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Nuts&Bolts<br />
sound waves behave like ripples in<br />
a pond, with alternating crests and<br />
troughs. In <strong>the</strong> case of water, if you<br />
looked at a cross-section of <strong>the</strong> water<br />
surface it would look like this:<br />
Affordable, Remarkable <strong>High</strong> Performance<br />
Stereo Components that Honour Music<br />
Waves move continuously, of course,<br />
at <strong>the</strong> speed I mentioned earlier, some<br />
345 m/second. However, imagine that<br />
<strong>the</strong> wavelength of <strong>the</strong> wave (that is,<br />
<strong>the</strong> distance between one crest and <strong>the</strong><br />
next one) is equal to one of <strong>the</strong> room’s<br />
dimensions, or is a simple submultiple<br />
of one of <strong>the</strong> room’s dimensions. In this<br />
illustration, <strong>the</strong> wavelength is exactly<br />
half <strong>the</strong> length of <strong>the</strong> room:<br />
It’s easy to visualize what happens.<br />
As <strong>the</strong> wave bounces back and forth<br />
between <strong>the</strong> opposing walls, <strong>the</strong> crests<br />
are always at <strong>the</strong> same spot, and <strong>the</strong><br />
troughs are also at <strong>the</strong> same spot. The<br />
result is frequency response that is only<br />
a caricature of what it should be. The<br />
frequencies at which standing waves can<br />
be set up are known as room modes. Any<br />
two parallel surfaces can support room<br />
modes.<br />
By <strong>the</strong> way, if <strong>the</strong> room is square, or<br />
if <strong>the</strong> dimensions are multiples of each<br />
o<strong>the</strong>r (for instance a room that measures<br />
3 meters by 6 meters, with perhaps a<br />
2 meter ceiling), you can get multiple<br />
standing waves at <strong>the</strong> same frequency,<br />
for even more devastating acoustical<br />
damage.<br />
In small rooms, <strong>the</strong> room modes are<br />
closer toge<strong>the</strong>r than in large rooms. If<br />
two or more modes coincide, <strong>the</strong> standing<br />
wave problem gets worse.<br />
of waves would look like this:<br />
out from <strong>the</strong> end where <strong>the</strong> speakers are,<br />
with <strong>the</strong> ceiling also rising toward <strong>the</strong><br />
listener. That will scatter <strong>the</strong> room<br />
modes across <strong>the</strong> spectrum.<br />
However that is not <strong>the</strong> only way to<br />
discourage <strong>the</strong> formation of standing<br />
Want to get <strong>the</strong> whole issue?<br />
waves. Anything that will allow sound<br />
waves to bounce in varied directions<br />
Of course, we know that it’s not ideal trying to read an article and discovering<br />
will dissipate standing waves. In homes,<br />
that we have left something lying around, That’s <strong>the</strong> and reason covering speaker up <strong>the</strong> designers text. But we<br />
Japanese screens with hard surfaces are<br />
can mail you <strong>the</strong> entire print issue. like It’s to avoid just $4.99, sharp Canada edges or on <strong>the</strong> speaker USA, plus<br />
especially useful. In professional surroundings,<br />
mail<br />
such as studios, <strong>the</strong>re are<br />
applicable taxes (in Canada). Elsewhere cabinets. it’s Since $8.60 those (Canadian), edges are including so close air charge. Order on line at https://www.uhfmag.com/Order.html.<br />
to <strong>the</strong> drivers, you get two sound sources<br />
commercial diffusors, such as those<br />
that are very close to each o<strong>the</strong>r and can<br />
made by RPG. Diffusing is a major topic,<br />
cause ghost images and <strong>the</strong> dread comb<br />
however, best left for ano<strong>the</strong>r time.<br />
filter effect. Note that any obstacle can<br />
cause diffraction, including <strong>the</strong> corner<br />
The practical side<br />
of a table for example.<br />
A living room is of course not a<br />
recording studio, and <strong>the</strong> requirements<br />
Diffusion<br />
of decor preclude <strong>the</strong> use of acoustical<br />
Since we have established that measures that a studio designer would<br />
standing waves require a pair of parallel not hesitate to use. However, some<br />
opposing surfaces, it may have occurred notions of acoustics can make <strong>the</strong> difference<br />
between a room that makes<br />
to you that not having parallel walls can<br />
be a good thing. And that is indeed music listening pleasant and one that<br />
true. If you are calling in an architect makes you regret you didn’t take up<br />
to build your room, you can make it flare some o<strong>the</strong>r hobby.<br />
Diffraction<br />
Unlike standing waves, diffraction<br />
is a problem only at medium to high<br />
frequencies, where it can do an excellent<br />
imitation of an early reflection. As a wave<br />
travels past a sharp edge, it will diffract,<br />
radiating out as though <strong>the</strong> edge were a<br />
new source of sound. The resulting set<br />
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ULTRA HIGH FIDELITY <strong>Magazine</strong> 25