Earlier I designed subwoofers to go down to 20Hz and it
seemed to be very important. Later I realized that music and
movies have very minimal information below 30Hz and it's much
more important to have good quality bass on 30-60Hz range
and good integration to main speakers.
I have always preferred closed subwoofers enclosures with
electrical correction, because of smaller groud delay and
better phase response. With proper driver (low Q) the bass
reflex enclosures will give quite nice sound.
Also it's important that subwoofer can produce sound loud
enough without no compression or distortion. This is very
important with current DVD movies since they have such large
dynamics. If you adjust the volume in order to have natural
sound level for dialog, then the effects (explosions etc.)
are very very loud.
My Old subwoofer
My current subwoofer system is far from optimal, but
produces quite nice bass for movies.
Earlier I had two subwoofers with complex electrical correction
for frequency response down to 20Hz. My old subwoofer system
was very simple:
- Subwoofer amplifier module Simex BA-150
- JL Audio 10W0-4 driver in 51 liter closed enclosure
Picture of my old subwoofer.
The subwoofer amplifier has fixed 6dB "boost" in 30Hz (quite wide
effect, about one octave). The closed enclosure with "high" roll-off
frequency fit's quite nicely to the fixed boost of the amplifier
module and bass extends down to 30Hz.
Why new subwoofer
I did build new subwoofer mainly because of following reasons:
- I needed better linearity / less compression
- In future I will move from apartment to own house and naturally
then listening levels will be higher. Also room size will get bigger
and therefore more sound pressure is needed.
- Old subwoofer is ugly. See picture above.
Design of the subwoofer
First I had to choose subwoofer driver for the new DIY subwoofer.
Selection was quite easy because I wanted 15" driver with following
- Qts about 0.4
- Fs about 20Hz
- Sufficient BL for 15" driver
- Big Xmax (for linearity, even though manufacturer's claim for
Xmax doesn't tell much because every manufacturer has different
method of measuring Xmax. But usually when you have big Xmax you will
have little bit more linearity.)
- Possibility to cross over at 120Hz
- Cheap price naturally...
First I did simulate with some car audio subwoofers, like Peerless
R.15. Most of the car audio subwoofers had too high Fs for closed box.
But soon found out that there aren't many suitable subwoofers. Then
the project didn't move on for some monts, but then my friend found
out that Adire Audio drivers could be purchase from Europe also. I
did check parameters of Adire Audio drivers and found out two very
interesting models: Tempest and Maelstrom. Maelstrom would be nice
subwoofer if you could fit 300 liter enclosure, I can not fit that
big enclosure to my current living room. Also Maelstrom is quite
expensive (compared to Tempest).
I usually prefer closed subwoofers with Qtot near 0.6, well damped
and controlled sound. But because of my changed listening habits (now
90% movies, before 90% music) and the fact that I don't have too much
room for the enclosure, I decided to build Qtot 0.71 (butterworth
alignment) subwoofer. With Adire Audio Tempest that is about 125 liters,
which is quite big box (I'm used to 10" subwoofers).
I simulated the driver in closed 125 liter enclosure. Then I added
the frequency response of my subwoofer amplifier module:
Tempest and BA-150 simulated frequency response. The drivers response
is calculated by formulas in
Subwoofer DIY Page and Simex BA-150 frequency response is calculated
by formulas in
In Janne Ahonen's page there was instructions to change the subsonic
filter's frequency and Q value. I decided to modify my BA-150 to have
lower subsonic value and bigger Q value. This was done by changing
resistor R27 from value 180000ohm to 270000ohm. Simulated results of
As can be seen from the graph, now the bass extends lower because
the peak of subsonic filter is much lower.
If the increased peak (=increased Q value) will decrease the
transients too much then I have "plan B", which is to change the
resistor R26 from 18000ohm to 82000ohm. This will move the subsonic
filter to 10Hz and decrease the Q value of filter to 0.9. Testing
is required to find out if the large Q values ruins the sound. This
would also decrease the bass level below 30Hz.
These simulations doesn't take into account the Dolby Digital
amplifier's crossover. I have Harman/Kardon AVR-2550, which has fixed
100Hz lowpass filter for speakers with "small"-setting. Also room
gain is not taken into account in these simulations.
As can be seen from frequency response simulations the -3dB points
are at 20Hz and 200Hz (without H/K 100Hz lowpass) and therefore
subwoofer is very suitable for LFE use. Usually the frequency response
of subwoofer's low end is improved by decreasing the lowpass filter's
frequency. This can be done with 2 channel system for music listening,
but not in Digital Surround system since subwoofer has to produce the
whole range of LFE channel. This will be major improvement compared to
old subwoofer system, in which I had to lower the lowpass frequency in
order to increase the level of very low bass (<30Hz).
After acoustical design I could start the mechanical design of
the subwoofer. I had vision in my mind of enclosure, which front
panel (and maybe back panel) is(/are) made of real wood. And the rest
of enclosure is made of MDF, which is painted to black. Inside enclosure
there is "matrix" of MDF to minimize the "panel span" (free board without
Here are my initial drawings (made with PovRay):
After measuring the location where subwoofer will be put and thinking
how it should look like, I did some changes to model: made front and
back panels little bit bigger than the rest of the enclosure, also
changed material according how it's really going to look like. Also
added small cleats to MDF-corners to hide the ugly edge of the MDF.
back (back panel removed).
(This model is final version, except that I will be using many smaller
holes in the internal bracing instead of big holes.)
2005-01-03 The front and back of the subwoofer will be made of
Acajou wood. See
picture of the