Null Phase Of Two Sine Waves

Sound Notes Sound basics Without sound life would not be able to be. sound waves Sound is in a wave. Sound vibrates through the molecules and it is only the energy that moves Good Vibrations when the speaker vibrates so does the air around it the moluclues dont move very far they just pass on the energy Sound is our perception of this vibrations Through matter Sound waves can travle through matter For sound t move through things they must have two defined characteristics-elasticity and inertia Elasticty-compress then return to original shape Inertia- Object in motion stay in motion and object at still stays at still Sine Wave frequency is the distance between the bottom and top of wave energy when cone moves out is called compression when the cone moves back it is called rarefaction this going from push out to in is one cycle Frequency/pitch the amount of cycles is called frequency higher the frequency higher the pitch Period period=1/frequency 20 cycles per second is a period of .5 seconds per cycle Wavelength Wavelength is the actual physical distance covered by one complete cycle. based on speed of sound sound wave travels about 1130 feet/second wavelength=speed of sound/frequency Amplitude Amplitude is the height of the sound wave sound of higher amplitude are louder Adding sine waves Every musical sound is composed of a combination of sine waves Phase when 2 waves of the same amplitude and frequency come in contact with each other the create a new wave with the same frequency but doubles the amplitude these 2 waves are in phase

Harmonics -the tone of a voice or instrument is cause by its specific wave form -the creation of a sound by combining several related sine waves -inherent to musical instruments, or by means of electronic combinations -Fundamental note is the loudest of the set of sine waves. The following harmonics sine waves will be composed of frequencies which are multiples of the original -The quality of an instrument is a direct reflection of the quality of the harmonics, the result of

a good instrument is resonances Non-harmonic relationships -drums and other similar instruments are know as non-harmonic, because the sound is made of of waves which are not multipliers of the fundamental note Waves you hear -20Hz-20000Hz THE electrical representation of Sound Signal Voltage/Amplitude -an audio signal is an electrical representation of a sound. -audio signal is proportionally identical to the sound wave it represents Properties of electricity -voltage, current, resistance and power Power voltage x current = power, power is measured in watts Resistance/Impedance Resistance allows us to use electrical current reactance is frequency based Impedance like resistance is measured in ohms ohms law impedance is symbolized with a “Z” [I=E/Z] [Z=E/I] [E=I x Z] Power Calculators [P=E x I] P=power in watts, E=electrical potential in volts, I=current in amps dB or not dB....that is the question the decibel is both electrical and acoustic values Logarithms Logarithms are exponents base is number being raised, log is power being to which it is raised, and antilog is the resultant number. dBm dBm is a measurement of electrical power, it is 1 milliwatt dBu dBu is a voltage measurement, .775 volts is the zero reference for dBu dBV & dBv 0 dBV = 1 volt rms dBv and dBu both refer to .775 volts dBW dBW referenced to 1 watt

Mic Level includes microphones, record cartridges, and tape heads no signal to -20 dBu Line Level -20 dBu to +30 dBu (24.5 volts). It includes outputs, preamp outputs, mixing board outputs, and amplifier inputs Speaker Level all levels above +30 dBu, mostly the speaker outputs of power amplifiers How these levels work together...

Perception of Sound Measurement of Sound Sound Pressure A source which vibrates the air is transferring energy to the air which is then radiated in the form of sound waves. In other words a sound source radiates acoustical energy. the measurement for power is the acoustical watt and there is a huge difference in loudness from the lowest acoustical watt we can hear to the highest Relative vs. Absolute Levels there are many factors affecting how loud a sound is and it's hard to measure for example doubling power at a sound source doesn't double the sound it actually creates a barely perceptible shift in the sound pressure level (approx 3 dB) because of all the factors, our common measurement of loudness is SPL, and it measures the difference between two values, rather than measuring the values themselves it is a ratio value and is expressed by the decibel Sound Pressure Level (SPL) dB SPL SPL is treated as the same way as voltage calculations in Ohm's Law dB SPL = 20log(P1/P2) the doubling of 10log to 20log in the calculation reflects the resistance component in dB SPL 3 dB an increase of 3 dB represents the smallest perceptible change most ppl can hear in order to get this change you need to double your power 6 dB an increase or decrease of 6 dB SPL reflects a 2 to 1 ratio in SPL, yet it represents only the first noticeable change in the perception of sound 10 dB if you increase 10 dB most people perceive this as doubling loudness but to do this....you need to increase power 10 times So if I have a 100 watt amp with an SPL of 95 dB, I would need a 1000 watt amp to double my loudness dB PWL db PWL is the value referenced to 1 watt of acoustic power and follows the same 10 log conversion scale as dBW The Three amigos Volume power level, loudness, or sound intensity Level the ratio of a quantity's magnitude to an arbitrarily selected magnitude for examples SPL is expressed in dB relative to .0002 dynes/sq. cm Gain gain is the increase in power or voltage of an audio signal the opposite of gain or a decrease in signal level is called attenuation Loudness Most people use this to refer to volume or SPL but it is actually much more complicated Fletcher – Munson developed a set of equal loudness contours based on the perception of sound @ 1 kHz, and a system of evaluation known as phons the curve these men developed flattens out @ higher sound pressure levels

A, B, C weighted scales we use different scales on our sound level meters to accomplish reading sound the way we actually hear sound A weighted scale – reflect the ears sensitivity at low listening levels the meter measures SPL levels along the 40 phon curve and reflects the lower frequencies that the ear experiences at this sound pressure level B and C weighted – these scales reflect the flattening of the FM curves @ higher sound pressure levels we use these for higher SPL events such as rock concerts