Tag: Noise Elimination

The Sound of Freedom? NIMBY!


One pleasant feature of my northern Virginia home, less than five miles from the Pentagon and a couple of blocks from I-395, is the sound of freedom that occasionally envelopes my neighborhood.

On some days, it happens as early as 7:30 a.m., often hourly, sometimes more. Sometimes in tandem. And often well into the evening hours, at low altitude. I love it.

Noise Elimination


Noise is always around us. We need sounds to warn us of danger, so plugging our ears with uncomfortable earplugs is not always practical. Traditional passive techniques for noise control include isolation, such as done in recording studios, and shields around noise sources. Industrial equipment is a prime source of unwanted noise, and new designs can reduce fan noise without heavy shielding. We are always looking at ways to reduce noise, such as with jet aircraft designs and barrier walls for road noise. As discussed later, noise reduction techniques even increase auto fuel economy!

Many times unwanted sounds are generated inside machinery such as a heating system. Using trial-and-error techniques to isolate the sound source can take months to find. A new method, called a Sound Camera, analyses all sounds emanating from the device. The original method used one microphone as a fixed reference, while another microphone scanned the object using a robotic system, but the scan time was too long. Adding more microphones reduced the scan time, but a full system of microphones would cost well over one million dollars! By using an array of 1,024 low cost hearing aid microphones, the Sound Camera quickly finds noise sources when tested in an anechoic chamber.