How do recorders make sound?



How do recorders make sound?

In: Other

Air bounces around the inside, with just the right pressure from blowing into it, it makes a whistle-like noise. When you cover the holes that air has less places to escape from and will deepen the tone as a result.

I’m assuming you mean the instrument?

Basically the air you blow through the mouth-piece interacts with the hole right in front of it, creating a chamber of “excited air” down the length of the instrument. It’s complicated (beyond a 5 year old), but the “length” of this excited air in the tube of the recorder is what determines the sound the instrument makes. As the recorder player moves their fingers over certain arrangements of holes it changes the “length” the excited air vibrates which produces a different notes. Its similar to how a guitar player uses their fingers to shorten the length of the vibrating strings and produces different notes.

Have you ever made a ‘toot’ sound by blowing air over the mouth of a bottle? You’ll notice if you try to do this, that there’s a certain ‘sweet spot’, an angle and position for your mouth that works best, and others not so much. It’s not quite blowing *into* the bottle, and it’s not quite blowing *past* the bottle, it’s kind of in between.

What’s special about that ‘sweet spot’, is that the movement of air sets up something called a standing wave, inside the bottle. A standing wave is a certain kind of looping feedback cycle. First some air is forced into the bottle. This raises the air pressure inside the bottle. That air pressure bounces around inside a bit, according to the size and shape of the cavity, and then it comes back out the mouth of the bottle as a little tiny high-pressure wave. This wave interferes with the stream of air being blown, and diverts the stream so now it’s blowing *past* the bottle instead of into it. This causes the air pressure inside the bottle to fall, which pulls the stream back in the other direction, forcing a little air into the bottle. And then the cycle repeats. If this happens 100 times per second, then you’ll hear a 100Hz tone.

A recorder is part of a family of instruments called “fipple flutes,” sometimes also called block flutes. A fipple is a mouthpiece with a narrow channel which directs air past a gap at just the right angle, so that you don’t have to worry about finding the sweet spot. And then by manipulating the air pressure and covering and uncovering holes on the recorder (and thereby changing the size of the cavity), you can get it to produce different pitches. Tin whistles and ocarinas are also examples of the fipple flute family.