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12" Woofer Sonotube Subwoofer
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Introduction
Design
Results
Future Plans




Introduction

Click Here for Larger ImageAfter buying the Martin Logan Aerius I loudspeakers I felt the bass was a little weak. I liked what bass they had but they just didn't go low enough. So I started looking at the subwoofers that were available in the stores and couldn't afford any of the ones I liked (spent all my money on the Martin Logan's). So I decided to build one. Here's how I did it. 



Design

Click Here for Larger ImageAfter much research I decided to build a Sonotube sub. There is a ton of information on the net describing people's projects. I didn't want to spend hours building a cabinet only to find that it didn't sound very good. I figured the sonotube was the easiest way to get my feet wet in DIY speaker building without devoting a boatload of time and money. I would recommend this approach to anyone who is building their first subwoofer. Checkout the links to see some other peoples projects that I thought were pretty good.  I won't spend a lot of time describing construction technique or the merits of various designs. Its already covered in great detail on the net. 

Now I had to decide on the speaker I would use. After looking at the Shiva , Titanic and the ACI SV-12 , I decided to go with the SV-12. The main reason was that it would dip down to the lowest frequency according to the cabinet design program I was using. Another benefit is that they offered a trial version of  Winspeakerz to aid in the design.  Since my amplifier only has a Dolby Digital 5.1 output I also needed an amplifier. ACI had a package deal so I got a PSA-1 amplifier with the speaker. 

After modeling the cabinet using Winspeakerz and WinISD I ended with the following cabinet.WinISD is nice because it will provide the flattest frequency response automatically but it doesn't model driver excursion.Winspeakerz models driver excursion but doesn't provide the flattest response. Both programs gave pretty much identical results . The end result was was a compromise between a ported design and a sealed one. I can't remember now why I picked the volume I did. I think it was the smallest cabinet that gave a three db down frequency of 20 hz using ports. I figured I would listen to the sealed cabinet and decided at that point if I wanted to add ports. As it turned out I really liked the sound of the sealed design for music but  it didn't go low enough for home theater and ended up adding ports. This gave the rumble that makes movies exciting but it definitely wasn't as accurate as before. 

I had originally thought that I could set the cabinet sideways on the floor hence the square ends on the tube. After trying it, I didn't like how it sounded and added legs to the bottom to make it upfiring. The tube is covered with a brown cloth sock and the ends are painted with Rustoleum Stone Creations paint. It could use a couple more coats of paint. 



Results

Click Here for Larger ImageI'm fairly happy with this design. It's much cleaner than any commercial subwoofer in this price range (about $400). Its so clean that its deceiving how loud it is. I might, however, have a tuning problem as it seems to bottom out a little easier than I would like. I definately wouldn't use two 2" ports again. I don't think they flow the air that is required.There aren't any funny noises coming out of them but it just doesn't seem that enough air is moving when the woofer is really jumping. 

But, like I said, its not bad for my first effort. The PSA-1 works well. It has plenty of power (I can't turn it up past 25% of the minimum without bottoming the woofer) and I can adjust the crossover frequency as well as the phase. I guess I'll need to do some testing to see exactly what needs to be tweaked to give optimum output. 



Future Plans

Now that I've finished my center and rear speakers the subwoofer cabinet looks a bit crude. I'm going to build an MDF cabinet so that I can finish it with oak veneer like the other speakers. I'll probably try a passive radiator since it would make it much easier to tune. I'm also going to make the cabinet bigger (8.2 cubic feet) so it will go all the way to 20hz before rolling off. I'll post an update after its built. 



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