Rear Speakers

I’ve been known for saying “Rear speakers are a Commie plot against our North American way of life.” 

My good friend Andy Wehmeyer is known for saying “Rear speakers are a capitalist plot”.

We aren’t disagreeing. It might sound as if Andy and I are disagreeing – but we’re really not. We’re speaking to different audiences and for different reasons. 

First off, we are both using hyperbole – exaggeration for effect.

When I say rear speakers are a commie plot, I’m primarily speaking to consumers – consumers who often grew up in the rear seat of a car with by-nines in the back deck behind their heads, and tiny speakers up front. Those consumers identify rear speakers as the loud ones, and the ones which play all the bass. Since they want their system to play louder, and to have bass, their expectation is that rear speakers are an important part of this goal. Modern cars, though, either have the same-size speaker all the way around, or they have larger speakers up front than in the rear. This helps keep the front-stage effect working – but either way, it’s important to me to explain to a customer why the rears won’t dominate. Using hyperbole lets me get the consumer’s attention so I can explain my point more effectively.  

When Andy says that rear speakers are a capitalist plot, Andy is not speaking to consumers. He’s speaking to the industry – to us. He’s trying to keep us from being elitist snobs who won’t even leave rear speakers connected if the clients want them to be, and won’t sell rear-speaker upgrades no matter what. He’s wanting us to realize that rear speakers can be used without ruining the front-stage stereo presentation we work so hard to deliver.

Let’s assume that we are starting with a system design which includes $250 front 6.5-and-tweeter components, $150 rear coaxials, a digital sound processor, and a five-channel amp powering them and a trunk sub. 

Andy and I completely agree on how to improve this system without spending more money: go with $500 front components, leave stock rears on stock power, spend the rear-speaker install dollars on running new wires to enable the fronts to be powered actively, and then go with a fully-active scenario (tweeters on amp channels 1+2, midranges on amp channels 3+4, sub as it was on channel 5).

There’s no appreciable difference in the final cost to the consumer (basically, it’s the cost of the speaker wire). What has happened is, the bulk of the dollars are spent on the front stage – where the improvement is really obvious to our ears – rather than with upgrading rear speakers, which aren’t an obvious upgrade. 

So how do we use rear speakers without damaging the stereo presentation?

Do I leave OEM rear speakers connected? Do I sell new, upgraded rear speakers when requested? Yes, and yes. 

Do Andy and myself use several techniques to prevent rear speakers from damaging the front stereo image? Yes! Here’s my list.

  1. Make sure they aren’t too loud. That can be controlled via input gains if the rear speakers are amplified, through your DSP levels if the rears are managed by a DSP, or with the OEM fader if they are still connected to stock power. If your processor is managing the rear speakers, you can correct that in your processor. Note: If your client requires the system to be really loud, loud rear speakers may be a critical part of that.
  2. Use time delay – especially if they have to play loudly. If your client needs an insanely loud system, make sure the rears are amplified and on DSP-managed channels so you can apply time delay. Otherwise, the rears will interfere with the front-speaker frequency response.
  3. Send the rear speakers a difference signal. This means that both rear speakers play the same signal, and it consists only of sounds not shared by both channels. It’s only sounds which are completely on the far left, or completely on the far right. Anything shared by both channels is supposed to be in the center of the stage, and removing all that content keeps rear speakers from dragging the stage aft. The poor man’s difference signal is simply wiring the rear speakers out of phase. It’s not as effective, and I reserve this method for stock speakers driven by stock power. Notes: If you need the rears to help with volume for clients who want a lot of it, this may not give you the output you need. Also, if your OEM system has parking sensors which place the beep directionally, make sure that the two center sensors aren’t muted when using this approach.
  4. Make up for OEM locations. I’ve see rear-door tweeters mounted high in the door panel – which then get a straight shot at the driver’s left ear. In that case knocking the rear treble down with an EQ might be needed, or in some cases unplugging that rear tweeter might be needed. When upgrading rear-door speakers, use coaxials even if the stock provisions support a tweeter. Some rear-deck speakers are much louder on one side than the other, because of one headrest. That’s tough to correct without DSP management.
  5. Retain the OEM upmixer. With upmixed systems, the rear speakers are used to make the car seem larger than it is, by playing significantly-delayed sounds, and often deriving those channels through some form of difference calculation.
A left-right difference signal

The takeaway: worry less about whether or not Andy and I are disagreeing, and more about what your client’s expectations are – both when they walk in (before you make your sales presentation), and when they arrive to pick up the vehicle. Bias your budget allocation towards the front, get the best stereo sound from them you can, and use the above techniques to keep the rears at their best.