Hi Sound System Team

I realise this project might sits on the boundary between home and pa but I'm posting here as I think you guys will have more wisdom on the proposed tuning freq than the home system builders. Please advise otherwise if appropriate.

To avoid a load of newbie questions I've been working with CoPilot, who of course has learnt a whole lot from Reddit! Guess we'll see if it's given me good advice, I'm here to get a human expert sanity check.

I look forward to hearing from you and thanks very much in advance :-)

Requirements

• Use case: Subwoofer for a 10 x 8m shed (aka The Techno Shed) system used mostly at moderate volume, with occasional party‑level SPL.
• Music focus: Techno, house, minimal, electro, some pop and rock — strong energy in the 45–80 Hz band.
• System integration: Must work cleanly with Peavey PV1500 (40 Hz low‑cut, 100 Hz crossover) and Mackie C300 tops which I own already.
• Room behaviour: Avoid boominess and excessive low‑end buildup in a small reflective space.
• Build practicality: Must be easy to construct from standard sheet material with simple bracing and a slot port.
• Reliability: Must control cone excursion at party SPL with the PV1500’s available power.
• Warmth at low volume: Sub should sound full and present even when played quietly.
• Top‑end support: Sub must fill the missing low‑end below the Mackie C300’s natural roll‑off (~70 Hz).

Brief specs: Mackie C300 tops

• Type: Passive 12" + horn
• Power: ~300 W program
• Sensitivity: ~99 dB
• Low‑end roll‑off: Steep below 65–70 Hz
• Behaviour: Loud, clean, but no real bass → requires a sub.

Brief specs: Peavey PV1500 amplifier

• Power: ~500 W/ch @ 4 Ω, ~300 W/ch @ 8 Ω
• Filters:
  • 40 Hz low‑cut (always on),100 Hz crossover (optional)
• Behaviour: Strong mid‑bass power, reliable, ideal for a single 18" reflex sub. To power both tops and sub.

Design decisions

• Driver selection:
  • Chose Fane Colossus 18XB for high sensitivity, strong motor, good excursion handling, and proven reflex performance.
    • Availability in the UK is essential
• Cabinet volume:
  • Selected 160 L net as the optimal balance between tight control (smaller boxes) and warmth/weight (larger boxes).
• Tuning frequency:
  • Set tuning at 41 Hz to align with the PV1500’s 40 Hz high‑pass filter — avoids wasting power below the filter and keeps bass tight.
• Port type:
  • Chose a wide slot port for low air velocity, no chuffing, and easy DIY construction.
• Excursion management:
  • Slightly smaller volume + 41 Hz tuning chosen to keep excursion safe at high SPL with the PV1500.
• Integration with tops:
  • Designed bandwidth and tuning to hand over smoothly around 80–100 Hz with the Mackie C300s.
• Prioritised punch over depth:
  • Focused on the 45–80 Hz region rather than chasing sub‑30 Hz extension that the PV1500 filters out anyway.

Brief specs: Fane Colossus 18XB driver

• ~ £280
• Power: 1000 W program
• Sensitivity: ~98 dB
• Fs: ~35 Hz
• Xmax: ~7.5 mm
• Behaviour: Punchy, efficient, excellent in 140–200 L reflex boxes.

Design

• Cabinet type:
  • Simple rectangular reflex enclosure, ~160 L net internal volume.
• Tuning:
  • 41 Hz via a wide slot port sized for low turbulence.
• Bracing:
  • Window brace + side‑to‑side braces to stiffen panels without obstructing airflow.
• Materials:
  • 18 mm plywood for strength, weight, and ease of construction.
• Acoustic behaviour:
  • Tight, controlled bass with strong punch in the 45–80 Hz band.
  • Warm at low volume, clean at party SPL, minimal boom in small rooms.
• System match:
  • Designed specifically to complement the PV1500’s filters and the Mackie C300’s natural roll‑off.
• Practical build:
  • All panels fit cleanly on a standard 2440×1220 mm sheet with straightforward cuts.