Editorials

To Subwoof or Not to Subwoof

by Craig Chase

Close up of speaker feet at bottom of speaker

What is the purpose of a Subwoofer?

ubwoofers make deep bass. Specifically, a good subwoofer will deliver bass that can enhance speakers from 120 Hz down to 32 Hz or deeper. Some of the better subwoofers can deliver bass to 20 Hz, with the largest capable of going as deep as 5 Hz in a proper room. This wide variety of frequency limits for various subwoofers can cause a lot of confusion. Add to this the hype that frequents the arena of subwoofers, and many people just don’t want to bother.

In this article, we are going to try to simplify the process of what to look for in a subwoofer and discuss the merits of using a subwoofer with smaller speakers. To keep this discussion simple, we are going to go with the concept of delivering linear bass from 20 to 80 Hz. The reason for this is 80 Hz has been the standard for crossing over from a main speaker to a subwoofer for decades. In addition, it is widely accepted that bass is non-directional below 80 Hz. What this means is one cannot tell where the source of the bass is when the frequency is below 80 Hz. 20 Hz is the lower limit of human hearing, so we will use that for this tutorial. Now that we have established that we want to reproduce accurately the bandwidth from 20 to 80 Hz, let’s talk about the physics involved. Don’t fret, there won’t be any tests, and we are not going to complicate this.

What is a sine wave and why do I care?

All sound is made up of what we call sine waves. A sine wave looks like a roller coaster on a piece of paper. A good example of a sine wave in nature would be the ripples one sees when tossing a rock into a calm pond. The small, circular waves are quite similar in look to a sound sine wave. The difference is we cannot see a sine wave made by sound; we hear it.

This next bit of information will make it easier to understand why we need a dedicated subwoofer for good bass. The sheer SIZE of a sine wave from 20 Hz to 80 Hz is quite large. One of the fascinating aspects of auditory sine waves is that as the frequency goes lower, the sine wave gets bigger. Let’s explore frequencies, sine waves and another thing called an octave.

Each time we double the frequency, we go up one octave. From 20 to 40 Hz is one octave, 40 to 80 Hz is one octave, and 80 to 160 Hz is an octave. A 20 Hz frequency is a sine wave 56 feet long, 40 Hz is 28 feet, and 80 Hz is 14 feet. If one looks at the picture of the sine wave above, it shows 0-360 degrees. This represents one complete cycle at any given frequency. At 20 Hz, which is 20 cycles per second, that wave would be 56 feet in length and would need to be reproduced by the speaker 20 times every second. We are now getting the idea as to why a dedicated subwoofer is so important: a 6-inch driver is not very good at delivering a 56-foot-long sine wave. We have now established that it takes something special and powerful to make great bass.

People keep saying a subwoofer is hard to use.

The first thing to understand about a powered subwoofer is that it has everything one needs to make this elusive bass. It has the woofer, the amplifier, and the necessary inputs to receive a signal. Most of today’s amplifiers and receivers have subwoofer outputs. Connecting a subwoofer to your system isn’t any harder than connecting a streamer or CD player. The most common method is to use an RCA cable to run from your receiver to the subwoofer. Whether you are getting the subwoofer from a local store or directly from a manufacturer, they can help ensure that you have the right cable.

Let’s now talk about this concept that integrating a subwoofer is a hard thing to do. It isn’t a hard thing to do at all. One of the cool things about getting a subwoofer is that you get to play with it in your system over time and fine-tune it to your listening preferences. Your subwoofer will have a volume control on the back. Your receiver will typically allow adjustments of the subwoofer’s output so that you can get to a volume level that you like, and even change it as you see fit for different styles of music and movies.

Let’s see some real-life examples.

Now that we have discussed some basic ideas about subwoofers, let’s look at what one can do in a real-world system. We are going to examine a speaker that is limited to about 70 Hz in bass extension and is an excellent test case for the possibility of adding a subwoofer. This is the Magnepan LRS loudspeaker ($700 per pair). It is a quasi-ribbon loudspeaker that would have many audiophiles scoffing at the idea of adding a subwoofer into the system, as it is “too detailed” to benefit from a subwoofer. My 40 years of experience in audio tells me that there is no such thing as “too detailed” to benefit from a subwoofer.

The rest of the system will consist of a Parasound New Classic 200 pre-amplifier, a Michi S-5 power amplifier, and a Starke Sound Sub 35 ($1,880 MSRP). The Parasound has no built-in eq, but it does offer a unique feature, one can turn the sub on/off via remote. When it is turned off, a full-range signal is sent to the main speakers. When it is turned on, the subwoofer gets the signal below, in this case, 80 Hz while the rest goes to the main speakers. This will allow instant switching between both modes.

The Starke Sound Sub 35 is not the most well-known subwoofer on the market, but it has quite the pedigree. It was designed by Dan Wiggins, who has been a speaker designer for several audio companies over a period of decades. Mr. Wiggins understands how to build an accurate subwoofer as well as anyone on the planet. His Sub 35 uses a custom 12-inch woofer augmented by two 12-inch passive radiators and a dedicated 1,000-watt RMS amp. Mr. Wiggins is a proponent of subwoofers that are linear across their bandwidth, which is of vital importance in terms of accurately reproducing bass. The Sub 35 is rated to 20 Hz (+/-3 dB from 20 Hz to 120 Hz) and is relatively compact at 14.1 inches in depth, width, and height.

First, we will look at some measurements.

There is an adage that says, “seeing is believing,” and it applies here. We are going to look at the response curve of the Magnepan LRS from 200 Hz and down (frequency range) and contrast it to the combination of the LRS and the Starke Sound Sub 35 from 200 Hz and down. When looking at the two graphs, we can also then reference the low note on a Bass Guitar, Kick Drum, and Piano:

4 String Bass @ 40 Hz
5/6 String Bass @ 32 Hz
Kick Drum (Depending on size) @ 30-50 Hz
Piano/Keyboards @ 27 Hz

We could find even deeper elements in movie tracks and pipe organs, but even these standard musical instruments will demonstrate the viability of a subwoofer to achieve deep bass for a reasonable price.
Here is the response curve for the Magnepan LRS being run full range:

Here is the response curve for the Magnepan LRS and the Starke Sound Sub 35:

Both response curves were measured at the listening position, four meters from the speakers. The response curve without the subwoofer was run at 85 dB @ 100 Hz. At this point, the speaker was starting to sound strained, so I did not increase the volume beyond this point. The curve shows that, by 70 Hz, the response is down 7 dB. By 50 Hz, it is down about 13 dB and by 30 Hz it is down 30 dB.

The Magnepan LRS is a very good loudspeaker, and above 80 Hz, it can deliver sound that is competitive with speakers in the $2,000-$5,000 per pair range. It just cannot deliver accurate bass in the lowest two octaves. A kick drum or bass guitar will not be played accurately, in terms of depth and power through a Magnepan LRS, nor will it through the many otherwise wonderful stand-mounted speakers from a variety of companies.

Now, look at what happened when the Starke Sound Sub 35 is added to the mix and the crossover feature from the Parasound New Classic 200 pre-amp is sending the bass below 80 Hz to the subwoofer. The speakers are now playing at 91 dB at the same listening position without a hint of strain from them. This 6 dB increase represents four times the power going into the speakers, and it means a huge step forward in terms of proper reproduction of the music as the sound engineers intended.

Listening tests

As mentioned, the measurements as posted were all done with the Starke Sub 35 being dialed in by my ears. The listening sessions started with one of my favorite torture sessions for speakers: Neil Lofgren’s Live CD, side 2, track number 9 is titled “Bass and Drum Intro,” and it’s a gem. It features a duel between the bass guitarist and the drummer, hitting hard on the deepest notes they can get from their respective instruments. The deepest fundamentals in this track are in the 40 Hz range. I started the track with just the speakers playing, no subwoofer. It was pretty good, with a well-defined bass track.

Then I hit the “on” button for the subwoofer. The bass was now better defined and deeper, without a hint of boom. There were other benefits as well. With the subwoofer off, the Magnepan speakers were trying to deliver this 40 Hz bass, and it’s just not going to happen. But this has the effect of slightly smearing the frequencies that it can deliver, which is noticeable after this issue is resolved. With the subwoofer engaged, the Magnepans clearly had more dynamics, sounded cleaner, and had a better overall sound stage. The instruments all became more concise in their respective place on stage, which in turn made the performance more enjoyable. This is one of the most under-appreciated aspects of a good subwoofer, it makes the main speakers better.

Next up was another well-known bass track: Steely Dan’s “What a Shame About Me” from their “2 Against Nature” CD. This track features a synthesized bass drum that has a fundamental in the 20 Hz range. The Magnepans, on their own, hint nothing of this fundamental, and also suffered if I tried to drive them at even moderate levels. Their relatively small panels just can’t take this abuse. With the Starke sub engaged, we again experienced a completely new speaker system. The volume could be turned up to more listenable levels and a full range experience was enjoyed.

Several other discs from classical, jazz, and rock CDs plus some movies were also auditioned, with consistent results across the board: in every case, a properly dialed-in subwoofer made for a superior listening experience. The combination of the Sub 35 and the LRS speakers is stiff competition for speakers like my Harbeth SHL5-Plus XD which sells for $7990 per pair.

Conclusions

In today’s world, there are an almost infinite number of ways to increase the performance of one’s system. A good subwoofer can do the following:

Take an existing pair of speakers and make them better
Open up the speaker shopping experience to allow one to buy smaller main speakers while getting a full range sound
Increase the available clean volume level of most speakers

Almost all home theater receivers have dedicated subwoofer outputs. Over the last few years, an increasing number of integrated amps and receivers have also added subwoofer outputs. Many also can make installing and achieving the best sound quality a simple task, as they have built-in room correction (auto equalization) programs such as Audyssey, Anthem Room Correction (ARC from Paradigm-Anthem), and Dirac Live. It will be worth your time to delve into these companies’ auto-eq programs and learn about the benefits. Perhaps we will explore these in a future op/ed (hint to the editors).

There are some caveats here. It will take time and patience to get the most out of your new subwoofer. I purposefully did this test without the use of any of the correction solutions that are available, as I wanted to show that it isn’t as complicated as a lot of industry people say it is to dial in a subwoofer. In most rooms, the best place for a single subwoofer will be in a corner. Trust your ears. Play with different positions and volume levels, and don’t get frustrated if you find it takes a few trial-and-error sessions to get the “dial by ear” method right.

If you can get, or already have, a receiver, integrated amp, or pre-amp with one of the auto-eq systems built in, your journey to great subwoofer sound will be just that much easier. Have fun and enjoy the journey to even better sound!

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