AOpen XC Cube EX915: 775-socket SFF barebones

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A. Performance

Benchmark tests were performed using the most recent version of Sisoft SANDRA: 2005 Lite. The raw numbers are not directly comparable to results from earlier system tests.

The score here is directly related to clock speed and falls pretty much as expected.

The dual channel memory falls right in line with the reference data in the SANDRA database.
Interestingly, the reference data on the older 865PR chipset is better than the newer 915.

The current Futuremark video benchmark is 3DMark03, but the older 3DMark2001 (v330) was used because it is the one we used in a handful of SFF system reviews already. The 5359 score is double that achieved by the AOpen EZ65 with its Intel Extreme Graphics integrated video, and just a hair higher than the 5336 score of the ATI IGP 9100 video processor.

B. Power and Acoustics

The total AC power draw was measured using a Seasonic Power Angel AC power meter. The ambient temperature was 21°C during testing. SilentBIOS was set to Smart Control. No internal system temperatures are reported because the board sensors are not accessible as reported earlier. We do know that the CPU temperature remained below 63°C at all times.

AC Power
HDD Temp
Idle in Windows XP
30 dBA@1m
Idle, HDD suspended
28.5 dBA@1m
Full Load: CPUBurn
35 dBA@1m
* Sound Pressure Level measured 1 meter from front panel in 20 dBA ambient room.
The ISO 7779 "Seated Operator Position" SPL puts the mic 0.5m in front of and 0.45m above the table top. For the above system, this SPL measurement is 3 dBA higher -- 33 and 38 dBA/1m

The AOpen EX915 at idle in this configuration was fairly quiet, but slightly noisier than the similarly configured EZ65 we tested. The main sources of noise appeared to be hard drive and CPU fan related. The CPU heatsink fan spins faster than in the EZ65. The reason for this difference is twofold:

1) The fan speed is thermally controlled by the Smart Control of SilentBIOS rather fixed at 50% as it was in the review of the EZ65. It appears to be the same fan, of reasonable quality and decent acoustics at lower speed but not exactly quiet at the near 5000 RPM maximum.

2) The Intel 520 CPU runs much hotter than either the P4-2.53 or P4-2.8 used for the AOpen EZ65 review. The thermal fan controller keeps the fan spinning a bit faster even at idle.

The effect of hard drive vibrations on the overall acoustic could be easily heard. Panel resonance contributed significantly to the sound, and even clamping the whole system by grasping it firmly with both hands from the sides did not eliminate the aluminum hum. This is a common problem with almost all aluminum cases; the 1/3 density of aluminum compared to steel makes it resonate easily in sympathy with vibrations from the moving parts in a PC -- fans and drives.

Because the Smart Control fan controller is quite sensitive to CPU load, the CPU fan speed varies audibly as different programs and applications are accessed and used. The variability of the noise can be quite annoying, especially as the fan reaches high speed and different parts of the case vibrate and emit different kinds of noises.

A quick and dirty temporary elastic cord suspension of the hard drive was implemented to see how much of an effect the hard drive vibrations had on this setup. The overall noise dropped only about 1.5 dBA to 28.5 dBA @ 1m but the improvement was subjectively much more significant, because the more irritating hummmm noise mostly disappeared, and most of what remained was the more benign white noise of wind turbulence.

At high load, the system is not quiet. The sound is dominated mostly by the 70mm CPU fan, which high speed whine can be easily heard over the the hard drive and the PSU fan. The latter appears to be much lower in level than the CPU fan. As noted earlier, this is a 275W model rather than the 200W model used in the EZ65. Perhaps its fan is set to speed up a bit more slowly under load because its components can handle higher temperatures.

Here are some audio recordings of the EX915 system as configured and tested.

  1. MP3 sound recording of EX915 system in idle: 30 dBA/1m
  2. MP3 sound recording of EX915 system at maximum load: 35 dBA/1m
  3. MP3 sound recording of EX915 system in idle with Samsung hard drive suspended: 28.5 dBA/1m

The recording (#3) with the suspended hard drive may sound as if the fans are spinning faster than the first recording with the HDD mounted normally. This is not the case. This overall higher pitched sound is the effect of the case vibrating.


The recordings above were made with a high resolution studio quality digital recording system. The microphone is 3" from the edge of the fan frame at a 45° angle, facing the intake side of the fan to avoid direct wind noise. The ambient noise during all recordings is 20 dBA or lower.

A quick and simple way to use these recordings for valid listening comparisons is to play the quietest recording on only one speaker (or a pair of headphones) and set the volume so it is just barely audible a meter away. You must turn off any special sound effects, and set equalizer / tone controls to neutral or flat. Don't touch the volume setting afterwards, and use the same one speaker when you listen to any of the other files. The end result will be reasonably close to the actual recorded sound levels.

Here is a recording of a very quiet sound that is barely audible from 1 meter away even in a super quiet room.

For full details on how to calibrate your sound system to get the most valid listening comparison, please see the yellow text box entitled Listen to the Fans on page 3 of the article SPCR's Test / Sound Lab: A Short Tour.


In the XC Cube EX915, AOpen has taken the design used successfully in the EZ65 and adapted it to the 775 socket. From a performance point of view, the exercise works. Even with just the onboard video, the system's performance is quite good, and it's clear that the EX915 can be the equal of any 915-chipset based system. For 3D gaming, the main limitation will be the PCI Express video card chosen by the user. There is enough side-to-side ventilation to ensure good cooling of any video card. Use the best PCIe VGA with a high speed 775 socket processor, and you'll have a great gaming rig.

Things are not so rosy if you seek a quiet PC. The question here is not whether the EX915 system is too noisy (which it is, for me). Rather, it's whether ANY Intel Prescott-core CPU can be used in a SFF computer and maintain safe temperatures and low acoustics. The Intel 520 processor used in this review is about the slowest (read: coolest) socket 775 P4 available on the market, and it's already at 100W. Any faster 775 processor will exhibit higher thermals, so the CPU fan speeds reached during the testing is about the lowest you'll see in this system. Ditto the noise.

This is not to say manual control cannot make the EX915 a quiet PC, even with a hot Prescott. You can bypass the SilentBIOS Smart Control and use a hardware voltage controller to adjust the fan speed directly. This option is a bit more problematic than usual because you then need to monitor the CPU temp to establish a safe fan speed, but the temp sensors are not accessible in Windows. A motherboard BIOS upgrade might fix this, but the most recent one (mid-Nov 2004) did not. Still, as long as the system is stable, you know the temps are OK. The CPU heatsink / fan is actually reasonably smooth at lower speed so if it can be kept spinning slowly, it should be possible to keep the overall system noise down to under 30 dBA/1m at all times.

As with the EZ65, the EX915 AOpen SFF is attractive, well-finished and easy to assemble. However, we cannot recommend it if you seek low noise computing. If you really like the look of the case, choose an EX65 instead -- it offers the socket-478 865 chipset based board in the same case. Not only are cooler Northwood core P4s still available, the fan controller in the 865-based AOpen SFF boards is about the best embedded in any motherboard.

Much thanks to AOpen for providing us the XC Cube EX915 sample and to for the Intel 520 CPU loaner.

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