DIY Tube Subwoofer questions

[vasubandu]

I like the SVS cylinder subwoofers, and from what I have read, performance is the same as cubes.  I have been told that the round concrete forms are ideal to make them, and I was hoping that someone could make a suggestion as to the preferred thickness of the material.  Sonotube has diameters from 6 to 60 inches.  The thickness of the materials depends on the length of the tube.  So a 16 inch diameter tube ranges from .155 inches to 1.034 inches.  A 20 inch tube ranges from .242 to 1.616 inches, and a 22 inch ranges from .293 to 1.956 inches.  Those are for lengths of 3 feet and 20 feet.  

 

These are made from Cardboard, so my inclination would be to get the thickest material I could and have a 20 foot tube cut into 6 3.33 foot lengths or 6 2.83 foot lengths.  Of course then I would have to make a lot of subwoofers so as not to waste material.  But if two  subwoofers is good, then seven has to be great, right?

[CECAA850]

A tube doesn't have to be thick to be strong.  Get the proper length without worrying about the thickness and you'll be fine.  I assume there'll be a build thread coming?

[CECAA850]

Longer tubes are thicker as the pressure at the bottom of a taller column is greater than a shorter one when filled with concrete.  It's a non issue with a tube sub.

[ClaudeJ1]

2 hours ago, vasubandu said:

I like the SVS cylinder subwoofers, and from what I have read, performance is the same as cubes.  I have been told that the round concrete forms are ideal to make them, and I was hoping that someone could make a suggestion as to the preferred thickness of the material.  Sonotube has diameters from 6 to 60 inches.  The thickness of the materials depends on the length of the tube.  So a 16 inch diameter tube ranges from .155 inches to 1.034 inches.  A 20 inch tube ranges from .242 to 1.616 inches, and a 22 inch ranges from .293 to 1.956 inches.  Those are for lengths of 3 feet and 20 feet.  

 

These are made from Cardboard, so my inclination would be to get the thickest material I could and have a 20 foot tube cut into 6 3.33 foot lengths or 6 2.83 foot lengths.  Of course then I would have to make a lot of subwoofers so as not to waste material.  But if two  subwoofers is good, then seven has to be great, right?

4 is optimum.

[CECAA850]

1 minute ago, ClaudeJ1 said:

4 is optimum.

Are you referring to tube length?  Wouldn't that depend on driver and tune desired?

[ClaudeJ1]

Just now, CECAA850 said:

Are you referring to tube length?  Wouldn't that depend on driver and tune desired?

No, I was referring to 4 subs, not more, like he suggested.

 

[vasubandu]

Ha ha I thought I was joking about more than two. SO I guess the next questions are which  diameter has the best drivers and how much bigger than the driver the tube should be. I was assuming that it would be one size up, 20 an 18 inch tube for a 15 inch driver, 20-18, 22-21. Parts Express has 22 each of 10" and 12" but only 8 for 15" and 18" and only 1 for 21". Maybe Jeff at JTR would send me a few of his.

 

 

[vasubandu]

To be clear, I am looking for a driver that produces sound not just noise.  When I have my bypass on, it is set to 120Hz because I prefer for the bass to extend into substantive sound.  I often turn it off, but it is not clear to me if I actually get getting sound up to the 250 or so Hz that the  PB2 Plus can handle.  It would be great to find something that went up to 360 like the SVS PB16, but I really do not know what the sound quality would be like up there.

[mustang guy]

I have seen you here a while. Have you heard about how placement of subs is almost never the same place you would put a speaker? The reverse is also true. That is one of the main reasons speakers don't have subwoofers right inside speaker cabinet. There are a few monster speakers that do this, but at their own detriment. At about 80Hz, sound starts to become directional, so you can tell where it is coming from. Below that frequency, the sound seems to be coming from all directions at once. It is at this point that the best location of a speaker and the location of a subwoofer starts to become more obvious. If you ask a sub to go into the frequencies you want, you are likely asking it to do so in a bad location for a loudspeaker. It's not the best thing for the sound. Also, when you allow the subwoofer to overlap the speaker frequencies, you can get some funky comb filtering and almost buffeting sounds. To me it can be like a rear window of a car being down. 

 

It's up to you, but a subwoofer is designed to take care of the low frequencies. It has no place in the upper bass frequencies. For that you need a bass bin. Claude is the bass bin master where Carl is the subwoofer master. You are in good hands.   

[vasubandu]

Thanks @mustang guy that made perfect sense. So subwoofer cutoff at 80 and subwoofer placement based on subwoofer not speaker considerations? You really made this clear. Thanks.

[mustang guy]

9 hours ago, vasubandu said:

Thanks @mustang guy that made perfect sense. So subwoofer cutoff at 80 and subwoofer placement based on subwoofer not speaker considerations? You really made this clear. Thanks.

One more thing. As LFE (low frequency effect) cutoffs in AVR's are concerned, the default (and recommended by THX) cutoff is 120Hz. That is confusing, but only means that frequencies diverted from small loudspeakers will not be above 120Hz ever for a sub. That number can be lowered, but has little actual effect unless you have LFE that would go to some small speakers and needs diverted. What is important to note here is that if you set the LPF on the sub selector to 80Hz, it might not get that LFE between 80 and 120Hz. In fact that would simply be discarded since it was diverted by the AVR to the sub and the sub was told to cut it out. It is for that reason that if you are using an AVR with a sub, you are sometimes better to just turn the LPF to the highest frequency. You will be using the digital LPF in the AVR instead of the analog one on the sub.

[vasubandu]

2 minutes ago, mustang guy said:

One more thing. As LFE (low frequency effect) cutoffs in AVR's are concerned, the default (and recommended by THX) cutoff is 120Hz.

 

Thanks @mustang guy oddly enough 120 is where I set them some time ago after trying different things.  Even a blind squirrel finds an acorn every now and then. I will move it back.

 

Now about this crazy idea to make a 6-foot tall tube subwoofer with a bunch of drivers, is that worth thinking about or just nutty?  I read about dual-driver "push-pull" systems but have no idea how they are set up except that the drivers are pointed in opposite directions.  Must be some sort of timing involved. But what if we had a tube with 2 drivers pointed each way, or even 3 to be completely wacko.  Would that work?  And I am just wondering, not to say I would not try.

[mustang guy]

Who knows? Give it a try if you like. It would be cool looking! Realistically you are probably better off just building a sonotube sub. It's been a long time since I ran a design of a push/pull sub design, but as I remember there wasn't a whole lot of point to it. I think you just add 3db to the thing but lose the ability to port tune, passive tune or even box volume tune. (this is from memory from years ago, so it might not be 100% accurate)

 

If I were building a sonotube, I would go either ports or passive tune.