DLS ZM1, Z-match
General
DLS Z-match is an impedance-matching transformer for
speaker loads.
It can be used for transforming up or down the output
voltage from a car amplifier to the speaker/speakers.
You may have had the problem that you want to connect
two 4 ohm subwoofers in bridge mode to an amplifier.
Since most amplifiers are 2 ohm stable this is impossible
without destroying the amplifier. But with a Z-match you
ca solve this problem easily.
Transforming up
If a voltage is transformed up the amplifier normally
produces more power. This relation is useful if the spea-
ker/speakers has a high impedance, and the amplifier
tolerates low impedances.
With a DLS Z-match the voltage can be transformed up
with +41%, +100% or +182%.
It can be described that the amplifier senses a lowered
speaker impedance to half, to 1/4 or to 1/8.
Transforming down
If the voltage is transformed down the amplifiers output
impedance better matches a low-ohm load, for example
several speakers connected in parallel.
Here the transformer is used backwards and can trans-
form the voltage down to 70%, 50% or 35% of the full
voltage. The amplifier senses an increase of the speaker
limpedance to 2 times, 4 times or 8 times.
By using different combinations the impedance can be
changed in more than 25 different steps.
Besides the use as an impedance-matching transformer
the DLS Z-match evens the impedance peak that occours
at the resonant frequency and in that way the impedance
load is improved for the amplifier.
CAUTION!
If an amplifier is loaded with a lower impedance than it is
designed for it can be damaged, especially if the load
lasts for a longer period.
DLS takes no responsability for damaged amplifiers or
speakers if they have been connected to a DLS Z-match.
DLS Z-match is mainly designed for increasing the
amplifier output by loading it with a low impedance load.
(not lower than the lowest load recommended by the
producer). Be aware that when the amplifier output
increases the damping factor gets lower. The damping
factor is the amplifiers ability to control the speaker cone
movement as precise as possible. This means that an
amplifier with a low damping factor will be worse when
the amplifier is loaded down and the output gets higher.
The higher output power is achieved on the cost of lower
damping factor.
On the other hand, when transforming up the speaker
impedances the damping factor will be increased
accordingly.
Maximum power handling capacity for the DLS Z-match
is 500 Watts.
Z
Z i
G
>
1. Output impedance of the amplifier
A modern car amplifier is always designed in such a way
that it tries to give a constant voltage output independent
of the speaker load impedance.
Let us study this drawing:
In this example the amplier has an output power of 50
Watts in a 4 ohm load. V
Load
Output (V)
Power (U
2
/ Z)
8 ohm
16 Volt
16 x 16 / 8= 32 Watt
4 ohm
14 Volt
14 x 14 / 4= 49 Watt
2 ohm
12 Volt
12 x 12 / 2= 72 Watt
1 ohm
8 Volt
8 x 8 / 1= 64 Watt
This amplifier is recommended by the producer not to be
loaded below 2 ohms, it is what we normally say, 2 ohm
stable. It can be loaded with a speaker impedance of 2
ohms in stereo mode without beeing damaged. If it gets
too hot there are hopefully some protection circuits that
shuts the amplifier down until it has cooled off. Amplifiers
that are used at high volumes for long periods might need
to have an extra cooling with one or more fans.
We can see that the output power increases when the
speker load decreases, down to two ohms. At 1 ohm load
the output power gets less again, so it´s no meaning to
load the amplifier that low. The amplifier will probably be
damaged after some time, and the distortion will also
increase.
All amplifiers has an internal impedance, see the drawing
above where it is called Zi. As the amplifier is loaded with
lower and lower speaker impedances the loss of heat
increases in Zi. Maximum output is obtained when the
speaker impedance load is equal to the internal
impedance of the amplifier. In the example above the
internal impedance seems to bee around two ohms.
It is not obvious that all amplifiers can be loaded down to
it´s internal impedance. Many amplifiers have protection
circuits that shuts the amplifier off, and some amplifiers
will broke at low impedance loads.
Conclusion: An amplifier can not be loaded below the
limit set by the producer. High ambient temperatures, long-
time playing at high volumes and speakers with a ”mean”
impedance curve demands a good external cooling and
here the DLS Z-match can be used only to improve the
impedance matching between amplifier and speakers.
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