A Transmission Line Subwoofer

Designed & Built by Yves Mattei

This design is a single fold transmission line using a 330mm (12") Audax driver (HD 33 S 66). The port loads out the back. Very little stuffing is used.

It as a SubWoofer in a
Home Theater System with an active 4th order low pass at 70 Hz. Since the cross-over is low, upper resonnances ( > 150 Hz ) are not a big problem. This line is not optimized for higher crossover frequencies.


  • From 50 Hz to 100 Hz driver and terminus are in phase (+/-10°)
  • The - 3dB point is near 45 Hz
  • At the Fr of the line (40 Hz) driver and terminus are 90° out of phase
  • Below 40 Hz they are out of phase

The stuffing could have be better optimised, reducing the effect of the null at 140 Hz.

If I were to do it again I'd make the terminus a bit larger. (or use the line for a 10"/ed)

Since originally putting this project together more stuffing has been added making this a true TL. The preliminary results are that the stuffing improves the performance of the speaker. (details as they become available/ed)

Line Configuration
  Audax PR 330 M0*
  Physical length 1.6 m     Sd 538 cm^2
  Physical fs at 1/4 wl 54 Hz     Vas 264 liters
  Acoustic 1/4 wl (measured) 2.13 m/40 Hz     Cms 6.5 e-4 N/m
  Measured c' 0.75c     Cas 1.9 e-6m^5/N
  (speed of sound in the line)     Mms 52 g
  Begining cross section 838 cm^2     Fs 27 Hz
  Terminus section 262 cm^2     Bl 13.6 N/A
  Taper 1.6 : 0.5 Sd     Re 5.8 Ohms
  First odd harmonic 140 Hz     Qms 6.7
  (null of driver, max of terminus)     Qes 0.28
  Max of terminus 90 Hz     Qts 0.27
  (level of the terminus is 3 dB below the driver )     Pmax 150 Watts
  Stuffing 50 mm Rockwool     Xmax +/-4 mm


* Audax HD 33 S 66 replaced by PR 330 M0


  1. Testing: Monacor MCE2000 electret capsule mounted in an amplifer g=100 that I built. I used a sinewave generator and a oscilloscope.
  2. The data on the phase was made using comparative measures with the dual trace scope

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