Crane Song AVOCET II - Manual (Page 42)

All musical instruments and transducers produce harmonics as well as fundamentals. To the best of
our ability to discriminate, we will be concentrating on the fundamental tones in this piece of music. If
your loudspeakers have significant harmonic distortion, they can complicate or confuse the test. Many
studio loudspeakers are designed for high power handling at the expense of tonal accuracy or
distortion. This test is not for them. If you want accurate bass, it’s time to replace the loudspeakers
and probably hire an acoustician with a distortion analyzer.
Start by evaluating the satellite system with the subs turned off. Listen to the bass at a moderate level
equal to or slightly louder than the natural level of an acoustic bass. Listen for harmonic distortion: if it
doesn’t sound like a “transparent” acoustic bass, fix the problem with the satellites, first. Listen for
uneven notes. If the lower note(s) of the scale are successively softer in level than the higher notes,
then you have a perfect candidate for a subwoofer. If intermediate bass notes are weak or strong
(uneven bass), the satellite loudspeakers may be too close to the corners, in a node or antinode, the
listening position may be in a standing wave, or the satellites themselves poorly designed. It may be
time to bring in an acoustician. But if the satellite bass is even, you can move on to the next step,
adjusting the subwoofers.
Spanish Harlem , in the key of G, uses the classic 1, 4, 5 progression. Here are the frequencies of the
fundamental notes of the bass. If your loudspeaker has sufficiently low harmonic distortion, it will not
affect your judgment of the power of the bass notes, which are already affected by the natural
harmonics of the instrument.
49 62 73 65 82 98 73 93 110
As you can see, this covers most of the critical bass range. If the lowest note(s) is weaker than the
rest, then you are a candidate for a subwoofer. My satellites behave in the classic manner, with the
lowest note (G, 49Hz) slightly low in level, but the rest fall in a balanced line. I’ve been in small rooms
where one or more of the intermediate notes are emphasized or weak, which suggests standing wave
problems. Repositioning the satellites may help. Avoid equalization, which is a nasty band aid...proper
acoustic room treatment is the cure. You could conceivably add a subwoofer out of phase at the
frequencies in question, but that’s a technique that should remain confidential between you and your
analyst. Fix the acoustic problems first and you’ll be happier.
If your satellite system passed the initial examination, next step is to decide on a starting
(approximate) subwoofer location. A satellite-subwoofer system has tremendous flexibility, offering in
theory the best of two worlds. The satellites can be placed on rigid stands at ear level, far from
corners and side walls, reducing floor and wall reflections and comb-filtering in the midband. And the
subs can be placed on the floor, in the position that gives the most satisfactory bass response,
integrated with the satellites. If you only have one (mono) subwoofer, start by placing it in the middle
between the stereo speakers. Contrary to popular belief, stereo subwoofers are important, they can
improve the sense of “envelopment”, the concert hall realism that bass waves are passing by you.
Authorities are split on the issue whether a mono or stereo subwoofer setup is more forgiving of room
modes. I prefer the sound of stereo subwoofers. A complete discussion ofhow to place the satellites
would require another article, but let’s start by saying that you may have to deal with reflections from
the side walls by placing absorbers in critical locations. Consider consulting a competent acoustician.
Assuming your satellite system passes the listening test, it’s time to find the right crossover frequency,
phase and woofer amplitude that will just supplement the lower notes of the scale. Start by placing
the subwoofers next to and slightly in front of the satellites. First we must determine the proper
polarity for the subwoofers. If your system uses XLR input connectors, build a polarity reversing
adapter for this part of the test. This is easier with only one channel playing. Put on the MRCD with
full bandwidth pink noise, at a moderate level (70-80 dB SPL). Adjust the crossover to its highest
frequency, the phase to 0, and turn up the subwoofer gain until you’re sure you can hear the woofer’s
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