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THX Ultra2 Reference Level Calibration, the Good News and Bad News

post #1 of 53
Thread Starter 
So I finally got around to calibrating my system to THX Ultra2 specs.

The Ultra2 spec is 85db with pink noise at -20dFS from clipping for each speaker, and 85db for the sub -30dFS from clipping (and flat to 20hz, @ 115db), in a room no less than 3000cubic feet.
(My room just happens to be exactly 3000cubic feet.)


So here is my results though:

My DSP's and pre-amps meet the spec, it has around -30dbFS of headroom away from clipping.

I'm meeting it at my LP with my mains, but just barely... That is with SEOS's and 9100watts @ 8 ohms of amp head-room across the 7 SEOS's (when I get around to finishing them all).

Ok, but what about the subwoofers?
Well... 8 of my 18's with 20kW is JUST enough to meet the spec (when summed all together). So I'd glad I'm adding more subwoofers and watts, soon-ish...

So in summary: if you ignore the fact that you need between 15 to 30db (and dFS) of headroom, then just about everyone's system can do it (almost).
But if you factor that in, then it is pretty much unobtainable to most normal-joe systems / gear / budget.
[God help us all.]

The more headroom you have the better, of course...



Here is a quick vid, this is with two SEOS's, and 8 of my 18's and roughly 30kW's.

Way beyond it or just meeting it? (You decide.)

Edited by BassThatHz - 12/9/13 at 10:53pm
post #2 of 53

Congrats on meeting the THX Ultra2 spec! Correct me if I am wrong, but you are using sealed subs, right? That's why it takes so much power and so many subs to hit that level. A ported system tuned to 16 Hz or so will (likely) hit that level at 20Hz with 1/4 the drivers and power—isn't that what @notnyt is going for? But THX Ultra2 spec has nothing to say about 8hz levels, and I'm sure your response is flatter than just two ported subs would allow for.

Nevertheless, I've heard strong argument for and against bothering with single-digit hz. When it comes to deep bass, clearly there is no free lunch. But it matters not—you met THX Ultra2 spec with a dedicated pressure-chamber home theater space, and that's quite exceptional and awesome.

I wish more people understood the value of dynamic headroom. I recently found myself debating with someone who thought 20 Watts/channel was more than anyone in their right mind would ever need.


Edited by imagic - 12/10/13 at 7:37am
post #3 of 53
Quote:
Originally Posted by imagic View Post

Congrats on meeting the THX Ultra2 spec! Correct me if I am wrong, but you are using sealed subs, right? That's why it takes so much power and so many subs to hit that level. A ported system tuned to 16 Hz or so will (likely) hit that level at 20Hz with 1/4 the drivers and power—isn't that what @notnyt
 is going for? But THX Ultra2 spec has nothing to say about 8hz levels, and I'm sure your response is flatter than just two ported subs would allow for.


Nevertheless, I've heard strong argument for and against bothering with single-digit hz. When it comes to deep bass, clearly there is no free lunch. But it matters not—you met THX Ultra2 spec with a dedicated pressure-chamber home theater space, and that's quite exceptional and awesome.


I wish more people understood the value of dynamic headroom. I recently found myself debating with someone who thought 20 Watts/channel was more than anyone in their right mind would ever need.

Yep. And if it ever stops snowing and siht stops breaking I'll get the lumber for this. Rear cylinder went out on my truck yesterday, off to change that now frown.gif It's snowing. Bah.
post #4 of 53
The question is, is that level tolerable?

Seems like most people, and I mean AVS people though not necessarily the crazies among us, say that reference is way too loud.
post #5 of 53
Quote:
Originally Posted by noah katz View Post

The question is, is that level tolerable?

Seems like most people, and I mean AVS people though not necessarily the crazies among us, say that reference is way too loud.

Agreed. I can't tolerate reference. It is one thing to demo for 30 seconds, but no way for actual listening for any length of time.eek.gif
post #6 of 53
If my wife and I are doing movie night and no kids are home, I go as high as -10 depending on the movie. Most of the time, -15 is plenty hot for me.
post #7 of 53
"Rear cylinder went out on my truck yesterday, off to change that now..."

damn. you make it sound like swapping out a water pump. :-)

"The question is, is that level tolerable?"

i don't actually think that is "reference" for a home size room. for some reason, measured spl in a large room seems much lower than in a small room...and that's measured at the same level. the folks who actually set the "reference" are the tv industry guys and there is a monster document that discusses all of this, but i forget what it is called. iirc, 'reference' in a something the size of an average living room is about 76-77db, not 85.

the other thing is redirected bass will further increase the subwoofer channel demands. with 7 channels redirected (coherent), its about 125 db or so. :-) they don't tell you that at 'big buy' while demonstrating thx rated subwoofer with 10" driver.
post #8 of 53
Thread Starter 
Yeah, sealed isn't the most efficient, that's for sure.
I have never tried to watch a THX movie at Ref Level before, so I couldn't even tell you if it's too loud or not. I normally just set it to whatever sounds realistic and/or unlikely to bottom my subs or make me go deaf.
post #9 of 53
Thread Starter 
I think there is really four milestones to consider, and could be used as a gauge (in THX-land at least):

Goal 1) Just being able to hit 85db with pink-noise at all seats (from each speaker).
Goal 2) Just being able to burst up to 105db on ALL channels, and 115db on the sub, and be flat to 20hz and under 4-10% THD.
Goal 3) Having an additional 20-30db of DSP and Amp headroom beyond the pink-noise 85db calibrated level.
Goal 4) Having speakers that can (realistically) handle all the above without exploding. (Yikes, that's a tough one!)
post #10 of 53
Quote:
Originally Posted by LTD02 View Post

"Rear cylinder went out on my truck yesterday, off to change that now..."

damn. you make it sound like swapping out a water pump. :-)

It is smile.gif

Thought i just blew out a cylinder.. nope, metal brake line blew... so redid the entire brake system in the back... new cylinders, drums, lines, pads, springs, and a new fuel filter, fuel lines, and oil change for good measure. Took about 3 hours working slow.
Quote:
Originally Posted by LTD02 View Post

"The question is, is that level tolerable?"

i don't actually think that is "reference" for a home size room. for some reason, measured spl in a large room seems much lower than in a small room...and that's measured at the same level. the folks who actually set the "reference" are the tv industry guys and there is a monster document that discusses all of this, but i forget what it is called. iirc, 'reference' in a something the size of an average living room is about 76-77db, not 85.

the other thing is redirected bass will further increase the subwoofer channel demands. with 7 channels redirected (coherent), its about 125 db or so. :-) they don't tell you that at 'big buy' while demonstrating thx rated subwoofer with 10" driver.

Reference levels hurt on the higher frequencies... i just boost the crap out of the bass instead, can't take the super loud highs.
post #11 of 53
Quote:
Originally Posted by BassThatHz View Post

I think there is really four milestones to consider, and could be used as a gauge (in THX-land at least):

Goal 1) Just being able to hit 85db with pink-noise at all seats (from each speaker).
Goal 2) Just being able to burst up to 105db on ALL channels, and 115db on the sub, and be flat to 20hz and under 4-10% THD.
Goal 3) Having an additional 20-30db of DSP and Amp headroom beyond the pink-noise 85db calibrated level.
Goal 4) Having speakers that can (realistically) handle all the above without exploding. (Yikes, that's a tough one!)

Reference is indeed an incredibly tall order.

To ensure proper level setting, test tones can differ wildly. Good Read:

http://www.meyersound.com/pdf/cinema_technical_papers/cinema_calibration_tech_report.pdf

Most BluRay content out now is more compressed for home use, differing from the Theatrical Mix, and playing back at your receiver's 'Reference' could be way too loud.

Most BluRay releases have digital clipping. I'd like to say it is rare, but it isn't. The better your speakers track that signal, the worse it will sound.

A well done soundtrack properly using the dynamic range available without clipping in a very well treated room (absorption 'mimics' a larger space in the MF/HF region) and low distortion speaker playback should be enjoyable, with the loudest parts startlingly loud. I like to refer to the movie Drive, after the Pawn Shop holdup.

A 7.1 track with a coherent bass sound to all channels, all within 0.1dB of digital clipping will ask 128dB out of your subwoofer. I can think of very few who can do this with low distortion, hence the plurality of "-10dB systems" out there, me being one of them.

The loudest instantaneous single effect in a film I have measured is ~125dB. The loudest prolonged (0.125s or greater) effect I have measured in a film is a hair over 122dB. Folks, this is LOUD. I measure in the digital domain, no DA/AD converters, no rolloff. Just the data on the disc.

JSS
post #12 of 53
Quote:
Originally Posted by notnyt View Post

It is smile.gif

Thought i just blew out a cylinder.. nope, metal brake line blew... so redid the entire brake system in the back... new cylinders, drums, lines, pads, springs, and a new fuel filter, fuel lines, and oil change for good measure. Took about 3 hours working slow.
Reference levels hurt on the higher frequencies... i just boost the crap out of the bass instead, can't take the super loud highs.

I do a lot of twin cylinder engines so I read it as an engine cylinder... haha I was thinking to myself wow just going to pull the motor and break it down real quick... alright then. lol
post #13 of 53
Quote:
Originally Posted by Shan87 View Post

I do a lot of twin cylinder engines so I read it as an engine cylinder... haha I was thinking to myself wow just going to pull the motor and break it down real quick... alright then. lol
LOL! I was thinking the same thing, as your car's ENGINE has cylinders too!

I thought, "man, that guy knows he has to replace a back cylinder in his engine? How does he know that??? eek.gif
post #14 of 53
I'm with Not, the high can literally be ear piercing. Pump up the bass and have some fun.
post #15 of 53
I must be a rare breed when it comes to movies. There are many people who listen to music louder but I watch all my movies at reference assuming the recording is good.
post #16 of 53
Quote:
Originally Posted by wvu80 View Post

LOL! I was thinking the same thing, as your car's ENGINE has cylinders too!

I thought, "man, that guy knows he has to replace a back cylinder in his engine? How does he know that??? eek.gif

I've been building and tuning engines way longer than speakers smile.gif Last time I timed myself, was under two hours from start to finish to pull an engine and replace it one I had built the day before... this was in the street in front of my house. Now I have a proper garage, though I need to build a sub for it. Due to lack of space. I'm probably going to mount it up between the speakers somewhere.

post #17 of 53
^LMAO at Not. I guess Moggie isn't the only Jack of all trades around these parts. Reminds me of a guy on the GTR forum who did a full upgrade of 800hp to the wheels all DIY on a $90k car that already produced 600+ with easy bolt ons and Cobb app. You just never know where such a knowledgable person resides.

Not, you use iPhone's panorama feature for the garage pic?
Edited by audiovideoholic - 12/10/13 at 11:34pm
post #18 of 53
Quote:
Originally Posted by audiovideoholic View Post

^LMAO at Not. I guess Moggie isn't the only Jack of all trades around these parts. Reminds me of a guy on the GTR forum who did a full upgrade of 800hp to the wheels all DIY on a $90k car that already produced 600+ with easy bolt ons and Cobb app. You just never know where such a knowledgable person resides.

Not, you use iPhone's panorama feature for the garage pic?

android, android dev here wink.gif
post #19 of 53
Thread Starter 
Wish my garage was that big... I can barely fit my power tools in my current one, which leaves no room for throwing wood around.
Maybe in the next house I buy I'll have something proper... but then I'd have to build another theater. But I haven't even finish this one! (DOH!!!)
post #20 of 53
Quote:
Originally Posted by notnyt View Post

android, android dev here wink.gif

Mechanic...
Android Developement...
Electrical Engineering...
Carpentry...

What other tools am I missing in your repertoire?

Quite the wealth of knowledge. I've learned a lot from you over the years man.
post #21 of 53
Quote:
Originally Posted by notnyt View Post

I've been building and tuning engines way longer than speakers smile.gif Last time I timed myself, was under two hours from start to finish to pull an engine and replace it one I had built the day before... this was in the street in front of my house. Now I have a proper garage, though I need to build a sub for it. Due to lack of space. I'm probably going to mount it up between the speakers somewhere.


ugh i so miss having a nice garage


when i started building this i didnt have one so i did all the work outside ( engine overhaul + built and installed a twin turbo kit )



atleast now i have a nice shop down at the farm to work on it , it's in the middle of getting a new engine, upgraded turbos, and a larger nitrous kit installed
post #22 of 53
Quote:
Originally Posted by BassThatHz View Post

So I finally got around to calibrating my system to THX Ultra2 specs.

The Ultra2 spec is 85db with pink noise at -20dFS from clipping for each speaker, and 85db for the sub -30dFS from clipping (and flat to 20hz, @ 115db), in a room no less than 3000cubic feet.
(My room just happens to be exactly 3000cubic feet.)


So here is my results though:

My DSP's and pre-amps meet the spec, it has around -30dbFS of headroom away from clipping.

I'm meeting it at my LP with my mains, but just barely... That is with SEOS's and 9100watts @ 8 ohms of amp head-room across the 7 SEOS's (when I get around to finishing them all).

Ok, but what about the subwoofers?
Well... 8 of my 18's with 20kW is JUST enough to meet the spec (when summed all together). So I'd glad I'm adding more subwoofers and watts, soon-ish...

So in summary: if you ignore the fact that you need between 15 to 30db (and dFS) of headroom, then just about everyone's system can do it (almost).
But if you factor that in, then it is pretty much unobtainable to most normal-joe systems / gear / budget.
[God help us all.]

The more headroom you have the better, of course...



Here is a quick vid, this is with two SEOS's, and 8 of my 18's and roughly 30kW's.

Way beyond it or just meeting it? (You decide.)

Sorry if this is a dumb question... but ... If you have a THX Ultra cert AVR, and set it up with the test tones per normal setup procedures (75db), doesn't that get you what you're doing now if your gear can handle it?
post #23 of 53
"Sorry if this is a dumb question... but ... If you have a THX Ultra cert AVR, and set it up with the test tones per normal setup procedures (75db), doesn't that get you what you're doing now if your gear can handle it?"

that is kind of what he was getting at with his post...most systems can do 75db just fine. it is the 20db of uncompressed headroom at the seat that gets tough and the 30db+ of headroom in the bass that is beyond most systems even those with "thx rated" marketing bling. (30+ because of redirected bass, so it can actually be almost 40 depending on how many channels is redirected and the nature of the signal (coherenet or incoherent)).
post #24 of 53
So it's all about the headroom?

The 75 db tones are actually calibrating for 85 db playback/105 db peaks on the mains. Subs it cals for 105 with 115 db peaks. No?

EDIT- just read the first post again. Awesome.... now I'm shopping for headroom.

The vid is not working for me.
Edited by pdxrealtor - 12/19/13 at 3:29pm
post #25 of 53
Quote:
Originally Posted by MKtheater View Post

I must be a rare breed when it comes to movies. There are many people who listen to music louder but I watch all my movies at reference assuming the recording is good.

I'm with you..... I think a lot has to do with room treatments and proper calibration of the system. Reference in the beginning for me was not even doable. Now that I'm almost dialed it's not as much fun to watch below.,
post #26 of 53
Thread Starter 
Quote:
Originally Posted by LTD02 View Post

"Sorry if this is a dumb question... but ... If you have a THX Ultra cert AVR, and set it up with the test tones per normal setup procedures (75db), doesn't that get you what you're doing now if your gear can handle it?"

that is kind of what he was getting at with his post...most systems can do 75db just fine. it is the 20db of uncompressed headroom at the seat that gets tough and the 30db+ of headroom in the bass that is beyond most systems even those with "thx rated" marketing bling. (30+ because of redirected bass, so it can actually be almost 40 depending on how many channels is redirected and the nature of the signal (coherenet or incoherent)).

LTD02 beat me to it, even if your AVR is THX Ultra2 "bling" rated (nice one LTD I like that wink.gif ), it doesn't automatically mean you'll actually be THX capable at all (as per above and below).
The 75db thing is merely a courtesy, because 99% of people think 85db pinknoise is too loud. Not sure if any/every AVR corrects for that difference or not. (I would hope so, otherwise everyone needs to be running at +10db on their AVR's to actually be at THX Reference SPL wink.gif )

I don't use an AVR and my gear isn't certified by THX (that I know of).
I'm certifying it myself: BTH-Ultra2 certified system tongue.gif
Quote:
Originally Posted by pdxrealtor View Post

So it's all about the headroom?

The 75 db tones are actually calibrating for 85 db playback/105 db peaks on the mains. Subs it cals for 105 with 115 db peaks. No?

EDIT- just read the first post again. Awesome.... now I'm shopping for headroom.

No, the THX standard is:

Speakers-> 85db for a -20dFS pinknoise signal WITH 20db of amp burst-power headroom below clipping (i.e. 105db peaks without clipping)
Subs-> 95db for a -20dFS pinknoise signal WITH 20db of amp burst-power headroom below clipping (i.e. 115db peaks without clipping), and be -3db @ 20hz

For Ultra2 you need to do all that, in at least 3000cubic feet and be 4-10% THD (or better).
[and that's ignoring the THX-video standards.]


I should really make a DVD iso with -20dFS pinknoise on it for everyone to attempt, followed by a 60hz 0dFS burst, 20hz 0dFS burst, and 2khz 0dFS burst track.
For safety reasons it would go like this:
Step 1) Play the pinknoise track on the disc at 85db at your seat. (if you readjust levels after this point, tis an automatic THX failure.)
Step 2) Disconnect all your speakers and subs (just in-case they would blow up)
Step 3) Play the burst tracks. If your amps and DSP's clip, or otherwise explode, then you just failed the THX standard. biggrin.gif
Step 4) If you've reached this point successfully and are brave enough to continue, connect your gear back up and repeat step 3.
Step 5) Play a THX intro disc, just to double-confirm

Step 6)


Congratulations you are officially THX Reference certified (and BassThatHz-Ultra2 certified tongue.gif)



Edited by BassThatHz - 12/20/13 at 1:10pm
post #27 of 53
How do you know what the THX standard is? Every time I have looked I came up empty, except for really shallow marketing stuff. Is there a white paper that can be downloaded for free?
post #28 of 53
So, in other words my THX certified AVR wont qualify? Haha.

I have REW and understand how to do the test tone 85 @ -20 but how would I do the bursts? I like blowing stuff up.

I officially have an excuse to buy more gear. Ive been thinking of upgrading to the jbl 3678s anyways..



Lol @ the simpsons video. I would like to make that my intro screen that plays everytime before we watch a movie!
post #29 of 53
Thread Starter 
Check it out. I just made the file. Good luck trying to pass it wink.gif

If nothing else... it will help to tell the difference between -20db pinknoise and 0db burst power. eek.gifbiggrin.gif



and the raw sound file (if you don't like youtube quality):
ReferenceLevelPlaybackOptimizer.ogg 3957k .zip file

I decided not to make it a DVD iso, too much effort and too big an upload.
post #30 of 53
"How do you know what the THX standard is?"

for a long time, thx has been coy about what exactly its certification means...because of course if consumers knew that 85/105/115 was the standard, then everybody with 85/105/115 could say that is where they are without paying thx any money.

http://www.thx.com/consumer/thx-technology/thx-reference-level/
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