Ohmic Audio Labs Knowledge Base

🔧 INSTALLER LEVEL: T/S Parameter-Based Selection

The Q-Based Selection Matrix

Flowchart showing how Qts ranges guide sealed, ported, bandpass, or avoid decisions, with Fs, Vas, Xmax, sensitivity, and system goals used as follow-up checks
Start with Qts to narrow the enclosure family, then sanity-check Fs, Vas, excursion, and packaging before you decide on the final volume and tuning. This keeps the box recommendation tied to the driver's real behavior instead of marketing labels.

Qts determines the fundamental character of the driver and the enclosure type that will get the best from it:

Qts below 0.30: Highly damped. These drivers are designed for ported or bandpass enclosures. In a sealed box they produce less output and excessive damping — tight but thin. Think of competition-grade woofers and high-efficiency pro-audio subwoofers.

Qts 0.30–0.50: The ported sweet spot. In a properly tuned vented enclosure these drivers produce excellent extension and efficiency. Sealed works too — produces a higher Qtc but acceptable performance. Most "audiophile" subwoofers targeting music reproduction fall here.

Qts 0.50–0.70: Flexible. Either enclosure type works. Sealed produces a Qtc near 0.707 (Butterworth alignment) with moderate box volume. Ported works well too. Beginner-friendly territory — harder to go badly wrong.

Qts 0.70–1.0: Sealed only. Ported alignment becomes difficult — the driver's light damping combined with ported loading creates a peaked, one-note response. Sealed box air spring provides the additional damping needed. Common in budget subwoofers with lightweight motors.

Qts above 1.0: Sealed in small box. These drivers are effectively car speakers with heavy cones, not subwoofers. Performance as subwoofers is limited. Avoid for serious builds.

Matching Fs to Enclosure Tuning

The relationship between Fs and enclosure tuning determines frequency extension:

Sealed: System resonance Fc is always above Fs. The smaller the box, the higher Fc climbs. For deep bass extension: use a driver with low Fs (25–35 Hz) and a box large enough to keep Fc near Fs.

Ported: Port tuning frequency Fb is typically set to 0.7–1.0 × Fs. Setting Fb too far below Fs extends apparent bass but reduces output and increases excursion at Fb. Setting Fb equal to or above Fs maximizes efficiency but sacrifices deep bass extension.

Rule of thumb for music reproduction: Target Fc (sealed) or Fb (ported) at 35–45 Hz for full musical bass. Home theater and demo systems can target 25–35 Hz with appropriate power.

Rule of thumb for SPL competition: Fb = test frequency ± 2 Hz. Everything else is optimized around maximum output at that one frequency.

Sensitivity and Power Matching

Comparison chart showing tradeoffs between SPL competition subs, sound-quality or music-focused subs, and budget daily subs, including enclosure bias and power-demand notes
This comparison keeps the decision practical: target output, enclosure bias, and power demand all move together. The right woofer is the one that fits the build goal, not the one with the most dramatic advertising.

The power required to produce a target SPL is directly governed by sensitivity:

P_required = 10^((SPL_target - Sensitivity - 20×log(1/d)) / 10)

For a 12" driver with 87 dB sensitivity at 1W/1m, targeting 110 dB at 1 meter:

P = 10^((110 - 87) / 10) = 10^(2.3) = 200W

For a 12" driver with 92 dB sensitivity, same goal:

P = 10^((110 - 92) / 10) = 10^(1.8) = 63W

The 5 dB sensitivity advantage requires only 1/3 the power. This is why competition drivers optimize sensitivity aggressively, and why "400W RMS" doesn't mean "loud" if sensitivity is low.

Real-World Driver Recommendations by Category

These are example drivers as of early 2025. Always verify current specifications.

ENTRY LEVEL MUSIC (Qts 0.5–0.7, sealed or ported, $50–150):

MID-RANGE SQ (Qts 0.4–0.6, music reproduction, $200–400):

SPL COMPETITION (Qts 0.3–0.45, high sensitivity, high power, $200–800+):

ULTRA-COMPACT (Qts 0.6–0.8, very small sealed, $100–250):

COMPETITION SPL EXTREME (Qts 0.25–0.4, bandpass or massive ported, $500–2000+):

Key takeaway: Match Qts to enclosure type first, then power handling to amplifier, then price to budget. A $150 driver in the correct enclosure outperforms a $400 driver in the wrong box.