Better Car Audio With Guitar Effects

Automotive sound is a huge deal; for many people, it’s the place to listen to music. Back in the 80s, you were lucky to get anything more than two door speakers in the front of the car. Fast forward to today, and you can expect a 10-speaker system in an up-spec’d family sedan.

[Josh] has a car, and wanted to improve the sound. In particular, the aim was to improve the sense of space felt when listening. A car is a relatively small space, and the driver sits in close proximity to the front speakers, so it’s difficult to get a good soundstage.

[Josh]’s approach was to create a “surround” effect for the car stereo, by feeding a left/right difference signal to the rear speakers. This was achieved by the use of a series of op-amps that buffer and then generate a mono signal that represents the difference between the left and right channel. For optimum results, [Josh] wanted to delay the signal being sent to the rear speakers, with a longer delay making the soundstage feel bigger, as if reflections are coming from farther away in a bigger room. To do this, [Josh] simply hooked up the signal to a Boss DD-3 Digital Delay guitar pedal – an off-the-shelf solution to an otherwise sticky problem. The DD-3 gives [Josh] a variable delay time with reasonably high fidelity, so it’s a perfect way to get the project done quickly.

The final piece of the puzzle is a filter. The difference signal doesn’t actually sound all that pleasant to the ears by itself, especially when it comes to transient high-pitched sounds like cymbals, so a lowpass filter is implemented to cut these higher frequencies down.

[Josh] made everything adjustable, from the filter to the delay, so it’s simple to dial things in until they’re just right, rather than relying on calculation or guesswork. The general idea is to feed the difference signal into the rear speakers at a low enough volume and with a subtle delay so that it adds to a general feeling of being in a larger room with the sound coming from all around, as opposed to listening to very loud point sources of audio.

It’s a cool project that we imagine would be very satisfying to dial in and enjoy on the road. What’s more, it’s a fairly straightforward build if you want to experiment with it yourself on your own car. Perhaps your problem is that you need an auxiliary input to your head unit, though – in that case, check out this Subaru project.

15 thoughts on “Better Car Audio With Guitar Effects

    1. I made precisely that kind of effect: by replacing the original speakers with simple 0.5 W ones, I got a lot of distortion. Very fun, but didn’t last so long….

  1. 30-odd years ago, I would have loved to have had a simple, affordable way of shifting the timing of the signal and being able to move the center stage
    VS just dropping the volume of the speakers nearest to you.
    Actually I wouldn’t mind having that now. Anyone got a low budget way of doing it??
    Ab-so-lut-ly has to handle wave/uncompressed files though!

    But It was a such heady time for being the, rare, yahoo who had built sealed enclose woofer cabs instead of those awful, muddy, ported bass whistles that most people were rolling around with.
    I wanted to be able to hear if the bassist was using flat wound or round.

    The sound difference was worth every minute of wood fitting, math futzing and vehicle interior fitment fiddling.
    Plus there was the need for pulling of wires through tiny crevasses and then soldering connections after fishing the wire. Fun times for the tinkerer in me!

    OoHhhh but it was made the daily drive time so much better.
    …and accidentally turned into quite a nice conversation piece sometimes!
    Some rather fuzzy but warm memories of that period, floating around in the back of my little brain.

    Thousand dollar cassette decks and CDs were just coming onto the scene.
    Sheesh, Somewhere, I think I’ve still got a thick file folder full of old paper brochures, schematics, wiring diagrams and owners manuals for most of this crap.

  2. This sounds like a non-passive and nicely tweakable version of the old “Hafler quad” system. We tried this years ago with a $75 GE portable stereo system and 2 extra speakers – we hooked the “rear speakers” in series and out-of-phase to each other and fed the “+” sides off the “+” sides of the amp.

    It worked surprisingly well on live recordings.

    Note also that this could only be done w/certain amps – there was a serious risk of destroying the output transistors w/others, but I don’t recall the circuitry particulars. The active approach is probably much safer in that regard.

  3. For anyone looking for a plug and play solution: https://www.minidsp.com, The 2×4 HD is the best value, with fir filters, parametric eq, time delay, matrix routing and limiters on every input and output.

    A dsp should honestly be the very first purchase for anyone modifying car audio, second is sound insulation.

    1. Building something similar with a beefy microcontroller or perhaps programmable logic shouldn’t be hard, but as you said that’s a plug and play solution.
      The main advantage of using a DSP is that it can be simply reprogrammed to add effects instead of daisy-chaining actual electronics, but many people think analog is “superior” (whatever that means).

    2. Took a quick look and of course it seems I would need the $500 unit(sigh….), in order to get (all of)the
      individual channels.
      The options for the two way rear channels also perks up a fellows ears.

      No need for any mono subwoofer connections.
      I prefer a good 3 way speaker with decent woofers.

      Now back to my broke-assed whining; :P
      Looks like an interesting motivation to get an old relic motivated for a “carputer”

      The snag of it is: I’m just stuck with a crappy budget
      and scrounging through whatever older PC hardware that comes my way.
      Kind of limits the options when you have to roll that way. :(

      1. You should be able to cobble together a system for under $50 from a 10 year old netbook running Windows XP and a multi channel USB “soundcard” I just got a nice soundblaster for $20 at a thrift store, see them at yard sales as well. Lots of free VST plugins for delay, EQ, etc. which can run in vsthost shell http://www.hermannseib.com/english/vsthost.htm just don’t enable networking on a clean XP install and you are good to go. Cheap 12volt to 19volt adaptor will probably be the only new thing you need to buy.

    1. One must always consider the time investment in designing the support circuitry, creating a PCB, building it into an enclosure, testing and tuning it…

      As someone who designed and built a guitar pedal from the ground up, yes – an op-amp is worth 30 cents. But you can’t do jack with just an op-amp in your hand.

  4. I played with the halfer setup in the 80’s and had a Mr2 with the rear two speakers in this mode with a switch to revert for talk radio and other mono sources. And yes, I thought of putting a rat shack BB delay in the “rear” channel.Most live recordings have some ambient stereo even if most is tracks off the board. If spaced pair live miked or binaural, the sound with this simple setup is quite astounding.

    With every car a quad channel or more delivery system, it’s a shame that virtually all recordings are just 2 channel. Most music from The Decade were mixed down to various wonky 4 channel formats. The discrete quad masters are for the most part are release-able. Some are out there.

  5. Yup. Did that about 25 years ago in a Nissan 300Z. Best car stereo I ever built. Also added precise delays to all channels for perfect arrival times at the driver’s location and used active equalization to get the response flat to within a db or 2. Building a sub-woofer for a car that small and leaving usable luggage space was a challenge. Very large voice-coils on smallish speakers and custom active equalization worked it’s magic, there. Too bad the car wasn’t mine. :-)

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