Angelo Farina Angelo Farina
Industrial Engineering Dept.
Industrial Engineering Dept.
University of Parma - ITALY University of Parma - ITALY HTTP://www.angelofarina.it HTTP://www.angelofarina.it
IMPULSE RESPONSE IMPULSE RESPONSE
MEASUREMENTS
MEASUREMENTS
Traditional time-domain measurements with pulsive sounds and omnidirectional transducers
Electroacoustical measurements employing special computer- based hardware, a loudspeaker and an omnidirectional
microphone
Time Line
The Past The Past
The Present The Present
Electroacoustical measurements employing standard sound cards, 2 or more loudspeakers and multiple microphones (2 to 8)
The Future The Future
Microphone arrays for capturing high-order spatial information
Artificial sound sources employing a dense array of
loudspeakers, capable of synthesizing the directivity
pattern of any real-world source
Impulsive Impulsive
sources
sources
Basic sound propagation scheme Basic sound propagation scheme
Omnidirectional receiver Direct Sound
Reflected Sound
Point Source
Direct Sound
Reverberant tail
Traditional measurement methods
Traditional measurement methods
8 novembre 2010
8 novembre 2010 Misura della Risposta all'ImpulsoMisura della Risposta all'Impulso 66
Balloons Balloons
Size influences low frequency spectrum Size influences low frequency spectrum
Firecrackers
Very good power and spectrum, highly repeatable Very good power and spectrum, highly repeatable
Firecracker Vs. Dodechaedron
Comparison in Patras’ Odeion Comparison in Patras’ Odeion
Dodechaedron Dodechaedron
Firecracker Firecracker
Firecracker Vs. Dodechaedron
Comparison in Patras’ Odeion Comparison in Patras’ Odeion
Dodechaedron
Dodechaedron Firecracker Firecracker
The “clap machine”
Good frequency response and repatibility Good frequency response and repatibility
Verification of the repeatibility Verification of the repeatibility
The “clap machine”
The “clap machine”
The “clap machine”
Example of a pulsive impulse response Example of a pulsive impulse response
Note the bell-shaped spectrum
Note the bell-shaped spectrum
Microphones
Microphones
Pressure and velocity microphones Pressure and velocity microphones
Pressure microphone
(Bruel&Kjaer) Velocity microphone
(Microflown)
Omnidirectional microphones Omnidirectional microphones
ISO3382 recommends the usage of omni mikes of no more than 13mm ISO3382 recommends the usage of omni mikes of no more than 13mm
These are the same microphones usually employed on sound level meters: These are the same microphones usually employed on sound level meters:
Sound Level Meter Sound Level Meter (records a WAV file on the (records a WAV file on the
internal SD) (left) internal SD) (left) Measurement-grade Measurement-grade
microphone and microphone and preamplifier (to be preamplifier (to be connected to a sound card) connected to a sound card)
(right)
(right)
Microphone directivity patterns Microphone directivity patterns
Omnidirectional ( 100 p,0 v) Subcardioid ( 75 p,25 v) Cardioid ( 50 p,50 v)
Hypercardioid ( 25 p,75 v) Figure-of-Eight (0 p, 100 v)
Pressure+Velocity Microphones Pressure+Velocity Microphones
Variable pattern microphone:
Neumann U89i variable-pattern microphone
Spatial analysis by directive microphones Spatial analysis by directive microphones
The initial approach was to use directive microphones for gathering some The initial approach was to use directive microphones for gathering some information about the spatial properties of the sound field “as perceived by information about the spatial properties of the sound field “as perceived by the listener”
the listener”
Two apparently different approaches emerged: binaural dummy heads and Two apparently different approaches emerged: binaural dummy heads and pressure-velocity microphones:
pressure-velocity microphones:
Binaural Binaural microphone (left) microphone (left)
and and
variable-directivity
variable-directivity
microphone (right)
microphone (right)
Test with binaural microphones Test with binaural microphones
Cheap electret mikes in the ear ducts Cheap electret mikes in the ear ducts
Capturing Ambisonics signals
A tetrahedrical microphone A tetrahedrical microphone probe was developed by probe was developed by Gerzon and Craven,
Gerzon and Craven,
originating the Soundfield originating the Soundfield microphone
microphone
Soundfield microphones
Soundfield microphones Soundfield microphones
The Soundfield microphone allows for simultaneous measurements of the The Soundfield microphone allows for simultaneous measurements of the omnidirectional pressure and of the three cartesian components of particle omnidirectional pressure and of the three cartesian components of particle velocity (figure-of-8 patterns)
velocity (figure-of-8 patterns)
Directivity of transducers Directivity of transducers
Soundfield ST-250 microphone Soundfield ST-250 microphone
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250 Hz
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500 Hz
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1000 Hz
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2000 Hz
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4000 Hz
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8000 Hz
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