Rockford Fosgate 100 用户手册
– 23 –
D
YNAMIC
P
OWER
M
EASUREMENTS
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.
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
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
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
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.
and phase that can occur in a typical loudspeaker.