Loudspeaker Room Placement -- Part 1
Subject: Speaker
placement sanity check
Date: 8/10/2000
4:42:45 PM Eastern Daylight Time
To: wes@onhifi.com
From: Hoffman, David W
(Dave)
Here's an item that everyone says is free and has the
potential to make the greatest sonic effect in your system. Yes, I'm talking about speaker
placement. My problem, though, has been that when I find the positioning that both sounds
the best to me and has the best SPL readings, I find the speakers -- Totem Tabu's on May
Audio Rubberwood stands -- a mere two feet
away from the wall behind them (let's call it the back wall) [Note from Wes: No,
let’s not -- see article below]. This flies in the face of the Golden Mean or rule of
thirds (or fifths) that you read about. Everyone is always talking about getting the
speakers out into the room and away from boundary interactions.
Then I came across some information put out by Robert E.
Greene that really showed me that my own efforts were, in fact, born out by a paper
written years ago by Roy Allison. To distill what was said, the basic points were that one
of the three distances to the boundary surfaces should be short. This would usually be the
woofer (more on this later). The second point is that one of the distances should be
fairly large, say four or five feet. And third, the remaining distance should be quite
different from the first two. To quote REG "A good rule of thumb is that the product
of the smallest and largest distances should equal the square of the middle
distance." When I put my own distances into this formula I get:
- distance of woofer to floor: 33"
- distance of woofer to back wall: 24"
- distance of woofer to side wall: 45"
which fits the equation almost exactly -- 33 squared = 1089
and 24 x 45 = 1080
What I see from this is that either everyone else is always
talking about the optimum placement of floorstanding speakers (i.e., speakers
where the woofer is a foot or less away from the floor) into a room. Or there is some
other quality of music that is not being addressed by the aforementioned formula, and I
must be missing it. What do you think and what have your experiences taught you about this
subject?
Thanks!
Dave Hoffman
I get a lot of mail concerning speaker placement -- and one
of the hot topics is the near-ubiquitous “Rule of Thirds,” originally posited,
in print at least, if I recall correctly, by Harry Pearson.
Speaker placement just might be the single most important
element involved in system setup. Poor placement can rob even the greatest speaker of its
magic (not to mention its bass!), while canny placement can coax far more out of a modest
loudspeaker than most people would ever believe. But when we say “speaker
placement,” what we are really talking about is the interaction of a sound source
with an enclosed area -- in other words, room acoustics.
That’s a complex subject -- one I’ll address
another day -- but right now, you’re waiting for an answer you can use, so I’ll
get down to the real nitty gritty. In the meantime, if you want to explore acoustics in
detail, I recommend F. Alton Everest’s comprehensive Master Handbook of Acoustics.
You can also download a superb essay in PDF form by Glenn D. White at the AudioControl
website -- which is even cooler, because it’s specifically concerned with small
room acoustics.
Before we start, let’s get one troublesome bit of
terminology out of the way. The wall behind the loudspeakers is the front
wall because it is the wall the listener faces. Some writers refer to this as the rear
wall. They’re wrong. (My wife has helpfully suggested that we refer to both the wall
behind the loudspeakers and the wall behind the listener as the rear wall --
that should clarify matters!)
The “Rule of Thirds” is a rule of thumb -- a
quick’n’dirty way to come up with a starting place for fine tuning a
speaker’s placement. Roughly, it suggests that, in a rectangular room, the speakers
should start out a third of the way into the room (with one of the short walls behind
them) and the listener should be located at approximately two-thirds the way into the
room. Then, dividing the distance from long wall to long wall by thirds, one would get a
rough starting place for the speakers.
Since this was only intended to give a starting place, the
listener was then expected to fine tune the position by adjusting the speakers’
positions. Usually two things would happen -- the first would be that the speakers would
be moved back toward the front wall until that wall’s bass reinforcement could be
heard. The second would be that the listener would move his or her listening position
forward and back (usually back) until a good blend of direct and reflected sound was
achieved. And generally, no matter how far the speakers or the listener was moved from the
starting point, when asked how he came up with that particular placement, the hardworking
audiophile would respond, “I used the Rule of Thirds.”
My problem with the “Rule of Thirds” is that it
works less than a third of the time. If you want to put your faith in a
quick’n’dirty rule of thumb, I recommend the good ol’ isosceles triangle,
which doesn’t tell you where in the room to place the speakers, but does a great job
of establishing a relationship between the speakers and listener. To use this one, the
distance between the two speakers should be 2/3 the distance of a line drawn from the
centerpoint of an imaginary line marking the front plane of the speaker cabinet to the
listening position.
The problem with any blanket rule on speaker placement is
that you must deal with a tremendous number of variables. Even if you are blessed with a
symmetrical room (and I, for one, never have been), the way it has been constructed will
affect its sound -- your listening room will sound totally different from another
one with the same dimensions if yours has a suspended wooden floor and a sheetrock ceiling
and the other has a cement floor and a suspended ceiling.
And, of course, not all speakers behave alike -- placement
considerations for a MartinLogan electrostat might be quite different from those of a
B&W Nautilus.
Given that there’s no one answer that will serve,
I’ll offer two that I’ve found effective. The first is remarkably similar to the
formula Dave Hoffman has found effective and, unlike the ROT, this one’s
really based on the Golden Mean. It is outlined in detail at Cardas Cable’s website
at the URL www.cardas.com/insights/roomsetup.html
and is intended for an idealized rectangular room (“Golden Cuboid” or 10’
by 16’ by 26’).
It requires a little math, but it’s bone simple.
Multiply room width (RW) by .276 and you will come up with the distance from the side wall
to the center of the woofer. Multiply room width (RW) by .447 to obtain the distance from
the front wall to the center of the woofer’s face. This number should also be the
distance between the two speakers (center-of-woofer to center-of-woofer). This gives us
the following values:
- Speaker to side wall: RW x .276= 4 feet 4.992 inches
- Speaker to rear wall: RW x .447= 7 feet 1.824 inches
- Speaker to opposite side wall: RW x .724= 11 feet 7.008
inches
- Speaker to speaker: RW x .447= 7 feet 1.824 inches
Now you can use the isosceles-triangle proportion to
determine your listening position and you have a fairly good idea of what the final
positions will be. HOWEVER this is not necessarily your final setup -- now is the
time to tune by ear, your ear. If that means moving the speakers drastically, by
all means do so. It’s your hi-fi, and it should sound the way you want it to.
No matter how scientific this process seems, your ear should be the final arbiter.
...Wes Phillips
wes@onhifi.com
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