Posts Tagged ‘speakers’

But I know what I hear

This week, New York’s Museum of Modern Art is opening its first major exhibition of sound art, “Soundings: A Contemporary Score”.  Through November 3rd, visitors will be able to immerse themselves in auditory pieces designed by sixteen of the most innovative contemporary artists working with sound.

Forty-Part Motet

Not to be outdone, on September 10th the Metropolitan Museum of Art will present Janet Cardiff’s “Forty-Part Motet”, pictured above.  This first foray into sound by the Met (to be installed in Fuentidueña Chapel at The Cloisters) combines forty separately-recorded voices from forty loudspeakers into a 16th century choral ensemble, a synthesis that the New York Times notes has brought visitors to tears.  The Times also provides audio clips from the MOMA exhibition, noting that “while you can close your eyes to an image you hate, you can’t close your ears to a noise”—a risk without a parallel in the visual arts.

Drop-less droplets

In a setup that’s equal parts science and Harry Potter, scientists at Argonne National Laboratory acoustically levitate liquids in midair to further critical pharmaceutical reasearch. Using a technology originally developed by NASA to simulate microgravity conditions, the pharmaceutical droplets are suspended in midair using standing waves of inaudible ultrasound generated by small speakers above and below.

By suspending a drug this way—free from any container or other physical contact—scientists can study its various forms and the ways it might be absorbed by the body. Not to mention putting on a pretty cool show in the process!

Just how speedy is sound at the Olympics?

Well, it turns out not fast enough!  Years ago, in addition to a traditional starters pistol, Olympic officials started placing loudspeakers behind the athletes so that the sound would reach each athlete at the same time.  It turned out however that the athletes would continue to wait for the sound from the actual starters pistol to arrive.  Even with the loudspeakers, the speed of sound was still slowing down the athletes furthest from the starter pistol.  While we are talking about tiny fractions of a second, with Olympic runners and swimmers, it really makes a difference.  Starting at the Vancouver winter games and this summer in London, they are using a silent pistol that is completely electronic and generates a beep from the loudspeakers only (although it does make a flash).

omega110.jpg  False start: Usain Bolt was caught out in Daegu last summer

[via The Atlanticdailymail.co.uk]

Visualizing modes

The Graves on SOHO VoIP blog tipped us off to this cool video showing the vibration of a square plate at different frequencies. By covering the plate with salt, we can see the areas where the plate vibrates a lot (the salt rolls away) and the areas where it doesn’t vibrate at all (the salt collects). These spots and lines of little or no movement are called nodes. As the driving frequency (and sound) gets higher and higher, the patterns (called mode shapes) get more and more complex (and cool looking!)

This behavior is a great example of why we don’t use big speakers (woofers) to generate high-frequency (treble) sound. Instead of moving in unison like a piston, the speaker cone resonates internally at high frequencies, and different parts of the cone are moving in different ways, like a group of uncoordinated smaller speakers. This causes a poor frequency response, with lots of peaks and dips — often referred to as “breakup”. Smaller drivers (tweeters) are more at home with high-frequency sound, since their resonant “breakup” occurs at frequencies near or beyond the limit of hearing.

This is also a great way to visualize the analogous effect of room modes. Instead of a vibrating plate, a room is full of vibrating air, and at certain frequencies there will be points or areas in a room’s volume — nodes — with very little sound. This is most pronounced in hard, reverberant rooms, and at low frequencies. Still, even though the effect is more subtle in normally absorptive rooms, it can wreak havoc with the reproduction and recording of low-frequency sound, so identifying and managing room modes is a common task in the design of recording studios and listening rooms.