XCPU Case Review Methods

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XCPUs Case Performance Testing Methods: Acoustic and Thermal

Cases have two performance features that are critical to their applicability for system builders. One, how effectively can the case flow air through the chassis to provide sufficient cooling to keep components cool and two, how much noise is produced. When case shopping, these two qualities are typical for most users. In one case, a prospective buyer may wish to sacrifice cooling efficiency for quiet operation, such as in a home theater PC application or a quiet office environment. In other cases, users who wish to install high end components and push those components to the limits may sacrifice the quiet for the cooling.

The acoustic testing is accomplished by using the sound metering available with a Protek 6300 digital multimeter. The system is assembled as typical, except the 12 VDC supply to the CPU and the HSF are disconnect and the video card removed. The system is powered up such that all the included fans representative of the case are spinning at full speed. The sound intensity is then measured at 1, 2 and 3 feet away from the case, with the system placed in four orientations: front, left side, right side, and back. Prior to taking active measurements, the room is made as quiet as possible by powering down any external equipment or gear, and ambient background (random noise of the meter) is recorded, the resulting measurements are then noise total above ambient, therefore if ambient noise at the microphone is 30 dB, and the case measures 50 dB in one orientation, the total sound above ambient is 20 dBA.

Thermal testing is done using a 4-channel, data logging type-k thermocouple data recorder. Four thermocouples are mounted to the case, two interior and two exterior. The interior sensors are in two different locations. One is placed approximately 1 inch off center from the rear exhaust fan, positioned such that the HSF is between the sensor and the exhaust. With respect to the HSF, the sensor is suspended about 1 inch from the intake of the HSF. The standard HSF used for this measurement is the Zalman 9500 copper fan, in this orientation the sensor will measure the immediate ambient air temperature as it presents itself to the CPU.

The second interior thermocouple is mounted at the lower end of the case approximately 2.5 inches from the surface of the motherboard. To mount the thermocouples two threaded rods are inserted into the edge mount points into the standoffs for the standard ATX form factor at either edge, thus the top edge nearest the CPU will represent the upper half of the thermal zone, and the thermocouple located on the lower point measures the lower half. A case with sufficient air flow should produce temperatures between these two zones with differences that are small to nonexistent.

For the exterior, a sensor is mounted (taped flush to the grill) 1 inch off center of the front intake fan, and the second about 1 inch off center to the rear exhaust fan. If there is no front intake fan, the sensor is then located at the next intake fan closest to the front of the chassis.

The data logger is then set to sample all 4 temperatures every 30 seconds. Data sampling starts with the system powered down and the room cooled to approximately 20 degrees C, this is sampled for 15-30 minutes to establish a base temperature. The computer is then booted up to idle for 15 to 30 minutes to collect temperature readings at idle. All room cooling is then shut down, and the CPU is loaded with an instance of prime95 as well as CPUID HW Monitor (both readily available for download). The HW monitor will show CPU and GPU temperatures, and will also track max temperatures for the run. After 15-20 hours at load, the cooling in the room is restored, at this point the delta from ambient to internal should spike then settle back into the normal delta observed through the entire heat up sequence


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