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Choose 2 Channels or 4 Channels – Speaker Amplifier Buying

Choose 2 Channels or 4 Channels

How do I choose 2 channels or 4 channels when I decide I need an amplifier for speakers?

When you’ve committed to upgrading your sound system this question might have been very sharp and clear in your mind.

Let’s dive into a real world example. This could happen if you talked with a sales person and they go to the effort of trying to understand your motives. Often there is a hidden complication or twist that comes from a difference of understanding what can be done.

Tip for Better Communication: Ask open-ended questions when you’re in discovery mode.

This is pulled from an online discussion. Jim is the inquisitive shopper.

Overhead drawing of car and 4 door speakers Kevin Hulsey

Jim: is there a way to wire the left door speakers together such that they run as a stereo channel off one input, or is this only for subwoofers?

Barry: Two doors, two speakers wired together means you have one input which cannot be stereo. It doesn’t matter what type of speaker it is, that is going to result in one channel of sound.

In this example the same input signal will be played back from the front left door and the rear left door. Is that what you want?

What do you want?

“the same input signal will be played back from the front left door and the rear left door.”

Jim: Isn’t this how it already is since all the speakers are mono?

It was mostly just hypothetical because I wanted to know if I should buy a 2 channel or 4 channel amp, but I understand now. Appreciate the help!

line drawing of Mono vs Stereo Signals
Mono vs Stereo Signals sent to two speakers
Barry: No. I think the confusion is because we’re using a prefix, “Mono”, to mean one, yet we’re talking about different parts of the signal chain.
The input starts with the source, or the program material. We assume you’re playing music that’s made to have Left and Right channel separation(Stereo sound).
The next step is a division of this signal that takes place at the radio. I don’t know what radio and vehicle sound system you have so I’m making an assumption that it’s the standard radio with 4 speaker outputs, Front Left, Front Right, Rear Left and Rear Right.
For the pleasure and comfort of the passengers we have all 4 speakers on 4 separate outputs. By adjusting the Balance and Fade controls in the radio you can find that you will be able to play a mix of as few as 1 speaker up to all 4, redirecting the emphasis or loudness throughout 4 quadrants of the interior.
Let’s go back to the music, which we assume has Left and Right separated, in Stereo sound. The radio sends the Left channel sound to both the Front Left and the Rear Left speakers, and so on for the right side. For your decision, we’re not done.

Choose 2 Channels or 4 Channels?

Why do we buy a separate high power amplifier for speakers?
  • Greater clarity
  • More power to better drive less efficient aftermarket speakers
  • and a bit more loudness and fullness to the sound.

Ask yourself two questions

  1. Do I want all 4 speakers, front and rear, to get these improvements?
  2. Is it possible I mainly want to improve the sound where I sit?
Choosing a 4 channel amplifier is usually a safe decision. Some car amplifier manufacturers don’t even offer 2 channel amplifiers, as the market has dictated they aren’t in high demand.
Normally we can still use a 4 channel amplifier as a 2 channel amplifier.
If you begin using the 4 channel amplifier as a 2 channel amplifier that offers an upgrade path.
Sometimes it makes sense to use the 4 channel amplifier as a 3 channel amplifier. 
Is it a horrible idea to have more options with one purchase? Talk with your sound system designer. 
Further reading:

Barry Schanz
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