Thiel ss2 Verweisanleitung
Thermal Compression
Subwoofers achieve deep bass response even though
their enclosures are usually quite small in proportion to the
driver cone area because they are equalized. Without
equalization the response might extend only to 50 Hz or 40
Hz. The lowest frequencies are boosted to provide balanced
system response to low frequencies. A consequence of this
boosting is that much more power is delivered to the driver
than in a normal, unequalized speaker. The power supplied to
the drivers at 20 Hz can be 20 or more times normal. This
large amount of power results in the coils running hot even
during only moderately high demands.
driver cone area because they are equalized. Without
equalization the response might extend only to 50 Hz or 40
Hz. The lowest frequencies are boosted to provide balanced
system response to low frequencies. A consequence of this
boosting is that much more power is delivered to the driver
than in a normal, unequalized speaker. The power supplied to
the drivers at 20 Hz can be 20 or more times normal. This
large amount of power results in the coils running hot even
during only moderately high demands.
A significant problem stems from the fact that the
electrical resistance of copper is strongly temperature
dependent, having a temperature coefficient of 0.39%/
dependent, having a temperature coefficient of 0.39%/
°
C.
Therefore, when the voice coil temperature reaches 200
°
C,
the resistance has increased by 70% which causes a
reduction in current, and, therefore, output, by 4.5 dB.
reduction in current, and, therefore, output, by 4.5 dB.
The situation is actually more complicated because
resistance is only one of three components of driver
impedance (although the largest at most subwoofer
frequencies), the others being motional and inductive
impedance. The following graph shows the total impedance
of the drivers in the enclosure and also the resistive, motional
and inductive components that combine to produce it.
impedance (although the largest at most subwoofer
frequencies), the others being motional and inductive
impedance. The following graph shows the total impedance
of the drivers in the enclosure and also the resistive, motional
and inductive components that combine to produce it.
Frequency
Amplitude - dB
-25
-15
-5
5
15
1
10
100
1000
Frequency
Amplitude - dB
-25
-15
-5
5
15
1
10
100
1000
Total impedance of the SS2 (top line) and its components of resistance (at 0 dB), motional
impedance and inductance.
impedance and inductance.
Top to bottom: total impedance at 200
°
C, at room temperature, and the sensitivity
change at the elevated temperature.
6
Since the resistance is the only one of these three
impedance components that is temperature dependent, the
impedance does not increase with temperature uniformly at
all frequencies. Where the other components are major
contributors to the total impedance, near resonance and at
higher frequencies, the impedance does not increase as much
as it does at other frequencies. Therefore, the shape of the
total impedance curve changes and therefore the frequency
response changes. The following graph illustrates, from top
to bottom, the impedance at 200
impedance does not increase with temperature uniformly at
all frequencies. Where the other components are major
contributors to the total impedance, near resonance and at
higher frequencies, the impedance does not increase as much
as it does at other frequencies. Therefore, the shape of the
total impedance curve changes and therefore the frequency
response changes. The following graph illustrates, from top
to bottom, the impedance at 200
°
C, the room temperature
impedance, and the change in frequency response that
results. You can see that the sensitivity has decreased 2.5 dB
at 40 Hz but 4 dB at 20 and 80 Hz.
results. You can see that the sensitivity has decreased 2.5 dB
at 40 Hz but 4 dB at 20 and 80 Hz.
A Solution
The SmartSub incorporates a solution that consists of
measuring voice coil temperature in real time and using
this information to adjust the gain and frequency response
of the amplifier to correct the sensitivity and response
changes that would otherwise occur. This correction
ensures that the output is not compressed or imbalanced
during high demand.
this information to adjust the gain and frequency response
of the amplifier to correct the sensitivity and response
changes that would otherwise occur. This correction
ensures that the output is not compressed or imbalanced
during high demand.
Heat sensor on voice coil