Specifications

WHY DO WE NEED SPEAKER BOXES?
A Hi-Fi speaker for home use is always mounted in
a box to reproduce the best possible sound.
Traditional mounting in cars are in a door side or in
the hat rack, this is a simple baffle mounting. You
can of course achieve a better sound in your car by
using suitable speaker boxes.
In a correct adapted box the sound is improved and
the power handling capacity increases.
If you have a subwoofer in your trunk and a pair of
"open air"- mounted speakers in the hat-rack the air
pumping from the sub will effect the hat-rack speakers
and make the cones move a little ruining the sound
from them. This is one of many good reasons to use
boxes also in your car.
Normally we use boxes for the subwoofer but also
the rest of the speakers sounds better mounted in a
suitable box.
We will now describe the different types of boxes
normally used in a car.
SPEAKER BOXES, GENERAL
Build your boxes in a stable and air-tight material.
The best is MDF-board, 19 mm, or particle board,
22 mm. Larger boxes must have braces inside to
avoid resonance. The box must be completely air-
tight. Use sealing compound in all joints, also in the
hole for the cable. The size of the box are decided
by the speaker data, but also the car type and music
have an influence on the box size. Deep bass
demands larger boxes than disco music.
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VENTED BOXES
A speaker in a vented box has higher efficiency (3
dB) and higher power handling capacity than in a
sealed box. In a vented box the sound from the spea-
ker and the port work together creating a higher sound
level. The sound from the port must come out in the
same phase as from the speaker otherwise the sound
result is real bad.
The size of the box are decided by the speaker data
just as in the sealed box. Also the car type and mu-
sic type have an influence on the box size.
Often the size of the car decides the practical size of
the box. A smaller box has a higher resonant
frequency than the larger one. The size of the box
should not be so large that the speaker plays below
it´s own free air resonance (Fs), then it looses in
power handling capacity.
The port in a vented box should be mounted on the
same side of the box as the speaker. But sometimes
this is impossible. The port opening inside the box
must have a free area behind the port, to the wall
behind, of at least the port diameter. There must also
be a free area in front of the port. A large sub needs
a larger port to avoid whistling sounds. Use ports
with conical openings to avoid this. The port must
also be fastened properly to avoid rattle.
As port material 3" or 4" PVC tubes are normally
used. In a correct tuned box you should be able to
feel the air pumping out from the port. At high volumes
the air can blow out a burning match, if not the box
and port are mismatched.
The port does not have to be fully inside the box as
long as the area and length are correct. for example
you can mount the port through a hat-rack. In a small
box this can have an effect on the box tuning since
the volume changes, avoid such small boxes.
Suitable port diameters for different speaker sizes:
8" 4 - 8 cm
10" 6 - 10 cm
12" 8 - 15 cm
15" 10 - 15 cm
Sometimes you need two or more ports in a box.
You can convert from one to two or more ports as
long as the total port area is the same.
All DLS subwoofers works well in vented boxes.
SEALED BOXES
Sealed boxes are easy to build. The size is not critical,
but it can´t be too small. The speaker data such as
Fs, Qts, Vas and X-max decides the size of the box.
Large speakers need larger boxes. Two speakers
need a box of the double size etc. The box must be
completely air-tight. Sealed boxes are normally used
for door-panels or kick-panels. Most 4", 5,25" and
6,5" speakers can be used in sealed boxes.
A sealed box should be filled with acoustic wool up
to 75 - 100%.
A sealed box has a lower efficiency than vented boxes
but they can handle high power and are easy to build.
A subwoofer in a sealed box creates a tight bass
suitable for the audiophiles listening to classical mu-
sic, jazz and soft rock.
DLS subwoofers can be used in vented boxes
as well as in sealed boxes.
If you use a 30-40 Hz subsonic highpass filter on the
line input of your amplifier you will achieve a tight
and well-defined bass in your bass-box. ( All GENE-
SIS series 3 amplifiers as well as the DLS amplifiers
have a built-in subsonic filter.)
L(cm) =17914 x
d
2
Fc
2
x Vb
L = port length in cm
d = inner diameter of port in cm
Vb = net volume of the box in liter
Fc = Box resonant frequency in Hz
PORT LENGTH CALCULATION
The following formula can be used:
DLS SOUND HANDBOOK - SPEAKER BOXES