Brolin's Sub Woofer Page

Background  Solution  The result  Technical data for the sub  Pictures  Technical data for the woofers used  Loudspeaker links and email

Background To top of page

I have a pair of speakers called F3-Lyd Trapez-X, a 3-way Danish speaker design from 1987 with an excellent sound reproduction. The Trapez speakers are driven by two power amplifiers each 250W r.m.s.   The frequency response of the Trapez-X is around -3dB down at 50 Hz and below at 30 Hz the speaker is -10dB down. A 10" woofer from Focal is used and the woofer has a free air resonance Fs=24 Hz. I like very low and powerfull bass reproduction so assistance in the lower end was needed.

F3 Trapez-X, an oldtimer still going strong !!!

Solution To top of page

I surfed round the Internet and after a few hours i found the The Subwoofer DIY Page, a serious loudspeaker page with lot of formulas and design hints. I bought two woofers equal to the ones in my Trapez-X speakers and designed (all the formulas was put into an Excel worksheet) a ported speaker with the two woofers mounted in an isobaric configuration to reduce cabinet volume to the half . A separate power amplifier is used to power the two woofers and an active crossover is used at the power amplifier input. The woofers used have a low equivalent volume resulting in a small box with a very good bass reproduction. Woofers with a higher equivalent  volume (such woofers are often less expensive) can also be used, but the goal was a relative small box. 

The result To top of page

The reproduction of the music has got i new dimension in the lower end. Now i can feel the music even at lower volumes. The difference between CD's with sub bass or not can now be heard. Just to mention a few of my CD's, where the sub really makes a difference :

• - Mark Knopfler - Gold heart
• - Mark Knopfler - Wag the dog
• - Eric Clapton - Unplugged

Technical data for the sub To top of page

• - Design: Ported System, 2 ports, isobaric configuration
• - Internal volume: 35 litres
• - Port diameter: 60 mm (2,36 inches) (each port)
• - Port length: 220 mm (8,66 inches)
• - Frequency response: 30-60 Hz - 3dB (with crossover), -10 dB down at 20 Hz
• - Active crossover: low pass at 60 Hz, 36dB/octave
• - Amplifier: 2x120W r.m.s.
• - Outer dimensions: 350x350x550 mm (13,8 x 13,8 x 21,6 inches)

Pictures To top of page

The Sub woofer without front protection. Only one of the woofers are visible the other one is hidden in the cabinet.	The Sub woofer with front protection.	In this position (corner placement on the floor with the front backwards with 3-4 inch. to the walls) the bass coupling to the room is maximum.

Technical data for the woofer units used To top of page

The woofer units used are equivalent to Focal 10 C 5411 DB but only with one voice coil.

Loudspeaker links and email To top of page

The Subwoofer DIY Page

Speaker online - Germany

Jamo - a Danish manufacturer of loudspeaker boxes

Vifa / Scan Speak - a Danish manufacturer of loudspeaker units

Focal - a French manufacturer of loudspeaker units

Visaton - a German manufacturer of loudspeaker units

Last revised: 25122003