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A 4 ohm speaker may experience a drop in impedance 4-
6 times lower than its nominal (printed) impedance. A
speaker will also create phase shifts in the signal that is
passed through it. These phase shifts happen because
a speaker is an inductor (voice coil) and a capacitor
(compliance of the surround/spider), as well as a resistor
(voice coil wire).
To simulate a speaker the
Audio Graph PowerCube
measures output power into 20 different loads. It tests at
8 ohms, 4 ohms, 2 ohms and 1 ohm. Each of these
impedances is also tested at –60°, –30°, 0°, +30° and
+60° phase angles. These different impedances and
phase angles represent the shifts in impedance and
phase that can occur in a typical loudspeaker.
Information Cubed
The data acquired in the testing procedure is then graphed
in the form of a 3-dimensional cube, hence the name
PowerCube
.
The
Phase Angle
is expressed on the horizontal axis, the
Output Voltage
is presented on the vertical axis and the
Impedance
is displayed on the Z axis.
Output Power,
in
watts, is listed on the left hand side for each impedance
at each phase angle.
29
–60° (Cap)
0°
(Ind) +60°
1Ω
2Ω
4Ω
Impedance
8Ω
20V
60V
100V
8Ω –60°
–30°
0°
30°
60°
4Ω –60°
–30°
0°
30°
60°
2Ω –60°
–30°
0°
30°
60°
1Ω –60°
–30°
0°
30°
60°
20 W
20 W
19 W
20 W
20 W
38 W
35 W
35 W
36 W
38 W
66 W
60 W
58 W
60 W
64 W
100 W
87 W
84 W
87 W
100 W
*If a Bridged/Mono, test amplifier sees 1/2 impedance (2Ω test amp sees 1Ω)
Audio Graph – The PowerCube
Amplifier:
Serial No:
Owner :
PUNCH 4040 14.4V x 4
B1AB13A000016
ROCKFORD CORPORATION
Rated Power : 20W at 4 Ohms
IMPEDANCE
MANUFACTURERS
RATED OUTPUT
MODEL BEING
TESTED
x4 = STEREO
MONO = BRIDGED MONO*
VOLTAGE FROM
BATTERY
OUTPUT VOLTAGE
AT THE RAILS
(MOSFETS)
*
*
*
*
PHASE ANGLES
"MOTION OF
SPEAKER"
{
POWER
IN
WATTS
{
{