Download Drum Volume Control

Aaron Gipp, Victor Salov, Udara Cabraal
Introduction
 Overpowering volume of drums in small venues
 Methods of controlling volume already in place
 Drum shields
 Dampening Pads
 Electronic Drums
 Pitfalls of current methods
Objective
 Create more pleasant listening experience
 Utilize Active Noise Cancellation for volume control
 Attenuation of up to 6 dB in three directions
 Minimal distortion between “dry” and “wet” signal
Scope
 Single 12” Tom instead of entire drum kit
 Complexity of 3D spherical waves
 Apply theory to one drum and extrapolate to full kit
 Attenuation in single directions
 Only one speaker for cancellation
 “Nodal lines”
 Cancellation at single point if too complex
Original Design
 Low-Pass and High-Pass Filters
 Eliminate sounds not associated with drum
 Bessel Filter design for exceptional linear phase
 Eighth-order
Original Design
Images taken from: http://www.dspguide.com/ch3/4.htm
Original Design
 Pre-Amplifier
 Op-amp circuit for preliminary amplification
 Vout = Vin(1+Rf/Rg)
 Op-amp: TI LM741CN
 Rf = 33.44 kΩ
 Rg = 1.989 kΩ
 Vout = 17.812Vin
Image taken from:
http://en.wikipedia.org/wiki/File:Operational_amplifier_noninverting.svg
Original Design
 Inverter
 Op-amp circuit used to invert polarity of signal
 Resistor values nearly identical for unity gain
 Theoretical 180° phase shift for all frequencies without
time delay
Original Design
 Inverter Design
 Vout = Vin(-Rf/Rin)
 Op-amp: TI LM741CN
 Rf = 38.75 kΩ
 Rin = 39.14 kΩ
 Vout = Vin(-0.99)
Image taken from: http://en.wikipedia.org/wiki/File:OpAmp_Inverting_Amplifier.svg
Original Design
 Final Amplifier
 Op-amp circuit used to control gain of inverted signal
 Almost identical to pre-amplifier
 Vout = Vin(1+Rf/Rg)
 Op-amp: TI LM741CN
 Rf = RV6NAYSD503A-P Clarostat 50kΩ single-turn ½
Watt potentiometer
 Rg = 1.476kΩ
 Vout ranges from 1.000Vin to 34.198Vin
Op Amp Golden Rules
 The op-amp has infinite open-loop gain.
 The input impedance of the +/− inputs is infinite. (The
inputs are ideal voltmeters).
 The output impedance is zero. (The output is an ideal
voltage source.)
 No current flows into the +/− inputs of the op amp.
 In a circuit with negative feedback, the output of the
op amp will try to adjust its output so that the voltage
difference between the + and − inputs is zero
(V+ = V−).
Original Design
 Additional Parts
 Omnidirectional MIC48 Multimedia Computer
(electret) Microphone

50Hz-16kHz frequency range
 665-AS05008PR2R PUI Audio 2” 8ohm .4W speakers

550Hz-4.5kHz frequency range
 Drum-Striking Apparatus


Consistency in measurements
Same height, same location on drum
Original Design
 Inherit drum signal with microphone
 Filter sound
 Invert
 Amplify
 Project back at source for cancellation
 “Dry” and “wet” signals propagate in opposite directions
Circuitry Testing Procedures
 Take measurements of the input vs. output V.
 Check for phase shifting on the inverter.
 Vary input voltages and frequencies for inputs and
check for gain.
 Measure signal attenuation if it occurred.
Phase-Shift Testing
Used 39K resistors *2, 1.5K resistor *1
Tests for Original Design
 Tested Pre-Amplifier for similar frequencies
 Tested for unusual amplification or phase shift
CHAN2
-0.002
-0.001 Seconds
0
0.001
0.002
1 kHz, 0.2Vpp
0.003
2
1.5
1
0.5
0
-0.5
-1
-1.5
-2
-2.5
-0.0004
Volts
CHAN1
Volts
2.5
2
1.5
1
0.5
0
-0.5
-1
-1.5
-2
-2.5
-0.003
CHAN1
CHAN2
-0.0002
0
Seconds
0.0002
550 Hz, 0.2Vpp
0.0004
Tests for Original Design
 Tested Pre-Amplifier with Inverter for similar
2.5
2
1.5
1
0.5
0
-0.5
-1
-1.5
-2
-2.5
-0.0015 -0.001-0.0005
2.5
2
1.5
1
CHAN1
CHAN2
Volts
Volts
frequencies
 Tested for unusual amplification or phase shift
0.5
0
CHAN1
-0.5
CHAN2
-1
-1.5
0
0.0005 0.001 0.0015
Seconds
1 kHz, 0.2Vpp
-2
-0.0004
-0.0002
0
0.0002
0.0004
Seconds
550 Hz, 0.2Vpp
Tests for Original Design
 Tested final amplifier for similar frequencies
 As potentiometer varies, we progress from unity gain
to a gain of ~35
0.15
6
0.1
4
2
0
-0.05
CHAN1
-0.1
CHAN2
0
CHAN1
-2
CHAN2
-4
-0.15
-0.2
-0.002
Volts
Volts
0.05
-0.001
0
0.001
0.002
Seconds
1 kHz, 0.28Vpp min gain
-6
-0.002
-0.001
0
0.001
0.002
Seconds
1 kHz, 0.28Vpp max gain
Tests for Original Design
 Tested all three components for similar frequencies
 Clipping for max gain from exceeding supply voltage
 Unsmooth due possibly to high frequency
 DC offset due to input offset voltage of op-amps
8
6
CHAN1
CHAN2
Volts
4
Volts
0.35
0.3
0.25
0.2
0.15
0.1
0.05
0
-0.05
-0.1
-0.002
2
CHAN1
0
CHAN2
-2
-0.001
0
0.001
0.002
Seconds
1 kHz, min gain
-4
-0.002
-0.001
0
Seconds
0.001
0.002
1 kHz, max gain
Drum Sound Experiment
 Created using device for consistency.
Drum Sound Experiment
 Created using device for consistency.
 Replicated multiple times to check
consistency.
Drum Sound Experiment
 Created using device for consistency.
 Replicated multiple times to check consistency.
 Measured using microphone and oscilloscope.
Drum Sound Experiment
 Created using device for consistency.
 Replicated multiple times to check consistency.
 Measured using microphone and oscilloscope.
On average we saw
this in Voltage vs.
Time plots:
Successes
 Inverter worked (phase shift of 180°) for all frequencies
with minor amplification
 No noticeable phase shift for pre-amplifer
 Incorrect amplification in inverter/pre-amplifier
compensated by final amplifier
 Drum-striking apparatus able to produce consistent
measurements
Challenges
 Unsmooth signals for three-component system
 Phase shift for final amplifier at max gain and high
frequencies
 Ex: 1 kHz => 2°


5 kHz => 13°
10 kHz => 30°
 Op-amps unable to source sufficient current to power
speaker
 Max voltage without distortion = 0.2V => 0.005W
 Filters’ original purpose deemed unnecessary
 Original microphone not reliable
New Design/Replacements
 Shure SM57 and Shure SM48 dynamic microphones
replace electret microphone
 Increased reliability and sensitivity
 Mixer to replace pre-amplifier
 Less distortion (smoother signals) at high frequencies
 Behringer Eurolive B215A (400W), Marshall MG30DFX
(30W) powered amplifier/speaker combinations to replace
old speakers
 More “head room”
 Broader frequency band
 Lower distortion (1% vs 5%)
Tests for New Design
 Verified that old speakers would not be able to support
voltage above ~0.2V
 Ch1 = input to final amplifier, Ch2 = input to speaker
0.6
0.4
Volts
0.2
0
CHAN1
CHAN2
-0.2
-0.4
-0.6
-0.0015
-0.001
-0.0005
0
Seconds
0.0005
0.001
0.0015
Tests for New Design
 Re-tested inverter circuit for new prominent
frequencies of drum (up to 500Hz)
-0.01
2.5
2
1.5
1
0.5
0
-0.5
-1
-1.5
-2
-2.5
CHAN1
Volts
Volts
 Later learned frequency content up to about 6kHz
CHAN2
-0.005
0
0.005
Seconds
162Hz, 4Vpp
0.01
-0.01
10
8
6
4
2
0
-2
-4
-6
-8
-10
CHAN1
CHAN2
-0.005
0
0.005
Seconds
233Hz, 15Vpp
0.01
Tests for New Design
 Verified microphone could inherit signal and interpret
frequency, and inverter could invert signal
100Hz
1kHz
Tests for New System
 Tested for phase response of system and air
 Distance between microphone and speaker = 0.0m
 Setup: FG => Marshall => SM57 => mixer
 Ch1 of scope measured output of FG
 Ch2 of scope measured output of mixer
 (Phase difference)/(frequency difference) constant in
linear phase system
Tests for New System
 D=0.0m
 t=time delay (approximately) in ms
frequency
1
2
3
4
5
6
7
8
9
10
Avg Slp
t
100Hz
78
81
78
77
77
81
80
78
79
80
79
.86
2.4
200Hz
163
161
167
164
167
166
165
164
166
165
165
.21
.57
300Hz
184
188
185
185
186
185
186
184
185
185
185
.31
.86
400Hz
215
217
218
216
216
218
214
215
216
216
216
.17
.47
500Hz
234
232
235
233
231
233
233
233
232
233
233
.19
.54
Tests For New System
 Similar test for D=10cm
 Phase delay due to air = Phase (D=10cm) – Phase
(D=0cm)
 Expected phase calculated for vsound in air = 343.2 m/s
Frequency
Average
Phase delay
due to air
Expected
phase
100Hz
2.3
283.4
10.49
200Hz
150.3
345.5
20.98
300Hz
170.3
345
31.47
400Hz
232.9
16.8
41.96
500Hz
264.8
31.9
52.45
Tests for New System
 Similar test for D=20cm
 Phase delay due to air = Phase (D=20cm) – Phase
(D=0cm)
Frequency
Average
Phase delay
due to air
Expected
phase
100Hz
348.5
269.6
20.98
200Hz
165.1
0.3
41.96
300Hz
182.6
357.3
62.94
400Hz
262.5
46.4
83.92
500Hz
317.7
84.8
104.90
Tests for New System
 Tested for cancellation of a single frequency by





pointing two speakers at each other
Setup: FG => Marshall => SM57 => mixer => inverter
=> Behringer
Measured SPL with Sound Level Meter
Cancellation at certain points called “nodes”
Discovered this orientation would create standing
waves
Pointed both signals in same direction from then on
Tests for New System
 Took measurements of dry drum signal from ten feet
away with Sound Level Meter
 30 samples, average = 76.24, standard deviation = 4.23
 Deemed SPL meter somewhat unreliable, took
measurements with scope
Tests for New System
 Based on system/air non-linear phase response, we can
only cancel narrow band of frequencies
 Re-sampled drum to select peak frequencies above
0dB (193.5, 196, 212, 230, 236 Hz)
Frequency
Average
Distance (m)
193.5Hz
328
1.615
196Hz
327.1
1.602
212Hz
348.8
1.556
230Hz
207.9
0.836
236Hz
283.1
1.14
Tests for New System
 Varied distance between microphone and speaker
between aforementioned values (1-2m separation) and
tested with varying volumes
Voltage Signal and FFT plot of drum by itself; 8.83Vpp for 1s, 2V/div; 500Hz
span, -25dBoffset, 5dB/div
Tests for New Design
Original Signal
D=1.4m with arbitrary amplitude
gain
New Design Successes
 Most of frequency content above 500Hz far below 0dB,
so cancelling narrow band might have worked
 System can inherit sound, interpret frequency, and
invert signal
 Learned both “dry” and “wet” signals must travel in
same direction
New Design Challenges
 Non-linear phase response associated with electronics
(different frequencies delayed by different amounts)
 Air being a dispersive medium (different frequencies
will travel faster than others)
 No notable attenuation; peak-to-peak voltage always
rose, average must be computed “by sight”
Recommendations/Future Work
 Using DSP, create filter bank for all prominent
frequencies
 Measure system phase response for all prominent
frequencies
 Implement linear-phase filter for each frequency,
delaying each to match frequency with longest phase
delay
 Compensate for system non-linearity and air dispersion