When adding loudspeaker elements to your embedded system it can be nice to match the impedance to your amplifier to get as much of the energy created in your amplifier out through the speakers.
This was a challenge we faced when building this installation last spring. We wanted to use the four speaker elements in the picture below connected to one of these. But how should we connect them to the amp to match the impedance?
Speaker elements with 8Ω impedance
In this post we’re going to give you a brief overview over how to do this.
CLARIFICATION
This is a post about how to transfer as much as possible of the energy created by the amplifier over to the speaker element. This does NOT say anything about the possibility to connect different kinds of amplifiers to different kinds of speaker elements. Remember to always follow your amplifier’s loudspeaker impedance specifications.
Matching the Impedance
All amplifiers and speakers has an impedance. For an optimal power transfer the amplifier’s impedance should be equal to the total impedance of the speaker elements.
- If the speaker impedance is too low, the amp will have to work too hard (i.e. deliver too large current) and possibly overheat.
- If the speaker impedance is too high, the amp will be unable to deliver full power, but this will not be dangerous to the equipment.
Read this article for a more detailed insight into audio-related impedance.
Calculating the Speaker Impedance
Some amplifiers have a single mono channel, many have two channels (stereo) and some have many channels (7.1 surround and such). When calculating speaker impedance, we work on a per channel basis, making the left and right channels on a stereo amp independent of each other.
Calculating total speaker impedance is equivalent to calculating total resistance in an electrical circuit. We will go through it anyway.
Series Connection
Two speakers connected in series to a single channel amp (source: http://www.bcae1.com/spkrmlti.htm)
When connecting your speakers in a series scheme you simply add each speaker’s individual impedance to get the total impedance. The example above would work well if you have an amp with 32Ω output impedance and two speakers with 16Ω impedance each.
Parallell Connection
Two speakers connected in parallel to a single channel amp (source: http://www.bcae1.com/spkrmlti.htm)
In parallel however, the total impedance decreases when adding more speakers to the circuit. The following equation is used when calculating the total impedance in parallel connection.
where R1 and R2 are the impedances of each speaker.
If we were to reconnect the two speakers in the series example in parallel instead, the resulting impedance would be 8Ω instead of 32Ω. So be careful when connecting speakers in parallel. The impedance can quickly become too low for the amp!
A Summary
Make sure the total speaker impedance isn’t lower than the amp’s output impedance. It can be higher, but then you might struggle with getting the volume you want.
To revisit our own challenge with our four 8Ω speakers and our two channel 4Ω impedance (per channel) output amp:
By connecting two speakers in parallel on each channel we will match the impedances perfectly, thus getting the most out of our amp while still staying safe.
Overview of how we connected our 8Ω speakers to our 4Ω amp (source: http://www.bcae1.com/spkrmlti.htm)
For more connection examples and several calculators, visist this excellent page.
