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The Beer Fridge

The "Beer Fridge" was my first subwoofer and was nothing fancy. Using Jaycar's 80W amplifier it performed quite well but the single port was a bit noisy when pushed hard.

Photo - Beer Fridge Subwoofer

The 80W amp has +4db boost @ 35Hz which gives around 105dB Peak SPL, which is enough to enrich your Home Theatre experience

Graph - Peak SPL

 

The single 100mm port keeps Air Velocity below WinISD's recommended limit of 17 m/sec.

Graph - Vent Velocity

 

The ends of the port were hand sanded for a flare of approximately 5mm, which was not sufficient to prevent "chuffing". This could have been avoided had Flare-it been available at the time. The grey line indicates actual velocity and the blue line shows where audible noise occurs. At full power, "chuffing" is indicated between 20hz and about 32hz.

Flare-it screenshot 5mm flare

 

Flares of at least 30mm radius would be needed to silence the problem. Since this size is beyond DIY efforts, a better solution would have been to use a pair of smaller ports

Flare-it screenshot 30mm flare

 

Cone excursion at low frequencies can be a problem at full volume. The red line is the Xmax of the driver, which shouldn't be exceeded by more than around 10%. This unit does not run a hi-pass filter, but could use one

Graph - Cone excursion

 

I wasn't quite sure what effect tuning frequency would have on the sound, so I made up a simple variable length port. This was adjustable from 190mm to 280mm, letting me try frequencies from 30.4hz to 26hz. I eventually decided 215mm / 29hz was the way to go, replacing the temporary port with a fixed length

Variable length port

 

It's funny how the wheel turns. This sub was bought by a friend, which financed the next one. Several years later, we did a deal on a better box (see the Slim-Jim project), and I was left with this enclosure. After removing the port, the size was 100 litres, which is perfect for use in round two of my Flare testing experiments.

 

Project file for WinISD Pro 0.50a7

The next speaker tackles port noise and box size

 

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