Recording - November 2014 - 8

Note to faithful writers: When sending your letters by email,
please remember to include your name and where you hail from.

Subwoofer setup revisited
I don't have a subwoofer in my studio. It might be the reason I have
to run back and forth to my truck to listen to my mixes so I can get
them close to what I want. But until I understand more, I'm afraid it
will just add to the confusion.
I'm already worried that in 2-way or 3-way monitor speakers, the
balance between the output of each driver may not be an accurate
representation of the frequency spectrum, because of the individual
circuitry of the crossovers and amplification of the individual speaker parts. So how can I be sure that with a subwoofer that the extra
bass I'm hearing isn't just from having the volume to the sub up more
than its share?
Is there some basic rule that I don't know about that will help all
this make sense, so I believe the proportions I'm hearing? It seems that
there must be a way to make sure the sound created by each monitor
part is amplified evenly. I've been recording on my own now for about
4 years and your magazine and articles have been so helpful, but I've
missed understanding this basic relationship between sound sources.
Craig Johnson
via email

Hi, Craig! That's a very good question, and David Bryce's article
on subwoofers that ran in our September 2014 issue addresses it
to some extent. Let me add a few words of my own.
Most subs let you set two kinds of filtering to help you determine where the handoff from mains to sub will take place. One is
a lowcut filter that takes the bass out of what goes to the mains.
The other is a lowpass filter that takes the highs and mids out of
what the sub is trying to reproduce.
David's article features a rule of thumb that has also worked for
me in my rooms: namely, not to use the low-cut filter at all. Send
audio through the sub to the mains and don't filter it, allowing
them to roll off their low end naturally. You'll only work with the
level and lowpass filter on the sub to produce a smooth transition
from mains to sub.
Why do I like to let the mains do all they can? Because a single
sub can't give you stereo separation. While the ear cannot tell
directionality of low frequencies, you can run into situations
where the low mids and upper bass content of a song is slightly (or
greatly!) out of phase between the left and right channels; mixing
them to mono in the sub can produce weird comb filtering effects.
Letting the mains do as much as they can in stereo avoids that, and
the sub will usually be reproducing stuff that should be centered
in the mix anyway, like kick drum and bass guitar.
Now, how do you figure out where to set the crossover? David's
article suggests listening to music with a clear walking bassline and
listening for notes that jump out or drop in volume. That's a good
simple start, but it doesn't take much to get a bit more precise.
You'll need an SPL meter and a tone generator that can play a
sine wave at a frequency you select. These are both available as
hardware devices from electronics stores or catalogs. You can go

cheap by getting apps for both purposes that will
run on mobile devices, but take special care with
the SPL meter; you might want to invest in a good
measurement mic, and make sure your SPL app
can access it. (At least one SPL meter app has
noted apologetically that below certain frequencies "it is not very accurate". Gee, thanks.)
Set up the SPL meter as close as possible to
where your ears are in your listening position,
then turn on the tone generator and set it to a sine
wave of 500 Hz. (You could start higher, but we're
testing bass here!) Adjust the volume to a really
comfortable listening level (I use 80 dB SPL) and
measure there, remembering that just turning the
volume up or down will alter the bass response
(thank you, Fletcher and Munson!). Then slowly
turn down the frequency of the sine wave and
watch what happens to the SPL readout. Ideally,
you'll have only a very small variation in SPL, no
more than 1 or maybe 2 dB, as you sweep from 500
Hz down to the low end of the sub's reach.
You might consider deliberately turning up the
sub too loud and trying to find the frequency
range where the SPL starts to rise, then turn it
down until everything lines up. Alternatively, you
could start with the sub turned down all the way,
figure out where your mains roll off, and then
slowly turn up the sub (and mess with the lowpass
filter frequency) until the SPL is smooth through
that region.
Note that your room plays a role in this! If you
have room modes that you haven't tamed, certain
frequencies will jump or drop and it will have
nothing to do with the sub. Moving or turning the
sub may help. Also note that I haven't started by
calculating room modes or attempting to figure
out on paper where the sub goes. Let's face it;
most home studios are small and cramped, and it's
often impossible to place a sub where the math
says it really needs to go. David's article has good
recommendations on where to start, and I suggest
placing the sub so it's not in the way and then dialing it in, moving it if you must.
By the way, you can test the crossovers inside
your main speakers this same way. But I wouldn't
worry much; modern speakers rarely ship with
severe hiccups there, and if your room's so flat
that your mains crossover is your worst acoustic
problem, you're doing great!
Thanks for your kind words and thanks for
reading!-MM

Write to us at: Talkback, Recording Magazine, 5408 Idylwild Trail, Boulder, CO 80301
Or save stamps and send email to talkback@recordingmag.com
8

RECORDING November 2014



Recording - November 2014

Table of Contents for the Digital Edition of Recording - November 2014

Contents
Recording - November 2014 - Cover1
Recording - November 2014 - Cover2
Recording - November 2014 - 1
Recording - November 2014 - 2
Recording - November 2014 - 3
Recording - November 2014 - 4
Recording - November 2014 - 5
Recording - November 2014 - Contents
Recording - November 2014 - 7
Recording - November 2014 - 8
Recording - November 2014 - 9
Recording - November 2014 - 10
Recording - November 2014 - 11
Recording - November 2014 - 12
Recording - November 2014 - 13
Recording - November 2014 - 14
Recording - November 2014 - 15
Recording - November 2014 - 16
Recording - November 2014 - 17
Recording - November 2014 - 18
Recording - November 2014 - 19
Recording - November 2014 - 20
Recording - November 2014 - 21
Recording - November 2014 - 22
Recording - November 2014 - 23
Recording - November 2014 - 24
Recording - November 2014 - 25
Recording - November 2014 - 26
Recording - November 2014 - 27
Recording - November 2014 - 28
Recording - November 2014 - 29
Recording - November 2014 - 30
Recording - November 2014 - 31
Recording - November 2014 - 32
Recording - November 2014 - 33
Recording - November 2014 - 34
Recording - November 2014 - 35
Recording - November 2014 - 36
Recording - November 2014 - 37
Recording - November 2014 - 38
Recording - November 2014 - 39
Recording - November 2014 - 40
Recording - November 2014 - 41
Recording - November 2014 - 42
Recording - November 2014 - 43
Recording - November 2014 - 44
Recording - November 2014 - 45
Recording - November 2014 - 46
Recording - November 2014 - 47
Recording - November 2014 - 48
Recording - November 2014 - 49
Recording - November 2014 - 50
Recording - November 2014 - 51
Recording - November 2014 - 52
Recording - November 2014 - 53
Recording - November 2014 - 54
Recording - November 2014 - 55
Recording - November 2014 - 56
Recording - November 2014 - 57
Recording - November 2014 - 58
Recording - November 2014 - 59
Recording - November 2014 - 60
Recording - November 2014 - 61
Recording - November 2014 - 62
Recording - November 2014 - 63
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Recording - November 2014 - 65
Recording - November 2014 - 66
Recording - November 2014 - 67
Recording - November 2014 - 68
Recording - November 2014 - 69
Recording - November 2014 - 70
Recording - November 2014 - 71
Recording - November 2014 - 72
Recording - November 2014 - Cover3
Recording - November 2014 - Cover4
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