EuphManRob wrote:It's called a resonating frequency. I am not by any means a physicist, but I believe every object (and every room) has one, often beyond range of human hearing (or production).
It goes beyond that when you are talking about room acoustics. In fact, resonance is usually bad in a room, even though it's good in the instrument. I've been pondering this for a while, so if you are interested, stick with me while I make a long statement about it.
In electronics, a circuit resonates when the capacitive reactance equals the inductive reactance. In simple terms, that means that the magnetic field (produced by electricity in an inductor) reacts to the electric field (produced by electricity in a capacitor) in time to reinforce the electric field reacting to the magnetic field. The time is controlled by the frequency of the alternating current. With DC, and inductor is just a wire and a capacitor is an insulator. In a tuba, DC is the same as blowing into the tuba without a buzz--which creates no resonance and no sound.
In acoustics, for a room or space to resonate on one frequency, the pressure pulses that make up sound have to be reinforced by pressure nulls as the sound reflects off the walls. The pressure nulls react to the pulses and the pulses react to the nulls in equal amounts, which means that pressure and vacuum reactance are the same. Just as in electronics, that greatly amplifies the energy at that frequency, which we hear as ringing. When it is unintended in electronics, it's called
parastic resonance--and resonance or ringing in a room is damaging vibration that distracts from the desirable sound.
Echo is when pulses are reflected back to the listener off a flat surface so that the reflection is just like the original, just delayed a bit, which creates a distinct secondary sound image. When two walls echo at each other such that the echo from one reinforces the echo from the other, then we get resonant ringing at that frequency. A simple echo is broadbanded and affects all frequencies, but a resonant echo is narrowbanded and affects only one or several frequencies. All echo, even the simple kind, is bad in room acoustics.
But reverberation is good, up to a point. Excellent reverberation, however, demonstrates a
lack of resonance. No one frequency rings, but all frequencies are damped equally as they bounce around.
That's different from a space that has no reflection at all, such as outdoors or an anechoic chamber. Instead of non-resonant reflections that create pleasing reverberation, you have no reflections at all, and the only sound you hear emanates solely from the instrument. We call such rooms "dead". Eliminating reflections is one way to eliminate ringing, but it also eliminates reverberation.
So, in any room, the most desirable acoustics are those that produce reverberation
without resonance on frequencies that are important to you. Small rooms are more likely to be resonant because the walls that face each other may be a half wavelength apart on frequencies important to us. For example, a room that has two walls that are 8 feet apart will resonate on C.
Even parallel walls in a big room can do that if they are multiple of a half wavelength, but the bigger the room, the more the sound is a mix of a greater number and length of paths, which has the effect of damping the resonance. But even in a big room, you'll hear ringing, and you can hear this as a variation in loudness of a constant note as you move around the room. The higher the note, the less you have to move to find the resonant nodes.
Resonance in room acoustics is always bad, so they kill it in small rooms by making them as dead as possible. The resulting sound is ugly and in my view not too helpful in understanding how we will sound "out front".
The best performance rooms are therefore big, and don't have flat walls that face each other. The walls opposite the sound source are usually made to be irregular to disperse the reflections over the maximum number of angles. Thus, the side walls usually angle away from each other and the back wall usually curves, or consists of curved sections, or has a range of bumpy treatments to disperse reflections. The ceiling similar consists of irregular or curved sections to disperse reflection.
So, sitting in a corner offers walls that diverge from the sound source, but you still get reflections from the opposing walls. Whether they are objectionable depends on the size of the room. The low ceiling bounces the sound back with no reverberation, which makes a small room sound dead. Generally, with tubas, you will hear resonance less if you sit where the resonance is minimum which is at the nulls between the nodes. That you can find only by experimentation.
I practice in my living room, which has a sloped ceiling that rises from about 8 feet high in front of me to about 22 feet high behind me. The wall to my right has a range of irregular treaments such as furniture, doorways and bookshelves to disperse without necessarily killing reflections. The wall behind me is a staircase leading to a loft that acts as a reflection trap. The wall in front of me is relatively small because the ceiling slopes down to it, and half of that is covered with furniture. The wall on the left is more distant than the ceiling, so it doesn't make as much sound in my ears as the non-resonant reflection from the ceiling and the wall behind me. It's about as good as it gets in a middle-class home. But it's still no match for the non-resonant reverberation of a large room.
Rick "hitting a 2-penny nail with a 10-pound sledgehammer" Denney
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