This blog post is an account of how I built and tested another subwoofer to compliment the rest of the system that I am running. I am no expert and am open to constructive criticism. Keep in mind that I have a very mild budget.
I wanted to be sure that the new subwoofer was going to add value to the system so I decided to do a little testing of the system before I built it.
The system is a 5 speaker system all running from a Linux machine (plays music movies etc)
I found a command line tool that allowed me to test each speaker individually at specific frequencies. The tool is called “speaker-test” and is available on the Ubuntu OS.
Here is an example:
speaker-test -D surround50:SB -f 150 -t sine
This command creates a sine wave at 150 Hertz using the surround50:SB device on the Linux machine. It cycles between all the speakers in your system one by one. If you are not sure what the audio device is you can find out by using the following command. aplay -L. This will list all the devices. I had to modify the listing a little for the speaker-test command to understand what device I was using. For example the device “surround50:CARD-SB,DEV=0” was listed. I changed that to “ surround50:SB” when I used the speaker-test command.
If you need to test each speaker individually without cycling you can use the -s flag.
So how do you know what dB they are functioning at? I used my iPhone. Probably not the best DB meter available but hey I have an iPhone and $2 to spend on an app. I downloaded this app. http://www.studiosixdigital.com/spl_meter.html.
I found that there was plenty of low end coming from the original subwoofer but no real punch around the 60 to 100 Hz area.
The enclosure I made was just a simple sealed enclosure as the gains in building a band pass or ported box (which I have already done) did not seem to be worth the effort and expense considering what I was after with this particular enclosure.
I managed to produce a nice punchy sound where it was lacking. All in all this compliments the system quite well and produces a more naturally sounding bass note where it counts.
I did notice that the sealed enclosure seemed to produce a pretty flat dB level from 100 Hz up to at least 1000 Hz so I installed a 12dB/Octave low pass filter to solve that problem. I used two LF1334 inductors in series along with a 400 micro fared capacitor rated at 100 volts. For more info see page 398 of the 2009 Jaycar catalog.
End result good bang for my buck 
UPDATE 20091223… I decided that I would go a bit higher again in frequency cut off so I grabbed a a single LF1336 and a 300 micro fared capacitor to replace the original parts as listed above. This now makes the frequency band of this sub the entire Bass Guitar. Much nicer sound now.
