So you bought yourself a gorgeous flat panel TV, set it up with a Blu-ray player and began watching a blockbuster movie like The Dark Knight. If you’re a regular reader of CANADA HiFi then I’ll assume that you’ve adjusted the picture controls of your TV with at least the help of a video calibration disc and now you’ve got pleasing visuals on your big screen. But you quickly realized that something isn’t quite right. The sound emanating from the TV is thin and seriously lacking in quality. And what in the world happened to all the bass that you recall from the movie theatre?
Most people know that video is only half of the equation. To complete the home theatre experience you need to outfit your room with decent speakers and what’s more – you need to set them up correctly.
In an earlier issue of CANADA HiFi we shared some great tips on how to place each of the speakers in a home theatre system to achieve ideal performance. This article, entitled “Improve the Sound in Your Home Theatre”, can now be read in the Audio Features section on www.canadahifi.com. In this issue I will focus exclusively on the subwoofer placement and offer some additional ideas previously not covered.
Just how important is good bass? Low frequencies are fundamental to proper reproduction of both music and movies. In music, the low octaves contain information from instruments such as a double bass, electric bass, kick drum, a baritone saxophone or even a pipe organ. Movies, in addition to their music scores, offer even more low frequency information – think of car engines, airplanes, gunfire, explosions and other various effects. Imagine listening to Pink Floyd’s “Time” and not hearing the deep, articulate bass line which defines the song. Or imagine watching a movie like Avatar and hearing boomy bass that hurts your ears.
Achieving a good, even bass response in all or most of the seating positions in your home theatre may take a little bit of effort but finding the optimal subwoofer placement will substantially enhance the enjoyment of your home theatre.
The long wavelengths of bass generated by a subwoofer interact with the walls in your listening room, and depending on the dimensions of the room and where you are sitting, they reflect back and forth length-wise and cross-wise, creating big peaks of bass energy and valleys or nulls of no energy. These peaks and valleys are called standing waves because they don’t change unless you change the physical dimensions of the room and the frequency of the bass tones. The goal of finding the best subwoofer placement is to defeat or minimize the intensity of the peaks and smooth out the levels of the nulls.
Like any other speaker, the subwoofer interacts with the walls and the furniture in the room and hence no subwoofer will sound the same in two different rooms. However, unlike all other speakers, there is no fixed, recommended placement position for the subwoofer. That’s because low frequency sounds are non-directional. In a properly set up home theatre, your ears should not be able to detect which direction the bass is coming from. If you can tell where the bass is coming from, your subwoofer level is set too high.
So what’s a good place to start? First, you should know that bass output will get stronger as you move the subwoofer towards a wall. In fact, moving a subwoofer near the corner of the room will maximize its output and enhance the overall bass response. At the same time, placing the subwoofer too close to a wall or corner may result in a less controlled bass response. Hence, to determine the best subwoofer placement you’ll have to find a good compromise between the amount of bass and the quality of bass.
On a side note, you might be interested to know that because of how a subwoofer couples with the dimensions of your room, you would have to sit in the corner diagonally opposite the subwoofer to hear the full impact of this subwoofer placement. And of course that’s not very practical.
If your room allows, experiment with the placement of the couch – you will find that as the distance from your TV changes, so will the amount of bass energy that reaches your ears. Generally, the closer you sit to a wall, the more sound pressure will arrive at your ears and hence you will hear bass with a greater intensity. However bass will also be uneven as you move along the wall – it will alternate between boomy and weak.
Subwoofers are large, heavy and cumbersome to move. It can take a lot of effort to move the subwoofer, then go to couch to evaluate the sound, then move the subwoofer again and repeat this process many times. But there is a much simpler method.
The easiest way to find a sweet spot for the subwoofer is to reverse the roles. Put the subwoofer in your listening position. Move the couch and put the subwoofer in the area where you would normally sit. Then play music with a sustained, deep bass line. Movie soundtracks are not recommended for this purpose because they offer only brief passages of bass. As the music is playing, crawl around the room with your ears close to the floor, listening for the best bass response. Good sounding bass should be tight, have good weight, without sounding overwhelming or boomy, and should have good articulation, instead of playing bass notes which all sound the same. Once you’ve found it, move the subwoofer to that spot and verify that the subwoofer sounds good in your listening area.
Large rooms, common in suburban homes, have a nasty tendency to really consume bass. The best solution to this is to use two subwoofers which will generate enough sound pressure to fill the room. But this solution has another advantage from which smaller rooms will also benefit, if the space permits of course. Using two subwoofers helps to distribute the bass frequencies more evenly throughout the room. Hence you will benefit from a better bass performance in more seating positions in your room.
When using two subwoofers, it is recommended that they are placed in diagonally opposite corners of the room. The front subwoofer’s phase should be set to 0, while the rear one’s should be dialed in to 180. If the bass sounds too boomy with the subwoofers in the corners, try moving them away from the corners. If this doesn’t help, try setting them up in the middle of the front and rear walls, or in the middle of the left and right walls.
It is important to set the right volume level so that the subwoofer blends well with the rest of the speakers. The goal is to find a volume level that works equally well with both movies and music. Start with the volume dial in its mid-way position and listen to some bass heavy CDs and movie passages. Adjust the volume dial slowly up or down until you find a balance that works well. With music, the bass notes should play deep without sounding unnaturally loud or overwhelming. With movies, you’ll know you found the right balance when you don’t have to reach for the remote every time that the movie goes from a quiet scene to an action sequence, and vice-versa. It is generally better to set the subwoofer level too low rather than too high. It is likely that you’ll need to make some finer level adjustments in the next few days after initially setting up your subwoofer.
Further improvements to a subwoofer’s performance can be achieved with acoustic treatment. Start by placing a bass trap in the corner closest to the subwoofer. Then bring another bass trap home and experiment with its location in different corners of the room. Keep adding bass traps and acoustic treatments until someone stops you. If no one stops you, stop yourself if your room starts sounding a little too acoustically dead. You don’t want to turn your home theatre into an anechoic chamber, which is what too much acoustic treatment will result in.
All modern AV receivers offer an automatic speaker setup and room correction system to reduce problems with acoustics in a given room. These systems can go a long way to improving the overall sound in the listening room, although most do little to help with the bass response. There is however one company which focuses on achieving a better bass response more than others – that company being Anthem. Its Anthem Room Correction (ARC) system, found in the company’s AV receivers and pre/pros, is capable of significantly flattening out the bass response in multiple listening spots. Those who desire an even higher level of bass performance in their home theatre should take a look at Anthem’s Perfect Bass Kit (PBK), a sophisticated system which analyzes the subwoofer’s response in multiple positions in your room, then sets the correct equalization parameters to attain optimal sound. The PBK system works with many Paradigm subwoofer models.
Of course, it’s unrealistic to think that you can implement all of these suggestions in your room, unless you have a large, dedicated home theatre room. The more of these tips you apply, the greater of a bass you will be rewarded with in your room. If you consider yourself someone who enjoys good quality sound, you owe it to yourself to find the right spot for your speakers and the subwoofer.
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