The feasibility of DIY subwoofers with with bookshelf speakers

[Wodgy]

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Originally Posted by trains are bad But for the port's volume, do you calculate it like the port was a solid cylinder, or is the port volume just the volume of the material the port is made out of?

Ooheadsoo is right... it's the volume inside the port cylinder (though not including the plastic).

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Also how can I find out how much my driver displaces? Guess?

Some people wrap their driver in a garbage bag then dunk it in water to see the displacement, but a safer way is to pour rice into the cone, measure how much rice there is, then that tells you roughly the displacement of the cone. For the motor, calculate it as if it were a cylinder using a ruler (the motor is not a perfect cylinder usually unless it has a rubber cover around it, but the approximation is good enough).

 

[trains are bad]

I built a Cerebrus, roughly inspired by that website, though my driver was a bit different. Reasons being that it's cheap, and it's small.

I'm somewhat happy with it overall. It picks up where my speakers leave off as far as low end extension, but it's true I still don't have a lot of punchiness. It has a huge amount of port noise, but I think I can take care of that by using a port that is flared in the inside as well as the outside. It gets plenty loud enough for my small apt and its contribution to HT/videogames is admirable as well. I'm shocked at how low it will hit. Not loud, but pretty low.

I have it crossed over very low (almost all they way down) because I'm not sure it integrates well with the speakers at higher frequencies. I havn't tried stuffing the ports, what should I use? Quilt batting OK?

Perhaps in the future I will experiment with using a larger sealed subwoofer.

 

[Wodgy]

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Originally Posted by trains are bad I built a Cerebrus, roughly inspired by that website, though my driver was a bit different. Reasons being that it's cheap, and it's small.

Fantastic -- you don't waste any time

That's impressive for DIY. I'm still working on finishing a pair of speakers (Zaph's Waveguide TMMs) that I started in April, and my last pair (MBOW1s) took me about nine months to finish.

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I'm somewhat happy with it overall. It picks up where my speakers leave off as far as low end extension, but it's true I still don't have a lot of punchiness. It has a huge amount of port noise, but I think I can take care of that by using a port that is flared in the inside as well as the outside.

You may want to play with the port length to adjust the punchiness. For a punchy sound, you need a bit of a hump somewhere in the 65-80 Hz range. This is one reason incidentally why I don't recommend sealed subs with Q under 0.707. Port noise is often an issue with ported designs. The internal flare will help, increasing the diameter will help too.

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It gets plenty loud enough for my small apt and its contribution to HT/videogames is admirable as well. I'm shocked at how low it will hit. Not loud, but pretty low.

Sounds good.

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I have it crossed over very low (almost all they way down) because I'm not sure it integrates well with the speakers at higher frequencies. I havn't tried stuffing the ports, what should I use? Quilt batting OK? Perhaps in the future I will experiment with using a larger sealed subwoofer.

I would stuff the ports then try crossing a little higher. Use tightly rolled up socks. Sometimes you can find plumber's rubber "corks" at hardware stores that fit your port, those work great too, but they can be a pain to find. Quilt batting is probably fine too, just roll it up tightly. The nice thing about a smaller driver sub is that distortion is low on the top end, so it is possible to cross a little higher than one might ordinarily do.

 

[trains are bad]

Well, in keeping with my previously stated audio philosphy, it ain't pretty, just raw mdf with visible screws and glue joints...but I listen with my eyes closed anyway

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I'm going to order some more port tubes to do an internal flare right now actually. I'm fairly confident that will fix it. If it doesn't WinISD shows that two 1" ports at the same tuning have a much lower 'mach factor', but I'm not sure if running 1" ports is ever done...PE doesnt' have any, but there is always pipe.

 

[ooheadsoo]

1 inch sounds like it'll completely restrict the airflow to the point where it'd be acting almost like an aperiodic design.