I heard there was a secret chord
That David played, and it pleased the Lord
Wikipedia says that "in physics, resonance is the tendency of a system to oscillate at a greater amplitude at some frequencies than at others. These are known as the system's resonant frequencies (or resonance frequencies). At these frequencies, even small periodic driving forces can produce large amplitude oscillations, because the system stores vibrational energy."
You don't need to be a physicist to understand this. Everyone knows when a kid is on a swing, pushing at the right time will keep the swing going, either adding energy or at least making up for what's lost to entropy, while pushing at any other time will probably result in a bigger-than-natural reduction in the swing's oscillation, and also maybe a hurt or angry kid.
Another easily understood example comes with sound waves; any musician knows this. When tuning a guitar, playing the 7th fret harmonic on the E string and the 5th fret harmonic on the A string should result in the same tone. Small variations in tuning make the combined sound 'bumpy', meaning that the sound waves no longer reinforce each other, but periodically negate each other in cycles based on how different the tones are. The more off the tuning is, the more frequent the sound waves kill each other, and the bumpier the combined tone becomes.
I submit that art creates a similar resonance that produces reactions in the people who experience it. Human beings are, after all, energy systems. There are sculptures, paintings, photographs, poems, stories, songs, and even architecture that have moved people throughout human history. Among these many media, however, music has a particular effect on me and many people I know.
Like every art form, music is created as an expression of some human condition. The audience that appreciates any music most is made of people who can identify with those feelings expressed in the piece by its composer. I heard it said once that sad songs are always more memorable and loved because they mean more to the people who hear them, which is, of course, because our sad life experiences always make a more lasting impression on us and always demand some kind of reconciliation, which can be partly found in song. In my opinion, this occurs because music, especially when created with a deep passion, carries with it some emotional 'resonant frequency' that strikes those individuals who are most 'tuned' to understand its message.
Sadness isn't the only emotion that touches people through music. My adolescent years are characterized by the many expressions of anger and discontentment found in my musical choices, many of which I still turn to when necessary (hence the FB nickname 'DamageInc' for all those people who asked). Happiness, too, can be conveyed via music. Throughout the history of Christianity, artistic works commissioned by the church were essential to its vibrancy, and still have an enormous effect on us today. Revolution and social change have been driven by music. In short, there is no variation of human emotion or experience which has not, in one way or another, been set to song in a moment (or a lifetime) of inspiration.
This is not news to anyone who's ever seen a favorite band in concert, or had to close his/her eyes at some point during a song in order to take in more than just the sounds, or been moved to emotion hearing a singer perform a certain way that speaks to his/her core. These experiences are deeper and more meaningful than sound waves travelling through some transducer to a listener's eardrum that results in neural impules in a familiar or desirable synaptic pattern. Of course, in the biophysical world alone, that's all that's happening, but another purely biophysical result is the release of endorphins, adrenaline, testosterone, etc. Such a hormonal release isn't a routine reaction to hearing just any old song.
I do realize, of course, that psychology also plays a role in how we feel about some music. That song that was played during our first kiss or dance, or at the funeral of a loved one, or the moment a car accident ruined your life, always becomes linked to that experience and all those emotions and hormones that went with it. I don't discount that. In fact, I think what happens during such an experience is that we become 'tuned' to that song in a very specific way. This emotional resonance can then be perpetuated by anyone who uses such an experience as inspiration to create their own artistic work. And the cycle continues.
Though the origins of my thoughts on sonoemotional resonance came earlier in the week, Tuesday I had an experience which only confirmed every word that was forming in my brain. I heard Jeff Buckley's cover of the Leonard Cohen song Hallelujah (this version in particular) on Pandora. It's beautiful, of course, but I found over the next 48 hours that I could not get the tune or that first verse (atop this post) or any of the chorus out of my head, and I don't mean in the annoying, earworm way. I mean in the way that I had to hear the song again. So today I found it, and listened to it more times than I'm comfortable admitting. Then I clicked to hear another cover by an LA singer named Kina Grannis. Yes, it was partly because she's pretty (what can I say; I'm only a man), but her rendition put my emotional resonance with this song at a new level. Her cover is here. In the hours since, I've listened to other versions of the song, including the original, so that I can not only fully appreciate the song's meaning, but learn to play it myself.