SOUNDSTAGE! ON HIFIFeatures Archives

August 15, 2000

 

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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