Second 1/3 Semester Flashcards
What happens when two waves are in phase
Constructive interference
What happens when two waves are 180 degrees out of phase?
Destructive interference aka they cancel each other out
What happens when two waves are not in phase
Constructive and destructive interference
Standing waves
When a sound reflects off a surface, the reflecting wave can interfere with the other sound waves in the room causing spots of enhanced and diminished sound known as nodes and antipodes
*the nodes are known as standing waves
What do we use in booth to prevent standing waves
Warble tone
Where does resonance occur in a tube closed at both ends?
When the zero and 180 degree phase points are at the tube ends
* this is where the tube length is half the wavelength and it’s even and odd harmonics
Where does resonance occur in a tube closed at one end?
A frequency with a wavelength 4 times the length of the tube
- and odd harmonics
- mimics ear canal
What are the factors needs in a medium to transmit sound?
Mass and stiffness
What is it called when a medium resists the flow of sound energy?
Impedance
Equation for impedance
Z=force/velocity
- impedance is how hard it is to obtain a given velocity of molecule motion
- measured in a unit called rayl (ohm is unit for electric impedance)
Two main components of impedance
Resistance and reactance
Resistance
(R) impedance caused by friction
*opposes all frequencies equally
Reactance
(X) opposition produced by mass (x sub m) and stiffness (x sub s) of a medium
- mass and stiffness are opposites
- dependent on frequency
Equation for total opposition due to reactance
X sub t=x sub m - x sub s
Equation for mass reactance
(X sub m)= 2(pi)FM
M is mass
F is frequency
Equation for stiffness reactance
(X sub s)= S/2(pi)F
S is stiffness
acoustic impedance using pythagoran’s theorem
Z sub a= square root of R^2+ (2piFM - s/2piF)^2
when do we have the resonant frequency?
when Xm-Xs=0
*here we are left with resonance only
how does otosclerosis affect resonant frequency?
raises it to 1200Hz, stiffness increase
how does dislocation of ossicles affect resonant frequency?
stiffness decrease, lowers it to 500Hz
acoustic admittance definition and equation
(Y sub a)
Y sub a=1/Z sub a
it is how easy it is to make particles vibrate–opposite of acoustic impedance
two components of Ya
conductance (G)
susceptance (B)
mass susceptance equation
1/Xm which is to say 1/2piFM
stiffness susceptance equation
1/Xs which is to say 2piF/S