Design partially original and partially ripped off from other websites
I would love for someone to write something up here in more
In the meantime, lets just discuss the principle. The basic
problem of speaker design is that the wave coming off the back
of the driver is 180 degrees out of phase with that coming
off the front. So in essence a driver with no enclosure makes
no sound, since the two signals cancel each other out.
Many speaker designs focus on simply destroying the wave coming
off the back of the driver. You cant just mount it in a small
box though, because
- If there is too much back pressure generated by the
enclosure, the movement of the cone will be restricted and not
as much energy will escape the front. So the volume of a
speaker box would ideally be infinite, so that no backpressure
is generated, and no funky waves bounce back at
weird phase angles and impinging on the cone while it is
trying to do its job.
- Unless you build a box like a tank, it will be hard to
prevent some of the sound from the back of the driver making
its way out of the box. This is why people end up putting multiple
of layers of MDF and loaded vinyl mats in their enclosures,
and generally building them to not resonate, etc.
Some speakers seek to transform a portion of the backside energy
and pipe it back out at a more suitable phase angle. The
wavecannon is fits in this category. The idea is
to make a resonant pipe with a driver placed in the middle
somewhere, so there is some length of pipe attached to the
front and some length attached to the back. The lengths of the
pipe are adjusted such that when the signals are exiting the
two ends of the device, they are in phase. It turns out that
the driver should be placed about 1/3 of the way down the
pipe, so one section is twice as long as the other.
The nice thing about this design is that you are using 100% of the
driver energy, which is more than can be said for most speaker
designs. It is also relatively easy to build. The downside is that
it has resonant modes, and so the frequency response will
not be flat. Fortunately the human ear is not very sensitive
to non-flat frequency responses at the low end. So while the
cannon isn't great for a general purpose speaker, it makes an
efficient, powerful, and easy to build subwoofer.
by Holly Gates