Wind instruments (technical name: aerophones) A. Brass instruments The players lips vibrate against each other and against the rim of a cup mouthpiece. Lips act as a valve, introducing puffs of air at just the right time to maintain oscillations of the air column Note that an instrument is classified as brass not because it is made of metal, but because it has this type of mouthpiece, which relies on vibrating lips. B. Woodwind instruments The player blows air against a sharp edge or through a reed The sound vibration usually begins at the mouthpiece. The rest of the instrument magnifies, and turns this vibration into a pretty sound Wind instruments are classified by mouthpiece types: 1

A. Brass Instruments Construction: Mouthpiece Mouthpipe Cylindrical section (with valves) Bell 2

Oscillations in a pipe (review) Trumpet: 61, 184, 306, 429 Hz 3

Acoustic impedance Definitions: Specific acoustic impedance: p – sound pressure u – speed of particles of media (air) S – cross-sectional area of the tube I – intensity For plane wave: Volume velocity:Acoustic impedance: ρ – density v – speed of sound For air: 4

Acoustic Impedance curve Acoustic impedance is a function of frequency Acoustic impedance curves have peaks at resonance frequencies Role of acoustic impedance in brass instruments At the frequencies of impedance peaks the excess pressure helps to open the lips (pressure cooperates with the lips) – regenerative or positive feedback 5

Bernoulli’s equation A1A1 A2A2 v1v1 v2v2 d1d1 d2d2 y 6

The bell All brass instrument have bells Bell changes spectrum of the radiated sound Bell changes acoustic impedance curve (both the frequencies and heights of the resonance peaks) Bell changes the radiation pattern, making it more directional at high frequencies (Why at high frequencies?) It allows more efficient radiation of sound by matching the high pressure inside the horn with the lower pressure outside The mouthpiece It shifts the frequencies of the impedance peaks, but has more dramatic effect on peak heights, especially enhancing low resonances. Popping frequency – the lowest resonance of a brass instrument mouthpiece ( Hz) Question: Estimate the length of the mouthpiece. 7

Valves Valves are more commonly found on brass instruments. Pressing a valve makes the air flow through an extra section of tube, temporarily making the instrument longer in between the mouthpiece and the bell. The slightly longer instrument gets a slightly lower fundamental harmonic, and a lower harmonic series. (A few valves are ascending valves, which cut off a section of tubing and so raise the pitch.) animation Slides (trombone) Seven positions of the slide are needed to play all desired notes of the scale These positions are not equally spaced (for a semitone down ~6% elongation) Problems with valves position and slides length 8

Woodwind instruments The player blows air against a sharp edge or through a reed Reed A thin strip which vibrates to produce a sound Usually made from “Giant cane” (bamboo), sometimes from synthetic materials Single reeds instruments: clarinet, saxophone Double reed instruments: oboe, english horn, bassoon, contrabassoon Free reeds: a) framed free reads - accordion, harmonica, bayan, ancient instruments; b) unframed free reads – some primitive instruments 9