Some hi-fi enthusiasts are sceptical, to say the least, that a subwoofer can improve the sound of a good two-channel system. But are they right to have their doubts? In this blog we explore some of the pros and cons of adding a sub to your system.

The first thing to note is that not all subwoofers are made equal. The vast majority of subs were and continued to be designed primarily for home theatre systems to provide slam and weight to movie sound effects. They often come as part of less expensive, high street speaker bundles.

Most of these AV subs are not particularly subtle. Their bass response will tend to be slow, undifferentiated and, for want of a better word, boomy. You might be happy with that for movies but you wouldn’t let them anywhere near your two-channel hi-fi system.

While clearly plugging a gap in the market, such units have given subs a bit of a bad rep in the hi-fi community. It’s understandable that some are wary of adding a subwoofer to their beloved systems.

But switch to a high quality sub, such as those made by REL, and the benefits are hard to ignore.

We’re focusing on the REL Serie T and Serie HT in this article - The T series comprising the REL TZero Mk3, the T5x, the T7x, the T9x and the T9x SE are all optimised for music.

The T series are certainly ready to rumble when an action movie demands it. It’s just that the HT series – the HT/1003 MkII, the HT/1205 MkII and the HT/1510 Predator – gives you more AV-focused bang for your buck.

Stuart Marchant, REL’s Business Development Manager for South East England and London, explains: “When sending an HT series an LFE (low frequency effect) signal they are on average 30 percent louder versus the equivalent model that focus on using ‘Hi-level’ as their main input. This makes all the difference when you want big powerful room filling impact and power.

“The T series are equipped with a ‘Hi Level’ input and a unique filter system which delivers the whole frequency range and superior timing, this in essence makes the sub as fast as the main speakers - unlike most subs. It also delivers the tonal characteristics of the amplifier for complete integration.”

The HT series units are also engineered with more powerful amplification than their T series equivalents with the HT/1510 packing a 1,000 watt amplifier compared to the top-of-the-range T9X’s 300 watts.

REL know it’s as important to match the correct amplifiers to the correct drivers regardless of power requirements. You can’t put a 1,000 watt amplifier in a T Zero as it will blow the driver. However, you do need a kilowatt of power and reserve to drive the 15-inch driver of the HT/1510 (Predator 2) in a dramatic cinema scene and do this with conviction.

Diving deeper into bass

But low end power is not enough to make a sub truly convincing as an AV or two-channel performer. Speed is also important.

“Bass counts for little if it isn’t fast,” says Stuart.

“With a fast sub those bass and deep bass sounds are delivered with immediacy and have a realistic impact. When an explosion happens it should make you want to flinch or duck, as it would in real life.”

Placement of a REL sub can also make all the difference to the bass performance.

By placing the sub in a corner of a room near solid walls you get reinforcement of the bass. REL say that you gain an extra 3db for every flat surface that you can use as a boundary.

“In effect it’s free power and enables the sub to extend deeper in response,” says Stuart.

“Room size and layout affect bass frequencies far more than mids or highs because their wavelengths are so long.

“Low frequency wavelengths can fold back on themselves causing bass cancellation points and bass nodes, or peaks, in all but the largest of listening rooms.

“Unfortunately, these bass cancellation points can occur right where your listening position is.”

The REL have a number of great articles including corner tuning your sub.

Not just about bass

A misconception is that a subwoofer is simply about improving the bass extension in your system. Yes a sub will do that, and then some.

But a good sub is also able to improve the soundstage, height, sense of space and scale by pressuring the room correctly, which underpins the mid and higher frequencies.

“Bass and deep bass provide the foundations for music. When you hear this then music sounds more realistic,” says Stuart.

“After all, when we listen to live music we hear all sorts of frequencies and some of them we feel, like the kick of a bass drum or the lowest double bass notes.

“Proper bass allows you to process the rest of the music as it should sound. It allows us to calibrate the rest of the frequencies, improving tonality and soundstage.”

Interestingly, having listened to many REL subs in our Portsmouth demo room, it is clear that even tracks with little or no bass or deep bass in them benefit from a sub.

Some of this maybe due to psychoacoustics, in other words the way we perceive the sound in our heads. But there are also physical effects, according to REL.

“There are multiple frequencies contained in voices and instruments that one wouldn’t normally think of as containing deep bass,” says Stuart.

“Think of the human voice. It exists primarily in mid-range octaves but within that there will be resonances, vibrations, reverberations, breaths and so on that contain lower frequencies.

“A REL sub will help present more of that information giving you far more detail and nuance to the whole of the music, not just the bass.”

Set the controls for the heart of the bass

Tuning a REL sub, which includes the correct placement of the sub in your listening room, is something closer to art than science, according to REL.

It involves setting the hi/low and crossover controls on the back to the preferred levels so that the sub sounds right, enhancing the sound of a system rather than overpowering it with bass.

Having positioned your sub in your room and then tuned the controls on the back of the unit, we reckon that even the most hardened sceptics would find it hard to deny the improvement in sound.

I know. I used to be one of the sceptics.

Thanks for reading.

Alan - Audio T Portsmouth

REL have some excellent articles on tuning your sub this which make it pointless repeating in this blog.

And check out these videos on the REL YouTube channel: