quick tube: any good for sonosubs?

[zzzz]

Hey everyone,

Just cruised by my local Lowe's and found what's called QuikTube which is 4 feet tall x 1 foot diameter, but it's thin probably 3-4mm. Probably weighed 10 lbs.

Would this work for a sonosub? I have a feeling it's too light.

Thanks

[WillyD]

It would work, assuming you were using a 10" or smaller driver.

[zzzz]

It would work, assuming you were using a 10" or smaller driver.

Thanks for your response. I a dforgotten about driver size. Should be no major problem.

Using the sonosub software it looks like the only way I can tune to below 20Hz is to use a 4 inch wide (or narrower) port and use a 3 foot long port tube within the 4 feet long tube? This only leaves 3-4 inches between the back of the driver and the port tube.

Is this feasible?

Thanks again!

[joecarrow]

I was wondering the same thing about using quik-tube as an enclosure. The local OSH has it here, and it seems like the paper is packed nice and tight, although maybe not that thick.

Is there anything to say that you can't have six inches of port sticking out of the cabinet? It might look a little different, but there shouldn't be any sonic problem.

I would have to say, however, that you want to watch out for pipe resonances. I don't know the sonosub software, but WinISD Pro alpha estimates the first pipe resonance. Three feet strikes me as a fairly long port, and it might just give you some trouble if you don't have a low crossover to the mains.

[JonP]

I've seen the stuff. It may be thinner, but a round (cylindrical) structure balances the forces, it should do pretty well. All the driver cone "back inertia" forces will be along the axis (thru the endcaps), which is very strong.

As I recall, Unibox does a good job of showing the port resonance, and Bob (?) Collo in Australia has sonosub and port calculating programs that are pretty cool.

A port diameter away from a wall or object is probably the bare minimum OK distance, but yeah, if you end up with a low enough resonance to be near the sub's operating range, it will be a problem.

[zzzz]

I've seen the stuff. It may be thinner, but a round (cylindrical) structure balances the forces, it should do pretty well. All the driver cone "back inertia" forces will be along the axis (thru the endcaps), which is very strong.

As I recall, Unibox does a good job of showing the port resonance, and Bob (?) Collo in Australia has sonosub and port calculating programs that are pretty cool.

A port diameter away from a wall or object is probably the bare minimum OK distance, but yeah, if you end up with a low enough resonance to be near the sub's operating range, it will be a problem.

Thanks for the responses. Unfortunately I am not an engineer and really don't get the whole resonance business. Can anyone explain the problem in relatively simple terms. While I have quite a bit of atmospheric physics in my background, I know little or nothing of acoustics.

Many thanks!

[---k---]

I've looked at the 8" and 10" tubes from Menards and Lowes. They are significantly thiner and more flimsy than the big diameter tubes. I would be worried about the durability of the sub with the small diameter tubes.

I can just picture it now: mount a 30 pound driver to two thick pieces of MDF and trying to flip the sub over, and it could just fold in half.

If you're looking at the same stuff I saw, I would pass on it and call concrete supply houses.

[zzzz]

I agree with you. I'll give the concrete people a shout now!

Thanks!!!

I've looked at the 8" and 10" tubes from Menards and Lowes. They are significantly thiner and more flimsy than the big diameter tubes. I would be worried about the durability of the sub with the small diameter tubes.

I can just picture it now: mount a 30 pound driver to two thick pieces of MDF and trying to flip the sub over, and it could just fold in half.

If you're looking at the same stuff I saw, I would pass on it and call concrete supply houses.

[joecarrow]

Thanks for the responses. Unfortunately I am not an engineer and really don't get the whole resonance business. Can anyone explain the problem in relatively simple terms. While I have quite a bit of atmospheric physics in my background, I know little or nothing of acoustics.

Many thanks!

Sure, I'll try!

A vented box is basically a helmholtz resonator ; the same general concept as when you blow air across the top of a soda bottle. The air in the bottle (box) acts as a spring, and is compressed by the relative movement of the air in the neck (port), which moves kind of like a solid mass. This type of resonance is like a spring and mass.

The problem is that as the frequency increases (wavelength decreases), the physical shape of the air in the port starts to matter a lot more. Standing waves can appear, and the port starts to make sound of its own- like a flute or pipe organ. Here's an explanation of that: http://dev.physicslab.org/Document.a...nancePipes.xml

You really don't need to pay attention to the math in those pages, but it's there if you want it. The overall effect is that the air in the port starts to get its own thing going on, which gets in the way of what the port/box system would otherwise do. This shows up as peaks and dips in the response, and potentially audible notes that hang on for longer than they should.

[dlneubec]

Hey Joe,

I've often wondered about the phase of the ports ouput and if that would factor in your decision as to where to place it, ie front, download or back.

Unibox has this check box for including effects of port resonance and I don't know when that should be a consideration and used and when not. Doesn't it depend on the orientation of the port?

Any thoughts?

[zzzz]

Thanks Joe for that explanation. In the atmosphere we really don't consider boundary effects on fluid flow all that much, with the exception of the people who're into the Earth-atmosphere boundary layer thing.

Is there a rule of thumb that relates the air speed through the port, the port width and the tuning frequency of the sub? I'm just wondering how narrow and long the port can get before resonance, turbulence etc have noticeable effect on the quality of the sound being output?

[---k---]

Yeah, people say you should limit port speed to around 26 m/s or .08 the speed of sound. I think you can push that a bit, especially as the frequency that you exceed this is pushed lower and lower. If you're exceeding it bellow 25hz, you'll likely never hear the chuffing. But, the lower the better.

[joecarrow]

Dan,

The port output tends to be fairly low in frequency, so if you check that the distance between the port and the woofer, it's almost always below the suggested center-to-center spacing for drivers on a baffle, which is about 1/2 a wavelength. When you consider a vented box that's really long and tube-like, you really do need to consider how the port and driver combine- but you also need to consider pipe resonance of the whole box.

Sorry, I can't really comment on what Unibox is doing with port resonance. It could be in the documentation, or there might be an expert who knows.

Zzzz,

Here's an application that someone put together to quantify when port chuffing becomes audible:

http://www.subwoofer-builder.com/flare-it.htm

The way you can tell that you'll start getting a resonance is to consider the length of the port and the speed of sound. If you have a tube one meter long, and the speed of sound in air is 343 meters per second, then you have a full wavelength at 343 hz. Resonance in a pipe can become a problem around 1/16th of a wavelength (so I've heard), so you would divide 343/16 to get 21 hz. The closer you get to a full wavelength, the worse it is. 21 hz would start to have some effect, then 42 hz might be more noticeable, 84 hz would be even worse, etc.

The lowpass on the sub will prevent you from exciting the port resonance with higher frequencies, but turbulence can be a noise source to get the resonance going independent of the musical input frequency. Bottom line- there are vented box designs that you rarely see, and it's not for nothing.

[---k---]

yeah, if you hit that check box in Unibox, it will plot the pipe resonances on the graph. you'll see the squiggles in the FR graph. The squiggle can be quite large and scary to see. I hear most people say they want the first resonance up over 200hz. The figuring is that this is well outside the sub range after the crossover, and therefore won't get excited.

Unibox always calculates the first resonance. It shows it in a box near the bottom.

I think the first resonance for my big sub is around 180hz. I haven't pushed it hard enough or listened closely enough to have ever heard a resonance.

[zzzz]

Yeah I saw that, but cannot figure out how to change the length of the port in Unibox, or more correctly, how to change the the port area as it's protected. What I can see as the pipe get's wider the resonance moves to lower frequencies. I am unsure if this is really related to port width or to port area.

yeah, if you hit that check box in Unibox, it will plot the pipe resonances on the graph. you'll see the squiggles in the FR graph. The squiggle can be quite large and scary to see. I hear most people say they want the first resonance up over 200hz. The figuring is that this is well outside the sub range after the crossover, and therefore won't get excited.

Unibox always calculates the first resonance. It shows it in a box near the bottom.

I think the first resonance for my big sub is around 180hz. I haven't pushed it hard enough or listened closely enough to have ever heard a resonance.

[---k---]

port diameter AND length.

so to decrease the resonance problems, you have to balance a smaller diameter port and greater port speed or having to raise the tune.

[theskuh]

The smaller Quicktube is fine if you have thick enough endcaps. It won't fold in the middle as long as your sub is not 6' long. I made a sonosub with a tcsounds oem 10 and passive.





Its thin but once it is glued together with the endcaps it is stronger than you would think. I wouldn't karate kick it in the middle but I think anything short of dropping a bowling ball on it it should hold up fine.