Audio Engineering

Speaker impedance

The Music Telegraph | Text 2019/01/21 [14:03]
Audio Engineering

Speaker impedance

The Music Telegraph| 입력 : 2019/01/21 [14:03]

▲ Monitor speakers

© PreSonus

 



The impedance tells you basically how much current will flow through a speaker at a certain voltage. So, ten volts of signal from your amplifier might produce two amps of current through the speaker. Double the voltage to twenty volts and the current will double as well. You’ll get four times the power because the power is voltage times current (2 x 2 = 4).

 

A lower impedance speaker will accept more power. For example, a 4 ohm speaker will extract more power from your amplifier than a 8 ohm speaker, about twice as much.

 

The problem most people have with speaker impedances is how to combine speakers safely without blowing the amplifier or speakers. Here’s how.

 

Speaker Impedance Diagram

There are two ways to connect speakers, series and parallel. See the picture.

 

For connecting speakers in series, the impedances always add. For example, the impedance of the series connection pictured is 16 ohms.

 

For connecting a number of speakers with the same impedance in parallel, the total is the impedance of one speaker divided by the number of speakers. For example, the impedance of the parallel connection pictured is 4 ohms (8 divided by 2).

 

For two speakers of any impedance connected in parallel, use this formula to compute the total impedance (Rt):

Rt = (R1 * R2) / (R1 + R2)

Looks complicated, but it’s not. Some examples follow. All numbers are in ohms.

Let R1 = 8, R2 = 4, then Rt = (8 * 4) / (8 + 4) = 32 / 12 = 2.7 ohms

Let R1 = 16, R2 = 8, then Rt = (16 * 8) / (16 + 8) = 128 / 24 = 5.3 ohms

Let R1 = 16, R2 = 4, then Rt = (16 * 4) / (16 + 4) = 64 / 20 = 3.2 ohms

 

 

Notice that the total for two speakers in parallel is always less than either speaker. That’s why you have to be careful paralleling speakers. You can quickly arrive at an impedance that is too low for your amp to safely drive. **Exerpts from Hank Wallace (http://zerocapcable.com/?page_id=223)

 

 

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