The best place to position a subwoofer can only be determined by careful trial and measurements by an experienced person using the appropriate acoustical measuring tools. When measuring a subwoofer system you are looking for a smooth extension of the frequency response from the main monitor low frequency cut-off (85 Hz when using the internal subwoofer bass management crossover) down to the subwoofer low frequency cut-off point.
Positioning the subwoofer correctly is part of the solution but the other major part is adjustment of the controls:
- The subwoofer response can be altered to adjust for the level of the subwoofer relative to the main monitors
- There is often a room interaction around the subwoofer low frequency cut-off so this can be attenuated
- There is the phase control which delays the subwoofer in 90° steps (at 85 Hz) to ensure that there is no cancellation at the crossover frequency due to the physical distance between the subwoofer(s) and the main monitor
After measurement the subwoofer often ends up placed close but slightly offset from the centre of the front wall, so this is a good place to start whether you have a measuring system or not. This gives the following benefits:
- Increased acoustical loading from the front wall and floor
- No cancellations from the front wall and floor
- A good excitation of all the low frequency room modes providing a smooth low frequency response
If the sound is still not quite right then try the following:
- Move the subwoofer slightly further to the left or right of centre so that different room modes are excited at different levels.
- Add a second subwoofer and place two subwoofers asymmetrically (relative to the side walls) against the front wall to excite different room modes at different levels. A useful by-product of this is the efficiency generated by mutual coupling.
- If there are two subwoofers then try moving them to the front corners as this sometimes helps with problematic rear wall reflections.
Some additional things to consider:
- Subwoofers can be flush-mounted but the only advantage is that the cabinet will take up less space in the room. No changes in the low frequency radiation load will occur.
- Subwoofers can also be placed facing the wall or with their side along the wall. In any position make sure there is enough space for the sound to come out of the reflex port. Remember that low frequencies are omni-directional.
- Do not place the subwoofer front baffle more than 60 cm from the front wall otherwise cancellations will be seen in the subwoofer low frequency spectrum.
Other tricks to try:
- Place the subwoofer in the listening position and move the measuring microphone to different possible subwoofer positions (along the walls) to see which position gives the best response. This is called subwoofer reciprocity principle and works because the frequencies that subwoofers produce are omni-directional. It is easier to move a small microphone around than a heavy subwoofer!