Crane Song AVOCET II - Manual (Page 39)

This is avery good starting place for setting up sub woofers. One could go farther and use a RTA and
experment and find the best place in the room for subwoofer placement.
This was written by Bob Katz, www.digido.com and is used with permission
Accurately Set Up a Subwoofer With (Almost) No Test Instruments
Bass frequencies are extremely important to sound reproduction. Everyone is interested in getting
their bass right, but most people haven’t a clue how to proceed. This article will help to settle the
process of integrating an active subwoofer with an existing “satellite” system. If your room and
loudspeakers are good, you’ll only need two test CDs and your ears to adjust your subwoofer. If your
room is not so good, or you want to refine the sound even further, then we’ll discuss the best way to
integrate test equipment measurements with your hearing. The simple listening test will also reveal if
your room has problems and if it’s time to hire an acoustician.
Let’s review the basic requirements for smooth, extended bass response.
Conquering the Room
Many people are proud of the “ideal dimensions” of their listening room. In general, the larger the
room, the fewer audible problems with low frequency standing waves (nodes and antinodes). To
getsmooth and even bass requires ceilings taller than 10 feet, width greater than 12 feet, and length
greater than 25 feet (30 or more for deep bass). Dimensions (including diagonals) should not be
multiples of identical wavelengths, to avoid buildup at octave resonances. Of course, larger rooms
may need absorption to keep the reverberation time down, but standing waves don’t tend to build up
awkwardly in larger rooms. It’s also important to use absorption so that the decay time at low
frequencies is roughly similar to that at mid and high frequencies. This is called a “neutral room.”
Lightweight, flexible walls act as diaphramatic absorbers, where some bass frequencies will escape
out the walls, never to return. In my opinion, the ideal is a solid concrete (block) wall, but proper
construction with plaster lathe, wood, and/or double sheet rock can accomplish similar results. But
solid walls create problems of their own; a world-class room usually requires some absorption and/or
diffusion to deal with resonances and echos. Watch out for cavities within the walls, which can cause
resonances. Creating a large room with good bass response, interior acoustics, and outside isolation,
is the role of a professional acoustician. This article will share some secrets in the fine tweaking of
systems in good rooms; don’t dream of building a room from scratch without hiring an acoustician.
Speaker Mounting - Spikes or Isolators?
Soffit-mounting involves recessing loudspeakers into a cavity in the wall, with the edge of the
loudspeaker flush to the wall. Soffit-mounting requires the expertise of an experienced acoustician,
and is beyond the scope of this article. The main loudspeakers must be decoupled from the floor.
Heavy, rigid stands should have a top no larger than the bottom of the loudspeaker to avoid diffraction
(a form of comb filtering). I’ve had great success spiking speaker stands (using spikes, or “tiptoes”)
through holes in the carpet. Some authorities recommend a damping pad underneath a heavy, full
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