How To Integrate A Subwoofer Into Your 2-Channel System

Subwoofers have long been considered the bastard child of stereo systems, almost universally derided for “one-note” bass due to experience with bad home theatre setups. While this is 99% true, it is not because adding a subwoofers is a bad idea in and of itself, it’s because most subwoofers simply suck. 

 Let’s look at what a subwoofer is supposed to do and what it usually does. Almost no speakers are full-range in that they don’t produce much bass below say 60 or even 100Hz. This is where the feeling of scale and power in music comes from. In home theatre where the speakers are often small for aesthetic reasons, those speakers may not even make bass below 150Hz which includes the lower notes of a piano or male voice. A subwoofer is necessary to fill in the missing information of these smaller, bass-limited speakers. The thinking is simple— take the big driver out of the main speaker boxes and move it to a discrete location away from view in the form of a subwoofer. 

What actually tends to happen is that the subwoofer becomes an afterthought in the quality of the whole sound because you don’t look at it and it truly is an “extra” piece which is not readily evaluable unless you investigate independently of the main speakers. The net effect is that manufacturers try to save as much money as possible on subwoofers and so long as it makes any kind of bass note it will fool people long enough in a demo to make a sale. It’s a sad state of affairs with most products thoroughly failing the accuracy test.

Now, as should be evident over the last decade, we do not shy away from controversial opinions or going against the grain if we believe that it can benefit our customers’ listening pleasure. This why we do confidently proclaim that subwoofers can be effectively used in both home theatre and even the highest end 2-channel systems with zero detriment and only improve the listening experience. The trick is - it’s extraordinarily hard to do. Nonetheless, this article is going to give you the tools to best choose and integrate a sub into your system.

Let’s isolate a few factors which determine whether a sub helps or hurts a system and then look at what you need to do to guarantee success in each. These are:  

  • Quality of subwoofer
  • Size of subwoofer vs. room
  • Placement in room
  • Rolloff, volume and integration with main speakers

Quality of subwoofer

As mentioned above, the vast majority of subwoofers are simply garbage. This is due to two main factors. The first is the driver used. Mostly these are large (especially larger than 10”) with either flimsy cones, insufficient travel, poor magnet design or force and materials which are inherently ringy. A quick way to tell whether a subwoofer is going to make tones above where it should (overtones) is to tap the cone. Does it sound like a dead thud or does it sound like a paper cup? If it sounds like a paper cup, then you are hearing frequency overtones far higher than the root frequencies of the bass the sub will make. It should be dead sounding. Remember subs should only make low bass, not midrange! If they make these midrange tones, they badly colour your main speakers. A good bass driver has a heavy magnet, long throw and relatively stiff and inert diaphragm. This results in a linear frequency response. Next, look at the quality of amplifier it uses. Most use dirt-cheap Class D amplifiers. There’s nothing inherently wrong with a Class D amp for a subwoofer because they are high power and the usual drawbacks like high frequency distortion are unheard in the low notes of a sub anyway. However, some of these amps are so cheap that they are both unreliable and incapable of controlling the driver accurately. A quick test is to turn the sub up all the way and see if there is any movement of the driver. On some of the worst subs you can actually hear noise as a result of the amp having such high distortion. The crossover and volume potentiometers also play a role in this. Some volume knobs are so bad that they actively EQ the bass when used at their lower levels. Finally, the box of a subwoofer and the general configuration of the drivers makes a huge difference. Subwoofer boxes are usually made as cheaply as possible and the resonance of the cabinet can be clearly heard. Test a sub by itself with no speakers playing and check to see if you can hear any midrange coming from the sub. If you do, there’s a problem in likely all the components of the design. Generally whether a sub is ported, sealed, or uses a passive driver greatly affects the linearity of the bass, however each design style can be made effective. Sealed subs tend to have the least problems, but the lowest output. Ported subs tend to have the most problems but the highest output. Passive radiators tend to give the best of both worlds (but cost more). Also, by virtue of physics, small subwoofers tend to be easier to make accurate. There are smaller panels in the box to vibrate and smaller woofers have less flex and distortion. Of course these have lower output, but consider whether you actually need more!

Here are our current favourite subwoofers at various price points:

 

Kanto Sub 8 REL T-zero REL T/7i REL S/3 SHO

 

Size of subwoofer vs. room

For anyone who’s read our choosing a speaker article or visited us in store, we are fanatical about making sure people choose the speaker that is the right size for their room. This is because bass quality is determined almost entirely by the room itself, not the speaker. With subwoofers this is hugely compounded. The short answer is to chose a small subwoofer for small rooms, medium for medium, large for large etc. Don’t try to put a large sub in a small room. The energy that the sub will make will be so exacerbated by the room modes that it will usually massively decrease your bass performance. Some overtone bass notes which are being canceled by your room modes will actually get quieter the harder the subwoofer pushes on the fundamental note while the others that are accentuated by the room will get much louder. It’s a wider spread of the low to high modes which makes the subjective bass even more uneven. Also, small rooms can’t generally make long bass notes anyway, so using a large subwoofer is overkill and because small subs are generally easier to make accurately, the frequency errors of a larger sub in a small room can otherwise ruin a good pair of speakers.

Placement in room

As with speakers, the placement in the room determines exactly which bass notes will be accentuated or diminished based on the dimensions of your room. You can check a room mode calculator to see this. The advantage a subwoofer has over a pair of large speakers is that it can be moved just about anywhere in the room and remain visually acceptable. Speakers cannot. In this way, subwoofer placement can much more sympathetically work with your room modes in order to give you the most even bass response in your listening position. Harbeth P3ESR REL T7iIn all but the largest rooms, it is almost always preferable to choose a small accurate speaker and a small accurate sub rather than a large accurate speaker because the tuning available of moving and adjusting the sub in isolation will always yield better bass than the bigger speaker which is locked in limited placements. Don’t be surprised if placing the subwoofer near your chair or in an opposite corner from the speaker sounds far superior. This is because the length of bass wave that is emphasized changes depending on where the sub is in relation to walls, your listening position and the main speakers. Sometimes having a sub in the perfect “anti-location” running out of phase and pulling, while your main speakers push can create an averaging of the amplitude highs and lows of the bass modes. Experiment thoroughly with odd placements and you will be surprised how massive the difference in bass is. In fact, in all but large rooms, it is almost always better to not have the subwoofer near the main speaker. Some customers ask whether it’s better to have two subwoofers than one in order to maintain the stereo bass of the recordings. In almost 100% of the cases this is not true. Two is theoretically better if all factors are perfect, however in real life it is almost never the case! First of all, bass below 80Hz is non-directional. Neither the recording nor the subwoofer has any stereo information to recreate at these frequencies. Given the difficulties of placing one subwoofer is beyond the capabilities of the vast majority of regular people, adding two simply compounds all the variables mentioned above. Certainly using two large subs in a small room is simply asking for trouble. If using two subs, always downsize dramatically.

Rolloff, volume and integration with main speakers

Experimenting with placement must be done in tandem with adjusting the volume, phase and rolloff of the subwoofer. Because the notes that the sub is affecting will change as it is moved around the room in both frequency type and volume effect, you need to dynamically gauge whether you should reduce or increase the sub volume at each trial location. The best way is to have another person adjust these dials as they move the sub. Repeatedly listen to the same song or frequency sweep during each test. Having too low a rolloff results in a gap in bass between the sub and your speakers making it sound artificially thunderous but lacking warmth. Too high a rolloff makes a congested and bloated sound. 

Connections

All subwoofers have at least an RCA input for line level connection from your preamp or variable output on your amplifier. Do not use the record or tape output! These are fixed and you will have maximum bass at all times no matter what your main volume is set at! Some subwoofers have left and right inputs. If your preamp has left and right outputs, use two RCA cables for these. The subwoofer combines the channels inside. If your preamp has left and right outputs but there’s only one on the sub, use a Y combiner adapter. These can be had for $5 or so. Lastly, if you don’t have a subwoofer or preamp output on your amp or preamp, subwoofers such as the RELs we sell have a specific high level input which runs off your amplifier’s speaker binding posts. This cable simply piggybacks on your main speakers and does not draw any power from your amp. In this way, no matter what your system is, there’s a sub for you.

The payoff

Finally, what does a good quality sub, setup in the right place with the right volume and crossover do to your system? In short, it’s incredible! The simple fact is that most people’s speakers are not making full range bass, or even good in-room bass due to their placement. A subwoofer can work with your system to actually fix some of its problems of both omission and commission. The basic effect is of a more authoritative sound, more energy, more punch and more liveliness. That elusive quality of “being there” or engagement can be massively increased. Ironically too, if you nail the setup of the subwoofer you can actually improve the definition of soundstage and instrument placement. This happens somewhat by cleaning up the bass mode issues to un-congest the lower midrange, but it also happens because of the way the human brain works. When the whole sound picture is missing the brain can’t really relax and accept it as real, but when you add that missing bass, all the tumblers fall into place and “click” allowing your brain to jump to the next level of believability. For listeners of classical music this is especially noticeable, but all types of music can benefit.

Hopefully these points have cleared up some of the misconceptions about using subwoofers in 2-channel systems. If you’re ready to begin the integration process, come talk to us specifically about the details of your system - room, speakers, amp, listening position, style of music, current bass problems. It’s only with this kind of direct in-person conversation that we can begin to give you the best bass that a subwoofer can provide. We also do at-home setups. It’s well worth the money.

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