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How loud is loud, how to measure it? Is THX calibration bad for your health?

sarumbear

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I am an electroacoustics engineer. We are a rare breed. When I got my M.Sc. my class of six were the only ones in UK. I am now retired from engineering and audio is my hobby. You can find more about me on the about page on my profile.

The behaviour of the sound (acoustics) and how we hear it are very complex to formulate. We are dealing with the physical and the physiological, and at the interaction is our brain. We should not assign objective values to what we experience. They are not solid repeatable values. There are no Precision Instruments, nor Klippel to objectively measure how we hear. Add the complexity of music as the source material and it becomes impossible to formulate the sound coming from a speaker in a domestic environment with any precision. Think of this if you plan to read further. What I am about to explain is not objective but also not subjective. It is based on my knowledge that has been accumulated during 50 years as either an electroacoustic engineer, a recording engineer, a speaker manufacturer, and a Hi-Fi hobbyist.

How loud is loud?

When we hear a sound, depending on where we are, what mood we are in, what age we are, etc., we judge the sound level as low, normal, high, etc. Human physiology psychology confuses our perception of sound levels. What we complain of to be very loud one day can be perceived as pretty normal the next day. Our hearing system is inherently auto levelling anyway but our brain plays tricks on how we perceive levels. Sitting alone in a room the sound level of a club dancefloor is unbearable but we do not complain about it when we are dancing for hours. This is not dissimilar to how we perceive changes between brightness levels. But unlike our eyes, high sound levels permanently damage our hearing. (Extreme brightness is known to damage eyes but it is almost impossible that we experience such high brightness levels in our daily life.)

There are two aspects of defining loud. One is for short periods and the other is accumulated dose. Short periods, of a few seconds are measured with a Sound Pressure Level (SPL) meter. Accumulation is measured by a Sound Dosimeter. It is the latter that almost all audio hobbyist are unaware of and it is lack of the latter that caused many 70s rock stars to become deaf.

How to measure it?

The sound pressure (P) is the average variation in atmospheric pressure caused by the sound. The unit of pressure measurement is pascal (Pa). Sound pressure level (SPL) is the pressure level of a sound, measured in decibels (dB). It is equal to 20 x the Log10 of the ratio of the Route Mean Square (RMS) of sound pressure to the reference of sound pressure (the reference sound pressure in air is 2 x 10-5 N/m2, or 0,00002 Pa). Or, in other words is the ratio of the absolute sound pressure against a reference level of sound in the air.

Naturally, the purpose of measuring sound is not only for music. If we are measuring noise, it makes sense to apply a filter on the type of frequency range it has as our hearing has different sensitivity at different frequencies. (Remember the Fletcher Munson curve?) Those filters are named A, B & C. dBSPLA is the most used as it is the industry standard to define how noisy any environment is. For measuring the level of music playing we should not apply any filter. Music has the same range as our hearing system is designed for. Any filter will skew our readings.

SPL meters used to be prohibitively expensive for a hobbyist or so cheap that they were nothing but toys. This has changed with smartphone apps and modern devices, iPhone especially. Huge scale manufacturing and software calibration allowed an iPhone by itself to almost reach Class 2 classification (2dB tolerance suitable for everyday use outside a lab). This level of error is more than satisfactory for hobbyist’s needs. Do not take my word for it, read the conclusion reached by the US CDC.

My favourite app is called SPLnFFT. It is iPhone only. You can find it at the Apple App Store. Have I told you that it is free? It is incredible that such a powerful and elegant app is given away.

Will it affect my health?

THX standard says that at reference level (-20dBFS, the broadcast/professional reference level) a Pink Noise should generate 85dBSPL at the audience position. As you can see from the simple chart below this means the theatre's sound system is expected to produce 115dBSPL without audible distortion.

Speaker%20reference%20level.png


Let’s fire SPLnFFT app and start playing some soundtracks at the 95dBSPL average level. (Don’t try Pink Noise as it will be an unbearable experience.) This is what your app screen should look like.
EDIT:
Here are two 12 minutes samples of the Dolby Pro encoded stereo track of the films Team America World Police (2004) on the left and Dune (2021) on the right. You can clearly see that the soundtrack is routinely above the reference level and often stays at 10dB above, which is 95dBSPL.

index.php
Screenshot 2021-12-19 140431.png


The circles are at 10dB increments and the green to yellow transition is at -20dB LKFS. Measured with TC Electronics Loudness Meter.
EDIT ENDS

IMG_2367.PNG


95dBSPL: Very noisy, exposure time should be limited to less than 2.5 hours
. And, you are already in amber for the dose of sound your body can handle.

This is at 95dBSPL average level. Imagine what will your body feel when you increase the level by 20dB to reach the peaks in the soundtrack?

If going to the cinema is bad for your health how come nobody talks about this. Well, a lot of people talk about it in the industry. Many theatres have overridden the calibrated levels of their sound systems because people were complaining. The main reason no action is taken is because we go to a cinema rarely. A frequent moviegoer is defined as someone who goes to the cinema once a month. But is that the same when you have a home theatre? What is the point of having a home theatre if you are going to use it just once a month, after all?

As far I can see, and I hope someone will show me that I am wrong, watching films at THX levels frequently can be bad for your health.

Let us try music instead. Many posters on ASR talk about listening to music at an average level of 85dBSPL. This what I see while playing IGY by Donald Fagen (Opening track of the Nightfly Album.)

IMG_2368.PNG


85dBSPL: Too loud, exposure time limited. How long do you listen to music a day? Am I risking my health? I’m afraid all the medical studies available point us to the one answer: yes, you are. 85dB average dBSPL is too loud for enjoying music.

I hope I added something to the great cumulative knowledge of ASR. Feel free to ask questions, but please stay on topic. For instance don’t ask me why I used the Nightfly album. Well if you must; because it was once called "one of pop music's sneakiest masterpieces," which I totally agree.

A member has posted this video on page 15. I copied it here for your information.

 
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dc655321

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Let us try music instead. Many posters on ASR talk about listening to music at an average level of 85dBSPL. This what I see while playing IGY by Donald Fagen (Opening track of the Nightfly Album.)

IMG_2368.PNG

Agreed: 85dB avg is quite loud for most domestic listening.

A couple of questions:
Were you using I.G.Y. version from 1985 cd?

The DR-14 calcs put that track's rms at -19dB with peaks at -2dB.
Would you base the discrepancy between your phone app's readings and the DR-14 results on the app's inability to capture peaks?

Finally, for the "dose" aspect: any idea what would be a physiologically reasonable exposure to 85dB rms music, or references to look at?
 

solderdude

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Also see: https://www.audiosciencereview.com/forum/index.php?threads/music-how-loud-is-loud-video.22434/

Most recordings are mixed at around 80-85dB average SPL and when the monitors and sound engineers got it 'right' the sound in your home (no EQ or special measures) may be too bassy.
Fortunately at more moderate (less active) listening levels of around 70-75dB average the sound, due to 'room effects' (kind of compensating a bit for equal loudness contours) is tonally reasonable balanced.
when EQ'ed to Harman or some other room targets it will also sound fine around the same levels.
To me, the same reason applies to headphones. Most don't listen at 80-85dB average (longer listening sessions) and due to equal loudness contours we need some bass boost.

Funny thing about the nightfly.. it only sounds good to me on excellent speakers. It is cold and dry (a bit hard) sounding on lesser systems.
I sometimes use it as a 'quality gauge'.
For more enjoyment (at lower listening levels) I added a small bass boost to the entire album.

Is THX calibration bad for your health?​


The solution is simple... when doing the calibration put a finger in your ears. It is not obligated to listen along when doing calibration.

You only get 1 pair of ears and they have to last you a lifetime. No fixing later on. Don't be the idiot.
 
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sigbergaudio

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storing

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95dBSPL: Very noisy, exposure time should be limited to less than 2.5 hours.

Where does this app get that information from? Does it use one of the standards and which one (has to be tricky as international app maker, some countries definitely use more strict exposure times than others). It looks ballpark correct based on what I vaguely remember from lectures, but when looking it up online one can fine wildly varying numbers (both less and more strict).
 
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sarumbear

sarumbear

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Agreed: 85dB avg is quite loud for most domestic listening.

A couple of questions:
Were you using I.G.Y. version from 1985 cd?
I have no idea. I was streaming from Spotify.
The DR-14 calcs put that track's rms at -19dB with peaks at -2dB.
Would you base the discrepancy between your phone app's readings and the DR-14 results on the app's inability to capture peaks?
DR-14 data is on the signal and the entire track. I was measuring the output from the speakers. There is a volume control in between, hence no correlation to the what is on the track relative to 0dDBFS. I also listened a part of the track hence the average calculation will be different. See the footer where it says: 84 seconds.
Finally, for the "dose" aspect: any idea what would be a physiologically reasonable exposure to 85dB rms music, or references to look at?
That is a very complex and a medical subject. I am not qualified. There is a decent Wiki article that can be a good start to learn more. However, SPLnFFT does have a dosimeter built in and measures the dose over time. I mentioned that in my post.
 
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sarumbear

sarumbear

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Where does this app get that information from?
I don't know. The author is pretty visible on the Internet. You may ask him directly.
Does it use one of the standards and which one (has to be tricky as international app maker, some countries definitely use more strict exposure times than others).
You are talking about Health & Safety laws. I am talking about expected medical consequences. I am not a medical expert, hence cannot explain further.
It looks ballpark correct based on what I vaguely remember from lectures, but when looking it up online one can fine wildly varying numbers (both less and more strict).
As it is a medical issue, it is highly unlikely that there will be consensus on any data. Remember the COVID19 comments from the experts? However, they all agree that exposed to loud noise is detrimental to your hearing and the definition of "loud" is too loud for our body to handle. That is the point I wanted to pass on to the ASR members.
 
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sarumbear

sarumbear

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sigbergaudio

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Isn't Decibel X a subscription product?

Hm, perhaps it was in the past? The one I have is called Decibel X : Pro, and it's not subscription based. Don't remember what I paid for it. Since I already have it it doesn't show the price in the app store.
 

Jimbob54

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Not qualified to comment or challenge the science, but you tested movie soundtracks, which I am taking as meaning the accompanying record of the songs /themes. Which is not the same as the exposure to sound during watching a movie. Which may include silence, quiet dialogue and of course very loud action

Unless you mean you played "noisy" movies and used the app during playback of the whole movie?
 
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sarumbear

sarumbear

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Not qualified to comment or challenge the science, but you tested movie soundtracks, which I am taking as meaning the accompanying record of the songs /themes. Which is not the same as the exposure to sound during watching a movie. Which may include silence, quiet dialogue and of course very loud action

Unless you mean you played "noisy" movies and used the app during playback of the whole movie?
I did two tests. One was movie soundtrack the other was music.

There is a dosimeter on the app. Try it and see what it says in your case.
 
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sarumbear

sarumbear

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Hm, perhaps it was in the past? The one I have is called Decibel X : Pro, and it's not subscription based. Don't remember what I paid for it. Since I already have it it doesn't show the price in the app store.
Mine is Simply Called Decibel X. Maybe the Pro is the subscription model. Also maybe, they were charging a flat fee and now switched to subscription.

Anyway, Decibel X seem to offer a bit more information than the SPLnFFT, especially on the dosimeter, but I rather prefer the simple and elegant UI of the latter. Not to mention that it is also free!
 
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sarumbear

sarumbear

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sarumbear

sarumbear

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Is THX calibration bad for your health?

The solution is simple... when doing the calibration put a finger in your ears. It is not obligated to listen along when doing calibration.

You only get 1 pair of ears and they have to last you a lifetime. No fixing later on. Don't be the idiot.
I think you missed my meaning. I was not talking about the issue during the calibration, but the result of the calibration. If you calibrate your HT to THX spec (hence used their calibration method) you will have a HT that may be a health risk. That is because you will be exposed to loud levels of sound while otherwise enjoying films.
 

solderdude

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If you calibrate your HT to THX spec (hence used their calibration method) you will have a HT that may be a health risk

Why ? Isn't there a volume control ? I assumed calibration is more for correct L-R, rear and center speaker volume matching.
 
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sarumbear

sarumbear

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Why ? Isn't there a volume control ? I assumed calibration is more for correct L-R, rear and center speaker volume matching.
Yes there is but that should be fixed once the reference level is calibrated. That is what level calibration means. In cinemas the volume control is behind a lock.
 

abdo123

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Will it affect my health?

THX standard says that at reference level (-20dBFS, the broadcast/professional reference level) a Pink Noise should generate 95dBSPL at the audience position. As you can see from the simple chart below this means the theatre's sound system is expected to produce 115dBSPL without audible distortion.

View attachment 173104
This is for the LFE channel, not for speakers. for speakers it's 10dB lower!!!
 
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