Why do I need a subwoofer?

What is a subwoofer?

What is a subwoofer exactly? The common notion is that it is a large square box with a large driver in the middle. And it’s big. Very big (did I just mention that again?).

The sole purpose of a subwoofer is to reproduce the deepest of bass and to take over the reproduction of this part of the sound stage. Your speakers are not supposed to play the deepest tones, as this makes it more than difficult to place them correctly.

For home use there's typically two types of subwoofers available. Sealed and ported subwoofers. Sealed subwoofers consist, as their name suggests, of a sealed cabinet and a the bass reflex subwoofer is very similar in looks, but it's usually a little large and has one or more holes (ports). As a general rule the sealed subwoofers are a little smaller than their ported brother, but can't play as loud. The bass reflex subwoofers are a little larger and can typically play a little louder.

Very often a subwoofer is a square box with a build in amplifier and a large loudspeaker (the driver). The bigger the box, amplifier and driver, the louder the subwoofer can play – in general.

In order to reproduce the deepest bass a lot of power is required from the amplifier, or a large membrane area is needed (a big speaker driver). If both is present it is just great.

Why do I need a subwoofer?

Everybody needs a subwoofer. Eventhougth you bought the biggest speakers available (nothing wrong with that by-the-way) you still need a subwoofer.
If you want deep and clean bass in abundance – and who doesn’t? – then you need to get yourself a subwoofer.



Speaker Placement

When you come home with the speakers of your dreams you most likely already decided where to put them in the living or in your listening room. But maybe that specific position isn’t the most optimum speaker placement; sound wise. The problem is that you will not find out before you actually connect them to your amplifier and start listening to them.
Here I will try to shed some light on the typical problems you can bang your hand against when placing your speakers, as well as trying to explain how you can get the most out of your speakers by placing them correctly in your room.

Why is an on wall placement such a good idea?

For the most speakers an on wall or corner placement is really not a good idea as they are simply not designed to be mounted close to or on the wall, or in a corner for that matter. Many speakers are designed so they can be placed close to the back and side wall, but not directly on the wall.

Why is that? It is mostly all about the bass and the reproduction of bass, especially the deepest of bass. The lowest frequencies are the least directional and they are easily impacted by a change in their nearby environment. This means that even small movements of a speaker can (and usually will) have a great impact on the sound. The bass can get louder but also quieter or less detailed.

If the speakers are not placed perfectly they will also not sound as good as they can; which is a shame. In the worst case you will experience a muddy sound and it will be hard to pick out details or difficult to understand the dialog in a movie. The bass can be very dominant and almost rumbling or not be present at all in the soundscape; all with the same set of speakers.

All this comes down to the placement of the speakers and how they are designed. And let us not forget the room as this is also contributing a lot to the overall experience.
It can be more than difficult to place your speakers, so they sound correct. Mind you in the listening position that is. If more than one seat should be able to enjoy the full potential of your speakers it starts to become very difficult. In other words: Take good care when you place your speakers as their placement will directly impact the soundstage.

So where do I put my speakers then?

Well, that is the real question and one that does get answered that easily. A good rule of thumb is that there should be about 30cm to the back wall and about the double to any side wall, or the other way around. As long as the distance between the side wall and the back wall are not equal you should be pretty safe.
If you do not want to dust off your measurement microphone and measure your way to the most optimum placement, then the best (and only?) option is trail and error.

Before you start moving your speakers around you should put some music you know well and then sit down and listen to it. You are creating a baseline. Now you are ready to move around your speakers. When you have found a position that you like, note down the distance to the walls and try another position. You can always return to the position of your choice if you have noted down its placement.

But what about an on wall speaker?

This type of speaker most be designed to an on wall placement, right? Yes this is most definitely the case. And it really makes a lot of sense to design a speaker to an on wall placement, but… Of course there had to be a but.

Some on wall speakers are designed to reach all the way down to the lowest two octaves (30-50Hz), but that is asking for trouble. It all about placement and reproduction of the deepest of bass in the listening position. As the deepest bass interacts with the room it is almost certain that the bass reproduction will not be ideal in the listening position when the speakers a located on the wall on opposite side of the room. This is to do with the fact that the deeper the bass gets, the less directional it becomes. The sound below 80Hz is in fact omni-directional – it is spreading at equal loudness in all directions (also behind the speaker). This also means that it is no longer possible to recognize from where the deepest tones originates. You can’t hear if the sound is coming from behind you, from the left of the right or even above you.

In order for you to get the best possible bass reproduction and the best possible soundscape (the bass really binds the soundstage together) you need to be able to divide the sound into the directional sound and the omni-directional sound. By doing this you will be enjoying the full potential of your speakers in your living or listening room and at the same time provide you with great flexibility when it comes to speakers placement – this applies to all types of speakers.

A speaker with a frequency range starting from about 70-80Hz and capable of playing all the way up to 20kHz will be dramatically easier to place than a full range speaker. It will not be as likely to produce bass-modes (peaks and valleys) in the listening position. A full range speaker (20-20kHz) will, on the other hand, be very difficult to place and at the same time get a smooth and even soundstage. You are likely to end up with a ideal (sound wise) placement in the middle of the living room floor which is likely to be very impractical at best.

It’s all about the bass

As already discussed it is the bass that completes the soundscape and without the last two or three octaves you will quickly feel that there’s something missing. The bass should not just be present it must also be as even and smooth as possible. If there’s small peaks or valleys any dialog can easily become hard to understand and you will inevitably end up turning up the volume, just to hear what is being said.

Enter the subwoofer

If you are keen about getting your speakers to perform at their best and at the same time do not want to go on too much of a compromise with rest of your interior, well, then you really must consider investing in a subwoofer and preferably some bass-management as well.

A good subwoofer does not need to be of the same as a coffee table, but if you have a large room your need a bit of horse power to “pressurize the room”. If you’re shopping for a subwoofer you need to ask yourself how loud do I actually need to play all the way down to 20hz?