Manual-4
OPERATING INSTRUCTIONS
Since the RA 27 features a unique form of realtime
analyzer, we highly recommend that you read this section
before performing an alignment with pink noise. If you’ve
never used an analyzer before, use these instructions on your
first occasion. You’ll be delighted at how simple it really is.
BACKGROUND NOISE CHECK
Any background noises such as air conditioners, talking,
wild animals, traffic and the like can cause false readings on
the analyzer display if the pink noise volume through the
speakers is not loud enough to drown these noises out. Before
turning on the Pink Noise, turn up the LEVEL control on the
RA 27 until some of the green and red LEDs respond on the
display: now you’re looking at background noise. Slowly turn
the LEVEL control back counter-clockwise until all the green
and red LEDs are off, and no background noise is showing on
the display. You will now have to run the pink noise volume
through the speakers loud enough to make sure that the
LEVEL control is not turned clockwise (up) from this setting,
otherwise the background noise will falsify the readings.
PINK NOISE RUN-UP
Turn down the mixer output controls
before
switching on
the Pink Noise, so that you don’t detonate your speaker
cabinets. Now switch the PINK NOISE button
ON
on the RA
27 and turn up the mixer and EQ LEVEL controls slowly
until you hear pink noise through the speaker(s). There is a
Pink Noise Output Level Adjustment on the rear of the RA27
– use a 1/8" screwdriver to vary the amount of Pink Noise to
the mixer if necessary.
MICROPHONE PLACEMENT
You should perform the pink noise test with at least
two
different test microphone locations
for each separate channel
of EQ. Since speaker dispersion characteristics can vary
greatly, it is desirable to look at a couple of different areas
with the mic to obtain an average for the entire listening area.
If you are using one equalizer channel for both speakers
(mono), place the mic in the center of the left half of the
listening area and adjust for green LEDs with pink noise
through the left speaker. Now move the mic to the center of
the right half of the listening area, run pink noise through the
right speaker and observe the analyzer LEDs: use the RA 27
LEVEL control to center the response for as many green
LEDs lit as possible. For each frequency that requires a
different adjustment than the left channel, note the original
setting of the slider, then adjust it so that the green LED
above it is lit and then note this new slider position: the final
setting should be half-way between these two slider positions,
resulting in an average response for the left and right chan-
nels. If you are running stereo, use two mic locations for each
channel, averaging in the same manner if there are differ-
ences. Analyze one channel at a time.
ANALYZER SETTINGS
Select either the ±3 dB or the ±1 dB WINDOW on the
analyzer. We recommend starting with the ±3 dB setting, then
switching to the ±1 dB mode for fine-tuning frequencies
above 400 or 500 Hz. The crest factor(peak response) of true
pink noise causes considerable LED flutter in the ±1 dB mode
below about 500 Hz, thus it is expedient to use the ±3 dB
setting for these frequencies.
INITIAL SYSTEM ALIGNMENT
Before using the equalizer for adjustment, use the analyzer
to align other equipment in the system (EQ should always be
a
last
resort after you’ve corrected response problems
everywhere else). With all EQ sliders flat (centered) adjust
the electronic crossover frequencies and level controls (if
used), passive crossover controls, speaker placement and
alignment, etc. to get as many green LEDs lit as possible on
the display. Only after this is done should you use the
equalizer sliders to flatten the system (see next step).
EQUALIZER SLIDER ADJUSTMENTS
Now adjust each slider up or down as necessary until the
green LED corresponding to the same frequency is lit; if the
red is lit, move the slider down until green comes on. If
yellow is lit, move the slider up to obtain green.
If you can’t get one or more green LEDs lit with their
sliders fully boosted or cut, make a slight adjustment in the
Pink Noise volume or LEVEL control to get these bands in
the green. Then re-adjust the remaining sliders. You will also
notice that adjusting one slider may affect the LED readings
on the adjacent bands: this is due to the presence of frequen-
cies half-way between the two bands, which will be affected
by both sliders. Not to worry: simply nudge the adjacent
slider until the green LED lights up again.
FINAL EQUALIZER ADJUSTMENTS
Once the RA27 is all “greened out”, you’re done with the
pink noise alignment test. Now the speakers are properly
coupled to the specific room and the overall system response
is accurately aligned. This alone will make a great improve-
ment in most systems,
but don't stop at flat
necessarily. Now
that the RA 27 has given you a consistent starting point, feel
free to make further slider adjustments during the perfor-
mance or sound check to enhance overall sound quality.
Fatten the bass, smoothen the mids or sweeten the highs to
taste. You will probably find that these adjustments will be
consistently set above or below the Pink Noise test settings
the same amount at each performance; make a note of these
further adjustments to save future tweaking during perfor-
mances. For example, you note the pink noise settings and
find later that you like to have 3 dB more boost at 63 Hz for
more low-end punch during the performance. Next time,
green out the analyzer during the pink noise test (get all LEDs
green before making any further adjustment), then immedi-
ately bump up the 63 Hz slider 3 dB as indicated by the front
panel calibrations so that you’re tuned up before the show
starts (slick, no?).