D'Amore engine'ring SMD IM-SG User manual

IM-SG
Impedance Meter /
Signal Generator
Owner’s Manual

2
Table of Contents
The Purpose and Benefit of This Tool 3
What is Included 3
About the Design 3
Specifications 4
Power Requirements 5
General Notes for using the IM-SG 6
Compensating for test harness impedance 7
General Notes for Measuring Raw Speaker Drivers 8
Finding the Resonant Frequencies of a Vehicle or Room 9
Finding the Resonant Frequencies of parts (finding rattles) 10
Using the IM-SG to tune the response of an audio system 11
Checking the Impedance of Speaker Cables or Signal Cables 13
Checking the Final Speaker Load on an Amplifier 15
Finding the Resonant Frequency of a Driver (fS)16
The Significance of fS18
Finding the Resonant Freq. of a Sealed Box System (fC)21
Finding the "Q" of a Sealed Box System (QTC)23
Finding the Volume of a Subwoofer Enclosure (Vb)25
Finding the Tuning Freq. of a Ported Box System (fB)27
Finding the Tuning Freq. of a Passive Radiator System (fB)29
Finding the Resonant Freq. of a raw Passive Radiator (fP) 30
Finding the characteristics of 4th order Bandpass Box 31
Finding the Thiele / Small (T/S) paramters of a driver 33
Troubleshooting 46
Limited warranty information 47

3
The Purpose and Benefit of the IM-SG
The D'Amore Engineering IM-SG was designed to test the
impedance of raw speaker drivers, loaded speaker
enclosures, passive crossover networks, audio signal
cables, speaker wires, and multi-speaker systems over the
entire audio frequency range. In addition it can also be
used as a stand-alone signal generator for both sine wave
and pink noise for system tuning.
What is Included?
The IM-SG
Impedance test harness
Y-adapter
This manual
Pride of ownership
About the Design
The IM-SG combines 4 powerful analog blocks in one
package: A continuously variable audio frequency sine
wave generator (you can't do that in digital ), pink noise
generator, analog audio amplifier, and a precision balanced
instrumentation amplifier to measure voltage and current.
Combine all of this with a powerful digital microprocessor to
do the math, and we have a very powerful and useful tool.
There are many possible uses for the IM-SG. Some of the
more common uses will be discussed in this manual. You
may be able to find other uses.

4
Specifications
Impedance Measurement Range
1 ohm-100 ohms with 0.1ohms resolution
Low Impedance Measurement Range
0.00 ohm- 0.99 ohms with 0.01 ohms
resolution
Operating Range of Battery
9.5 Volts - 6.4 Volts
Sine Wave Generation Frequency Range
greater than 8Hz - 20kHz in two ranges
Frequency Measurement Accuracy
greater than 99.5%
Impedance Measurement Accuracy
greater than 99% from 0 ohms - 30 ohms
greater than 96% from 30 ohms - 99 ohms
Pink Noise Generation Flatness
20 Hz - 20 kHz +/- 2.0dB
Sine Wave Generation Frequency Response
8 Hz - 15 kHz +/- 0.8dB
8 Hz - 20 kHz +/- 1.5dB
Battery Voltage Low Warning
7.2 Volts
Generator Output Voltage (unloaded)
725 mV RMS
Output Impedance of Signal Generator
10 ohms

5
Power Requirements
Pull the silicon rubber boot off of the unit by starting at one
end and pulling off towards the other end. On the back side
you will see the battery compartment. Slide battery
compartment cover off towards bottom end of unit to reveal
the 9V battery compartment. Insert a fresh 9V battery, make
sure the wires are routed around the battery. (If they are
under or on top of the battery the door may not close
properly) You are ready to go. Do not run this unit off of
any power source other than a 9V battery. Wall adapters
are electrically noisy, as are vehicle electrical systems.

6
General Notes for using the IM-SG
The Off button - Hold for 3 seconds to put the IM-SG to
sleep
The On button - Hold for 1 second to wake the IM-SG
When the IM-SG is powered up, it will display the condition
of the 9V battery. It has 3 different messages depending on
the condition of the battery.
Battery Good - The battery's voltage is greater than 7.2
Volts.
Battery Low Replace Soon - The battery's voltage is
between 6.4 Volts - 7.2 Volts.
Battery Bad Replace Now* - The battery's voltage is below
6.4 Volts and accuracy cannot be guaranteed.
* The accuracy of the IM-SG is not affected by the condition
of the battery unless the battery voltage is below 6.4 Volts.
In this case, it will not proceed to boot up, but instruct the
user to replace the battery instead. This insures accuracy
at all times.
Range button* - Press to cycle through the modes
(Low Range > High Range > Pink Noise)
Low Range = approximately 8 Hz - 600 Hz
High Range = approximately 600 Hz - 20 kHz
Pink Noise = All frequencies from 20 Hz - 20 kHz
* The Range button only cycles through the modes if the
impedance being measured is over 0.50 ohms.

7
General Notes for using the IM-SG continued
The rotary knob - Rotate slowly to sweep through the
frequency range.
The display - The display shows the generator frequency "f”
and the measured impedance "Z" simultaneously.
Harness Compensation
If making critical measurements, like those needed when
trying to derive Thiele/Small parameters for a speaker driver
(Page X), the IM-SG can compensate for harness
impedance to obtain the highest accuracy possible.
1. Turn on the IM-SG by holding the On button for 1
second.
2. Adjust frequency to approximately 500 Hz.
3. Connect the test harness to the IM-SG and short the
red and black test leads together by clipping them
together.
4. Wait for Impedance reading to settle, it should settle to
less than 0.50 ohms, if not you may have a defective
harness. The reading must settle to below 0.50 ohms
to continue.
5. Press and hold the Range button for 3 seconds.
6. The IM-SG will display "CALIBRATED", the impedance
should now read 0.00 ohms or -0.00 ohms. A lower
case "c" is displayed next to the symbol to indicate
that the reading is now compensated for test harness
impedance!
7. Compensation is canceled by powering the IM-SG off
and then back on.

8
General Notes for Measuring Raw Speaker
Drivers (out of box)
When measuring raw speaker drivers it is important that the
room in which the speaker is being tested is quiet and the
air in the room is still. If a fan is blowing and air is moving
in the room it will cause inaccurate readings. Remember, a
speaker moves air, and air moves a speaker.
When testing a woofer, it is best if the woofer is away from
boundaries and has adequate airflow at the back side of the
magnet if the speaker magnet is vented. If the magnet vent
is blocked, or if the woofer has boundaries such as sitting
on a table, it can cause inaccurate readings.
One accurate method for testing woofers is to suspend
them between two wood studs that are suspended parallel
to the ground between two tables. If this is just not
practical, you can set the woofer on a sturdy table and
place something under two sides of the magnet; making
sure the magnet vent is not blocked off.
Midrange and tweeter speakers can be measured while
sitting on a table, or by holding them in the air away from
obstacles.
Make sure the speaker is not connected to an amplifier
or damage to the IM-SG could occur!

9
Finding the Resonant Frequencies of a
Vehicle or Room (For max SPL)
1. Connect IM-SG to any auxiliary input of a source unit or
amplifier to use the IM-SG as a signal generator. Turn
the volume of the source unit or amplifier gain down.
2. Turn on the IM-SG by holding the On button for 1
second.
3. Power on the audio system
4. Increase volume to a moderate level
5. Starting at around 20 Hz, slowly turn the frequency
control up. Sweep between 20 Hz - 80 Hz while
listening carefully.
6. There will be one or more frequencies that play louder
than the others. Note these frequencies.
7. This allows the SPL competitor to select tones or music
that has frequencies that match the frequencies found
using the IM-SG to achieve the highest SPL score in
competition.

10
Finding the Resonant Frequencies of vehicle
parts (finding rattles)
Most of the interior and exterior parts of a vehicle, and even
furniture and other items in a living room can be subject to
mechanical resonance. A door panel for instance, at some
frequency it has a natural resonance frequency, or a
frequency at which it will start to vibrate due to its physical
properties. These can be very hard to find playing music
because the rattle of this component may only occur once
in a while, or only with specific music. With the IM-SG it is
easy to find such rattles. Once these rattles are found they
can be made quiet by tightening something that is loose, or
by applying a damping material such as the popular
adhesive mats.
1. Connect IM-SG to any auxiliary input of a source unit or
amplifier to use the IM-SG as a signal generator. Turn
the volume of the source unit or amplifier gain down.
2. Turn on the IM-SG by holding the On button for 1
second.
3. Power on the audio system
4. Increase volume to a moderate level
5. Starting at around 20 Hz, slowly turn the frequency
control up. Sweep between 20 Hz - 150 Hz while
listening carefully.
6. It is likely to find many different things rattling, each at
their own frequency. If no rattles are found, increase the
volume and repeat step 5. Use caution not to damage
speakers from overheating. Have fun finding and
correcting all of those rattles!

11
Using the IM-SG to tune the response of an
audio system
By using the IM-SG with an audio spectrum analyzer (RTA)
or with a inexpensive handheld SPL meter, it is possible to
analyze the frequency response of an entire audio system
and correct the response with equalization or by swapping
phase of individual speakers, or by adjusting crossover
points.
RTA Method
1. Connect IM-SG to any auxiliary input of a source unit or
amplifier to use the IM-SG as a pink noise generator.
Turn the volume of the source unit or amplifier gain
down.
2. Turn on the IM-SG by holding the On button for 1
second.
3. Power on the audio system
4. Press the Range button twice to activate Pink Noise
mode.
5. Increase volume of source unit to a moderate level
6. Place the RTA's microphone in the listening position
7. View the system's frequency response on the RTA
8. Look for holes or peaks in the frequency response of
the system. Many times just swapping the phase of the
rear channels or subwoofer channel will clear up some
of these.
9. Adjust tone controls and equalization to flatten any
peaks or dips in the system's frequency response.

12
Using the IM-SG to tune the response of an
audio system - continued
SPL Meter Method
1. Connect IM-SG to any auxiliary input of a source unit or
amplifier to use the IM-SG as a sine wave generator.
Turn the volume of the source unit or amplifier gain
down.
2. Turn on the IM-SG by holding the On button for 1
second.
3. Power on the audio system
4. Increase volume of source unit to a moderate level
5. Place the SPL meter's microphone in the listening
position
6. Slowly sweep the frequency on the IM-SG while
viewing the SPL meter. Look for holes or peaks in the
frequency response of the system. Many times just
swapping the phase of the rear channels or subwoofer
channel will clear up some of these.
Adjust tone controls and equalization to flatten any peaks
or dips in the system's frequency response.

13
Checking the Impedance of Speaker Cables or
Signal Cables
With the IM-SG's low impedance mode and harness
compensation it is easy to test the impedance of power wire,
speaker cables, signal cables, and more. A few examples
are listed below.
Testing Power Cable
1. Follow the instructions on Page 7 for to calibrate the IM-
SG to compensate for test harness impedance.
2. Connect one end of the test harness to one end of the
power cable, and the opposite end of the test harness
to the other end of the power cable. It doesn't matter
that you cannot fit the entire cable end inside the small
alligator clips on the test harness. Just make a good
connection to a number of strands that comfortably fit
the alligator clip.
3. Set the frequency to around 50 Hz
4. If the wire gauge is 4 AWG or larger, it might be hard to
measure unless measuring a complete spool of at least
100 feet because the resistance is so small.
5. It is a good way to compare two different types of wire
as long as both spools are the same length.
Testing Speaker Cable
1. Follow the instructions on Page 7 for to calibrate the IM-
SG to compensate for test harness impedance.
2. Connect the test harness to the positive and negative
wires of the speaker cable at one end. Short the
positive and negative wires at the opposite end of the
cable.
3. Set the frequency to around 1 kHz

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Checking the Impedance of Speaker Cables or
Signal Cables - continued
4. Wait for the impedance reading to settle before
reading it
5. This is a good way to compare two different types
of wire as long as types are the same length.
6. Vary the frequency, see how it performs across the
whole audio spectrum
Testing RCA cables
1. For this measurement the IM-SG does not have to
be calibrated for harness compensation as the
harness will not be used for this test
2. Connect one end of the RCA to be tested to the IM-
SG directly. Short the other end of the RCA cable
by using a shorting plug.
3. Set the frequency to around 1 kHz
4. Wait for the impedance reading to settle before
reading it
5. This is a good way to compare two different types
of wire as long as types are the same length.
6. Vary the frequency, see how it performs across the
whole audio spectrum
7. Also try shaking the cable around to check for
intermittencies in the cable. If the RCA has any
breaks in the cable or connectors the impedance
will jump up quickly.

15
Checking the Final Speaker Load on an
Amplifier
With the IM-SG it is possible and useful to test the
impedance of a speaker system be it a component set, an
individual speaker, or a multi subwoofer setup.
1. To measure the fB, make sure the room or area around
the subwoofer is quiet and free from moving air.
2. Connect the test leads to the speaker system, if it has
multiple voice coils they all need to be connected. A
parallel connection will work fine. Make sure there is
no amplifier connected or damage to the IM-SG
could occur!
3. Turn on the IM-SG by holding the On button for 1
second.
4. After the unit is operating, turn the frequency down as far
as it goes. Then slowly sweep the frequency all the way
through the audio range while watching the impedance.
5. This is a good way to look at the impedance rise of the
subwoofer system and to make sure the minimum
impedance of the subwoofer system does not drop
below safe limits for the amplifier.

16
Finding the fS of a Raw Speaker Driver
The fS is the speaker's natural resonant frequency. This will
give you some idea of the usable bandwidth of the speaker.
Generally the speaker will not produce usable output below
the frequency of fS.
1. To measure the fS, make sure the driver is ready to be
measured (read General notes for measuring raw
speaker drivers on page 8).
2. Connect the test leads to the speaker, if it has multiple
voice coils they all need to be connected. Connecting
the coils in parallel will work fine.
3. Turn on the IM-SG by holding the On button for 1
second.
4. After the unit is operating, adjust the frequency to the
low end of the fSrange in the chart below. Then slowly
raise the frequency until the peak in impedance is found.
If you go too far and pass the peak, just back down the
frequency until the peak in impedance is found. Figure 1
shows the impedance curve for a 15 inch woofer we
tested. We measured the fS to be 24Hz.
5. Record the Frequency where the Impedance reaches its
maximum value within the range of interest. This
Frequency is the fS.
Typical values for fSare listed in the table below to give you
an idea of where to look for it.
Speaker Type
fSRange
Subwoofer
10 - 50 Hz
Midbass
20 - 150 Hz
Midrange
30 - 900 Hz
Tweeter
400 Hz - 5 kHz

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Figure 1, Impedance curve of a single 4 ohm voice coil, 15
inch subwoofer. Notice the fSat 24 Hz.

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The Significance of fS
Subwoofer - The fS value of a subwoofer is the frequency
at which the cone naturally resonates, or vibrates at. This
is one of the factors that determine how low a subwoofer
will play. Example: A subwoofer with an fS of 35 Hz is
going to have a harder time trying to reproduce a 25 Hz
tone than a subwoofer with a fSof 20 Hz would. The fSis
also one of the main factors that go into calculating
subwoofer enclosure volume and tuning frequency.
Midbass / Midrange - The fSvalue of a midbass or
midrange speaker can be looked at as a limit for where the
highpass crossover should be set. Example: A 6.5 inch
midrange was measured to have an fSof 60 Hz. This
speaker should be crossed over (high pass filtered) higher
than 60 Hz to protect the driver from over excursion and
damage. We suggest setting the high pass filter on
midbass drivers  octave to 1 octave higher than the
driver's fS for best power handling. Use  octave higher if
using a 24dB/Octave crossover, and 1 octave higher if
using a 12dB/Octave crossover. This is not law by any
means, just a suggestion and very good place to start. If
the midbass driver has its own sealed or ported enclosure
it's possible that lower crossover frequencies can be used.
24dB/octave Example: For  octave higher, take the
measured fS and multiply by 1.41. So for measured fSof
60 Hz, crossover should be set at 60 Hz X 1.41 = 85 Hz.
12dB/octave Example: For 1 octave higher, take the
measured fS and multiply by 2. So for measured fSof 60
Hz, crossover should be set at 60 Hz X 2 = 120 Hz.

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The Significance of fS - Continued
Tweeter - Most tweeters have a measureable fS frequency.
There are some types of tweeters, (ribbons for instance)
that have an almost flat impedance across its operating
range. For this type of tweeter, follow manufacturer's
recommendations for crossover frequency. For all moving
coil type tweeters, we can measure the fSjust like a
subwoofer or midbass driver; you just have to look for it
more carefully. Typically, the impedance peak is not as
high as a subwoofer or midbass driver. Figure 2 shows
the impedance curve of a common 1.0 inch tweeter.
Figure 2 shows the impedance peak to occur at 1.59 kHz.
This is the fSfor this tweeter. This information is useful for
determining a safe crossover frequency for this tweeter.
We suggest setting the high pass filter on tweeters 1
octave to 2 octaves higher than the driver's fS for best
power handling. Use 1 octave higher if using a
24dB/Octave crossover and 2 octaves higher if using a
12dB/Octave crossover. This is not law by any means,
just a suggestion and good place to start.
24dB/octave Example: For 1 octave higher, take the
measured fS and multiply by 2. So for measured fSof 1.59
kHz, crossover should be set at 1.59 kHz X 2 = 3.18 kHz.
12dB/octave Example: For 2 octaves higher take the
measured fS and multiply by 4. So for measured fSof 1.59
kHz, crossover should be set at 1.59 kHz X 4 = 6.36 kHz.

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Figure 2, Impedance curve of a typical 4 ohm, 1" tweeter. Notice
the fSat 1.59 kHz