Australian Lab Notes - November 2010 - Steve Turvey

In my last Lab Notes we discussed testing of 50-ton cranes and electric buses. This time I’m reporting on another batch of testing that falls beyond traditional IT categories - car stereos.

In this month’s example, our customer, a large car accessory store, was investigating opportunities to purchase a new line of car stereos from China to rebrand and sell through their local stores. While many of the respected industry brand names already hale from Chinese production lines, the units on this particular shortlist were completely unknown in the West.

The questions the Lab was tasked to solve were simply: “Is the audio quality up to scratch?” Are these units going to be reliable on Australian roads”?

Testing of the audio quality is not complicated, although the units required DVD video, SD cards, USB thumb drives and MP3 CD media options to be tested.

In the past, we’ve evaluated players that are capable of playing MP3s from various media, but at times the navigation ranged from poor to “the unit completely ignores any music that is not sitting in the root of the device or disc”. Happily all these stereos were very capable, both in terms of audio quality and the ability to correctly read different media formats.

Testing for reliability, including how these devices behave on rough roads, including corrugated, outback dirt roads was not such a simple task. We considered purchasing an off–the-shelf vibration table - but what fun is that? We also really preferred to test vibrations in all three axes to truly simulate a car jolting around - I had some truly terrible stretches of road in mind.

Fearlessly, or perhaps recklessly, we therefore embarked on constructing our own test custom vibration test rig. This rig consisted of several large concrete blocks (foundations) a sub-woofer amplifier, a Jaycar Response Power Bass Rocker (PBR) and other ancillary bits and pieces. If you’re not familiar with the PBR, it’s an interesting device which began as an early, but unsuccessful, gaming accessory. The PBR was originally an integral part of a shock vest, worn when playing a video game. Each contact or shot that hit a player triggers a thump in the chest from the vest.

In effect, the PBR is a heavy duty speaker, but instead of the beefy voice coil being connected to a paper cone to produce sound, it is instead connected to a large slug of metal that produces substantial vibrations as it is driven back and forth.

Jaycar, the distributors of the technology, suggest you attach a couple of the units to the underside of your lounge chair, hook them up to your cinema sound system so that any sound produced by your sub-woofer is also translated as a vibration through your chair.

In our custom made, fully controllable, measurable, triple-axis vibration rig, we mounted the car stereos into a cradle connected directly to the PBR. The PBR was hooked up to a 150W sub-woofer amplifier which, in turn, was linked to a programmable audio frequency generator. This enabled us to simulate a vast range of vibration frequencies.

I have to admit we thought the rig would destroy the car stereos, particularly when playing back CDs. To our amazement, all-but-one of the units performed perfectly - without a single glitch or stutter. Only one unit experience any problems at all, skipping just three times. The vibrations it was managing were the most violent we could produce.

We shook the living daylights out of those stereos. It is, when you think about it, a touch ironic - we shook them all night long.