Tag Archives: room acoustics

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Sound is a Product of Where it is Heard

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The makers of some of the marvelous devices that we purchase in order to hear great sound want us to believe that all the magic is because of their equipment.  But its not that simple. 

We usually think our audio gear is the primary sources of the sound environment we cherish.  Many of us can’t resist joining the never-ending chase for better amplifiers, speakers, virgin vinyl, digital-to-analogue converters and the like. And there is no shortage of companies and marketing experts who are happy to feed our search for audio perfection.  But the ostensible requirement for “good” or “high end” equipment ignores the huge effects that spaces have on the sounds that reach our ears.

For Dennis Foley, the wise and sometimes frustrated acoustical expert who offers short videos on YouTube, room size is the single most important variable in determining how well or badly something sounds. The folks that come to him for help in producing great sound usually want to talk about their $3000 turntables, $6000 amplifiers, or their rare English speakers–the same kinds used as monitors in recording studios. But he wants to talk about the usually inadequate amount of space where they will be used.  Roughly the ideal room for music should be at least 20 feet wide and 21 feet long, with a ceiling height of 11 feet.  And things only get better if there is even more volume.

Why does a room’s characteristics trump the relatively small qualitative differences between inexpensive and expensive audio equipment?  It gets complicated, but most rooms are simply too small to accurately reproduce a full range of auditory content. For starters, virtually every modest-sized space has a resonant frequency, meaning a particular sound pitch it “likes” to amplify. For example, I know a pleasant local restaurant with a great menu and only lit by candles.  All of its small rooms have a soft romantic glow: a perfect visual representation of what is meant by “fine dining.”  Yet this old inn actually sounds like a Chuck E Cheese on a Saturday afternoon. The problem with the restaurant is that its “intimate” small spaces contain a lot of hard surfaces or old-fashioned glass windows. They can’t help but reflect and amplify sounds at certain frequencies. In one especially regrettable room, the spaces love the lower frequencies of male voices—especially baritones. Give a male patron several glasses of wine and a seat in one of the few tables, and he can become the acoustic equivalent of a fire alarm.  Deafening. In slightly more technical terms, the room’s “mode” peaks at around 400 Hz. It loves sound in this range and is helped by very reflective glass. Your rooms have different modes.  You can hear them if you run a “sweep” of a tone-generating oscillator in them. The mode appears when a given frequency on the oscillator gets noticeably louder.

Many times the first mode in a room is in the bass range, where too much energy and long sound wavelengths have no place to go, so they just build into a mass of indistinct sound. A low note can produce a wave that is 20 feet long. The problem of this too-big-for-the-room energy is that it spills out of its path and makes a sonic mess.  A frequent result is the head-rattling boom of “one note” bass.  Our ears have been trained to accept these non-musical artifacts if dead thuds as the real deal.  But “muddy” base is not very musical.

In these situations, great equipment won’t help.  Something that will may seem to be counterintuitive.  Your music in a modest sized room will probably sound better if you listen at a more modest volume level.  As Foley would say, if you listen, a room will tell you what it can handle.

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Remarkable Features of Sound

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Because we grow up with our senses mostly intact, we naturally take them for granted. We rarely pause to explore how various receptors make connecting to the world possible.

Details about the sensory equipment we carry are fascinating, none more so than sound and hearing. Their obvious importance rests uncomfortably near their precarious fragility. Exploring this subject in The Sonic Imperative over the last few years was not exactly a vacation, but it was an interesting visit to a different geography that is often overlooked. The journey revealed many surprises, including these three:

  1. The speed of sound is relatively slow. We think of breaking “the sound barrier” as the very definition of “fast.” But in the broader perspective of sound physics, our atmosphere puts a considerable drag on the distances a voice, piano or evening thunder can cover. Sound travels through the air at about 1125 feet a second. That’s about three football fields long, or a little more than the length of the long side of one block in Manhattan. When you watch nearby fireworks, they usually come with a delay between the explosions of color and their sounds; the relative delay is obvious. Lightning gives us an the same sense of the huge gap between the speeds of light and sound. Light travels 186,000 miles in the same second that sound covers a few hundred feet. And here’s the interesting point that is also an advantage to humans and other animals. The relative slowness yields what is sometimes called the “shadow” effect in listening. We have two ears  6 or 7 inches apart. That’s enough to give our binaural hearing a chance to hear the difference in the arrival of sound to one side and then to the other: one reason music in a great hall or on a good system is so pleasing. Even if we can’t see them, we can locate instruments or singers in a dimensional “soundstage.”

2. Another unusual feature of hearing is that sound may be the most persistent of all senses. We never shut our ears as we do with our eyes. And although its unfortunate that adults have usually lost some hearing acuity due to age and abuse of hearing receptors, most of us actually start picking up sounds in the womb at about 30 weeks. We hear our mothers before we are born. Equally unusual, there is some evidence to suggest that hearing and its brain functions survive for a short time even after death is pronounced.

3. Home music listeners have to face hard truths about the limits imposed by a listening room. Most domestic spaces are too small to accurately produce low frequency sound energy: the very source of what gives music so much of its punch and presence. The fact is that low frequency sound “waves” require a lot of energy and are long: often longer than the available space. The sound produced by a nice fat bass note produced on a piano or a bass guitar at 40 Hz unfolds fully only in a space of 28 feet or more. No such problem exists for higher notes in the musical scale, which may have waves which are just a few inches in length.

Why is the lower number a problem? A sound wave that does not have sufficient space for its full cycle will distort, a bit like waves that break against a cliff. We obviously can’t see it, but sound energy that has insufficient space to play out as it should results in what I think of as “wads” of faux bass: a lot of boom but not much musical clarity. Sound engineers often call this undefined low-note energy “one-note base:” an indistinct rumble of low frequency wave energy bouncing off walls or ceilings before it has run its course. To a careful listener the effect is “muddy” or “boomy.” One reason we cherish big old spaces like Paris’ Notre Dame Cathedral is that its 400-foot length is a perfect acoustic for its two organs and singers. To be sure, we have grown tin ears that accept dead thuds of low frequency sound as base.

It can be a revelation to accurately hear low notes as they are meant to be heard. This is one reason audio in a good movie theater or concert hall is usually going to sound better than audio of the same program reproduced in a 20 by 12-foot living room.  One cure is to listen to music at at a moderate listening level, which is usually handled better by a room of limited size.

These and other interesting facets of sound are explored more fully in a host of books, including—a pitch is coming: The Sonic Imperative: Sound in the Age of Screens.