Archive for the ‘Technical’ Category

Frozen spring

One of the things one learns studying acoustics (and many other physics topics) is that the behavior of a complicated physical system can often be simplified into an analogy of masses and springs.  The gobs of air that surround us have elasticity and they have mass, and these are the properties that allow waves to travel through the air as sound.

Perhaps a more intuitive example of a spring-mass system can be found in any toy store: the classic Slinky.  The familiar coil toy can be used to demonstrate lots of different wave phenomena (longitudinal waves, transverse waves, standing waves), and when that gets boring, it is more commonly used to demonstrate walking down stairs.

We recently came across this high-speed video of the very interesting spring-mass behavior of an extended Slinky at rest, dropped from height, in which the bottom end of the Slinky seems frozen in mid-air.  There are excellent technical explanations of what is going on out there (and probably on a tricky physics midterm or two), but suffice it to say that it all goes back to the interplay between mass and elasticity as the Slinky simultaneously contracts and falls.

[Via kottke.org, @jenvalentino]

FFFFT (the fast fast fast Fourier transform)

No, it’s not the sound of the air being let out of your tires!

Researchers at the Massachusetts Institute of Technology have just published a ground-breaking computational method for analyzing digital signals, including sounds and images.

The Fourier Transform is a way to break a complicated signal down into its most basic components, and it’s how computers manipulate things like acoustic and visual information—everything from your jpeg and mp3 files up to complicated acoustic measurement and analysis gear that consultants like ourselves use daily.

Fourier Transform

The last major improvement in the efficiency of the Fourier Transform came in the 1960s, with the advent of the “Fast” Fourier Transform (often denoted FFT).  That was a long time ago, but the FFT is still the method of choice for on-the-fly number crunching in everything from cellphones to video games to high-end audio and graphics workstations.

The new algorithm that MIT has devised (a “nearly optimal sparse Fourier transform”) is substantially faster than the FFT for a large range of realistic and useful cases—up to 10 times faster.  It isn’t hard to imagine that such a major leap in efficiency will lead to smaller, cheaper, and more powerful electronics, since the work they do under the hood just got a whole lot easier!

[via MIT News. Graphic: Christine Daniloff]

Building Design + Construction Magazine – Enhanced Acoustical Design

Just in case you missed the August issue of Building Design + Construction Magazine, there was a very interesting article on Enhanced Acoustical Design on page 45.  Truth be told we may be a bit biased as we helped with the article – but you can earn AIA/CES credit for reading it too!

Building Design + Construction Enhanced Acoustical Design

 

See the unseen

To promote their new vibration analyzer, measurement instrumentation company Fluke commissioned some amazing high-speed video of—you guessed it—things vibrating!  Putting the fascinating physics of vibrating plates and cylinders aside, you will have to admit that it’s interesting how a cymbal deforms at 1,000 frames per second.  (And if that doesn’t do it for you, the shaking basset hound at the end is pretty nice too!)

Catch a wave

You may know that the sounds you hear travel through the air as waves, but the invisibility of air makes this concept a tricky one to visualize.  For those who like physics demonstrations (and who doesn’t), we recently came across this video of a series of pendulums—and the pendulum is perhaps the most accessible form of wave motion we witness in everyday life.

A pendulum’s length determines its frequency, just as sound waves in air have a frequency that corresponds to pitch.  The demonstration superimposes different frequencies to illustrate traveling waves, standing waves, beats, and “random” noise, which are all phenomena that come from mixing different frequencies together.

Noise-reducing city canyons

After a nearly two-year editorial process, we are happy to announce that we’ve recently published a technical paper in the peer-reviewed acoustics journal Applied Acoustics.  Performed in cooperation with our acoustic colleagues at Chalmers University of Technology in Sweden, the research explores what happens to noise as it travels over the city canyons formed by streets and backyards between rows of buildings—such as those common in New York City.

Although the details are rather technical, the bottom line is that these canyons reduce noise—so the more street canyons between you and that noisy highway, and the wider these canyons are, the quieter the noise will become.

This field of acoustics research helps to improve the acoustic models that acousticians and city planners use to predict noise.  Implemented in software, these models can map out how traffic and new development will impact the soundscape of a property, a neighborhood, or even an entire city.