MOD-08CABINET DESIGNPAGE 8 OF 14

Thiele-Small Speaker Cabinet & Port Calculator

Design Sealed (Acoustic Suspension) and Vented (Bass-Reflex) enclosures, Helmholtz port tube lengths, and Golden Ratio box dimensions.

OSC-1: 440 Hz

BENCH PRESETS:

ALIGNCabinet Enclosure Alignment

F_SDriver Resonant Frequency (f_s)

18 HzEBP ≈ 108 (Favors Vented)90 Hz

Q_TSDriver Total Q Factor (Q_ts)

0.2 Q0.65 Q

V_ASEquivalent Compliance Volume (V_as)

5 L160 L

PORT-DPort Internal Dia

3.5 cm15 cm

PORTSPort Count

CABINET MECHANICAL BLUEPRINT & LOW-FREQUENCY ROLL-OFF CURVE

Golden Ratio Box: 55H × 34W × 21D cm

Internal Volume Vb

39.2Liters

1.38 Cubic Feet

-3 dB Cutoff (f3)

37.1Hz

Half-Power Bass Limit

Port Tube Length

20.1cm

7.9 in (1× Ø7.6cm)

Tuning Freq (Fb)

36.8Hz

55×34×21 cm

TECHNICAL MANUAL // MOD-08 REFERENCE SHEET

How It Works & Acoustic Engineering Principles

#thiele-small#bass reflex#port length#sealed box#qtc#vas#helmholtz

GOVERNING ELECTRO-ACOUSTIC EQUATIONSI / IMPERIAL VERIFIED

V_b(sealed) = V_as / [ (Q_tc / Q_ts)² - 1 ] | L_port = [ (23562.5 × D² × N) / (V_b × f_b²) ] - (k × D)

V_asDriver Equivalent Compliance Volume (Liters)

Q_ts / Q_tcDriver Total Q factor (Q_ts) and Target Sealed System Q (Q_tc, ideally 0.707)

f_b / V_bPort Tuning Frequency (Hz) and Net Internal Cabinet Air Volume (Liters)

D / kInternal Port Diameter (cm) and End-Correction Factor (k ≈ 0.732 for one flanged end)

Physical Mechanism & Theory

An unmounted woofer suffers from acoustic short-circuiting as rear-wave pressure wraps around the cone to cancel front-wave bass. A Sealed enclosure traps the rear wave in an airtight air spring; designing for Q_tc = 0.707 (Butterworth alignment) yields maximally flat bass extension paired with crisp, Critically Damped transient impulse response.

A Bass-Reflex (Vented) enclosure uses a tuned port tube to create a Helmholtz resonator excited by the rear of the cone. Near the tuning frequency f_b, the air mass inside the port radiates in phase with the front of the woofer while dramatically reducing cone excursion, extending the -3 dB cutoff (f_3) up to half an octave deeper than a sealed box.

Studio Bench Rules of Thumb

01.Efficiency Bandwidth Product (EBP = f_s / Q_es): Drivers with EBP < 50 excel in sealed boxes; drivers with EBP > 90 thrive in vented bass-reflex enclosures; EBP 50–90 works well in either.
02.Watch Port Air Velocity (Chuffing): Use a wide enough port diameter so air velocity stays below 17 m/s (5% of Mach 1) at full excursion to prevent audible wind turbulence.
03.Keep Port Clear of Rear Wall: Leave an internal clearance behind the port opening equal to at least one full port diameter (D_port).