TOA Canada - Impedance considerations when connecting equipment
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Impedance considerations when connecting equipment

We often get support calls asking about what 900 and 9000 series module do I use to match up to a particular device output impedance.

Basically we need to consider the following simple two points;

  1. Impedance matching of inputs and outputs is only important when transferring power.
  2. When the connection is transferring signal, we only need to make sure the device output impedances are significantly lower than the inputs.

Let's look at the two simple conditions.

Power Transfer

Low impedance speakers, typically 4 to 8 ohms, will require an amplifier of the same output impedance. We say this is matched because the two impedances are very close to the same value and the available current from the amplifier power supply is able to deliver the expected power to the speaker. A large miss-match here (speaker has too high an impedance) and the power capabilities of the speaker will not be realized or worse, the speaker (speaker has too low an impedance) will draw too much current and the amplifier will burn out. Therefore it is important to keep these types of impedance requirements matched as close as possible. Keep in mind that speaker impedances will vary over a fairly large range from the manufacturers stated rating. As an example, an 8 ohm speaker may actually vary from 4-40 ohms or so depending on the frequency sent to the speaker.

Signal Transfer

A typical scenario here is providing a connection between a microphone, analog phone system or audio source device to a mixer input. Typically these source devices will have an output impedance of 600 ohms or so. Since we are not transferring power or large amounts of current, we only need a signal voltage strength representative of the source to arrive at the input, very little current is used. Inputs, because of this type of requirement, usually have a high impedance in the range of 10K ohms and draw very little current. So a good connection would be 600 ohm output to a 10,000 ohm input.

So the next time you need to connect one device to another, consider if you are transferring power or a signal voltage.

Contact our Technical Support Team for more information or with questions. 1-800-263-7639 x 320 or technicalsupport@toacanada.com