Monacor CAAD 3.0 Handbuch Seite 15

NOTE
The box data are almost exclusively fixed by the bass
driver. However, a complete speaker box also includes
midrange and high range speakers. You can select
suitable speakers out of the info file "Speaker". Watch
that the speaker capabilities correspond with each
other and that the frequency ranges are overlapping
each other. By suitable selection of the cut-off fre-
quencies for bass/midrange and midrange/high range
a crossover can be calculated. The additional driver
volumes must be added to the box volume.
Bass reflex
Cone area (Sd) cm 2 : By the size of the cone area the
minimum area of the bass reflex opening is fixed.
This parameter is decisive for further calculations.
Port area (Ap) cm 2 : The programme calculates a mini-
mum area of the bass reflex opening to avoid distor-
tions and wind noise in the reflex opening. In case
the calculated minimum area is greater than the area
of your individual bass reflex tube, the following
information can be useful:
Tube model
Tube diameter in mm
Area of one tube in cm 2
Area of two tubes in cm 2
Area of four tubes in cm
2
If with the following calculation this error message is
displayed:
"Port length must be > 3 cm and < box depth"
it must at first be checked if the port length is greater
than the box depth or lower than 3 cm (compare with
the screen at the right). If the port length should
exceed the box depth, the port area (Ap) must be
reduced. If it should be lower than 3 cm, the port
area must be increased. The error message in case
of a lower value than the minimum port area can be
disregarded. In this case, however, there may be an
inconvenient wind noise.
General rule:
Greater opening area = longer reflex tube
Loss factor (Ql): It is impossible to make an ideal
combination of driver and box which does not show
any losses (friction losses, unwanted openings,
reflections). Ql can only exactly be measured after
the box has been finished. The below-mentioned list
is the result of researches which have been made
among others by Richard H. Small. It can serve as a
guideline for the calculation of bass reflex boxes until
you have made your own experience.
Box volume in litres:
Ql standard value:
Additional volume (Vb+) in l: The additional volume
is the addition of the air quantities occupied by
driver, crossover system, and the bracings (to rein-
force the box). If the final box suggestion is dis-
played by the programme, this volume is considered
and included.
The parameter input for bass reflex boxes is finished
here. Please pay attention to possible error messages.
MBR-35 MBR-50 MBR-70 MBR-110
35 51 70
9.6 20.4 34.2
19.2 40.8 68.4
38.4 81.6 136.8
below 35 35-70 above 70
10 7
The results of the box calculation are displayed on the
screen at the right. Most parameters should be known.
However, a few must be explained:
BRK = Bass reflex channel
The reference sound pressure (SPL = Sound Pressure
Level) is calculated of the driver data fs, Vas, and Qe,
and can sometimes be slightly lower than stated by the
manufacturer!
The quotient fs/Qt (EBP = Efficiency Bandwidth Pro-
duct) shows (according to Richard H. Small) if a driver
is suitable for a special box type:
EBP below 50 for transmission line
EBP 50-99 for closed boxes
EBP 100-149 for bass reflex
EBP 150-250 for horn systems
All above-mentioned values are just guidelines and are
not to be taken too strictly.
The reference sound pressure (SPL = Sound Pressure
Level) in dB is calculated of the driver data fs, Vas, and
Qe, and can sometimes be slightly lower than stated
by the manufacturer!
α is the relation of the equivalent volume of the driver
110
and the box volume (Vas/Vb).
95
h is the ratio of the resonance frequency (fs) of the
190
driver and the resonance frequency of the reflex open-
380 ing (Fp/fs).
With the last parameter CAAD 3.0 gives dimensions
for a speaker box, suitable for the inserted driver. The
additional volume has already been considered. The
displayed data are inside box dimensions.
With bass reflex boxes you can fix your own box
dimensions and have the resulting parameters calcu-
lated. Activate the option field "Set own box dimen-
sions" and change the data in the boxes for the box
dimensions.
If the option field "Set own box dimensions" is not
activated, the inserted data are disregarded and over-
written.
Band pass
Attenuation (S): In this field you insert the attenuation
factor (approx. 0.4–0.7). It influences the transient
reproduction and the box dimensions. With S = 0.4
there is a very "strong fat" bass while with S = 0.7 a
"HiFi" bass is obtained.
System Q (Q't): The system Q (Q't) is composed of
the Qs of the speaker and the rear closed volume of
the band pass box. Q't = 0.7 is a good value for a
start but it must never be lower than the Q't value of
the driver. Otherwise this would result in a box of
5
unlimited size. You can try different combinations of
S and Q't to change the bandwidth and the fre-
quency response.
Port area (Ap) cm
mum area of the bass reflex opening to avoid distor-
tions and wind noise in the reflex opening. If the cal-
culated minimum area is greater than the area of
your individual bass reflex tube, the following infor-
mation can be useful:
2 : The programme calculates a mini-
GB
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