FINEBox-X™ 2

FINEBox-X™ 2
Non-Linear High Power Box Design Program
For Hi-Fi, PA and Micro loudspeakers
Micro Loudspeaker / Receiver Box Design ........................... 4
15 inch PRO-Sound Woofer .................................................. 8
15 inch Bass reflex Enclosure ............................................. 11
15 inch Bass reflex using Isobarik (dual) Woofers ............... 12
8 inch Woofer in different Enclosures .................................. 13
Closed box .......................................................................... 14
Bass Reflex Enclosure ........................................................ 15
ABR – Passive Radiator Enclosure ..................................... 18
Band Pass Enclosure .......................................................... 19
10. InterPort Enclosure ............................................................. 20
11. Multiple Drivers and Ports or ABR’s .................................... 21
12. Spliced Simulated + Measured Responses ......................... 22
Appendix: Special settings for Micro Speakers ................... 23
FINEBox is the ideal cabinet design software for all loudspeakers including micro and
PA drivers.
Simulation of voice coil (VC) temperature and compression at high power in closed
box, vented box, ABR, band-pass and inter-Port alignments. All non-linear T/S
parameters + thermal data can be imported directly from FINEMotor.
Figure 1: FINEBox 3D Power Compression Response versus Time
Figure 2: FINEBox calculated Compression using import from FINEMotor
Figure 3: Compression with Ferrofluid + Tighter Air gap from FINEMotor
1. Micro Loudspeaker / Receiver Box Design
Micro loudspeakers and receivers can be designed in FINEMotor and imported into
FINEBox, where the acoustic loading / box volume and tuning can be simulated.
(See the Appendix for special micro settings)
(You may go to Settings and select: Display values with extra precision
Figure 4: 15mm micro speaker in closed___/Band pass___/ damped InterPort___
Note that you can display the sensitivity in two different modes:
1) Max. Theoretical Sensitivity
(This is very useful for micro speakers)
2) Std. Loudsoft Sensitivity
(This is the lower conservative Loudsoft SPL)
Note: The Max. Theoretical Sensitivity is using the original formula based on Re
The Std. Loudsoft Sensitivity is most valid for normal / Hi-Fi drivers
We will start a 15mm box design by importing a FINEMotor file (with T/S parameters
and thermal data) directly into FINEBox by pressing the FM3 button.
(Fig. 5) defines the additional information. The first is the distance from winding to
diaphragm, which here is 0, since the VC is glued directly to the diaphragm. The
second number is the thermal conductivity, which here is the lower number 0.45
Wm/K for isolating materials. The linear excursion Xmax=0.276mm is also imported.
Figure 5: Thermal Info Input
Fig. 6 shows the complete driver data, imported from FINEMotor. The thermal time
constants of the VC and motor are automatically calculated.
Figure 6: Complete 15mm micro speaker data imported from FINEMotor
The FINEMotor FM3 import is necessary to take advantage of the high-power
thermal calculations of VC temperature, motor temperature, power compression etc.
See page 2.
You may also directly input the individual driver (TS) parameters (for example from
Klippel), see the woofer example below. In that case the High-Power Thermal
calculations are NOT applied, because the mechanical dimensions are only known
from the FM3 files.
However you can freely change for example Qts, and immediately see the change of
the response in the box. Or if you want to see the effect of higher BL, you can watch
Qts change and observe the response changes.
Figure 7: Direct input of TS parameters (from Klippel a.o.) High-Power Thermal not
available in this mode
Now the 15mm micro speaker/receiver unit is put it a closed box volume of 0.1 L
(100ccm) by selecting the upper left button “Closed Box” and adjusting the (Front-)
volume to 0.100 L by rolling the mouse wheel. This is shown as the blue curve in
Fig.4 (Button #2).
Figure 8: FINEBox Acoustic Loadings
The blue curve (#2) has an impedance peak close to 400 Hz, which is the resonance
Fs. The input voltage was adjusted to give an Xmax excursion of 0.28mm, (= Xmlin:
max excursion with VC still in the gap). This gives a max SPL of 81dB at 0.1m
defined by the frequency range indicated by the green line. See also later Fig.11.
In contrast the red curve #3 is a bandpass design, with a small hole (port) in front of
the speaker. This port is tuned to 5000 Hz, after which the response drops at higher
frequencies. Again the input voltage was adjusted to give a max excursion of
0.28mm, giving a max SPL of ~83.7 dB at 0.1m. However there is a very large peak
at 5000 Hz.
Choosing the InterPort option (Figs.4 & 8) and adjusting the interport Q to 0.9, (Fig.
9) brings down the peak and gives a quite flat Bandpass response. The high
damping (lower Q) is made by covering the (inter-) port with a cloth or felt, which will
pass air but add damping. Actually the front port can be damped in the same way.
Max SPL (2-5 kHz) is dB.
The VC and magnet temperature is in the upper right picture. The VC is at 28.9C
which is no problem. See the next two sections regarding high power simulations.
Figure 9: Setting of Port Q and damping
The ports can be changed by modifying the port diameters (Fig. 10), and the length
will automatically be calculated according to the chosen tuning frequency. A flange
(trumpet-like design) can reduce port noise/whistling.
Figure 10: Change of Port diameters and calculated lengths
Figure 11: Excursion of 15mm closed/Band pass/InterPort from Fig. 4
Fig. 11 shows the VC excursion of the 3 designs, where the input was set to produce
0.28mm (Xmlin) at the resonance frequency (Fs) in the box. Because the excursion
is increased at low frequencies, the design with the higher box resonance (green #4)
can produce a higher SPL in the pass band. In order to prevent problems, it is
advisable to insert a high pass filter to limit the low frequencies below Fs.
2. 15 inch PRO-Sound Woofer
We will show how a typical 15inch PA woofer and Bass Reflex enclosure was
simulated in FINEBox with regards to driver non-linearities and compression at
various power levels.
The driver is Celestion Frontline 15, which has a die-cast aluminum frame,
4in/100mm voice coil and a large ferrite motor.
Frontline 15 main data:
Nominal impedance
Rated Power (Pink Noise)
Voice coil Travel Xmax (+/-)
Voice Coil Resistance (DCR)
Force Factor
Free air Resonance (Fs)
Moving Mass incl. air load
Effective Cone Area
W (rms)
sq. cm
Since we have previously modeled the Frontline 15 woofer in FINEMotor, we can
import the non-linear T/S parameters and thermal data directly into FINEBox by
pressing the “Read Unit” button.
Use 40mm and 700 Wm/K for initial input, see next page. (This is the 15inch Reflex
Box.fb1 example file).
Press the driver button to view these data (Fig. 12), which include mechanical
dimensions plus voice coil and magnet system masses besides the thermal Time
Constants. (For example the voice coil Time Constant indicates the linear start of the
exponential voice coil heating, i.e. similar to the charging of a capacitor).
Figure 12: 15inch woofer data imported from FINEMotor
Note the (VC-) former conductivity is increased from 0.45 for Kapton to 700 Wm/K in
order to estimate the cooling of the ø60mm pole vent. Distance from coil to former
top is 40mm, and the bottom plate is tapering to 7mm, so the thickness is set to
7mm. Set power to 600W.
The voice coil thermal Time Constant is 15.45 seconds compared to 1926.63 s for
the Magnet (system), Fig. 12. So the voice coil will heat up much faster than the
motor, also because the magnet and steel mass is much higher than the voice coil
Open the 15inch Reflex Box.fb1 example and select one of the 3D view buttons
and view the high power response using the non-linear T/S parameters
(Bring the response in view using the –10dB arrow). Fig. 13 shows the perspective
3D view. Note the 3rd axis, which is Time. The response on the “left rear wall” is the
initial low frequency system response, which can also be viewed below on the 2D
normal frequency response curve.
The blue “carpet” shows what happens with the response when the 600W high input
power is applied for a long time.
Figure 13: 3D Frequency / Time response with “Curtain”
Note: You can rotate the 3D curve left/right and up/down by dragging! And the divider
between 2D and 3D windows can move up/down.
Between 10-100 seconds the curve is changing in SPL level and response shape
first due to heating of the voice coil, which is increasing the DCR value, and later
heating of the magnet system.
Figure 14: Time Curtain setting
Figure 14 shows the “Digital Clock” used to set the time of the “Glass Layer” Curtain,
to select a detailed response. Use the slider to adjust.
Note: The time axis is logarithmic enabling the user to see both the short voice coil
time constant and the much longer magnet system time constant.
Figure 15: VC and motor temperatures
Set the time Curtain at 10min10s (=610s), and the Temperature view (Fig. 15) shows
the high temperature of the voice coil (284.0C) and magnet system (30.3C). At this
time the magnet system has not yet heated up. Selecting max time = 4:00:00 shows
the motor + voice coil fully heated which gives a magnet system temperature of
57.2C, while the voice coil is 305.5C (from 15inch Reflex Box.fb1 example)
3. 15 inch Bass reflex Enclosure
Due to the very low Qts we can expect to use this woofer with a bass reflex
enclosure having a volume much lower than Vas. Accepting the default volume of
25L and selecting a tuning frequency Fb of 63Hz (Use the mouse wheel for easy
tuning and Volume) gives a rounded QB3 type response with –3dB at 90Hz. View
these details on the lower 2D frequency response, Fig. 16. However we would like
some more bass extension. Press Step and change the volume to 44L and the new
curve #2 (blue) shows a –3dB point of 65Hz and this response is quite close to a B4
(4’th order Butterworth/maximally flat).
Note: Use
to export the response + impedance to FINE X-over, and here
calculate the actual power with crossover. For example the real power in this woofer
would go down from 600W to 209W with one series 2.2mH inductor
Figure 16: 15inch Bass Reflex Box at 600W, 25L___/44L___
When the [1] [2] buttons next to the 2D frequency response are selected, we also see
a copy of the “curtain” frequency response i.e. the response WITH compression
(solid line). In this case at the max time (4:00:00) and 600W power, the response is
no longer flat, but has a peak at 100Hz.
The difference between the dashed and solid curves is the compression. The
compression of the blue curve (#2) is only 1dB at 100Hz, increasing to around 6dB
below and over this frequency (less due to VC inductance).
Fig. 17 shows the port for the 63Hz tuning: The flange reduces port noise.
Figure 17: Flanged Bass Reflex Port
4. 15 inch Bass reflex using Isobarik (dual) Woofers
Figure 18: Alternative Isobarik (dual) Woofers
The Isobarik concept is simply two woofers put together face to face. Two examples
are shown above, and effectively the two woofers will perform as one “super-” woofer
with double mass and half Vas and impedance when the two Voice Coils are
connected in parallel.
The previous bass reflex box of 44 litres is shown in Fig.19 as the orange response,
and the red response is an Isobarik consisting of two of the same 15” woofers. Note
the box size is now only 22 litres, due to the Isobarik principle. (The red curve was
moved 1 dB up for clarity).
Figure 19: 15" Isobarik Woofer in 22L Bass Reflex Box
(+1 dB up for clarity) /
Single woofer in 44L Bass reflex Box___
5. 8 inch Woofer in different Enclosures
We are going to build several enclosures using the same 8inch woofer to
demonstrate the difference in performance. (Saved as example files). The driver is
SEAS L22RN4X/P, which has the following data:
SEAS L22RN4X/P main data:
Nominal impedance
Long Term maximum Power
Linear voice coil Travel (p-p)
Voice Coil Resistance (DCR)
Force Factor
Free air Resonance (Fs)
Moving Mass incl. air load
Effective Cone Area
sq. cm
6. Closed box
Let us start with a closed box. Select the Closed Box Alignment and press Reset to
erase the other simulations. Since the Qts is quite low we can expect that a volume
much smaller than Vas will work. Let us therefore try with a 25L closed box, which is
also the default volume.
We have previously modeled the L22RN4X/P woofer in FINEMotor, which means
that we can import the non-linear T/S parameters and thermal data directly into
FINEBox by pressing the “Read Unit” button.
The distance from the voice coil winding to the top of the former is approximately
20mm, but we are setting this value to 0 in order to estimate the effect of the open
voice coil and phase plug, which provides better cooling. Set the Former conductivity
to 226 Wm/K for aluminum.
All Driver Parameters can then be viewed by pressing the driver button, see Fig. 20.
Figure 20: Data imported from FINEMotor
All we have to do in FINEBox is now to set the input power. The L22RN4X/P woofer
is rated at 125W (Long Term Max by IEC 268-5), which is simulated music signal
with 1minute On and 2 min. Off. This is effectively a duty cycle of 33% and we may
therefore set the input power to 1/3 of 125 W, which is 41.7W to see the long term
The closed box response is well damped with a box resonance of approximately
45Hz, indicated by the peak on the shown impedance curve
Be sure to select max time by pulling the time slider to the right. Press Step and type
125W as power (nom). The dash-dot curve is the ideal response and the solid curve
is with compression. #2 ideal response is ~5dB higher in SPL, but with the
compression increased from 1.5 to 4dB at higher frequencies (until impedance rise),
we actually only get 2.5dB more SPL. However the compression around resonance
is much reduced, less than 1 dB.
Figure 21: Closed box compression at 41.7 and 125W
Figure 22: VC and motor temperatures
Set the time Curtain to 2min25s (=145s), and Figure 22 shows the high temperature
of the voice coil (148.5C) and magnet system (23.1C) with 125W input. At this time
the magnet system has not yet heated up. Selecting max time = 4:00:00 shows the
motor + voice coil fully heated which gives a magnet system temperature of 45.2C,
while the voice coil is 167.7C.
By pressing the Vent & Xmax tab we get the actual unit displacement (excursion) in
millimeters (mm). The max displacement is reaching 8mm below resonance, which is
7. Bass Reflex Enclosure
Press Step and the Bass Reflex alignment button. The new simulation is red and
shown by the active button #3 (Fig. 23). (You may right-click the #1 button to turn if
off for now). This response is unacceptable with the high peak at 60Hz. The solution
is a lower tuning frequency Fb. #4 curve (green) is therefore tuned to 27Hz and gives
a nice QB3 type response with a rounded corner. The dashed responses are the
driver (unit) SPL alone. (The long time responses are not shown for clarity)
In order to make a B4 (maximally flat/ Butterworth) response we need a larger
volume. The last curve #5 (violet) is a 36 L box and is tuned to 30Hz. Note the corner
is now filled out.
Figure 23: Four different Bass Reflex Simulations
Figure 24: High Power Bass Reflex versus Closed Box
In comparison let us examine the high power responses after 4 hours input, in detail.
Set the “Digital Clock” (Time Curtain) to 4:00:00 and see the compressed responses
(2D Controlss [1] & [2] must be depressed). Since we want to compare the last #5
response (bass reflex) against the first (closed box #2) we can turn off buttons #3
and #4 by right-clicking them (right-click to turn on again). See Fig. 24.
We now see two new curves below the previous. These are the system responses
after 4 hours transferred from the 3D view and we see both responses are about 4dB
lower above 200 Hz, but the reflex curve now has a large bump at 50Hz compared to
the closed box, which has a more flat response. Unit and port responses are shown
as dashed for the bass reflex simulation.
So both responses are compressed at higher frequencies but the reflex curve has
changed to a non-flat response with a pronounced bumpy bass, which was not the
At this point you can use FINEBox to experiment and test alternative tunings,
alignments, boxes, drivers etc. Even changes to drivers can be suggested with
FINEMotor and simulated in FINEBox.
Press the “Vent and Xmax” tab and we get curves over unit displacement, Fig. 25
(the previous high power curves are also visible). The closed box has a max
displacement of 13mm below 50Hz, which is a little more than allowed (10.5). The
reflex in comparison shows reduced unit displacement around 27 Hz due to the reflex
port “taking over”, but increased displacement below 20 Hz. However the energy
content of normal music is much reduced below 20Hz. The bass reflex design may
therefore be preferable.
Press the button: “Reflex port Velocity” in 2D controls (#8). This curve is the speed of
the air in the port (vent) and is much too high at low frequencies. The rule is to keep
the vent speed below 15m/s to avoid “whistling”. Press the “port” button to edit the
port dimensions, see Fig. 8. Let us increase the port diameter to 10cm. Curve #6
shows the resulting vent speed, which is now acceptable. We may select the flanged
option to further reduce noise.
Figure 25: Vent Speed and Xmax of closed and Reflex Box
The port length is 81.7cm, which may be too large. Choosing a smaller diameter will
increase the vent speed at low frequencies and it may be possible to find a good
compromise between port diameters and vent speed, because the energy content of
normal music is reduced below 20-50Hz.
8. ABR – Passive Radiator Enclosure
An alternative to the bass reflex enclosure is the ABR or passive radiator enclosure.
Instead of a tuned port tube a woofer without motor can be used as resonator. The
advantage is absence of port noise and suppression of un-damped resonances from
inside the cabinet. The ABR can be made using a shallow cone with surround +
added mass for tuning.
Fig. 26 shows the 36Liter bass reflex box tuned to 27 Hz from the previous example,
as the blue curve. The red curve is the comparable ABR having a moving mass of
70g to provide close to the same tuning and pass band response. The ABR data are
shown in Fig. xxx. The Fs of the ABR is 15Hz, which causes a notch in the response
at that frequency, therefore changing the slope of the low frequency response. The
ABR Fs should therefore be placed well under the pass band.
Figure 26: ABR response
___ compared to bass reflex___
The passive ABR unit can be designed by pressing the [ ABR ] button to get the
dialogue shown in Fig. 27.
Figure 27: Passive ABR unit designer
The ABR unit will have its own resonance Fs just like the cone Fo (Use FINEMotor to
calculate the compliance and Fs of the ABR). Fig.27 shows the dialogue which is
used to specify the ABR. The moving mass is the combination of the passive cone
+½ surround, plus an added mass. Increasing the added mass will work like a lower
tuning frequency in the box.
Choosing an ABR with the same area as the woofer cone area Sd, puts high
demands on the excursion capability of the ABR. This is calculated in FINEBox under
the [Vent and Xmax] tab. The excursion can be reduced by choosing a larger ABR
diaphragm area, but the added mass must be increased. (by the power of 2). All this
is calculated automatically and the user can just experiment with different inputs.
9. Band Pass Enclosure
First we will press Reset and OK to keep only the last bass reflex simulation on the
screen for comparison. Then press the Band Pass alignment button. The new
simulation is blue and shown by the active button #2 (Fig. 28). However this
response is tilted and not good due to mistuning. Chance the tuning to 45Hz (press
the step button each time to keep the old responses) and see a nice symmetrical
response, but with limited bandwidth. In addition the box is quite large, 36+25 = 61L.
Figure 28: Band Pass simulations
Figure 29: Band Pass Response has less compression
The front volume can safely be made smaller, let us try 16 l and 47Hz tuning, which
becomes simulation #4. Interestingly the low end is unchanged and the top is much
reduced in level making the response more band pass. There are several ways to
design Band Pass systems and we will only show another here. Changing the front
volume to 10 l and the rear volume to 15 l plus 53Hz tuning we get a new more flat
Band Pass response (#5) slightly lower in level and with more high frequency
Fig. 29 shows the #5 response maintains the Band Pass shape with high input power
and has less compression.
InterPort Enclosure
In comparison let us test an InterPort design. A front volume of 20 l and 15l rear
tuned to 65Hz works fine (#6). The sensitivity is high but with less low frequency
Note the displacement of the band pass design #6 (Fig. 30), which exceeds Xmax
(dashed horizontal line close to 7mm) below 53 Hz indicated by the upper green wide
line. #5 is below Xmax down to 40 Hz, which is clearly better.
The InterPort displacements are high at low frequencies, like the previous bass
reflex. However the energy content of normal music is reduced below 20-50Hz,
which will limit the displacement.
Figure 30: Band Pass and InterPort unit displacements
Press the Ports button to design the InterPort. Choose between normal and flanged
port like the bass reflex, but in addition a simple port may be selected. Note the
option to keep tuning when editing port details.
Multiple Drivers and Ports or ABR’s
Sometimes it is an advantage to use more than one driver in a box. From 2017 you
can select up to 4 drivers connected in different ways, se Fig. 31.
Figure 31: Driver (Unit) combinations
Below are shown examples of 4 drivers in Parallel, Series and Series/Parallel (2 +2)
Figure 32: Set number of Bass Reflex Ports or ABR’s
Spliced Simulated + Measured Responses
Figure 33: Simulation with spliced response from 500 Hz
Further it is possible to mix a simulated response with a measured one from for
example FINE QC, or a simulated response from other software simulations, see
Fig.33. Here the simulated response 6_5 Woofer Large Dust Cap.FSIM was spliced
to the FINEBox 8inch bass reflex simulation at 500 Hz. In addition the level was
matched (at 500 Hz) by checking the Track level box [x].
The magnitude of the combined response may even be exported, for example to
FINE X-over. Export the combined response in the FSIM format, which can be read
by other FINE programs, by pressing the button.
1. Appendix: Special settings for Micro Speakers
This version will import fm3 files from FINEMotor 2012 and up.
Q values can now be lower than 3, to simulate ports with cloth etc.
One flange with correction
Two flanges with correction
No flanges with correction
No flanges without correction (use for small channels)
Volumes down to 0.0001L (=0.1ccm) – Use mouse wheel to step through range
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