Many music and film fans love to experience the clearest sounds. However, installing a 5.1 home theatre speaker set can be quite complicated even for an audiophile. 5.1-channel audio consists of five discrete, full range main channels (Left, Centre, Right, Left Surround, and Right Surround) plus an optional LowFrequency Effects (LFE) channel, often called “subwoofer channel”. This article will look into how to install a great surround sound system to make the listeners feel as through they are in the middle of the action.
Choosing the Room
Firstly you need to consider what the room is going to be used for. If this is a family room where kids play then you might want speakers mounted to the wall that are out of the way. If you plan to put speakers in a room that is used for activities other than watching TV, then you’d probably consider keeping the speakers small. On the other hand, if this is a dedicated theatre room, larger floorstanding speakers aren’t likely to pose a hazard to pets or kids.
Identifying the listening area
The layout of the room and how the positions of the speakers will affect sound need to be considered. A clear path between the listener and the speakers need to be created, e.g. if the speaker can not be seen by the listener, sound is being blocked. Speakers should not be hidden behind furniture or put too far from the TV.
The room size and the listening/viewing distance are the two criteria that drive any successful surround sound environment.
The first known factor when designing a new home theatre in the space where the home theatre will be. Product selection is often based upon the cubic volume of the listening environment.
Another factor to consider is the size of the screen and the distance from the screen to the centre of the seating area. Normally, moving to larger models in the manufacturers product line increases the possible distance from the loudspeaker to the listening area as the dispersion characteristics are optimised for longer listening distances. There are many manufacturers on the market producing different sized models and there is a loudspeaker to fit into any sized environment.
Practical Installation Considerations
Main Loudspeaker Positioning
Ideal loudspeaker placement is often compromised when working within the client’s wishes and room design restrictions. Often sound quality is third on the list after the room aesthetics and video requirements. However, with some attention to detail, it can be close rather than a distant third. A few of the more important recommendations found in standard are presented and discussed below:
- Standard: Left and right are positioned 30º from the centre and the rears are positioned 110º ± 10º from the centre. The loudspeakers should then be angled so that they point towards the optimum listening position.
- In practice: These angles are generally not respected in Home Theatres. The centre loudspeaker is usually in the correct place but the left and right loudspeakers are positioned according to the size of the screen (a practice inherited from the movie theatre ‘standards’). Multiple loudspeakers are used for the rear channels to increase coverage in the listening area and are positioned wherever is most convenient on the side and/or rear walls.
- Standard: All loudspeakers should be equidistant from the “sweet spot.”
- In practice: It is often difficult to place the left, centre and right loudspeakers equidistant front the “sweet spot” as the loudspeaker enclosures are normally positioned in the same plane, i.e. against a wall or in some cabinetry. The resulting timing differences are then electronically compensated for, using the processor. Unfortunately, this results in a compromise that is rarely referred to in most literature. The polar pattern of the loudspeaker is different at different listening distances and this cannot be compensated for in a simple digital delay.
- Standard: The front loudspeakers should ideally be placed at a height approximately equal to that of the listener’s ears (1.2 m / 4 ft from the floor). If the loudspeakers are to be placed higher or lower than the listeners’ ears, the loudspeakers should be angled vertically to point towards the listening position.
- In practice: It is generally recommended for the speakers to be positioned at least 1.2 m / 4 ft off the floor so the floor reflection does not dominate the frequency response. If the loudspeaker is placed close to the floor, for example, below a screen, two things happen: a deep and wide notch occurs in the bass (typically around 100-200 Hz) and the loudspeaker is loaded which increases the entire bass output. Subjectively, the result is a muddy but thin sounding bass and midrange masking which makes speech less intelligible. Conversely, be careful that the ceiling reflection does not start to dominate instead.
Below are some recommendations for subwoofer positioning:
- Close enough to the front wall and slightly offset from the middle of the room, 30 cm / 1 ft, to avoid the first pressure minima position.
- In a corner, close to both front and side walls. This position will maximise the system efficiency due to the corner loading. A second subwoofer in the opposite corner may be required to avoid localising a single subwoofer.
These locations are contrary to the common belief that the best position for the subwoofer is in the front, on the floor and in the middle of the room, equidistant from the side walls. This location can be a serious compromise since the subwoofer sits in the pressure minimum of the lateral standing wave. Also, it has to be remembered that:
- Adjustment of the gain (Input Sensitivity) and frequency response (Bass Roll-off) of the subwoofer is necessary to balance the subwoofer to the main loudspeakers.
- The subwoofer can also be flush mounted into the front wall or some cabinetry but the discussion of the position of the source relative to the room remains valid.
- The phase adjustment on the subwoofer at the crossover frequency is important to achieve a flat frequency response in the crossover region.
Centre Speaker Positioning
The centre channel will reproduce almost all of the dialogue. Ideally, the centre loudspeaker should be mounted above the screen as this will reduce the effects of the floor reflection as the reflection distance and angle are both increased. Although this is not always possible, the centre speaker should be lined up with the midpoint and aimed directly towards you for the best sound.
Adjusting the listening space
Room acoustics is an area of home theatre is often overlooked. It is important and challenging but with some consideration, good sound can be the result. In fact, some improvements can be made quite easily.
Wall surfaces, ceilings and floors can be reflective, diffusive or absorptive. Combinations of these are often used. Hard surfaces such as glass, concrete, dry wall or MDF reflect the sound. Soft materials such as carpets and curtains absorb the sound. The thicker the layer is, better is the absorption. Irregular surfaces such as diffusers or bookshelves diffuse and spread the sound around, as well as two parallel surfaces in a room sustain the sound energy bouncing back and forth causing flutter echo, standing waves or cancellation dips. Optimal acoustic situation is when you receive a natural direct sound from the speakers to your listening position (a.k.a. sweet spot) without the room reflections colouring the sound and the stereo imaging.
If the room is heavily damped (thick carpeting, heavy curtains and lots of upholstered furniture) there will be a loss of energy in the midrange frequencies. On the positive side, it should be remembered that an absorptive room usually results in more accurate imaging. If there is any doubt in the choice between two models based on the listening distance or room volume then select the larger model.
Conversely, if the room is minimally furnished and has many hard surfaces with little absorption (although that would be a rarity in a dedicated home theatre) then it may be possible to step down a model in the range. Such a room will tend to be highly reflective and support the loudspeakers’ output, so some adjustment of the room response controls will be necessary.
After following the steps above, even if you were not able to place your speakers in their ideal locations due to room and furniture constraints, you can rest easy knowing that your system can still sound great. Don’t worry about perfection, many home theatre receivers offer automatic speaker calibration that takes care of things for you.
We do not have any particular speaker brand recommendation, although it is best to use “voice-matched” speakers from the same brand and the same family or series within the brand. For a 5.1 setup it’s best to go for accurate speakers with a flat frequency response to avoid having any kind of ‘signature’ sound.
Give us a call if you have any questions and we will be able to guide you through the details of installation.
reference: install guide by Genelec