vineri, 16 ianuarie 2009

Constructie SubWoofer




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.

Results:

  • 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

Physical length 1.6 m
Physical fs at 1/4 wl 54 Hz
Acoustic 1/4 wl (measured) 2.13 m/40 Hz
Measured c' 0.75c
(speed of sound in the line)
Begining cross section 838 cm^2
Terminus section 262 cm^2
Taper 1.6 : 0.5 Sd
First odd harmonic 140 Hz
(null of driver, max of terminus)
Max of terminus 90 Hz
(level of the terminus is 3 dB below the driver )
Stuffing 50 mm Rockwool


udax PR 330 M0*

Sd 538 cm^2
Vas 264 liters
Cms 6.5 e-4 N/m
Cas 1.9 e-6m^5/N
Mms 52 g
Fs 27 Hz
Bl 13.6 N/A
Re 5.8 Ohms
Qms 6.7
Qes 0.28
Qts 0.27
Pmax 150 Watts
Xmax +/-4 mm

* Audax HD 33 S 66 replaced by PR 330 M0



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