Dear Anklebiters,
When doing a permanent install in a small room, how big is too big for speakers? Is it not detrimental to the human ear to have too high an SPL in an enclosed space? Does one simply judge decibel levels relatively with your ear?
Zack, Lakewood, CO
Jamie: Well, Zack, let me start by saying that I like your name. My dog is named Zack. And hopefully, this answer will get to you before you put too many decibels in that small room of yours. Since we are dealing with some pretty big generalities here, I'll try not to be too vague. I don't know the size of the room in which you plan to install your speakers, nor do I know what make or model of speakers they are or what kind of power amps you're using. So, I won't be talking too much about speaker placement. There are, however, some good books and computer programs that take into account your room dimensions, volume, wall materials, etc. Yamaha makes an excellent live audio reference DVD that you might want to check out as well as Rane's reference material.
Back to the question at hand: "Is high SPL detrimental to the human ear?" You bet your ass it is! High SPL will damage your hearing in any environment. So, if we are only going to concern ourselves with dBs, we will only need one piece of gear (besides our precious ears). And that, my friend, is a decibel meter. This is a very common instrument and you should be able to find one at your local electronics store. Or you can definitely purchase one online.
But before you fire up that new dB meter, let's get some reference for its use. Average human speech is 60 decibels. (By the way, a decibel is a tenth of a bel. According to Wikipedia, the bel was "invented by engineers of the Bell Telephone Laboratory to quantify the reduction in audio level over a one-mile length of standard telephone cable, and it was originally called the transmission unit or TU, but was renamed in 1923 or 1924 in honor of the laboratory's founder and telecommunications pioneer Alexander Graham Bell." If you really want to get into the math involved, check out http://www. phys.unsw.edu.au/~jw/dB.html.) A riveting gun at 30 feet produces about 100dBs. And if you happen to be on a runway when a 747 is taking off, you will experience 140dB at 100 feet. Obviously, that's very loud.
Now, with your dB meter in hand, you can check out how many decibels you are pumping into your small room. Also take into consideration the fact that distorted sound is more taxing to the ears than clean, pure tones. In other words, if you install crappy speakers and power them with cheap ampli- fiers, you will have a better chance of damaging the hearing of those who visit your small room than if you install good stuff.
Your ears, of course, will be the final judge. Good luck, Zack. P. S. My dog is an Australian Shepherd.
Tim: Unlike Jamie, I do not have a dog, but I find it interesting that the dog analogy has come up. You see, dogs in general have superb hearing ability. Dogs are able to hear frequencies that the human ear cannot detect. Needless to say, they are ultrasensitive to sound as well. What does this have to do with SPL, also known as Sound Pressure Levels?
The bottom line is that you're factoring this element into the planning process for your install. The decibel meter, as Jamie described, is an excellent tool in determining what volume levels should be acceptable in your room. One way of using it effectively is to take the meter to rooms similar to yours that have sound systems and take a measurement at peak usage. Make a chart of each room, type of speakers and power used and the decibel measurement, and make a comparison. There's much to be learned from those who go before us–sometimes what to do, and what not to do as well.
I'm almost always drawn to sound arrangements everywhere I go. Just the other day, I was in a well-known chain video store and noticed there were eight JBLs hanging from the ceiling. One of the speakers was clearly blown, crackly and distorted. It was annoying, yet the store kept the volume probably somewhere around 80 to 90dB. More than likely, all the speakers were daisy-chained and the employees didn't know how to fix the problem, so they just continued to play the annoying distortion at an uncomfortable level. My guess is that the employees probably "cranked" the system during closed hours and blew the speaker. Where am I going with all this? Well, these are all opportunities that I use to notice what works and what doesn't work.
The decibel meter will be a helpful resource to use on already-installed systems, including your own once it's in. But how do you decide what to buy that is appropriate for your situation? Well, see below for some facts from the National Institute of Deafness and Other Communication Disorders (www.nidcd.nih.gov)–with commentary.
The maximum SPL for human hearing is around 120 decibels sound pressure level, which is the level where people begin to experience pain due to the high sound pressure levels.
The decibel scale is logarithmic, meaning that a 10-decibel increase is a doubling of the perceived sound pressure level (this doubling requires using 10 times the acoustic power, however). Thus, the scale remains fairly low until around 60dB or so, which is where it begins to slope up much more steeply. For instance, doubling one only gets two, doubling two gets four, doubling four gets eight, doubling eight gets 16, doubling 16 gets 32–at first, the increases are small with a shallow slope, but they quickly build after a certain threshold. Layman's terms state the obvious; SPL becomes dangerous to the human ear exponentially.
Whatever speakers you end up installing, take the time to measure what volume (given the speaker and amp) levels fall within the suggested SPL in your room, and stay within that range. Always be aware that when you "turn up" the volume above the acceptable, safe range, the ability to damage ears doubles with each 10-decibel increase. Finally, a set of earplugs should always be around, and it's ultimately up to each individual to protect their own ears, but we always try to be responsible on the sound end. Good luck.
Some Facts from the National Institute of Deafness and Other Communication Disorders:
• 110 decibels–Regular exposure of more than one minute risks permanent hearing loss.
• 100 decibels –No more than 15 minutes unprotected exposure recommended.
• 90 decibels–Prolonged exposure to any noise above 90 decibels can cause gradual hearing loss.
And to supplement Jamie's facts, take a look at some sound measurements to give you a frame of reference in understanding what levels are acceptable or not:
• 60 decibels–Normal conversation
• 90 decibels–Lawnmower/motorcycle
• 110 decibels–Chainsaw
• 140 decibels–Rock concerts & firecrackers
140 DECIBELS AT ROCK CONCERTS! It's a miracle I can hear at all! (Actually, that number is not really accurate unless you were within a couple of feet of the main P.A. Most concerts–depending on the artist and the person mixing–run in the 95 to 110 range. The last Metallica show I saw ran about 112 at FOH. –Ed.)
