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Are you getting the "THX Reference Level" in the listening position? Do we really need such an output level in our home-theater rooms?

trl

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#1
I've seen several threads on Internet forums about measuring THX Reference Level on our domestic audio equipment from home. A very good article about the THX Reference Level would be http://www.acousticfrontiers.com/2013314thx-reference-level/. A very good read would be Techniques-for-establishing-and-maintaining-audio-loudness.pdf and cinema_calibration_tech_report.pdf, both attached to this post.

The idea behind finding the THX Reference Level for our home-use audio equipment is to ensure a good dynamic for watching movies, well...at least this is how the THX guys think that it should be, so I'm sure they're right, at least for cinemas. However, the desired reference level for watching/listening movies is 105dB SPL for full-range speakers and 115dB SPL for the low-end octaves, so for subwoofers. Given an in-home silence of 25-30dB SPL, that means a dynamic of about 75-80dB for the full-range speakers and up to 90dB for the low-end bass.

I tried to rich the THX Reference Level in my bedroom (15m2), but my Mackie subwoofer can't get to 115dB SPL, although my active monitors can get to the required 105dB but the level of distortions coming from both speakers and furniture, when playing -20dB pink noise, was rather high, so I gave up.

Then, I moved in my living room where room size is more generous (25m2) and the two SB1000 can hit 115dB SPL for sure. Stereo speakers used are CANTON GLE496 with a sensitivity of about 90dB/[email protected] I used a fixed-output 2V RMS DAC, but if using a volume controlled DAC a true-RMS multimeter or a scope can be used to accurately measure the output level for 2V RMS and mark the correct volume knob position. Of course, for balanced amplifiers a 4V RMS balanced DAC would be required and for those with built-in DAC in your home-theater system you will probably don't need to care much about the inside DAC's level.

I've used a Superlux ECM999 connected to Focusrite Solo Gen3 and measured my room's background noise and I found about 26-27dB SPL. Using REW to measure room's acoustics could be read here: https://www.audiosciencereview.com/...om-measurement-tutorial-for-dummies-part-1.4/. Same setup was used to measure speaker's output too. If you have a calibrated SPL meter it might be more simple; worth notice that apps like DecibelX might not be perfect for use here, because I noticed a 10dB higher reading than my ECM999/Focusrite with pink noise, although with 440Hz sine was identical readings.

Audio files to do the measurements are -20dB and were grabbed from https://www.atsc.org/refs/a85/ (also attached here) and I had them "checked" with foobar and its Peak-meter visualization and these are indeed -20dB files. To protect our hearing, the audio files used for such test are usually -20dB instead of 0dB, so we will need to measure a listening level of 85dB SPL, which is much safe for our hearing than 105dB SPL.

The amplifier used here was an Yamaha A-S701 that has about 185W/channel on 4 Ohms speakers, so enough "juice" to rich the THX goal, so while playing -20dB from above (with over-the-ear closed headphones, to protect my hearing) I was able to get a 85dB SPL reading from REW with volume potentiometer at 1 o'clock position. I usually listen to music with knob position somewhere between 11 and 12 o'clock (an absolute max. would be 12.5 o'clock, but for few second only), so I'm not sure I will ever want to listen to movies at such a high SPL level.

Worth mentioning that with -20dB pink noise my living furniture started to shake a bit and make lot of noises and when doing the "bass shaker" to test the woofers for 115dB SPL I gave up quickly do to the furniture sounds, despite my several acoustic panels from corners and between subwoofers and furniture.

To conclude: My living setup seems to be able to rich and get beyond the THX Reference Level (105dB for speakers and 115dB for subwoofers), but I will definitely not be using such a high output volume to watch movies with my family. Instead, my subjective setting for watching movies loud will be at least 3dB lower, if not 5dB. So for me peaks over 100dB SPL are simply too high to my ears, but of course, your mileage may vary.
 

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Martin

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#2
I love watching movies at THX reference level. My system and room easily hit the requisite volume levels. Unfortunately, my family does not share my enthusiasm. I can tell you from experience that Interstellar at THX reference levels is capable of knocking things off shelves in adjoining rooms. Luckily, nothing breakable. :p

Martin
 

Fluffy

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#3
I'm a home-theater sinner -

No subwoofer.

No receiver.

No calibration except for adjusting the volume by ear for each film.

Watch everything on computer connected straight to a TV.

Mix down everything to stereo using AC3 filter.

Only have stereo speakers.

And yes, I sail the seven seas.



The thing is, all the time you spend building your system, I spend watching movies ;)
 

BDWoody

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#4
I love watching movies at THX reference level. My system and room easily hit the requisite volume levels. Unfortunately, my family does not share my enthusiasm. I can tell you from experience that Interstellar at THX reference levels is capable of knocking things off shelves in adjoining rooms. Luckily, nothing breakable. :p

Martin
I too enjoy my movies at or very close to reference levels, which can mean a lot of energy moving through the shelves, windowframes, and sometimes the cat toy that squeaks when you squeeze it will squeak away when it happens to be too close to a subwoofer...

My 22 year old laughs at how I like my movies and music so much louder than he does.
 

Blumlein 88

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Those 85 db reference levels are for a cinema sized listening area. They should be lowered at least a little for smaller venues like your living room. My suggestion would be using 78 db for your home. Your peak will be limited to 98 db and 108 db in the low end. I find doing that almost everyone is happy with the levels for movies. I also will adjust volume up or down 3 db for particular movies as desired. But mostly I just set it and forget it there.

If setting it to full 85 db SPL I find it fairly tolerable on most movies, but it is on the loud side for many.

Here is a chart from the OP's link to the Cinema calibration report.

1580063855788.png
 
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Putter

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#6
I'm a home-theater sinner -

No subwoofer.

No receiver.

No calibration except for adjusting the volume by ear for each film.

Watch everything on computer connected straight to a TV.

Mix down everything to stereo using AC3 filter.

Only have stereo speakers.

And yes, I sail the seven seas.



The thing is, all the time you spend building your system, I spend watching movies ;)
Trolling. Nothing to do with OP.
 

Martin

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I too enjoy my movies at or very close to reference levels, which can mean a lot of energy moving through the shelves, windowframes, and sometimes the cat toy that squeaks when you squeeze it will squeak away when it happens to be too close to a subwoofer...

My 22 year old laughs at how I like my movies and music so much louder than he does.
LOL - We have one of those cat toys and it doesn't even need to be that close to the subwoofer. Sitting on the side table next to me he starts complaining. :D

Martin
 

raistlin65

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#8
Then, I moved in my living room where room size is more generous (25m2) and the two SB1000 can hit 115dB SPL for sure.
At what frequency?

These are the CEA2010 max burst measurements for the SB12-NSD, which is generally considered to be more capable than the SB-1000: https://www.audioholics.com/subwoofer-reviews/sb12-nsd-subwoofer/LSVSSB12NSDCEA2010CHART.PNG

Maybe with dual subs and room gain you are hitting 115db at 60hz and above. Certainly, below 40hz you're not going to get close to that. The good thing is that that's SVS subs have a limiter built in so the distortion won't get out of control so you cannot damage the sub by running it all out.

See Audioholics review for more measurements of the SB12

https://www.audioholics.com/subwoofer-reviews/sb12-nsd-subwoofer/sb12-nsd-measurements
 

trl

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Those 85 db reference levels are for a cinema sized listening area. They should be lowered at least a little for smaller venues like your living room. My suggestion would be using 78 db for your home. Your peak will be limited to 98 db and 108 db in the low end. I find doing that almost everyone is happy with the levels for movies. I also will adjust volume up or down 3 db for particular movies as desired. But mostly I just set it and forget it there.

If setting it to full 85 db SPL I find it fairly tolerable on most movies, but it is on the loud side for many.

Here is a chart from the OP's link to the Cinema calibration report.

View attachment 47507
I'm fine with peaks getting somewhere close to 95-100dB SPL. On music this means an average SPL of 75-80dB, while on movies this might be 5dB lower due to the different movies dynamics, so 70-75dB SPL.

The THX standard is only referring to peaks, so your recommended 78dB SPL seems too low for me for a living room, where the background noise is probably up to 30dB SPL.
 

trl

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At what frequency?

These are the CEA2010 max burst measurements for the SB12-NSD, which is generally considered to be more capable than the SB-1000: https://www.audioholics.com/subwoofer-reviews/sb12-nsd-subwoofer/LSVSSB12NSDCEA2010CHART.PNG

Maybe with dual subs and room gain you are hitting 115db at 60hz and above. Certainly, below 40hz you're not going to get close to that. The good thing is that that's SVS subs have a limiter built in so the distortion won't get out of control so you cannot damage the sub by running it all out.

See Audioholics review for more measurements of the SB12

https://www.audioholics.com/subwoofer-reviews/sb12-nsd-subwoofer/sb12-nsd-measurements
Yes, at around 60Hz, with both SB1000 and all four 8" woofers from the stereo speakers. However, I can't get over 100dB with bass due to the room furniture, so it makes no sense to hit the volume that high anyway.
 

Blumlein 88

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I'm fine with peaks getting somewhere close to 95-100dB SPL. On music this means an average SPL of 75-80dB, while on movies this might be 5dB lower due to the different movies dynamics, so 70-75dB SPL.

The THX standard is only referring to peaks, so your recommended 78dB SPL seems too low for me for a living room, where the background noise is probably up to 30dB SPL.
Well it isn't my recommendation. It was the conclusion of all the research Dolby labs put into finding a proper reference level. THX tends to stick with the max peak levels in their certification. My various experience and how people react to it tell me you'll get fewer complaints paying attention to Dolby guidelines. And the result is also very satisfactory.

While its true your home is noisier than a THX cert cinema, and you'll lose those few db of dynamic range, it won't impact you as much as you think. Most of the noise is in the low end, and even in normal living rooms in the area of our most sensitive hearing we can gear very near 0 db SPL. Plus very few situations will exceed short term instantaneous dynamic range of more than 70 db. You'll not be missing as much at a few db lower volume as you might think.
 

trl

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Not sure what you mean by that. Sounds like you just need more subwoofer.
SB-1000 can hit 115dB SPL by itself if placed in the corner and I have two such subs working together, but the reason why I can't get over 110dB is due to my room furniture, despite the acoustic treatment installed.

Not sure about your home room, but it's really hard to get over 110dB in a domestic home room without hearing strange noises coming from furniture, windows, doors or even from the heating radiators, especially when using pink noise or sines, where you could easily hear the room more than you hear the speakers.
 

trl

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Well it isn't my recommendation. It was the conclusion of all the research Dolby labs put into finding a proper reference level. THX tends to stick with the max peak levels in their certification. My various experience and how people react to it tell me you'll get fewer complaints paying attention to Dolby guidelines. And the result is also very satisfactory.

While its true your home is noisier than a THX cert cinema, and you'll lose those few db of dynamic range, it won't impact you as much as you think. Most of the noise is in the low end, and even in normal living rooms in the area of our most sensitive hearing we can gear very near 0 db SPL. Plus very few situations will exceed short term instantaneous dynamic range of more than 70 db. You'll not be missing as much at a few db lower volume as you might think.
Did you happen to have some link from the Dolby finding, please? Also, are you referring to 87dB SPL peaks or average listening level? Thank you!
 

Sal1950

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Just like at my IMAX cinima, I find the reference level playback painfully loud.
I'll normally set my level at -5 db and even -10 db on some loudly mixed movies.
YMMV ;)
 

trl

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I found this about Dolby Atmos: https://www.dolby.com/us/en/technol...tmos-home-theater-installation-guidelines.pdf and they recommend for manual calibration that "Each full-range speaker should be calibrated to produce the same C-weighted sound pressure level (SPL). The target SPL can range from 79 dB to 82 dB SPL(C) at the central listening position, depending on the room size, when driven with pink noise with an RMS level of ---20 decibels relative to full scale (dBFS). Calibrate the subwoofer level to give the same level for redirected bass content from fullrange speakers as those speakers produce in their pass bands. The target SPL can range from 79 dB to 82 dB SPL(C) at the central listening position, depending on the room size".

So 82dB with a -20dBFS pink noise means a peak levels during 0dBFS movies up to 102dB, per each full-range speaker! Every added speaker means additional 3dB, so in a5.1 or 7.1 scenario seems that Dolby Atmos might actually ask for a higher level than THX reference level.
 

Blumlein 88

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I found this about Dolby Atmos: https://www.dolby.com/us/en/technol...tmos-home-theater-installation-guidelines.pdf and they recommend for manual calibration that "Each full-range speaker should be calibrated to produce the same C-weighted sound pressure level (SPL). The target SPL can range from 79 dB to 82 dB SPL(C) at the central listening position, depending on the room size, when driven with pink noise with an RMS level of ---20 decibels relative to full scale (dBFS). Calibrate the subwoofer level to give the same level for redirected bass content from fullrange speakers as those speakers produce in their pass bands. The target SPL can range from 79 dB to 82 dB SPL(C) at the central listening position, depending on the room size".

So 82dB with a -20dBFS pink noise means a peak levels during 0dBFS movies up to 102dB, per each full-range speaker! Every added speaker means additional 3dB, so in a5.1 or 7.1 scenario seems that Dolby Atmos might actually ask for a higher level than THX reference level.
I seem to recall 83 db per speaker in the largest venues, but ok maybe it was 82 db. They actually specified somewhere in their earlier papers that doing stereo you only add 2 db, and so on for doubling to 4 channels etc. I don't recall their explanation for that. And they seemed to prefer using one speaker of the front pair for setting reference. As you see they mention room size, and the details were the source of the chart I posted.

Obviously one can do whatever they want, but I've found the guidelines adjusting level for room size to be very reliable in several rooms. You'll rarely get people complaining of excess loudness.
 
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#18
It really depends on the room. My HT is an open space with wooden walls. I can hit reference levels. but I sit very close (2.3m from centre speaker) My room offers little room gain, so the bass does not pressurise the space like it would in a sealed stone room. Probably also mean I need more subs...
 

raistlin65

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#19
SB-1000 can hit 115dB SPL by itself if placed in the corner and I have two such subs working together, but the reason why I can't get over 110dB is due to my room furniture, despite the acoustic treatment installed.

Not sure about your home room, but it's really hard to get over 110dB in a domestic home room without hearing strange noises coming from furniture, windows, doors or even from the heating radiators, especially when using pink noise or sines, where you could easily hear the room more than you hear the speakers.
OK. I see what you are saying. I don't know that 110db is a good magic number. I would imagine it can be more or less depending on the room and the frequencies being played.

I will offer a suggestion. I also own an SB-1000 (it is in my bedroom). And I can tell you that in a 25m2 room, you would get some benefit from dual subs that have much better <30hz output. Don't knock it until you try it :)
 

Bear123

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#20
SB-1000 can hit 115dB SPL by itself if placed in the corner and I have two such subs working together, but the reason why I can't get over 110dB is due to my room furniture, despite the acoustic treatment installed.

Not sure about your home room, but it's really hard to get over 110dB in a domestic home room without hearing strange noises coming from furniture, windows, doors or even from the heating radiators, especially when using pink noise or sines, where you could easily hear the room more than you hear the speakers.
There is no way possible that an SB-1000 can hit reference level down to any meaningful level of extension, nor can a pair, nor can four unless you are in a closet. I'm in a 2525 ft^3 room and my dual 18" subs with 19mm of rated XMAX just barely squeak out reference level with an REW sine wave sweep down low. Four SB1000's are not equivalent at any frequency to one of my drivers. I cannot hit reference without duals.

It does take some time to soundproof various items if one wants spirited listening levels in their living room without disturbing rattles and buzzes. However, I can listen at *actual* reference level LFE without many distracting rattles and buzzing. I normally don't listen much louder than 10-15 below reference but with subs 6-9 dB hot which results in output right at reference level.

It's also much more challenging for an individual speaker to hit 105 dB peaks at 12'+ listening distance without drastic distortion/clipping/compression. I am perfectly aware that my 91 dB speakers are in no way going to be clean attempting reference level playback, especially when one factors in 3-6 dB of eq necessary below Schroeder. But I'm fine with -10 playback....its the tradeoff I have made in order to have more exceptional music playback.

I also believe that max listening level for movies is often limited by system capability rather than actual SPL. As speakers start to distort/compress/clip the AVR, the sound becomes unbearably loud. My first system with $200 AVR and $150 bookshelf speakers would run you out of the room covering your ears at -10 MV. At a friends theater with full JTR 99dB+ speakers and equally capable subs, reference level was more comfortably clean, clear, impactful and not overly loud. I don't think common low sensitivity speakers driven by AVR's can achieve clean reference level at any normal 10' + distance. I'd bet most speaker/AVR combos will crap the bed before hitting a 95 dB sweep level.
 
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