A candid confession

I’ll admit it from the start – I’m a bass nut. If the bass isn’t right, everything else fails as well.

One of my consulting clients made a very interesting comment. I had provided active crossover optimisation and bass integration services. The most significant changes made were in the bass region where one particular significant peak was causing problems. He had turned down the bass to avoid the problem, but after I had used equalization to remove the peak, I was then able to increase the bass level overall. The curious result was that changing the bass room curve was the main factor behind perceived improvements in the midrange. Fixing a prominent bass problem meant a more pleasing and fuller tonal balance and the result was better midrange performance.

Fix the bass and everything else improves.

#1 – placement flexibility

Your mains should be placed to get the best stereo image and midrange performance, without trying to get the best bass as well. Having a dedicated bass speaker avoids having to compromise midrange to get better bass.

The best placement for the midrange is rarely the best for bass.

This is a “have your cake and eat it too” scenario.

Fig 1 – The difference between the best likely positions for the speakers and subs are shown here for a 4 x 6m listening room

There may be rooms in which the mains can be placed in the best spot for bass and everything else, but this would certainly be the exception rather than the rule. As part of my consulting work, I often measure all possible sub positions in a listening room. The positions marked in red are the sub positions that typically perform best. As you can see, these are not places that are suitable for placing full range speakers.

The freedom to place your sub where it performs best means a smoother frequency response. A sub can be placed where mains would never work. This can often include out of the way places like corners, behind couches and it’s also possible to install an “out of sight” integrated subwoofer.

#2 – freedom to choose the right number

In a stereo system, we need to have two speakers, but for a bass speaker this will often not be what you really need. In some cases, you just need one sub but in difficult rooms, you may get the best result from as many as five.

In most rooms, two or three subs will provide the best balance of cost and performance. Using multiple subwoofers, when set up correctly with the right placement, a smoother frequency response is created.

When using only full range speakers, it’s a case of letting the chips fall where they may in terms of bass performance. Subwoofers create the option to optimize the bass to a far greater extent.

#3 – great bass beyond the sweet spot

When you want to achieve great bass in more than one seat, subwoofers become even more important. This is especially true as the seats become further apart and even in more than one row. A row close to the rear wall will tend to have exaggerated bass compared to the front row. This issue tends to apply more to home cinema rooms, but when music is shared and not a solitary listening experience, subwoofers can be optimised to extend the good bass zone to more than one spot.

Fig 2 – Black: response in a seat in the back row of a cinema room. Magenta: response in a seat in the front row. Here you can see a common problem where achieving an even balance across the front row means a more bottom heavy result in the back row when closer to the rear wall. This means only one row will sound balanced unless multiple subs are optimized for both rows.

#4 – the ability to use EQ

A key aspect of getting great bass is EQ of the in-room bass response. Applying EQ to fullrange speakers can be problematic and most audiophiles have serious reservations about adding an EQ system. Adding EQ to a subwoofer is considered much more acceptable.

When EQ is applied to a subwoofer, the extra headroom also adds flexibility to apply some boost. This is inadvisable with your main speakers, but with certain limits can be done with a subwoofer.

Fig 3 – Impact of EQ on frequency response in one position. Before: +/- 8.5 dB, After: +/- 2.5 dB

#5 – creating a room curve

Most rooms have a bass response that deviates wildly from flat, often with +/- 15 dB peaks and dips. Often peaks will create a level of bass augmentation.

In a state of the art bass setup, the bass response is smoothed and in its place a room curve is created. The much smoother bass response will often sound most balanced with a degree of bass boost often referred to as a room curve. It’s not uncommon for an audiophile to choose a bass level 10 dB higher than the midrange as sounding correct, in a room with good acoustic performance in the bass range.

Fig 4 – Room curve illustration. This is a matter of personal preference which is also influenced heavily by source material. Where the ability to control the level of boost exists, I have found that it can vary from – 3 dB to + 20 dB. The average chosen boost is around 10 dB. When choosing the level by ear, listeners tend to set the boost at a higher level than they would think necessary.

My clients are very often surprised to find out how elevated their bass response is.

In the example below, the midrange level matches in before and after.

Fig 5 - The black curve represents frequency response in the main listening position before changes were made. The red line shows the final result. 10 dB divisions are shown. Existing response: +/- 10 dB (20 dB range). Modified response: +/- 5 dB (10 dB range) relative to the target curve. Most of the response below 200 Hz falls within +/- 3dB of the target curve.

In this example, bass integration was improved. Acoustic treatment (bass traps) were deemed unnecessary after a room analysis. Placement was optimized with measurements, crossovers were modified, EQ was applied and a room curve was added. It’s important that all these steps go before attempting to apply a room curve, since issues in the upper bass and low midrange region. The result in this case was a more controlled and accurate lower midrange region and enhanced bass performance, which in turn provided a perceived midrange improvement. The fuller bass serves as a foundation to the midrange.

#6 – enhanced dynamics, impact and weight

When you feel the urge to crank, nothing ruins the experience like a bass driver finding its mechanical limit. Much more common is a bass experience that is either under whelming or out of control in a way that diminishes the music. The right number of well-integrated subs can add impact and weight to the bass along with enhanced dynamics. There is a wealth of recorded material that takes on new life when the bass is completely under control and able to reproduce the full impact of bass that was recorded. The vast majority of full range speakers on the market are inadequate in this respect and prevented from optimal bass performance for the reasons discussed in this article.

I’ve left this final point to the end because it’s the only reason most people see to use a sub in a two-channel system. In reality, subs are simply a better way to reproduce bass in a room. This is not to say that it’s a bad idea to choose speakers with serious bass capabilities already included. The key point here is that in most cases, if you want the best bass possible in your room without compromise, you’ll probably need a sub.

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