David Miles Huber

See course syllabus
Hours (6:00 – 9:00, except field trips (DMH only) … which are 7:00 – 10:00)

Week 2
Acoustics and Studio Acoustics & Design (prepare by reading Ch. 2 & 3)

Next DMH class:
Week 4 (Tues & Thurs)
Microphones – Field trip to London Bridge. (7:00 – 10:00) (prepare by reading Ch. 4)
Microphone construction, theory and application.
london bridge recording studio
20021 Ballinger Way NE #A
Shoreline, WA 98155
P: 206.364.1525

A. The transducer
P. 37/38

B. Sound & Hearing: Sound Pressure Waves

1. Sound arrives at the ear in the form of a “periodic” variation in atmospheric (barometric) pressure.
2. Pressure waves propagate outward in air from a source in a 3-D fashion (can travel in solids in a roughly 2-D manner).
3. How Loudspeakers work
4. record player

3. Propogation of a wave (note: you need a baloon and slinky for

– an area of high pressure is set up… once released, the
compressed, high-pressure area exerts itself upon the
surrounding, lower pressure area… In short, the high
pressure wave is always moving from areas of high-pressure
to that of lower pressure (much like weather does in our

– Seattle Aquiarium example

– it is not the air (or other media, such as water), that moves, but the actual compression wave itself (show using slinky).

Betty saved Slinky, selling the Philadelphia factory and moving the operation to the small, western Pennsylvania town of Hollidaysburg. She steered its comeback with co-op advertising and a simple jingle that remains lodged in the brains of Baby Boomers everywhere. (“It’s Slinky, it’s Slinky, for fun it’s a wonderful toy/It’s Slinky, it’s Slinky, it’s fun for a girl and a boy. …”)

There have been few other changes. The prototype blue-black Swedish steel was replaced with less expensive, silvery American metal; later a plastic model was added. For safety reasons the Slinky’s ends were crimped in 1973. Clever people have found other uses for James’ toy, most notably soldiers in Vietnam, who found it made a great radio antenna when strung over tree branches. But today’s Slinky is not much different from the original. It’s still made on Richard James’ machines. And at $2, it costs only twice what it did 50 years ago.

4. Waveform Characteristics: Amplitude, Frequency, Velocity, Wavelength, Phase, Harmonic content and the Envelope of a musical/acoustic signal


– physical or atmospheric displacement, electrical signal level
– percieved as volume level


– rate of change of physical displacement or signal level over time

– perceived as pitch
– measured in Hertz (conveying number of periodic cycles/sec)
– The Cycle (plot 360 of a circle)
– find a round object and chart its rotation
– sine wave


– The speed at which a wave propagates through a medium
– in air = 1130 ft/sec
– much faster in solids
– tell story about older, helium “mini reverb hall”


– The physical length of a cycle (from node-to-node)
– distance increases as the freq. decreases (and vice-versa)
– 30 Hz wavelength = 37.6′
– 300 Hz wavelength = 3.76′

Wavelength Travel Within a Confined Space:

– Reflection of Sound (see page 47)
– mirror analogy
– Diffraction of sound

Frequency response:

– the charting of amplitude over frequency
– Flat response vs. intended design coloration


– In-phase & out-of-phase (read p. 31)
– try experiment with slinky!
– 0°, 90°, 180°, 270°, 360°
– electrical & acoustic phase cancellation

Complex Waveforms:

– IMPORTANT! multiple sine waves at various frequencies
combine and cancel to create a “single” combined amplitude
at one point in time… this is how “all” audio systems, sound
generators and hearing animals deal with sound!

Harmonic content:

– The balance of overtone frequencies work together to define
the sonic “character” of an instrument or sound generator.
– Difference in instruments and between “like” instruments (p.

– even harmonics tend to be “musical” in nature, following
music’s tonal structure
– note: odd harmonic distortion is not musical in nature and is
perceived as a harsh form of distortion

D. dB or not dB

Don’t worry about it, over time the dB will be 2nd nature to you

1. Logarithms

– a way of making extremely large, almost unfathomable
numbers manageable (Read p. 58 dB intro)
– candles in a dark room example
– if you don’t have a scientific calculator and the number from
which the log is to be derived… count the 0s (ie: log
1,000,000/1 = log 1,000,000 = 6)
– power = 10 log P1/P2
– double in power = 3 dB
– SPL = 20 log P1/P2
– double in SPL = 6 dB (seems wrong but the calcs work
out !)
– I’ve always been told that a double in SPL is 3 dB!
– See SPL chart on p. 60
– Work out a few examples with the class

E. The Ear

1. General Stuff

– Frequency response is generally 30 – 18,000 Hz.

– Threshold of hearing
– Threshold of pain 130-140 dB
– continued exposure = permanent damage
(often starting with the highs and working down)

2. Auditory Perception

– The ear is a non-linear device (doesn’t have a flat freq.

– Fletcher-Munsen equal loudness curve (p. 50)

– stereo loudness control
– why things sound better “LOUD!”
– optimum monitoring levels & why
– best to monitor at “home” listening levels
– if monitored loud, at moderate levels the sound
would be both bass & treble shy
– masking
– vacuum cleaner (WHAT?)
– tape asperity noise

– perception of direction

– intensity differences (head causing acoustic shadow)
– arrive time differences (5 ms = 15 dB shift?)
– perception of space (p. 69)
– cues to size and acoustic makeup of a room
– direct sound (incident)
– early boundary reflections
– reverb
– Spacialized & surround-sound reproduction


1. Basic design considerations

– isolation

– area to be built (Nashville bedrock, suburban housing
area, codes)
– transmission loss (p. 65, give basic explanation)
– double wall construction
– mis-matched impedance

– Floating floor (expensive fig 3.8 & inexpensive way fig

– drum riser (solid construction)
– Hung Ceiling
– Windows
– iso room, booth, flat design

– frequency balance

– a room should possess as little sound coloration as is
possible… ideally would absorb & reflect all freq.
– big no no… parallel walls (p. 77)
– dispersion in a room (p. 79 & 80)
– (high and low freq absorption)

– absorption (p. 84 & 85)
– need for in multitrack production
– too much in the 70’s & 80’s (US & UK)
– new designs for separation and live rooms in the 90’s

– (low freq absorption)

– bass buildup at boundaries (bass traps)
– walls
– floor-wall
– corners
– various bass trap designs (p. 86 – 89)

– reverberation

– cost factors

– even with the “Big Boyz”, beyond basic knowledge of the concepts… it’s often intuition

• Group discussion on your own acoustic situations/solutions

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