How to test your speaker’s impedance using a digital multimeter

How to test your speaker’s impedance using a digital multimeter

Too low impedance will cause a higher current to be drawn by the speakers from an amplifier, which can bring about damaging of the amp. On the other hand, if the impedance is too high, the dynamic range and the volume of the speakers will suffer. If you are worried about what is the impedance of the speaker, I will simplify it for you. It is the measure of current resistance caused by the speaker. How much current a speaker can resist can be confirmed using a multimeter.

There are two types of multimeters, i.e., analog multimeter and digital multimeter. In our case, we will dwell much on a digital multimeter, which has more advantages over the analog multimeter. A digital multimeter can measure several functions in one unit. The functions include resistance, voltage, and current.  Below is a guide on how to quickly estimate your speaker’s impedance.

Check the impedance rating of the speaker’s housing.

Manufacturers of the speakers are guided by the (IEC) International electrotechnical commission standards. They have what they call nominal impedance, which all the manufacturers have to adhere to. It should be well printed on the housing of the speaker or the speaker. Nominal impedance is the least impedance estimated for a distinctive audio range. What you will occasionally find on the label is 4,8, or 16 ohms. Some manufacturers will label the real measured impedance with its exact listed impedance. Most of the bass tracks frequencies will fall between 90 – 200Hz, the sub-bass could go to as low as 20Hz. The midrange track frequencies range from 250Hz – 2kHz. You should note that the real impedance is close to the values within the range and will upsurge as you increase in the frequency.

Detach the speaker from the housing

For easy access to the positive and negative terminals of the speaker, remove the speaker from its casing. Open the back of the cabinet and unscrew the screws attaching the speaker on the case using a screwdriver. If you a dealing with a loose speaker, this is unnecessary.

Disconnect power directed to the speaker

You will achieve this by removing the connections on the speaker from the amplifier. Be careful to avoid breaking the stands. When you conduct the test without disconnecting the power, you will have the wrong readings. It can also blow off your multimeter. Any wires connected directly to the speaker’s cone or soldered on the speaker’s stand should not be removed.

Set your digital multimeter to measure resistance

Like I stated in my first paragraph, using a digital multimeter to measure resistance is more straightforward and faster; you don’t need to zero the meter. Having selected the item to take action for this case, its the speaker, the next step to make is to insert the probes into their specific sockets. In most cases, a digital multimeter will have more than two outlets. The correct outlets for our instance are the one labeled COM and the one with an ohm sign Ω. After checking that you have the probes in the right socket, turn on the multimeter and select a range. Note that the selected range should be one that will obtain the best readings. To achieve the best readings, you have to choose a value that is less but close to the maximum amount of the range. In our case, get the knob at 200 ohms mark. A multimeter with a setting of 20 ohms will give a more accurate result. If necessary, the range can be changed.  Note that high DC can damage the speaker’s voice coil; hence, avoid multimeters that give too much DC.

Estimating impedance

To clip your speaker with a compatible amplifier, the assumption made after conducting the test is that; the resistance reading recorded on the multimeter is 15% less than the impedance. For example, a reading of 3 or 2.5 ohms on the multimeter will indicate a safe assumption nominal impedance of 4 ohms.

Connect the probes to the speaker’s stands 

To avoid obtaining wrong readings, check and confirm the labeling of the positive and negative positions on the speaker. In the case of soldering, the black colored wire denotes negative, and the red colored wire indicates positive. Connect the probes appropriately and obtain readings. The readings will be in ohms as it’s the resistance caused and not impedance, but you can approximate the impedance.

To obtain the exact impedance, you will need an instrument that will generate a sine wave. A signal generator that will give a sine curve at a given frequency or function generator with a sweep function will work. It is useful to note that some models will not provide accurate impedance. You also can measure impedance by incorporating a room EQ wizard software that will run in a computer to give the sine wave.

I am sure that when you come across an ambiguous speaker, you can determine its impedance. Getting the DC resistance of the speaker and determining the speaker’s impedance is the most straightforward way to go by. It works for most of the speakers, but for the case where a speaker system has capacitive properties, it may not work. The lowermost impedance occurs at a zero-frequency, making it a hazardous estimation. It’s now at this point you bring about the accurate methods. They may seem complicated, but more like the DC round-up method, which will take you less than 30 min to determine the impedance.

The reason why I am concerned about the lowermost impedance is for the good of the speaker. The ohms law states that voltage is equal to current multiplied by resistance. In that case, the voltage power to the amplifier will be constant, so when there is a drop in the impedance, it’s the amplifier to compensate for the drop. It will cause an overload to the amp, and if it fails to provide enough current to drive the speaker, the speaker will distort.