S OUNDADVIC E
Sounding Your Best, Pt. 2
This month we will continue looking at ways
to improve the sound of your PA system;
we’ll begin with driver alignment. Driver
alignment is a term that refers to the “time
aligning” of your speakers so all of the sound
comes out at the same time, which sounds
a little weird until you think about it. When
your audio signal is sent down the wires to
your amplifiers and finally to your speakers,
the electrical signal starts all of the speaker
components vibrating at the same instant,
which is called acoustic alignment.
This big phrase is actually a simple concept.
If we were to look at a cutaway of your
speaker cabinet, you would see that the
drivers (woofers) that may physically sit in
front of other drivers (horns) so that all the
sound exits the speaker enclosure at the
same exact instant. This is intended to make
things sound “coherent” and moving in a
unified wave at all frequencies. To do this,
all of your speaker cabinets should be the
same model and arranged edge to edge
when stacked on the subs. You also need
an amplifier for each type of component in
your speaker enclosure – your horns need to
have their own amp, the 12” speakers need
to have their own amp, the 15” speakers
need to have their own amp, and so on.
All of these amps also need to be controlled
should sound cleaner and punchier.
The concept behind system delay is that
you should delay the sound coming out
of your speaker system to match up with
the sound coming from the guitar amps on
stage. I have worked with many bands to try
to line up the guitar amps with the front of
the kick drum head. In theory, this creates a
coherent wave front from all the instruments
in the band.
For this you need to delay your PA to line
up with the sound coming off of the stage.
Measure the distance from the front of
dbx’s DriveRack series can help you optimize and align your sound system; the 260 model has up to 2. 7 seconds of alignment and zone delay available.
horn driver and woofers of different sizes
can have different acoustic centers. The
acoustic center of an individual driver is the
location where the sound is considered to
start its acoustic journey to the listener’s
ears. This is generally considered to be
the front plate of the speaker. You can tell
its location by looking at a speaker – it is
where the magnet assembly of the speaker
and the frame that supports the outer rim
of the speaker meet. Unless you have some
good speaker diagrams, you will need to
estimate this location, which should get you
to within a half-inch of its actual location.
You will also need to know the acoustic
center of your horn drivers, which is usually considered the front of the horn driver
where it bolts to the horn. This doesn’t
seem very exact if you have looked at a
horn driver closely, but it should be close
enough for most situations.
by a signal processor with a driver time delay
function. My favorite unit for this in the lower
price range is the dbx DriveRack PA. There
are other great units out there, but I have
about a baker’s dozen of these and all the
club sound guys in my area use them as well.
This delay can be done in feet/inches, meters
or milliseconds. In general, feet/inches works
best for most applications.
Begin with the speaker component that
is the farthest away from the front of the
speaker cabinet as the starting or “zero”
point. Every driver component in front of
that zero point will need to be delayed to
that speaker. Measure the distance between
the acoustic centers of the different speakers and dial in the delay time (feet/meters/
milliseconds) for each driver group. You
should also be able to do this for your sub-woofers, although if you have horn subs
this can be tricky and is beyond what we
can discuss here. When you are done, your
speakers will be “acoustically aligned” and
the kick drum head, or possibly the guitar
amp line, and measure to the “acoustic
center” of your PA. Go into the proper section in your digital signal processor and set
the delay of the PA for the distance you
just measured. Remember, this value may
change when you go from club to club and
venue to venue. You will need to measure
and input this value again every time you
set up for a show.
Now have fun and sound great!