The DIY JBL Tribute "Wide-Baffle" Monitoring Towers


  Project Log: The DIY JBL Tribute "Wide-Baffle" Monitoring Towers

Project Overview
The goal was to build a pair of high-sensitivity, high-power 3-way vertical tracking monitors optimized for mid-bass transient speed and room-filling dynamics in a 950-sq-ft basement shop. The final execution rejects modern "slim-tower" aesthetic constraints, using raw cabinet volume and high-efficiency pro-sound components to capture the effortless "live wall of sound" of vintage flagship studio monitors.
Enclosure Architecture & Mechanical Parameters
  • Cabinet Dimensions: 34.00" Height × 16.00" Width × 10.25" Depth.
  • Internal Airspace: 2.00 cubic feet net volume.
  • Material: 3/4-inch Arauco Premium ACX Plywood panels.
  • Internal Stabilization & Airflow Logic: Symmetrical horizontal internal window shelf braces. Due to the tight physical layout and the long internal PVC tubes taking up substantial internal real estate, the window cutouts were customized to maintain over 25 square inches of open area per brace.
  • Internal Pressure Transitions: This open brace area ensures that the internal cabinet volume scales perfectly across the zones. The bottom woofer partition features more open hole space than the actual port area, while the secondary woofer sits directly within the main port air lane.
  • Acoustic Treatment: Internal walls are mass-loaded using scattered industrial vinyl/carpet tile cutoffs to shatter uniform panel resonance. Asymmetrical internal poly-padding completely covers the back wall, bottom wall, and one side panel to trap parallel axis echoes while leaving the main internal air lanes unrestricted.
  • Aesthetics & Finish: Full-length, single-piece front baffle panels finished in a rugged grey industrial coating. Main boxes have small 1/4 roundover for a clean, utilitarian studio footprint.
Driver Configuration: Standard 3-Way Vertical Tracking
To optimize driver clearances and ensure unhindered airflow within the compact 8.75-inch internal depth, the cabinet layout uses a standard, high-efficiency 3-way alignment tracking from the bottom-up: Woofer–Woofer–Midrange–Horn (WWMH).
  • Tweeter (Top): PRV Audio D280Ti-S 1" titanium compression driver mated to a PRV Audio WG23-25 100° × 40° vertical exponential waveguide. The horn assembly is mounted flat at the top of the baffle centerline.
  • Midrange (Upper-Mid): Vintage JBL LE5-10 5-inch paper cone midrange (scavenged from a classic JBL L150 tower). Due to tight surface boundaries on the face plate, there was not enough room for a rear under-mount layout with a 45-degree chamfer. The driver was cleanly flush top-mounted onto the front baffle face.
  • Midrange Isolation: The JBL LE5-10 sits inside a dedicated, 100% airtight, dead-end 5" × 5" × 5" cube built from 1/4-inch plywood glued to the backside of the baffle plate. This 125-cu-in vault is packed with poly padding to completely swallow the driver’s rear acoustic wave.
  • Woofers (Bottom Array): Dual GRS 8SW-4 8-inch subwoofers (4-ohm nominal) stacked tightly together at the lower half of the cabinet face. The woofers are wired internally in series, presenting a 8-ohm nominal load per tower.
Low-Frequency Aerodynamics & Port Tuning
  • Tuning Frequency: 40.0 Hz—specifically target-tuned for maximum mechanical protection and absolute transient slam in the critical rock kick-drum region (the Neil Peart sweet spot). F3 34HZ
  • Port Design: Three vertical 16.50-inch long round 3" PVC tubes track straight down through the internal window shelf braces. The tubes are sealed airtight using thick beads of 100% silicone caulk to act as permanent vibration dampeners.
  • Port Exits: The ports vent out of the bottom cabinet. The exits are flush-trimmed and routed into smooth, aerodynamic flares using a ball-bearing roundover bit to eliminate boundary wind friction and air chuffing under heavy bass loads.
Ground Installation & Boundary Coupling
  • Terminal Connections: Pure, low-mass utility routing via flush-mounted Nuofany 4.0mm RC copper bullet connectors tapped directly through the cabinet walls, keeping the rear panels 100% flat for optional wall hanging via French cleats.
  • Standalone Floor Stands: Symmetrical 4-inch tall open-front riser pedestals built from Arauco scrap. The stand profile features a 2.25 x 14.5 front opening.
  • Internal Riser Ramps: A simple 45-degree triangular wooden wedge ramp is pinned inside the back lip of the stand. The vertical air columns blasting down from the PVC ports hit this ramp, smoothly turn 90 degrees, and exhaust out the open front mouth onto the floor plane, picking up free boundary gain for massive low-end room coupling.

Ground Installation & Dual-Mode Boundary Coupling
  • Terminal Connections: Pure, low-mass utility routing via flush-mounted Nuofany 4.0mm RC copper bullet connectors tapped directly through the cabinet walls (side or bottom exit). This keeps the rear panel 100% flat, enabling seamless transition between floor and wall deployment.
  • Dual-Mode Deployment Infrastructure:
    • Low Floor-Stand Mode: Enclosures drop straight onto independent, 4-inch tall open-front riser pedestals.
    • High Wall-Mounted Mode: The standalone floor risers unbolt in seconds, allowing the flat rear panels to mount flush against the basement block walls using heavy-duty 3/4-inch plywood French cleats secured with Tapcons.
    •  Crossover Logic
      The system completely abandons power-robbing, phase-shifting passive low-pass inductor coils on the bass lines, running a hybrid active/passive multi-amplifier infrastructure:
      • Passive Filter Network: 
        • Tweeter High-Pass: A 6.2 µF Dayton Audio DMPC film capacitor executes a 1st-order cutoff at 3,208 Hz to protect the PRV titanium diaphragm.
        • Attenuation Controls: Two vintage Alps 7811 40mm wire-wound 8-ohm pots featuring classic dime-slot adjustment dials. The 50 dB logarithmic taper allows micro-turn calibration to perfectly balance the 105 dB horn sensitivity down to a warm, uniform line with the paper midrange.
      • Crossover Network Optimization: As-Built Level Attenuation (L-Pads)
      To safeguard the vintage Alps 7811 wire-wound level pots from high-power thermal burnout, true fixed L-pad attenuation networks were designed and integrated. Unlike standard inline series resistors, these fixed L-pads preserve the required 8.0-Ohm nominal load seen by the first-order filter capacitors, keeping the crossover cutoff frequencies locked within a strict plus/minus 5% design window.
      1. Midrange Attenuation Network (JBL LE5-10)
      • Design Target: -6.0 dB Voltage Drop / 8.0 Ohm Input Impedance / 497 Hz Cutoff.
      • As-Built Topology:
        • Series Arm (R1): Two standard 8.0 Ohm (10W) resistors wired in parallel, yielding 4.0 Ohm / 20W power handling.
        • Shunt Arm (R2): One standard 8.0 Ohm (10W) resistor wired in parallel with the 8.0 Ohm Alps Pot/Driver network, yielding a 4.0 Ohm clamping leg.
      • Performance Metrics: System impedance measures a perfect 8.0 Ohm, 
        • added  12 µF + 5.1 Ohm RC shunt to roll off HF glare.
        attached to midrange feed after crossover.
      2. High-Frequency Attenuation Network (PRV Audio D280Ti-S)
      • Design Target: Deep Pad (~ -20 dB) to tame the ultra-hot 105 dB compression driver down to the 91 dB paper midrange floor / ~3,200 Hz Cutoff.
      • As-Built Topology:
        • Series Arm (R1): One salvaged vintage JBL 7.5 Ohm (10W) power resistor.
        • Shunt Arm (R2): One completely non-inductive Speer 1.0 Ohm (3W) Metal Oxide Film resistor.
      • Performance Metrics: The 1.0 Ohm shunt in parallel with the 8.0 Ohm pot network drops the load leg to 0.89 Ohm. Combined with the 7.5 Ohm series drop, the 6.2 uF capacitor sees an aggregate load of 8.39 Ohm. This achieves a heavy -19.5 dB input attenuation and safely shifts the tweeter crossover point by a negligible -4.6% down to 3,059 Hz (well inside the plus/minus 10% safety margin).
      Project Update: Shifting to Multi-Amp Active Triage (Sony STR-DE715 Sleeper Conversion)
      Overview
      While a basic 2.1 Class-D amplifier board (like the ZK-TB22) provided a decent proof-of-concept,  the system has been transitioned to a fully active, multi-amplifier architecture built around a modified vintage Sony STR-DE715 receiver.
      The video boards were completely gutted from the Sony chassis, transforming it into a high-current, 4-channel discrete Class-A/B power block. The channels are divided as follows:
      • Channels 1 & 2 (Mids/Highs): Driving the JBL LE5-10 midranges and horns.
      • Channels 3 & 4 (Bass Rail): Direct-coupled to the dual parallel 4-ohm GRS 8SW-4 poly woofers (40 Hz ported enclosure).
      Active Crossover Modifications (ESP Project 09)
      An Elliot Sound Products (ESP) Project 09 active crossover board was hardwired directly to the Sony’s internal power supply rails using silver Teflon milspec wire.
      • Topology: 4th-Order (24 dB/octave) Linkwitz-Riley alignment using a cascaded Sallen-Key layout (C and 2C parallel capacitor feedback configuration).
      • Original Component State: Populated with bulk 3.3 kΩ resistors and 100 nF (0.1 µF) KEMET film capacitors, yielding a 341 Hz crossover point.
      • The Component Swap: To raise the handoff cleanly above the midrange driver's 250 Hz \(F_{s}\), 16 core filter resistors were swapped out for 2.2 kΩ units.
      • Final Alignment: 511 Hz @ 24 dB/octave. (Alternative option considered: 2.4 kΩ for a 469 Hz handoff).
      • Level Matching: The active board's output buffers were configured with a +3 dB gain boost on the low-pass channel trimmers to bridge the sensitivity gap between the loud vintage JBL mid/horn top end and the less sensitive GRS poly woofers. Cabinet L-pads handle the final attenuation down to the bass floor.
      System Integration & The Cap-Free Midrange
      Because the active crossover provides an aggressive 24 dB/octave barrier at 511 Hz, and because the vintage Sony chassis features built-in DC protection circuitry, the passive 40 µF high-pass capacitor on the JBL LE5-10 midrange line has been completely removed.
      • Acoustic Benefit: Eliminates passive phase smear and impedance tracking issues near \(F_{s}\).
      • Electrical Benefit: Connects the Class-A/B amplifier stage directly to the midrange voice coil, maximizing the damping factor for lightning-fast transient response and pure, uncolored tracking.
      Upstream Input & DAC Configuration
      To drive the system via a modern streaming interface while maintaining a silent analog noise floor, the source chain is isolated digitally before hitting the op-amp input stage:
      • The Streamer: An onn 4K Streaming Device (2026 Gemini Model) outputs raw audio over HDMI to a TV. The onn remote's volume control is mapped via Infrared (IR) directly to the Sony's motorized volume pot for single-remote convenience.
      • The DAC: The TV passes a fixed digital audio stream via optical Toslink to a Turtle Beach Ear Force DSS outboard DAC.
      • Gain Management: The Ear Force DSS decodes and downmixes the stream, outputting a clean, low-impedance analog signal via a 3.5mm-to-RCA line directly into the ESP board's TL072 input op-amp stage, keeping the front-end entirely clear of clipping.
      Thermal & Mechanical Layout Options
      To keep the discrete Class-A/B outputs cool when driving the heavy 4-ohm bass arrays in a 950 sq ft basement, a 12V (0.24A) Intel CPU fan was integrated into the chassis layout.
      • The Power Source: Driven by an external DC wall wart plugged into the Sony's switched AC outlet, completely isolating the fan's motor noise from the internal audio ground planes.
      • Acoustic & Structural Filtering: Because the 12V fan is undervolted to run on a 5V rail, it is already acoustically quiet but sits near its minimum startup threshold.
        • Option A (Electrical Filtering): A 470 µF to 1,000 µF electrolytic capacitor can be wired in parallel right across the fan motor leads to absorb commutator brush noise.
        • Option B (Vibration Damping): To stop micro-vibrations from telegraphing through the metal chassis, the fan frame is isolated from the heatsink using silicone O-rings.
        • Option C (The 9V Upgrade): Upgrading to a 9V wall wart guarantees a 100% reliable fan startup kick while keeping the fan speed well below the audible noise threshold.

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