HVAC:| what does it stand for and what are the 3 things it causes?
Heating, Ventilation, Air conditioning.

Noise, flanking(noise brought in from another room through the ac vents), wind.

definition: Gobo
Used in the studio to isolate one sound source from another. Only effective at blocking frquencies whose WL’s are smaller than the dimensions of the gobo
6 foot gobo, what freqs can it block?
1130/6 = 188
definition: diffraction
Why does it happen?
the bending of a sound wave around an obstacle or object. This happens whenever the WL of a signal is greater than the dimensions of the obstacle.
Lower Frequency means longer or shorter WL?
Mass Law: 2 times the mass equals
___db increase in isolation
6db. Increases isolation
Mass Law: half the mass equals
___db decrease in isolation
6db. decreases isolation
What does TL stand for? And what is it?
Transmission Loss. A specific ratio in db between energy that goes in and goes out. The higher the TL, the better the isolation.
TL of 500hz 36 db. Sound going in is 100 db. How loud is the sound coming out?
65 db
2x freq = ___db change in TL
+6 db
1/2 freq = ___ db change in TL
-6 db
2x mass = ___db change in tl
+6 db
What does STC stand for and what is it?
Sound Transmission Class. A single number rating covering the TL performance of a construction between 125hz and 4khz.
Is STC a ratio or a single number?
Single number
Frequencies between 125hz and 4khz at a level of 97 db going through a material with a STC of 27 will be how loud coming out?
70 db
What does NRC stand for and what is it?
Noise Reduction Coefficient. An average rating of noise reduction. Average of 250hz,500hz,1khz,2khz. Is a number between 0-1.
NRC is an average rating through what freqs?
250hz, 500hz, 1khz, 2khz
Is NRC specific or broad?
Is TL specific or broad?
Is A.C. specific or broad?
Do TL and STC say anything about low frequencies?
What does AC stand for and what is it?
Absorption Coefficient. A specific rating for each freq. Is a number between 0-1.
A double wall partition can increase STC to ___db
What does a double wall partition do?
completely physically isolates one side of the wall from the other, making it very difficult for sound wave vibrations to pass through the structure.
Use of metal studs generally improves isolation by ___db.
Isolations principle tool is ____
True or False: Acoustically treating a room helps isolation.
False, you stupid fucker.
In a room, what 3 things happen to sound?
reflection, absorption, diffusion.
What is diffusion?
The scattering of sound from a single strong discrete reflection to a broad array of lesser reflections spread in many different directions. Spreads sound evenlly while eliminating audible discrete echoes.
Frequencies under 300 hz cause what problem in a room, and what are the solutions?
Standing waves. Fix with Bass traps, membrane absorbers, and helmholtz resonators
Frequences over 500 hz cause what problem in a room, and what are the solutions?
Flutter echo. Fix with absorbers and diffusors.
When were diffusors invented?
What are the 3 types of absorbers
Flexoral, frictional, resonant.
What kind of absorber uses heat and is good around 125hz-500hz
How do you improve friction absorbers?
Make them thicker or move them 3-6″ from wall. Moving improves them around 3-6″
Why does moving a friction absorber away from the wall improve it?
6″ is 1/4 of a 500hz WL.
In a WL, the highest point(1/4 through the full cycle) is what 3 things?
Antinode, max compression, max pressure
In a WL, the midpoint(1/2 through the cycle) is what 2 things?
Node, max velocity
What type of absorber is flexoral
What kind of absorber can be tuned?
What range of Freq’s are flexorals good at?
What does a flexoral absorber do to freqs above 500hz?
How does a helmholtz resonator work?
The resonant absorber consists of an enclosed volume of air tuned to a low freq, with gaps or openings that allow low freq sound energy in. The air inside acts ke a type of spring on the columns of air entering the slots. The cavity can also be filled with frictional absorbent, with the effect of widening the bandwith of effective absorption to more generally absorb low freqs.
Are helmholtz resonators broad or narrow band
Who is sabine
Worked on reverb time, figured out rb60 formula.
what is rb60
number of seconds required for the intensity of the sound to drop from the starting level, by an amount of 60 dB
What is the point of acoustically treating a control room?
To hear only the sound coming out of the monitors
What is a flutter echo
rapidly repeating echoes at high frequencies, which occur in small enclosed spaces between closely spaced parallel walls.
27.5hz, lowest note of piano
31.5hz, lowest C on piano, 1st band in a graphic EQ
261.63, middle c
highest C on piano, 4186hz
Speed of sound
1130 ft/s, 1 ft/ms
Fourier analysis
breaking down sound into individual sine waves
Fast Fourier Transform, analyzing sound with 3d graph showing all the freqs
What are the 10 bands of an eq?
C1- 31.6
C2- 63
C3- 125
C4- 250
C5- 500
C6- 1k
C7- 2k
C8- 4k
C9- 8k
What is the Freq range of a piano?
27.5hz to 4186hz
Haas effect
The brains ability to locate a sound source due to it’s earlier arrival to one ear than the other.
Highest pressure/amplitude
Root Means Squared. Average Amplitude.
Crest Factor
The Difference between RMS and Peak
Transverse waves
Displacement is perpendicular to motion. String wave. NOT A SOUND WAVE
Longitudinal waves
IS a sound wave. displacement is parallel to motion. Areas of compression and rarefaction.
The phjase of a periodic wave refers to it’s current position with respect to the completetion of a full cycle, measured in degrees. 360 degrees in a cycle.
the time it takes for a wavelength to complete once cycle
Just noticable difference. Between 0.5 db and 3db
Inverse square law
2x distance from sound source= -6db
Frequency of Alternating current power in USA
Frequency of Alternating current power in EU
10x power = ___db
+10 db
2x loud = ___db
2x SPL= ___db
2x distance
2x voltage
2x power = ___db
10 watts 2x loud = ___ watts
10 watts 2x power = ___db
90db 2x power = ___db
90 db 2x loud= ___db
100 db
90 db 10x power= ___db
100 db
106dbSPL 2xSPL= ___db
112 dbSPL
the line where everything sounds as loud as a 1khz freq
Parts of Outer ear
Pinna, Ear Canal, tympanic membrane (eardrum)
Parts of Middle ear
Hammer, Anvil, Stirrup
Parts of Inner Ear
Cochlea, Round Window, oval window, basilar membrane, stereo cillia(hairs), periymph (fluid)
What freqs do the base and tip of the cochlea pick up?
Base: high freq, Tip: low freq
Critcal bands
Parts of the ear that determine d
3 Ways to avoid masking
EQ (2 guitars, change eq on one guitar), Pan, Arrangement
below 35ms difference in arrival time to ears
above 50ms difference in arrival time to ears
between 35-50ms difference in arrival time to ears
5 kinds of stereo miking
xy, spaced pair, blumlein, NOS, ORTF
When did bbc begin regular stereo broadcasts
3 interaural cues
phase,spectrum, intensity
On a SPL meter, use dbA weightings for ___ level sounds
On a SPL meter, use dbC weightings for ___ level sounds
Mixing domains
Level, Frequency, Space
Dynamic Processing
Compression, limiting, dither