From the FanPosts -Joel
I am an audio engineer by trade. (The "RDO" in my SBNation name is a pun for the word "audio") So I would like to share a few thoughts - and perhaps clear up a few misconceptions - in the wake of Seattle's CenturyLink Stadium reclaiming the title of "the world's loudest" from Arrowhead.
During the past couple of months, I've seen a lot of people discussing the decibel – the common unit of sound measurement – in comment threads. It is widely misunderstood, largely because the decibel (which is abbreviated dB) is used for several kinds of measurements in the audio field, and they aren’t necessarily equivalent to each other. This often leads to formulas for different kinds of decibel measurements being used incorrectly.
Furthermore, the human perception of loudness is pretty subjective, and also depends on many factors – particularly the frequency of the sound. (I could go into a long explanation of frequency, but let's just say that frequency has to do with the pitch of the sound - for example, the difference between the sound of a bass drum and a piccolo) But let's not complicate this too much.
Using my trusty Radio Shack sound level meter (all sound geeks have one of these stashed away somewhere) and doing a little screaming, I find that I can generate about 100 dB for a sustained period (for example, like I would do when screaming "Deeeeeefennnnse" on third down at Arrowhead) at about one foot from my mouth.
Why did I mention how far away the meter was? Because it's very important. With every doubling of the distance from the sound source, the volume is reduced by 6 dB. Therefore, at two feet, the level would be 94 dB. At ten times the original distance, it is reduced by 20 dB. So if you were standing 100 feet away, my 100 dB "Deeeeeefennnnse" would reach you at a level of 60 dB - that is, a 20 dB reduction from 1 foot to 10 feet, and another 20 dB reduction from 10 feet to 100 feet.
So far, so good. But as we all know, I don't scream at Arrowhead alone. How does the number of people affect the overall level?
If we assume everybody at Arrowhead can generate a sustained level of 100 dB with their voice - which obviously isn't true, but to make this simple, we're going to say it IS true - you would get an increase of 3 dB every time you double the number of people, and an increase of 10 dB every time the number of people is multiplied by 10. So if you could somehow get 100 people to be one foot away from you, and each of them were screaming "Deeeeeefennnnse" at 100 dB, your perceived level would be 110 dB. If you could get 1000 people, then it would be 120 dB. How about 10,000? 130 dB. Or 78,000 screaming fans? In theory... 148.92 dB.
But before you go clamoring for a new attempt at the record - or blame the people in the yellow seats for not doing their part to get us to 149 dB - remember that this a theoretical figure based on every one of those people being one foot from you. And at Arrowhead, the overwhelming majority of the 78,000 are hundreds of feet away. As I have shown here, this distance has a far greater effect on the overall sound level than the number of people.
How much of an effect? Without using calculus (which I never learned in school) or computer modeling (I don't happen to have a Cray supercomputer handy) it's hard to say. But with what you now know from reading this article, you should be able to see that the figures of 110-116 dB for Arrowhead crowd noise - the ones measured during the 90s - were probably about right.
Let's go back to my voice and my Radio Shack meter. I can generate a sustained 100 dB with my voice. But just sitting here at my desk while I am writing this article, I can reach 110 dB with a short shout - maybe a little more than that if I am properly motivated... say, by Husain Abdullah intercepting a Raiders pass and returning it for a TD late in the game, which is when, as nearly as we can tell, the Arrowhead crowd apparently set the record. So add another 10-12 dB to the theoretical maximum.
In addition, the Guinness Book Of World Records apparently makes these measurements with what we audio geeks call the "A weighting," which takes all frequencies into consideration. (Some industrial sound level measurements are taken with a "C weighting," which only considers the frequencies to which the human ear is most sensitive) Without going into a lot of technical detail, using the A weighting basically makes for a larger, "sexier" number - especially if the sound being measured includes a lot of low-frequency information... like, I don't know... maybe people banging on the backs of their seats in a football stadium?
Finally, it's a good bet that the 90s measurements were taken with analog meters. (My Radio Shack meter - an older version of the ones they now sell - is analog) The modern digital sound level meters that Guinness uses have a feature that allows them to record the largest peak level they encounter with absolute precision. Once again, this makes the number bigger (and sexier) than you could measure with any analog meter, which can only show average levels. And any sound geek will tell you that instantaneous peaks will often be 10 dB higher than the average level the meter shows you.
All these factors were what allowed Arrowhead - during the Raiders game - to retake the record with a number that was so much higher than what was measured there during the 90s.
And trust me, Chiefs fans... the 0.1 dB by which the Seahawks fans exceeded the Chiefs fans is nothing! Remember how I said that perception of loudness is subjective? Even if their very lives - or homefield advantage in the playoffs - depended upon it, most people would not be able to recognize a loudness change of even one dB. So one tenth of one dB? Meaningless. In fact, I am surprised Guinness doesn't call it a tie.
(And as our own Joel Thorman correctly pointed out in a comment on the SBNation article about Seattle retaking the record, the placement of the meter makes a huge difference. Moving the meter even a short distance would very likely have given an entirely different result at both stadiums. Joel isn't a sound geek like me... but he's obviously talked to a few of them!)
I'd also like to address a few other points I have heard people mention.
One is that the seating capacity of the two stadiums is different, and ought to be considered. Not really true.
Earlier, I showed the theoretical maximum for Arrowhead's capacity of 78,000 would be 148.92 dB. For CenturyLink's capacity of 67,000, the figure would be 148.26 dB - not even three quarters of a decibel less. This may sound counter-intuitive, but that's the deal with logarithmic units of measurement. (In the sound business, we like to say that we don't write the laws of physics - we simply enforce them!)
And while it is probably true that CenturyLink's partial roof does reflect some sound back to the field, it's probably not that significant.
Remember how level decreases drastically as distance increases? That counts for reflections, too. Now... if the stadium was completely enclosed, there would be a different story. Reverberations would start building upon each other (particularly, I think, at lower frequencies) and pretty soon it would make a difference. But with CenturyLink's open roof... not so much.
Lastly... can you damage your hearing by being at a Chiefs or Seahawks game? Sure.
Prolonged exposure to levels above 100 dB can make your ears ring for quite a while afterwards, and repeated prolonged exposure to those kinds of levels can lead to permanent hearing loss. But few people at either stadium are probably being subjected to average levels of more than 110 dB - and even then, it's only for brief periods. You'd probably do a lot more damage to your hearing (and perhaps more importantly, your dignity) by attending a 90 minute Justin Bieber concert.
I know that for a lot of Chiefs fans, it hurts that Seattle has now reclaimed these bragging rights. When Seattle set the record in September, I was among those who thought, "No way! We have to get that record back!" But I was also skeptical about the measurement recorded there, because I knew from my own experience that the figures recorded in Arrowhead during the 90s were valid.
But once Guinness came to town and recorded a new Arrowhead record at the Raiders game - and I did a little research on my own, dusting off my own knowledge of this stuff - I came to realize that Chiefs fans have nothing to be ashamed about. Arrowhead is - and under Andy Reid, will very likely remain - one of the toughest venues in the NFL.
You Seahawks are welcome to come to town anytime. We'll be happy to show y'all how it's done.