Written by 3:04 am Analog

Part 4 of the mono series – How to totally blow your image!

Here’s the final installment of a four-part series by Roger Skoff – And now, the latest and greatest thing yet… Mono…


In the last three parts
of this four-part article, I’ve told you about the value of using monophonic
(“mono”) playback through your stereo system for testing your system and your
room; I’ve told you how to get it and how to use it, and given you some clues
about how to “dial-in” your listening room. This final part will be about using
a different kind of mono to get your speakers perfectly placed and to finish
the job on your room. 

For all that’s gone
before, we’ve used “straight” mono playback. Now, we want to change that, and
put your two speakers out-of-phase with each other. To do that is simple: Just
reverse either (but not both) the amplifier-end or the speaker-end leads on the
speaker cable to just one (it doesn’t matter which one) of your speakers by
connecting the red cable lead to the black speaker or amplifier terminal and
the black lead to the red terminal.

Once you’ve done that,
you’ll have a tool to provide the exact opposite of what you were trying for
before: Instead of “perfect speakers”, “perfectly” placed, in a “perfect” room
giving you a mono “image” the size of a U.S. half-dollar coin, playing your system
will then give you — just at your speaker/listening room “sweet spot” – a mono
image that’s absolutely huge and seems to have no location at all.

If you were to feed two
identical (both in content and amplitude) out-of-phase mono signals into a
single channel amplifier at the same time, what you’d get is total cancellation
and… silence – no information or signal at all except for the background noise generated
by the amplifier, itself.  When you do
the same thing with your ears (but only in a “perfect” room, with “perfect”
speakers, perfectly placed, and with yourself at the exact “sweet spot” in your
listening room), because your ears aren’t a single channel, but are naturally
“wired” for stereo perception, the result is not silence, but a total
cancellation of all differences (time, tone, phase, and amplitude) between the
sound arriving at your ears from one speaker and that from the other. These
differences are what would normally provide you with clues for localizing and
“sizing” the sounds you hear, and cancelling them means that you will have no
location clues at all: Everything you hear from your speakers will sound like
it has no source whatsoever and is coming from all around you – possibly even from
behind your listening position.

This is useful in two
ways: Because a complete lack of “locatability” of the sound source (let’s call
it total “blobby-ness”) can only come about as a result of perfectly identical
sounds arriving at your ears at exactly the same time from both of your
speakers, and because that can only happen if your room is perfectly
acoustically-symmetrical and your speakers are perfectly placed, this
out-of-phase mono playback is the perfect test for both your room and the
placement of your speakers.

To use it, just sit in
your normal position and listen. Assuming that you’ve done the basic steps
toward getting your room set up that were given to you in the last part of this
article, what you hear should already be at least reasonably “blobby”. To
improve it (to make it even “blobbier”), move one of your speakers (it doesn’t
matter which one) a little bit in some direction (right, left, forward or

What do you hear? After
moving the speaker, is the sound more focused? Or less? Or does it stay pretty
much the same? The object here is to destroy all focus entirely, so if there’s
no change, move the speaker more in the same direction. If it sounds worse
(blobbier), you’re on the right track; good! If it sounds more focused (less
blobby), you’re going in the wrong direction, so move your speaker back to
where it was, and then a little more in the opposite direction.

By continuing this
process, moving both speakers, each in turn, in small increments in all
directions, you will eventually get to a point where ANY movement of either
speaker in any direction will make the sound less blobby and give it a little
more of a sense of location or source. Bingo! That’s exactly where you want your
speakers to be, and when you go back to in-phase mono, you’ll immediately hear
that your “half-dollar” – the size of your mono “image” — has gotten
noticeably smaller.

Before you go back,
though; while your speakers are still out of phase, you may notice that something
else happens once you get your speakers in just the right positions: you may
suddenly notice that, instead of just being totally blobby, some point in your
room is calling itself to your auditory attention. What that will tell you is
that you have an acoustic anomaly of some kind that’s calling to you to be
fixed. It could be something (sonically) reflective or something – an open vase
or urn, for example – that encloses a resonating air space that’s “singing
along with” the music. Fix it by moving it, covering it, or (as in the case of
the “singing” vase or urn) simply filling it with something to keep it quiet.

There may be more than
one of these anomalies, and, as you fix them, you may want to re-check and, if
necessary re-diddle your speaker placement. Eventually, though, you’ll get it
as perfect as it’s ever going to be. That’s when to go back to “in-phase” mono
and listen to your now tiny mono image. The real treat though, will be when you
first go back to stereo and hear your system and your room imaging and soundstaging
better than you ever thought possible!

The stereo will be great,
but it’s the mono, in both of its forms, that will be what gets you there!

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