“Wait-and-See” Noise Control: Why Bet the Farm?

By May 27, 2020June 16th, 2020General, Noise Control, Quiet Design

In product design it’s not uncommon to take the approach of “waiting to see how noisy the machine turns out”, and only then consider noise control.  If you don’t know that it’s possible to estimate noise emission in advance, I suppose that’s your only play.  But it’s a risky one: by the time noise emission of a prototype is measured, the design is usually considered “done”.  The things you have to do to control noise after the fact are actually a lot more work (and usually less successful) than doing it right at the beginning.  

Some of the myths underlying the “wait-and-see” approach:  

  1. Noise happens.  Nothing about our design enhances or diminishes it.  
  2. Simple noise control materials will adequately absorb or contain the noise.  That’s their job, like a Band-Aid™ .
  3. The noise control materials will not interfere with performance.  They’ll be few, light, thin, small, inexpensive, and no trouble during manufacturing.  They won’t fall off or deteriorate over time.
  4. If that doesn’t work, we’ll use noise cancellation! (stand by for a future article on that topic…..)

“Intrinsically-quiet design” is far more effective:

  1. Minimize the noise being generated in the first place.  It’s a waste byproduct after all.
  2. Optimize the process and select quiet components to maximize performance while minimizing noise emission.
  3. Reduce or eliminate noise control materials to make the design more difficult for competitors to copy, and to actually optimize the device’s performance, weight, bulk, expense, power consumption, parts count, and manufacturing complexity.
  4. If “noise control-at-the-source” isn’t going to be adequate, we’ll know early and have time to adjust the design to effectively incorporate noise control materials.

Example

Full-rack and half-rack network servers are loud because they require dozens of fans delivering extraordinarily high rates of cooling airflow.  One such manufacturer (early on) inquired about adding “mufflers” to their “final” design prototype.  Of course the box was already as big as it was allowed to get, and every cubic inch of interior volume was already stuffed with circuitry.  So the sound attenuators would have to be mounted outboard.  But then they would have protruded into narrow aisleways (at both knee and head height) and would have significantly impeded cooling airflow, requiring the fans to be sped up to keep the unit from overheating.  In the end the attenuators’ benefit would have more or less exactly offset the increased fan speeds.  The only big change would be bad: an increase in the fans’ electrical power consumption.

In this case the cooling fans were ill-suited to the pressure/flow requirement, like riding a bicycle up a steep incline in high gear instead of low.  As time went on Nelson Acoustics taught the client to make fan selections in the proper “gear”, leading to much quieter and more energy-efficient cooling fan selections.  Even with generic fans in most cases.  And no mufflers.  

Conclusion 

The “wait-and-see” approach sometimes does succeed. It’s an exhilarating feeling no doubt, dodging that bullet.  But without knowing how and why, every future design will be plagued by the same unnecessary anxiety.   Eventually that luck will run out.    

Sometimes “wait-and-see” fails outright: there’s just no practical way to curb the noise emission.  When this happens the most common excuse is usually some variation of the myth(s) “noise control is impossible”, “magic”, “pure luck”, etc.     Of course that sounds better than “we gambled and lost”.  In any event it’s often much harder, perhaps even impossible, to succeed after the fact without completely re-designing the product.  

Wait-and-see machines that “succeed” after the fact are typically afflicted by last-minute, hurry-up, shoehorned-in noise control treatments.  These often end up fulfilling the myth that (marginally) quieter machines are weak, heavy, and inefficient.      

Noise emission is a system property, so noise control measures should be designed in from the beginning.  Proper noise control need not sap performance or be heavy, bulky, costly, etc.  Nelson Acoustics has extensive experience reducing noise emission of consumer products, IT equipment, commercial equipment and machinery.  

 

Copyright 2020 Nelson Acoustics

Previous entries in the series “Myths, Misunderstandings, and Magical Thinking about Noise”:

1. Noise Control is not Magic

2. Decibel Abuse

3. Careful with that dB Thermometer

4. The Forbidden Word – Soundproof

5. HOW much quieter?

 

error: Content is protected.