You’ve smoothed response with the equalizer, you’ve dialed in a house curve (most likely after deciding you didn’t like the way it sounded flat), and you’ve adjusted the sub level in relation to the mains. No wonder it sounds great! Listen to it for a couple of weeks, then bypass the equalizer. If it suddenly sounds bad to you – congratulations, you no longer have “untrained ears.” 

Regards,
Wayne


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## Vader (Jul 8, 2006)

Wayne,

I see (heard) what you mean tonight! I re-calibrated my house curve to see if I was indeed gaining some omph of the lower frequencies at the expense of some of the higher ones. I tried a lower slope of about 5dB/octave, re-calibrated the subs (interestingly, the gain barely needed to be adjusted), and watched "The Empire Strikes Back". The bass now sounded anemic to my ears, so I re-instated the 12db/octave curve. It sounds fuller, but not "boomy" as Mark suggested it might (it stays tight either way). I guess at some point I should just stop messing with it and enjoy it, huh?


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