Monday, February 27, 2012
Your Ears and Your Speakers
Cones, domes, ribbons, leafs, ring, and at one time ionic tweeters are speaker drivers used in attempts at filling in the last few (top) octaves of sound human ears can hear. Each driver manufacturer claims that their technology is the "best" and so it seems that it is. Some sound better off-axis (listening from the side instead of the front of a speaker), others have very low rise times (giddy up and go like an Olympic 100 meter sprinter vs. a Sumo wrestler), and still others have very low settling times (when the music is over, the tweeter stops equally as abruptly without continuing to wag like the tail of a dog). Each characteristic has its own sonic attribute. But how high and exactly what can the human ear detect? What are the limits of hearing all of this otherwise sales hype? Can a human being actually detect such advances or is this technology only measurable by laboratory instruments? What is the truth behind these so claimed technologies?
Most humans hear less and less high frequency sounds as time marches on (a kind way of saying as we get older, we go deaf). I remember as a youth walking into a room with a television on and hearing a dreaded high frequency whine. This happened to be the noise an old-technology fly-back transformer made which was 15,750 Hz, so my hearing at that age was at least that high. I also remember telling myself that "I could not wait for the day I would no longer hear this annoyance" and one day it did come. To tell you the truth, I miss it.
My hearing loss was a gradual process and one hastened by my selected profession. I was an aircraft flight line mechanic while in the USAF and I ran a chain saw for a year cutting down the forest for my driveway in Colorado. Gradually, the sweet tinkles faded like a beautiful sunset over the ocean. Or did they?
Hearing the actual upper frequency limit and detecting the effects of increased bandwidth are two totally different issues. Once you hear the difference between the two and understand how your brain interprets this information, you can "hear" beyond your physically-imposed limit (you can detect ultra-sonics without actually hearing them).
What the ear-brain understands well is how fast something happens, especially binaurally. This is how we know what direction a sound is coming from. It is this sense of speed or timing that is a factor in bandwidth; you may not be able to hear what a dog hears but if the fundamental note is within your discernible range, you can hear the difference between say a 10KHz bandwidth and a 20KHz bandwidth tweeter.
Just as you can "feel" bass (sub-sonics), say when going into a large church and listening to a 32-foot pipe organ, the information you detect is beyond what you can hear. What you detect is a vibration in your seat or movement of the air on your skin and that is processed by your brain as sonic information.
Adding these sub-sonics and ultra-sonics to your system therefore enhances the experience. I am about to add a super tweeter to my system. What I expect is that in doing so, when properly phased, it will also enhance the bass. Why? Harmonics! There is missing information our brain needs to reconstruct from what the electrical signal in the rest of your gear is trying to tell it.
So we are back to the weakest-link-in-the-chain concept of high fidelity where your stereo can only sound as good as the worst component (the weak link). Your ears, regardless of how high you can hear, are not the weakest link in your playback system although your ability to hear everything your system is capable of recreating does diminish with age (and the number of rock concerts you attended). If your dome tweeters can only reproduce sound to 15KHz, they will have one characteristic sound while those fancy ribbon tweeters that can reproduce sound to 40KHz will have another.
It is best to not limit the information available at the speakers (that is, do not make the speakers the weakest link in the chain) even if the rest of your system cannot reproduce it. A common phrase bantered about today is "what is your stretch?" meaning what are you going to do that taxes your believed limitations? Do yourself a favor and take your system up a notch (stretch it) by adding sub-sonic and ultra-sonic information your ear cannot hear. Audition quality speakers with outrageous bandwidths and see if you can hear the difference. Who knows...they may find their way into your listening room sooner than you think.