Beyond the "Black Box"

Enclosures should not be a design afterthought

Design News Staff -- Design News, November 25, 2008

Good things come in small packages - and large packages, too. The truth is, while logic may warn us that "beauty is only skin deep," when it comes to selecting technology products, the outward evidence of functionality and purpose can be just as important as what's going on inside in swaying a potential purchaser.

For better or worse, the "great equalizer" is becoming regulation. Standards and industry codes such as the National Electrical Manufacturers' Association (NEMA) rating system and the International Protection (IP) codes widely used in Europe tend to make designers think in similar ways. For instance, NEMA intrusion protection requirements often play a role in the material choices and in how an enclosure or cabinet is put together.

On the other hand, there is an expanding array of materials available to designers. Enclosures are no longer simply stamped steel. Polycarbonate plastics and fiber glass are becoming more important, though many still prefer the durability and price points of traditional metal enclosures. And, in all cases, methods of finish have often grown more sophisticated, too, ensuring that products can look good while meeting functional requirements.

Of course, enclosures have a vital functional role, too. Not only must they protect components from damage - and users from harm - they also must effectively support air handling. So, issues like fan placement and air flow need to get more attention. Moreover, since the combination of fan and enclosure usually contributes more than anything else to the audio characteristics of a product, it is important that designers recognize and master airflow and sound production issues. The choice of fan size -- common fan sizes include 40, 60, 80, 90, 120, and 140 mm -- and fan type can be a start. But not all fans are alike in terms of reliability, airflow, ability to operate successfully under flow restrictions, in particular, their sound output.

Furthermore, sound output includes not only the movement of the air but also vibration associated with motor operations - and this in turn is a product of both the mounting system and the inherent characteristics of the device. It is this last item that can be most critical. Simply picking a fan based on physical fit, published air handling rating, and price can be dangerous. Testing may show that the fan produces high levels of vibration. Or some fans in the same series may vibrate more than others if this aspect of design is not carefully monitored.

So, the bottom line is that enclosure design should not be an afterthought. Aesthetics, performance (including electrical and EMI aspects), sound and other factors need to be considered and built in from the start. That way you can ensure bang from your box and bang for your bucks.