The Subwoofer DIY Page
Subwoofer Integration
20 October 2018
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.

Note: 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 job!

John Whittaker (DIY Loudspeakers List)
John sent me a complete description of some tests he made with a Hsu subwoofer and his RD75 dipole speakers.

Conrad Drake (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 Loudspeakers List)
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 continuous variable phase correction to make the sub/satellite systems work together through the XO-point.

John Janowitz (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.

Richard Greene
Here's my advice:

  1. 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.    That means:
    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.
  2. Place your subwoofer in a room corner for maximum output and minimum harmonic distortion.
  3. 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)
  4. Fight standing waves with bass traps in each corner and/or a parametric equalizer such as the inexpensive Behringer Feedback Destroyer
  5. Measure (or listen to) the results from your listening position using a slow sine wave sweep such as track 5 on the Basszone test CD (slow sweeps fully excite room standing waves)
  6. Try to quiet everything that rattles in your house when playing  the slow sweep tone

David Kiwerski
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.

Richard Goodchild
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 situations)

Mehul Mepani
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

Related Links:
 A Hsu Subwoofer with a RD75 Dipole System
(John Whittaker)

The placement of a subwoofer
(By Ingvar Ohman, translated by Per Arne Almeflo)

Optimum frequency response curves in the bass range
(By Ingvar Ohman, translated by Per Arne Almeflo).