offGrid Car Bass

This article offers prescriptive guidance on how to add bass to any vehicle without touching a single car wire, connecting to any car battery, nor having to remove your dash to access the rear of your car stereo/HU (Head Unit).

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Design Goals

Strategically, the Conceptual Design involves the following four (4) items as minimum functional requirements:

#1 - Audio Transmitter/Input Source sends music to one or more
#2 - Audio Receiver(s)/Signal Processors (equipped with a
#3 - Power Supply), where the receiver(s)/processor(s) boost and output bass signals to #4 - Audio Drivers/subwoofers.

#1 is simply the device you play music from (whether streaming Spotify or local music library..).
#3 is simply a shoebox-sized portable power station like a jackery, delta ecoFlow, bluetti.. where an entry-level 300wH model for under $150 USD will supply bass for 25 hours depending on listening habits, setup configuration, choice of amp, subs, and AC-to-DC power adapter/transformer used..).

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Operationally, the Logical Design consists of using your smartphone as audio input to your audio receivers (vehicle stereo/HU AND bass amplifier), which target your speaker drivers for output (those in your vehicle AND subwoofers). The dotted lines illustrate how music is synchronized between car stereo/speakers and amplifier/subwoofer(s).

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Tangibly, the Physical Design comprises the following:

• 
  Smartphone in Driver's Seat
• Vehicle HU/stereo
• Amplifier under Driver's Seat
• Power Source/Supply under Driver's Seat (or Passenger's Seat if insufficient space to accommodate both with ample airflow/cooling..
• Subwoofer(s) Enclosure/Speakerbox in cargo hold/trunk/boot

Using a receiver with built-in Bluetooth reception and signal processor/low-frequency crossover (to filter out high frequencies and send only bass signals) allows a separate amplifier to operate with maximum power efficiency as the amp is spared from needing to boost any high frequencies so all of its amplitude gain targets only the bass range;

PLUS

The electrical current required to support signal processing/crossover-filtering workloads is drawn by the receiver instead of the amplifier.

i wired two (2) 4-ohm subwoofers in parallel by bridging both amp channels as one to essentially halve the impedance presented by the subwoofers (from 4 to 2 ohms), which effectively doubles the output power/wattage of the amplifier as driving a load of 2 ohms is half the resistance of a 4-ohm load.

 

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Requirements

The following list specifies the exact items used in my PoC (Proof-of-Concept) testing and validation; where possible, proper in relevance, and proven to shorten one's TTB (time-to-bass), some affiliate links are provided thru which i may receive undisclosed compensation for sharing (shameless disclaimer :)

• Philips screwdriver - NOT flat-head/blade
  
  
• 25 Ft of 14 or 16 Gauge Wire - if not compact sedan/coupe, i recommend 50' of 14 AWG if one or more of the following considerations apply to you:
  • Rookie/Accident-prone where extra wiring may come in handy
  • Got larger/longer vehicle where insufficient wiring is a deal-breaker (fewer connections/joins = fewer pts of failure, minimized signal degradation, and optimized noise isolation
  • Interested in maximizing bass by locating your subwoofer(s) enclosure in diff corners/dir/aim.. where the optimal location and orientation may cover additional distance/wiring
  • Quad-channel amps require twice the amount/length of wiring as Dual-channel amps because there are two (2) sets of POS and NEG terminals instead of one (1) pair
  • Dual subwoofers instead of single (or single woofer with dual-voice coils) where same as above, ultimately you have double the terminals to wire-up and thus require twice the wiring
  
  
• Power Source - use ur basic shoebox-size rechargeable/portable power station (ex. jackery ecoFlow bluetti..) of 300-Wh capacity or above; i use my Delta EcoFlow2 now, but tested for days on this $120 USD power station
  
  
  
• Power Supply/Transformer/Adapter - Unless your amplifier/receiver accepts AC current or your Power Source supports DC output greater than 12V/50A, you'll need a separate Power Adapter to transform the AC current from your Portable Power Station to the DC current that your amplifier/receiver requires and expects.
  
  
• Audio Transmitter - Simply use your existing smartphone to transmit audio. i played music over wireless Bluetooth using my Honor Magic v3.
  
  
• Audio Receiver(s) - 1st Bluetooth receiver is the HU/stereo in your vehicle (ex. CarPlay, Android Auto, Bluetooth dongle..)
  2nd receiver is the following amplifier located under the Driver's Seat (depicted on right; left is its Pwr Adapter/AC-to-DC Transformer which is plugged into AC port of portable Pwr station)
  
  
  Both amp models support BT 4.0 LE and after initial pairing, they consistently "auto-pair" smartphone-to-amp thereafter w/o fail; u can future-proof ur investment by drawing same total current in watts w/ same sub(s) but +$9 buys some longevity, such as a cooler amp running @ 2 Ω or simply drawing same wattage as before w/ cheaper amp model)
  $38 USD S220HS/TDA7498E
  $47 USD S350HS/TPA3251
  
  

• Audio Driver(s) - i presume any reputable 100-watt RMS sub for <$50 USD suffices for most, depending on one's bassheadedness; to gain shallow-mount options, i used an old 12" Pioneer TSA3000LS4 (400 watts RMS), which is apparently discontinued and superceded by the TSA301D4 with higher watts and lower price than i paid
  
  
  
  
  
• Woofer Enclosure - must match diameter and quantity of the sub u chose above, so i used a $42 USD sealed 12" shallow-mount box but get dual-ported to hit deeper/lower freq's + have addt'l cargo/trunk space to accommodate a bigger speakerbox than single, sealed, shallow-mount..
  
  

Steps

1. If not ready-to-go, 1st mount subwoofer into enclosure with philips screwdriver and connect wires (pos and neg)
2. Ensure the Power Source/Station is juiced up; w/ shoebox station, 300 Wh of run-time @full blast provides 35+ hrs of bass
3. Establish Bluetooth connection(s) from ur mobile phone to both vehicle and amp (#2 and #3 above, respectively).