Vibrating Window Negates Noise

[kach22i]

Windows for the Audiophile?


Vibrating Window Negates Noise
http://www.carnuts.us/viewtopic.php?t=857

Vibrating Window Negates Noise
Tracy Staedter, Discovery News


April 30, 2007 — The roar of jets. The shriek of car alarms. The din of traffic. All-intrusive noises can distract us from our work and keep us awake at night.
But help is on the way for the restless and sleepless. A noise-negating method that thwarts vibration with vibration could be available for use in apartments, hotels and offices in five years.

"A window acts like a loudspeaker and a membrane. If you control the vibration of the window, you can control transmitted noise in such a way that it is not acting like a membrane or a loudspeaker," said Thilo Bein, head of the business unit for energy, environment and health at Fraunhofer Institute for Structural Durability and System Reliability LBF in Darmstadt, Germany.

To make windows work less like loudspeakers, engineers thicken the glass to double or even triple panes. But that can drive up the cost of construction. Ideally they'd like to stop the sound waves in their tracks.

Bein and his team developed a method to do just that. They used postage stamp-sized patches made of a ceramic called piezoelectric material, which behaves both like a sensor and vibration generator when shot with an electric charge. (The material can be made transparent and imbedded in the glass, too, although the team has not yet accomplished this step with the window.)

Wires running through the window link the stamp-sized patches to a computer controller and an amplifier. When a sound-generated vibration rattles the window, the piezoelectric patch senses it.

That data goes to the controller, which in turn delivers a specific electric charge back up to the patch, causing it to vibrate at a phase that ideally cancels out the sound vibrations.

In laboratory experiments, they were able to reduce noise of 90-100 decibels (the sound of a subway or power mower) by 50 percent.

But getting the system to market may be harder than it seems, said Gary Koopmann, professor of mechanical engineering and director of the Center for Acoustics and Vibration at Pennsylvania State University in University Park.
"The main hurdle to transition it into a practical application is the cost," said Koopmann. Every window needs to be wired and maintained, which adds to the bottom line.

In addition, different kinds of sound, particularly those that are steady, are easier for the computer controller to respond to rapidly and generate an appropriate noise-canceling vibration. Sounds that disappear or change quickly are more difficult to manage, he said.

"For airport noise, the noise is transient. To have a control system respond instantly to a transient sound coming in is nearly impossible," he said.

Bein and his team will be working over the next year to make the system reliable and bring the cost down.

 

[IWalker]

When they say reduced the sound 50%, that means 3db, right? not 50db.

 

[Audiophiliac]

5db would be half. Every 10db is a doubling of percieved volume.

 

[SteveInNC]

A solution looking for a problem? It seems to me a double-pane window with evacuated airspace will beat this everytime, and cannot conceivably cost more than an active, piezo-based system.

The vacuum serves to isolate against all frequencies and gives insulation. I realize that many modern windows are argon-filled (or equivalent) but that's because that is cheaper than making a well-sealed evacuated unit. The original double-pane windows were evacuated, but over time, the constant pressure tended to break the seal, causing fogging and loss of insulation capability. Argon/nitrogen were the cheaper fix.

I would think that making a good sealed unit would still have to be cheaper than this active technology.

FWIW, this is not particularly new. Astronomers have been using "adaptive optics" in large telescopes for a long time. In this case, actuators dynamically change the shape of the mirror to compensate for atmospheric effects and other anomolies. The precision required in this case greatly exceeds that needed for acoustic damping; of course the $$ do too .

A more interesting approach from an audiphile perspective would be to use this technology for interior spaces to change the dynamics of the room. Imagine actively controlling the apparent room size and/or particular frequency compensation, rather than loading up the walls with diffusers and absorbers.

 

[tonyc]

I recently read a review (in Positive Feedback, I think) about dots which can be placed on windows to stop rattling. Not the same exact topic as this thread but windows are now suddenly interesting. I believe the company is Marigo and I had my Sonic Frontiers DAC treated with some dots when I purchased it many years ago. Their stuff does work.