Balanced Technology Extended (BTX) Thermal/Mechanical Design Information
40 Thermal and Mechanical Design Guidelines
5.1.2 Acoustics
To optimize acoustic emission by the fan heatsink assembly, the Type II reference
design implements a variable speed fan. A variable speed fan allows higher thermal
performance at higher fan inlet temperatures (T
A
) and the appropriate thermal
performance with improved acoustics at lower fan inlet temperatures. Using the
example in Table 5–2 for the Intel Core™2 Duo processor with 4 MB cache at T
C-MAX
of
60.1 °C the required fan speed necessary to meet thermal specifications can be
controlled by the fan inlet temperature and should comply with requirements in
Table 5–2.
Table 5–2. Acoustic Targets
Fan Speed
RPM
Thermistor
Set Point
Acoustic
Thermal
Requirements,
ca
Notes
~ 5300
High
T
A
≥ 35 °C
≤ 6.4 BA 0.38° C/W
Case 1:
Thermal Design Power
Maximum fan speed
100% PWM duty cycle
~ 2500
Low
T
A
= 23 °C
No Target
Defined
0.56° C/W
Case 2
Thermal Design Power
System (PSU, HDD, TMA)
Fan speed limited by the fan
hub thermistor
~ 1400
Low
T
A
= 23 °C
≤ 3.4 BA ~0.87° C/W
Case 3
50% Thermal Design Power
TMA Only
~ 1400
Low
T
A
= 23 °C
≤ 4.0 BA ~0.87° C/W
Case 3
50% Thermal Design Power
System (PSU, HDD, TMA)
NOTES:
1. Acoustic performance is defined in terms of measured sound power (LwA) as defined in
ISO 9296 standard, and measured according to ISO 7779.
2. Acoustic testing will be for the TMA only when installed in a BTX S2 chassis for Case 1
and 3.
3. Acoustics testing for Case 2 will be system level in the same a BTX S2 reference chassis
and commercially available power supply. Acoustic data for Case 2 will be provided in
the validation report but this condition is not a target for the design. The acoustic
model is predicting that the power supply fan will be the acoustic limiter.
4. The fan speeds (RPM) are estimates for one of the two reference fans and will be
adjusted to meet thermal performance targets then acoustic target during validation.
The designer should identify the fan speed required to meet the effective fan curve
shown in Section 5.1.3.
While the fan hub thermistor helps optimize acoustics at high processor workloads by
adapting the maximum fan speed to support the processor thermal profile, additional
acoustic improvements can be achieved at lower processor workload by using the
T
CONTROL
specifications described in Section 2.2.4. Intel’s recommendation is to use the
fan with 4 Wire PWM Controlled to implement fan speed control capability based the
digital thermal sensor. Refer to Chapter 7 for further details.
Note: Appendix F gives detailed fan performance for the Intel reference thermal solutions
with 4 Wire PWM Controlled fan.
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