Dls ZM1 User Manual

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 br idge 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 spea­ker/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 trans­form 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.

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:

>

G

In this example the amplier has an output power of 50
Watts in a 4 ohm load. V

Load Output (V) Power (U2 / 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 V olt 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.

Z i

Z

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.

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, long­time 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.

1

2. Speaker impedances:

Most speakers for car use has an impedance of 4 ohms.
The speakers can be connected in many different ways to
obtain the wanted impedance. They can be connected in
series, in parallel or other combinations.
Speakers with dual voice coils are normally connected
as if they were two speakers.
The examples below shows different ways to connect
speakers and the resulting impedance obtained when
using 4 ohm speaker elements.

2 ohm

1,33
ohm

When two speakers are connected in parallel the
impedance is halved.
When two speakers are connected in series the
impedance is doubled.
This is for identical speakers having the same impedance.

In the examples we see the speakers as resistors, a
component used for electronic devices which has a
resistance not varying with the frequency.

The resistance of a speaker can be measured with an
omh-meter. The so called DC resistance is normally 80 %
of the speaker impedance. A four ohm speaker has a DC
resistance of approximately 3,2 ohms.

The impedance is the resistance for alternating current
(AC).
All speakers has an impedance that varies with the
frequency with a peak at the resonant frequency (Fs).
The nominal impedance is the lowest impedance the
speaker has in the impedance curve, see the drawing
below.

1 ohm

8 ohm

4 ohm

2,67
ohm

At the resonant frequency the speaker has an impedance
of 15 - 30 ohms when the nominal impedance is 4 ohms.
The impedance curve is also influenced if it´s placed in­side an enclosure, and also how this enclosure is desig­ned.
Some types of vented boxes makes the impedance curve
more ”mean” as seen from the amplifier.
Some subwoofers has an impedance lower than the no­minal 4 ohms and can be very ”mean” to the amplifier. It is
not quite sure that an amplifier loaded with 4 ohms are
happy with that if it handles 4 ohm load with only small
tolerances. The amplifier in our example should be able
to handle also ”mean” 4 ohm speakers.

Two ”mean” 4 ohm speakers in parallel offers a resulting
two ohm load, but still a ”mean” two ohm load.
The amplifier in our example should probably don´t like a
”mean” two ohm load.
With the DLS Z-match you can improve the impedance
curve and the amplifier will sense a nicer load.

In the example above a”mean” two ohm load can be trans­formed into a nicer four ohm load to the price of a little
lower output, but improved sound.

This example should never be used. The speaker to the
right plays with four times more power than the two
others.

But the normal use of the Z-match is to increase the power
output from the amplifier by loading it down.

2

3. DLS Z-match:

DLS Z-match can be described as a transformer with many
taps (terminals).
An ordinary transformer has a primary side and a
secondary side.

Primary 100 turns 200 turns secondary
10 volt 20 volt

The transformer above has a primary side of 100 turns of
heavy copper wire on an iron core, and a secondary side
of 200 turns of not so heavy copper wire on the same
core.

This transformer transforms a primary voltage of for
example 10 volts to a secondary voltage of 20 volts.
If you connect 10 volts to the secondary side you will have
5 volts out on the primary side.

If the transformer is designed to be used for audio
frequencies, and for impedances of one up to 10 ohms it
can be used to transform the impedance of a speaker to
become higher or lower.

If a 4 ohm speaker is connected to the primary side, the
one with 100 turns, an amplifier connected to the
secondary side will sense a speaker impedance of 16
ohms.
This caculated with this formula: Zs = Zp x ( n2 / n1 )

2

If you repeat the calculations you will find that:
A four ohm speaker connected to the primary side, and

an amplifier connected to the secondary side senses:
On tap 1: 4 ohms

On tap 2: 8 ohms , the impedance x 2
On tap 3: 16 ohms, the impedance x 4
On tap 4: 32 ohms, the impedance x 8

If you connect the speaker to the secondary side, and an
amplifier to the primary side it will sense: (when the spea­ker is connected to the following taps)

0 and tap 1: 4 ohms, divided by 1
0 and tap 2: 2 ohms, divided by 2
0 and tap 3: 1 ohm, divided by 4
0 and tap 4: 0,5 ohm, divided by 8

This is the principles behind the Z-match. But it differs on
some points.
The transformer described above is a transformer with
separate primary and secondary windings insulated from
each other.

DLS Z-match is an auto-connected transformer with a
single winding equivalent to the secondary winding above.

In this way the power handling capacity is increased and
it makes the transfor mer cheaper and not so heavy.

Zp is the impedance of the speaker connected to the
primary side, in this case 4 ohms. n2 / n1 is the ratio
between the number of turns on the secondary side (n2)
and the number of turns on the primary side (n1)

In this case the ratio is 200 turns / 100 turns = 2.
This is also the ratio between the secondary voltage and
the primary voltage, 20 volts / 10 volts = 2.
Put the figures into the formula and the result is
Zs = 4 x 2 x 2 = 16.

If we connect our speaker to the secondary side instead,
and calculate the impedance the amplifier sees when it´s
connected to the primary side.
Here the speaker impedance will be divided by four and
the amplifier sees a 1 ohm load. With this simple trans­former I can increase a speaker impedance by four times,
or divide it by four.

If you add two taps to the secondary winding, one at 100
turns, one at 141 turns and add some more turns it can be
as below:

Primary side: Secondary side:

Tap 1 100 turns Tap 4 283 turns
for ex. 10 Volt gives 28 Volts

Tap 3 200 turns

4 x 8
3 x 4
2 x2
1 x 1
0

gives 20 Volts

Tap 2 141 turns

gives 14 Volts

Tap 1 100 turns

gives 10 Volts

The transformer losses will increase at frequencies over
10 kHz, especially when you use the x 8 terminal. This is
normally no problem since the Z-match is mostly used for
subwoofers.

When connecting speakers to a car amplifier it is very
important that no connections comes near and in contact
with the vehicle - ground. The same is for all connections
to the Z-match.

Transf ormer ratio:

4 ohm Volt

x 8 x 2,8

3

x4 x2

2

x2 x1,4

1

x1 x1

0

3