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Velocity, Frequency,
and Amplitude
| Question | Answer |
|---|---|
| What happens whe air is compressed? | There is a spring like reaction that pushes molecules apart (electrical charges repel when molecules are pushed too close). This repeating pattern of compression and rarefactions creates energy wave.. |
| Wave Motion | the transmission of energy from a source to a distant receiver without the transfer of matter between the two points (you don't feel air blowing out of a trumpet or violin. You just hear sound) |
| Sound is... | energy putting air particles in motion. The particles push on their neighbors, and so on, creating a repeating pattern of compressions and rarefactions |
| During sound wave motion, high and low pressure areas... | move through the air, but the molecules themselves do not move very far |
| What is the velocity of propagation? | the speed of sound. 1130 ft/second. at sea level at 70 degrees F with dry air. |
| What changes the speed of sound? | It changes slightly with atmospheric conditions. Temperature, humidity, and altitude. |
| What factors are taken into account in large PA systems at stadiums and festival concerts? | Temperature and humidity. These factors change timing of delayed speakers in the system during the show. Arenas and stadiums make changes with computers throughout the entire concert to work on speaker delays. |
| Sound travels faster in what materials? | Dense materials. The molecules are more closely packed. Sound moves faster in water than in air. Almost 3 mps in steel. |
| What does doubling frequency do? | It results in a pitch change of one octave. |
| Octave shifts are independent of... | starting frequency. they don't have to begin on a musical note. |
| How many octaves can most people hear? | About 10 octaves (20-20,000 Hz) |
| Wavelength | Distance between compression peaks or rarefaction valleys. Measured between any two points of equal pressure. Represents one wave cycle. |
| Waveform graph | Shows undulating lines of a wave. Peaks are pressure maximum. Troughs at pressure minimum. Cross on a line called the zero crossing. |
| What should engineers and mixers know about octaves? | Octaves translate into how we perceive music. |
| What is the octave 20-40 Hz used for in recorded music? | POWER. Isn't heard very often in record music, as most people don't have equipment to record it well. Generates excitement in crowd at concerts. Felt as much as heard because it takes a great deal of energy to produce. |
| What is the octave 40-80 Hz used for in recorded music? | POWER AND RHYTHM. Below 50 Hz is still in POWER range. Now moving into area where many rhythm instruments have their lowest frequencies. |
| What is the octave 80-160 Hz used for in recorded music? | RHYTHM. Most fundamental rhythm frequencies (drums, bass, stomping, etc.). Around 100 Hz, if too much energy, music can sound boomy. |
| What is the octave 160-320 Hz used for in recorded music? | RHYTHM and TUBBINESS. Higher basic frequencies of rhythm instruments like guitars. Frequencies above 250 Hz can make recordings sound tubby (lacking resonance, dull). |
| What is the octave 320-640 Hz used for in recorded music? | BOXY. Excess energy will make music sound like it's being played in a small room or big box. |
| What is the octave 640-1280 Hz used for in recorded music? | HORN-LIKE. Cup hands around the mouth or talk through a funnel or megaphone. That's an idea of how this octave sounds. |
| What is the octave 1280-2560 Hz used for in recorded music? | TINNY. Potential to emphasize sounds in a way that makes them sound tinny or brittle. |
| What is the octave 2560-5120 Hz used for in recorded music? | SIBILANCE and INTELLIGIBILITY. Critical for understanding speech and lyrics. |
| What is the octave 5120-10,240 Hz used for in recorded music? | PRESENCE and BRIGHTNESS. Important in giving sound its presence. Without it, sounds will sound distant and dull. |
| What is the octave 10,240-20,480 Hz used for in recorded music? | SPARKLE. Icing on the cake. Many don't notice it missing, but it can add life and clarity to music. |
| What are sibilant sounds? | Speech sounds like "sss" or "thhh" or "k" that have hissing |
| Doppler Effect or Doppler Shift | As sound sources move towards or away from us at substantial speed, sound waves are distorted and pitch shifts noticeably. As waves get further from the source, they spread apart, and they are closer when you are right by the source. |
| What quality of sound causes the Doppler Effect? | Sound travels so slow relative to the speed of light. |
| When is the pitch higher during the Doppler Effect? | The pitch is higher when the object is near you and the frequency is higher. It will be lower when it is further away. |
| What is doubling? | At 20 Hz, most consumer speakers make a sound, but they just double, and you actually hear a sound at 40 Hz. |
| Why can't most speakers reproduce the extremes of frequency at a volume we can hear? | At 20,000 Hz, most consumer speakers can't move quickly enough. At 20 Hz, they double. |
| What is a common range for some headphones and speakers? | 80-100 Hz to 10 KHz. |
| What is the unit for measuring loudness? | Decibel |
| Where do decibels come from? | Decibel is a tenth of a Bel, a unit developed by Alexander Graham Bel's telephone company for measuring voltage losses over miles of wire. |
| Why do we need decibels? | They allow us to measure different things related to loudness and translate one form of energy to another and still have it make sense. Easily converted between different systems (voltage, current, air pressure variations, etc.) |
| How does the decibel relate closely to physical experience? | the way we perceive sound is not linear, and neither is the decibel scale. |
| How are decibel measurements comparisons? | They are ratios of a measurement to a standard reference. Different letters follow dB to show what the reference is - dBu, Dbm, dB SPL, dBFS, etc. |
| Why can dB values be positive or negative? | Zero is always the reference, whether you're measuring air pressure, voltage, amperes, or anything else. Because zero is the reference, values may be positive or negative. |
| What is dB SPL and why do we use it? | decibels Sound Pressure Level. Used because we're discussing loudness and what we hear. |
| What is the reference value for dB SPL? | Reference is represented by a zero, but actual reference value is threshold of hearing, which is very small variation of air pressure. Few places where air so still that sound level is less than threshold of hearing. If there, you start to hear your body |
| Why are dB SPL measurements usually positive? | The reference for dB SPL is the smallest audible sound. |
| What is the volume of a conversation between two people, a few feet apart, in a reasonably quiet room? | 60-65 dB SPL |
| How does 70 dB compare to 60 dB? | Twice as loud. It takes a 10x increase in power to increase the sound pressure by 10 dB. |
| How is amplitude determined? | The loudness of a sound is determined by the amount of air being displaced. |
Created by:
mortehay000
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