|Recently, someone pointed out something that was
missing from my web pages about subwoofer design - methods and techniques used by people
to successfully integrate subwoofers into their audio systems. As this is as much a
subjective field as an objective one, I asked members of the DIY Loudspeakers List to
let me know about their methods they use to integrate subwoofers with their systems. The
following details some of the answers I received, and my own methods.
I don't necessarily agree with some of the methods detailed below, apart from my own!
If you'd like to add your own experiences or methods to this page, please contact me via e-mail.
First, my own method:
Ideally, your main speakers should be capable of performing down to below 80 Hz, the point
at which at which it's best to cross over to a single subwoofer, to avoid aberrations in
the low bass response. The crossover ideally should be an active system, however you can
rely on the natural rolloff of the main speakers if they are small. Normally, the best
response is obtained when the subwoofer is located in or near a corner, typically one that
is located to the rear of the listening position - experiment to find the best location
for the subwoofer in your room, the one that gives the smoothest sounding response without
boomy effects. Use a separate amplifier to drive the subwoofer, and adjust its volume
level to the point where you just start to hear the effect of the subwoofer during normal
music playback. If you follow these steps, you should end up with a system that has a
smooth response way down into the low bass frequencies - if your subwoofer is up to the
John Whittaker (DIY
John sent me a complete description of some tests he made with a Hsu subwoofer and his RD75
(DIY Loudspeakers List)
"Well, IMHO, the "best" way is with a SPL meter and a set up CD (such
as the Chesky one). Alternately, guesstimate the roll-off point of the mains; play some
full-blown piano; start with the sub turned right down & turn it up until you can
_just_ start to here it. Then turn it back down a notch. I guess that's the two standard
ways to get to first base with a basic system."
Jan Nielson (DIY
"My experience with sub-woofer(s) can be expressed quite clearly: Use 2 not 1 Use
the lowest possible XO - I would recommend 50-80 Hz. You must have some kind of
variable phase correction to make the sub/satellite systems work together through the
(DIY Loudspeakers List)
"Well, using the parapix amp, you have some flexibility. It has the RCA inputs if
you have that on your receiver, or it has the speaker level inputs, and the speaker level
outputs too. I've put one into my main system, and one into a little bookshelf system. You
should mention something about using a sub with the different types of inputs."
Here's my advice:
- Use low-pass filters that sharply restrict output over 80Hz. -- a
frequency response down at least 24dB at 150Hz. will make your subwoofer sonically
invisible almost 100% of the time = easier integration with main speakers.
24dB/octave low-pass filter -- crossover frequency up to 80Hz.
18dB/octave low-pass filter -- crossover frequency up to 60Hz.
12dB/octave low-pass filter -- crossover frequency up to 40Hz.
- Place your subwoofer in a room corner for maximum output and minimum harmonic
- If walls or the floor near the subwoofer rattle, use cement patio slabs
leaning on the wall(s) ... or under the subwoofer (down-firing) ... or extending in front
of the subwoofer (forward-firing)
- Fight standing waves with bass traps in each corner and/or a parametric
equalizer such as the inexpensive Behringer Feedback Destroyer
- Measure (or listen to) the results from your listening position using a slow
sine wave sweep such as track 5 on the Stryke.com Basszone test CD (slow sweeps fully
excite room standing waves)
- Try to quiet everything that rattles in your house when playing the
slow sweep tone
I have home-built satellite speakers (MCM 8" shielded woofer, Pioneer soft
dome tweeter and a Vifa aluminum tweeter) and an HSU clone sub (24"dia X 22"h)
with and Audio Concepts DV-12. The crossovers are Marchand kits set for 45Hz.
The satellites are about 1.5 cu'(approx 24"h x 12"w x 18"d),
1.5" thick MDF (2 layers 3/4"0 and weigh about 80# each. Alone, they have good
bass, but with the sub, everything is filled out nicely. The sub sits beside
then couch. They satellite amp is an Adcom GFA-535 and the sub amp is an Adcom
GFA-2535, A/B, and C/D bridged (the extra bridging I did myself, Adcom supplied the extra
components. The systems sounds good at all levels.
I would advise using a bi/tri amped system with active crossovers that
allow you to alter the crossover points. (I have a few. I am involved with
Band Pa and DJ systems, usually 3kw RMS or greater).
The best measuring device for audio systems in the human ear. I
personally have found that using tools to set a system up to the "correct"
values often does not create a sound that is pleasing to listen to. After all it
does not matter if the system is accurate if the sound is not pleasing to the people that
are listening to it. (You can tell that I am not a true audiophile & have to
deal with practical applications in front of paying customers) The best crossover
point can change from room to room that the system is used in. I find starting off
at a bass crossover point of about 150Hz and varying it near that point when playing the
type of music that will typically be played through the system usually shows where the
best point is. Trying different positions for the speakers (wherever is practical)
is often a good idea too. (Beware of partition walls as they can have strange bass
resonance effects. If you hear a strange bass response at about 80Hz try moving the
sub further away from the wall. False ceilings can also have an effect).
What you want from the subs is also important. As with anything it is
a compromise. The more you want to feel the bass, the lower the crossover point you
will want (Down to about 60 Hz crossover point providing you can still fully us the power
of your amp). However this will decrease the amount of bass you hear through your
ears. (and the more you annoy your neighbours ;).
If the acoustics of the room are still giving you trouble then the use of a
1/3 octave (31band per channel) graphic equalizer can sort many problems out. this
is particularly true when trying to combat resonance effects from the room or furniture.
(15 band eq's are often cheaper but may not give enough flexibility in some
I have a method which I tried once and was very successful. Here it is:
See the frequency response of the speakers, decide its bottom frequency if you have a
choice to set the crossover point. Let's say we do not have the choice and we set it at
80Hz on AV receiver. You can also configure the speaker as full range in the AV receiver
and set the low pass in the subwoofer where the speaker starts rolling off. That is
simple. Decide the placement of the sub (I do not want to cover this issue here, as my
subject matter is setting proper levels and phase). Get a frequency generator and generate
the crossover frequency. both, the main speaker and the sub will start emanating bass
frequencies. Set the phase when you get maximum sound. If you do not want to get into the
frequency generator business, have a lot of bass music and refer to some on-line info or a
book about the instrument that covers this narrow band near the crossover frequency and
play that recording.
Now must have set the bass levels to a crude extent. It is time to fine-tune
it. You get many CDs that give you sweep tones in the bass frequencies. Play the tone.
Keep the remote handy. Use a narrow range above and below the crossover point to set the
levels, the transition should be so smooth that you shouldn't feel the transition at all.
You may have a sweep tone ranging from 20Hz to 200Hz. To narrow it down keep an eye on the
CD/DVD player clock and hands on speaker woofer and subwoofer driver. Note the narrow
range of time when the sub stops and the speaker starts. Add five seconds on each side of
this point and put it in the A-B loop on the CD/DVD player. This small piece of of bass
track will keep playing in the loop now. Go back to the listening seat and listen to this
carefully. Set the levels from sub or from the AV receiver whatever till you cannot make
out when did the sub stop and speaker started. This gives you right amount of bass.