–60
°
(Cap)
0
°
(Ind) +60
°
1
Ω
2
Ω
4
Ω
Impedance
8
Ω
10V
30V
50V
8
Ω
–60
°
–30
°
0
°
30
°
60
°
4
Ω
–60
°
–30
°
0
°
30
°
60
°
2
Ω
–60
°
–30
°
0
°
30
°
60
°
1
Ω
–60
°
–30
°
0
°
30
°
60
°
85 W
84 W
84 W
84 W
86 W
162 W
157 W
156 W
157 W
162 W
273 W
258 W
251 W
256 W
271 W
390 W
356 W
346 W
352 W
390 W
Audio Graph – The PowerCube™
Amplifier:
Serial No:
Owner :
PUNCH 200.
2
14.4V x 2
ROCKFORD CORPORATION
Rated Power : 100 W @ 4 Ohms
IMPEDANCE
MODEL BEING
TESTED
x2 = STEREO
MONO = BRIDGED MONO
VOLTAGE FROM
BATTERY
OUTPUT
VOL
T
AGE
*
*
*
*
PHASE ANGLES
{
POWER
IN
WATTS
{
{
• Example of a Punch 200.
2
PowerCube
D
Y N A M I C
P
O W E R
M
E A S U R E M E N T S
About the Dynamic Power Measurements
The Audio Graph PowerCube is a test instrument used to measure the output of an amplifier in accordance with IHF-202 industry
standards. The IHF-202 standard is a dynamic power measurement and was developed as a means of measuring power in a
manner that best represents the Real World operation of an amplifier. Many manufacturers, including Rockford Fosgate, at times
will measure amplifier power into a fixed resistor (4 ohm, 2 ohm). While this method is useful in some types of evaluation and
testing, it is not representative of an amplifier that is connected to a speaker and playing music.
Music
Music is dynamic; the sound waves are complex and constantly changing. In order to simulate this, the IHF-202 standard calls
for the input signal to the amplifier to be a 1kHz bursted tone. This signal is input (on for 20 milliseconds) and reduced 20dB
for 480 milliseconds. The signal is gradually increased in level until the amplifier's output exceeds 1% Total Harmonic Distortion
(THD). At 1% distortion becomes audible, therefore, any power produced above that level is considered
unusable. Many
manufacturers represent their amplifiers' output power in excess of 10% distortion. They use many names for this measurement,
such as Total Maximum Power or Maximum Output Power. This is not indicative of the
actual usable output power.
Listening to Loudspeakers - Not Resistors
A loudspeaker is not a resistor. A resistor's value (resistance measured in ohms) is fixed. A loudspeaker's impedance is dynamic.
It is constantly changing in value, dependent upon the frequency of the input signal. Therefore, measuring power with the amplifier
loaded into a 4 ohm resistor is not the same as measuring power with the amplifier connected to a 4 ohm speaker. Most people
do not listen to music through a resistor.
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.
What is an Amplifier?
An amplifier by definition is a voltage generating
device, recreating the signal which is input to it
identically but with increased volume. It will be
connected to a reactive load (the speaker). The
impedance of this load and phase of the signal
passing through the load will vary, dependent upon
the frequency of the input signal (music).
Therefore, a perfect amplifier will be able to main-
tain the same output voltage regardless of load
characteristics and will not alter the signal it is
reproducing. A perfect amplifier when measured by
the Audio Graph PowerCube would present data
that forms a perfect cube. Unfortunately, amplifiers
are not perfect. The laws of physics generally prevent it. A great amplifier is about the best one can hope to attain.
As you can see by the PowerCube and as you will experience by listening, your Punch amplifier is a GREAT AMPLIFIER!
– 27 –
