BTX 250 - JBL Car Audio User Guide / Operation Manual

Active Subwoofer’s - Owner’s Manual         

BTX250

Owner’s Manual
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2

Introduction / Installation

J B L BASSTU B E BTX250

Thank you for choosing the JBL
BTX250. BTX250 has been designed
to provide the kind of high-perfor-
mance low-frequency reproduction that
used to require big, clumsy enclosures,
large amplifiers, and complex installa-
tion. To ensure maximum performance,
we strongly recommend that installa-
tion be entrusted to a qualified profes-
sional. Although these instructions
explain how to install the BTX250 in a
general sense, they do not show the
specific installation methods for your
particular vehicle. If you feel you do not
have the necessary tools or experience,
do not attempt the installation yourself;
rather, ask your authorized JBL car
audio dealer about professional instal-
lation options.
Remember to keep this manual and
your sales receipt in a safe place for
future reference.

Hearing WARNING!
Playing loud music in a vehicle can
permanently damage your hearing, as
well as hinder your ability to hear traf-
fic. We recommend using low volume
levels while driving. JBL accepts no lia-
bility for hearing loss, bodily injury or
property damage resulting from the
use or misuse of this product.

Your car and bass reproduction
Depending on the interior volume of
your vehicle and the dimensions of the
passenger compartment and cargo
area, reproduced frequencies below
80Hz may be boosted by nearly 12dB
per octave as frequency decreases.
This effect, known as the vehicle’s
“transfer function” or “cabin gain,” plays
an important part in shaping the overall
in-car response of the BTX250.
BTX250 is designed to reproduce fre-
quencies below about 100Hz, but
there may be other speakers in your
vehicle that reproduce some of those
same frequencies. It is important that
all the speakers work together to
reproduce frequencies they share.
Depending on the orientation of the
BTX250 and the distance from it to the
other speakers, the BTX250 and the
other speakers may be "in-phase" or
"out-of-phase". The resulting condi-
tions, known as constructive and
destructive interference, also play a
role in shaping the frequency response
of your system.
Fortunately, BTX250 has controls to
optimize both of these conditions and
their adjustment is explained later in
the manual.

CHOOSING A MOUNTING 
LOCATION
Choose a location that doesn’t interfere
with the loading or unloading of cargo,
fold-down rear seats, or opening or
closing of the trunk lid. The best loca-
tion is likely to be the front or rear cor-
ner of the trunk or luggage compart-
ment. 
These locations, in addition to being
out of the way, will provide the best
sonic reproduction in the 60Hz to
100Hz range because the woofer out-
put will be “corner loaded” against the
vehicle’s walls. In any case, BTX250
must not interfere with the safe opera-
tion of the vehicle.
Once you’ve chosen a mounting loca-
tion and made the necessary electrical
connections, you’re ready to mount
BTX250 securely to the mounting sur-
face (most likely the floor of the lug-
gage compartment).
Caution: Make sure mounting screws
will not puncture wiring harnesses,
brake or fuel lines, or the vehicle’s fuel
tank. Some or all of these may be
located behind or under the mounting
surface.

Horizontal Mounting: Lock the fixing
holders supplied (x2) on the metal bar
of the BTX250 on each side. Then find

the right place where the BTX250 will
be installed and mark the exact posi-
tion where the fixing holders will be
located (figure 1). Then remove the fix-
ing holders from BTX250. Screw the
fixing holders on the position marked
initially (figure 2). Put back in place the
BTX250 in the fixing holders and press
the lock to fasten the metal bar in posi-
tion (figure 3).

Figure 1

Figure 2

Figure 3

3

Connecting Your System 

J B L BASSTU B E BTX250

Figure 4. BTX250 connections and ter-
minals.
B+: Connect a wire (at least 4mm

2

)

between the vehicle’s + (positive) bat-
tery terminal and the "+BATT" terminal
on BTX250. You must install a fuse
holder with a 15A fuse within 50cm of
the battery. Route the power wire
through a grommet in the vehicle’s fire-
wall. 
If there is no factory grommet 
available, you must install one. 
B–: Connect a wire (at least 4mm

2

)

between the "GND" terminal on
BTX250 and a bare metal surface near
the mounting location. You may need to
scrape away some paint from the metal
surface to insure a good connection.
Use a screw and a lock (star) washer.
Remote: Connect a wire between the
remote terminal on BTX250 and the
remote output wire on your head unit.
This wire should provide between
+5VDC and +12VDC when the head
unit is on and no voltage when the unit
is off. 

Head units with dedicated 
subwoofer outputs (line-level):
Connect the subwoofer output from
the head unit to the line-level inputs.

Head units with two line-level out-
puts and two (or four) speaker-level
outputs: Connect the two line-level
outputs from the head unit to the line-
level input on BTX250. Or connect two
speaker-level outputs from the head
unit to the Universal Interface inputs on
BTX250, which correspond to the
linelevel inputs.
Note: The Universal Interface input
wiring harness included with BTX250
is color coded to correspond with the
speaker-level outputs of many after-
market head units and adapters sold
as accessories.

°  PHASE  180°   

°  PHASE  180°   

Figure 4 

Figure 5 

Universal Interface
color code:
White:           front left +
White/black: front left –
Gray:            front right +
Gray/black:  front right –

4

Tuning - Control and Functions - Adjustment   

J B L BASSTU B E BTX250

BTX250 provides several controls that
simplify sonic integration with virtually
any vehicle’s unique acoustic proper-
ties. Please read the following section
carefully to familiarize yourself with the
function of each control.
Figure 6. Locations of controls.

Phase Control: The phase control is a
switch located on the panel with the
electrical connections (see Fig. 6). This
switch will reverse the phase of
BTX250’s output with respect to its
input. When installing BTX250 with an
existing factory or aftermarket system,
depending on BTX250’s location in the
vehicle and the distance between it
and the other speakers in the car,
reversing the phase (by moving the
phase switch) may produce a discern-
able increase or decrease in the
amount of upper bass reproduced.
Although the position that yields the

most upper bass is technically correct,
you may choose the position that 
better suits your taste.

Gain Control: This control will adjust
the input sensitivity of BTX250. Use
this control to adjust the relative 
volume (loudness) of BTX250 with
respect to the other speakers in the
vehicle. 
Crossover: The crossover control
adjusts the amount of high-frequency
information present in BTX250’s 
output.
Bass Boost: BTX250’s interaction
with the acoustics of your vehicle may
produce a peak or dip in BTX250’s
response. For the vast majority of 
vehicles, these peaks or dips occur at
about 40-50Hz — around the frequen-
cy of a low bass guitar note. Use this
control to correct that peak or dip.
Adjustment between 0dB and +6dB is
possible. Although response without
any sharp peaks or dips is technically
correct, you may choose the position
that best suits your taste.
Power LED: The power LED will glow
green to indicate that BTX250 is oper-
ational.

1. Start with gain control set to mini-
mum and the crossover control and
bass control rotated midway, to 12
o’clock.

2. Choose program material with sub-
stantial bass content and turn the vol-
ume control on your head unit to three-
quarters of its total output (approxi-
mately 3 o’clock on rotary controls).

3. Adjust the gain control clockwise
until you start to hear some distortion
coming out from the BTX250. 
Then slightly decrease the gain control
counter clockwise.

4. Listen to your system, making a
mental note of the amount of upper
bass being reproduced.

5. Switch the phase control to 180°
and listen again for upper bass con-
tent. There may be more upper bass,
less upper bass, or no change at all.
The position that provides the most
upper bass is correct, but choose either
setting according to your taste.

6. Adjust the crossover control clock-
wise or counterclockwise until you hear
only low-frequency information. For
example, you should NOT hear any
vocals coming from BTX250 when
seated in the normal listening position. 

7. Adjust the bass-boost control clock-
wise or counterclockwise to suit your
taste.