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What speaker placement and listener position is optimum?

Box-speakers should be moved away from the walls. Loudspeakers radiate sound from all directions, not just from the front where the drivers are located. The lower the frequencies are, the more the sound will "wrap" around things in the listening room. Because of this "wrapping" effect, the initial sound wavefront from a loudspeaker can reflect off nearby walls, including the wall directly behind the speaker. If the speaker is too close to the rear wall, two things happen: the bass response will be increased due to reinforcement from the back wall and secondary reflections of mid-bass and mid-range frequencies will cause a secondary sound wavefront that is slightly delayed from the initial wave-front to come directly at the listener. Humans can detect slight differences in arrival times like this. This is how humans are able to use their ears to pinpoint the location and distance of a distant sound with some accuracy. In general, if the secondary reflections are very closely timed from the initial sound wave, the human brain will filter them out. This is why reflections from the speaker box itself are not usually noticeable. A good rule of thumb is to pull box speakers out at least 1.5 feet from the back wall of the listening room. 2-3 feet is better, but you may lose some bass reinforcement depending on your speakers and room size.

Side walls can be just as bad or worse. Ideally, each speaker should have an open door on its extreme side, but this is usually not architecturally possible. Try to locate speakers away from room inside corners and hard surfaces like fireplaces. These secondary reflections are difficult to eliminate and will muck-up the image. If you have to put one of two speakers in a corner, then the corner will have to be treated with sound-absorbing material. Sometimes a strategically placed chair or a tall cabinet next to the speaker in the corner will do the trick. The object is to tame the bass reinforcement so that the corner speaker will not have to be attenuated down by 3 dB or more with the balance control. This never works out well and results in poor overall sound balance. The following are preferred layouts for speaker placement in various room situations:


Case 1 has one speaker located in a corner and the other next to an open door. The fireplace is an early reflection problem. The cabinet breaks-up the corner reinforcement and the acoustic treatments take care of the fireplace and corner. The sub is reversed-phase and aimed a little at the fireplace to break up room resonances. The sofa is tight against the back wall to force rear wall reflections to be very early and not noticeable.


Case 2 has both speakers in corners. The only way to deal with reinforcement is to put lots of acoustic treatment there. The sofa is well away from the wall behind and that wall should have diffusers or absorbing curtains/panels as well.


Case 3 has neither speaker in a corner and the sofa is tight against the back wall. This is the easiest installation to get right. The only real concern is reflections off the side walls, which must be dealt with using absorbing panels or soft furniture.


Case 4 is the large-room case. The biggest problems here are reflections off the rear wall and the sidewalls. The rear wall can have diffusers or absorbers. The sidewalls need absorbers. Place a mirror on the sidewalls and look for the tweeters from the listening position to determine where the absorbing panels should be positioned.

Optimize the listening position using the following general rules:

  1. Form an equilateral triangle
    The listening position should always be one corner of an equilateral triangle. The other corners should be the speakers. This rule of thumb can vary a bit depending on the room and speaker specifics, but generally works well.
  2. Deep room configuration
    Cases 2 and 4 above are deep-room configurations. In these cases, the listening position should ideally be centered or slightly off-center in the room with diffusing or absorbing treatments on the rear wall. Positioning slightly off-center will avoid any unanticipated room resonance nodes. These are a result of "standing waves". Standing waves sustain themselves because the width of the room is an even multiple of the acoustic wavelength of the sound frequency being applied. These nodes can cause both cancellation of certain frequencies or amplification depending on which harmonic is resonating. Locating the listening position and speakers slightly off-center in the room avoids these "hot-spots".
  3. Shallow room configuration
    Cases 1 and 3 above are shallow-room configurations. In these cases, the listening position should be tight against the rear wall. No acoustic treatment is usually necessary on the rear wall.
  4. Subwoofer placement
    The subwoofer placement is critical. When it is placed properly, it disappears and many of the rooms natural resonant modes will be reduced. Often the best position is close to the listening position. When this position is chosen, you generally need to reverse the signal polarity from that of the the other speakers. This is easy to do on most systems. If there is no polarity reversal control on the preamp or surround-sound preamp, then this can be accomplished by reversing the speaker leads on all of the loudspeakers. This assumes that a line-level cable is run to the subwoofer, which is generally preferred. To eliminate low-frequency room resonances, the subwoofer can be moved and aimed in various directions until these are reduced or eliminated. Don't hesitate to aim it into a wall or a bookcase or fireplace. The direction that it aims will not change it's effect much.
  5. Stands and relative height with surround speakers Using stands can tame overly emphasized bass or make speakers sound thin. This is because full-range speakers generally need to be "coupled" to the floor to reinforce the bass. Whether or not you can use stands depends on the bass response of your speakers and whether you are using a subwoofer to compensate. The relative height of the speakers need to follow two rules: 1) the tweeter should be at the same level as the listeners ears and 2) left, right and center surround speakers should not be more than 2 feet different in vertical positioning. This means that if you must put your center channel on top of your TV monitor, the front left and right speakers should be elevated to at least to the center of the screen in height (tweeter height). In general, this will decouple the left and right front speakers from the floor, reducing the bass response. This is why it is preferred to elevate the TV monitor slightly and put the center channel under the monitor or screen. Then the left and right front speakers can remain on the floor where they can get bass reinforcement.
  6. Toe-in to the listening position
    Since most tweeters deliver the flattest response directly on-axis, it is usually better to toe-in the speakers so they are directly aimed at the listener position. If they are wide-dispersion speakers intended for two or three listeners, aim them between the listeners.
  7. Planar speakers should be moved further away from the walls
    Planar speakers generally radiate directly from two sides. This magnifies the secondary reflection problem that box-speakers have. In order to avoid high-amplitude secondary reflections that muddy-up the image, planars should be located several feet from the back wall. In fact, the optimum location is really in the middle of the room. If you cannot accommodate this placement, then you should consider not purchasing panel speakers. The general rule is 4 feet from the back wall or more.

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