To produce any harmonics the pipe has to be excited by a wavelength that is short enuff for a tube to sustain it... and a small cylinder like these used as a sub will be cut off way before it gets anywhere near that phenomenon... and if it starts to get that long, make it into an ML-TL... do note that the resonances aren't across the diameter of the cylinder but over its length (ie it doesn't matter what shape the cross-section is.
dave
dave
It's already said several times, it's too small for standing waves. If there are no standing waves, there are no enclosure induced harmonics either - without a base resonance, there are no harmonics.
I stumbled across this thread, so I thought I would chime in. About a year ago I built a pair of the bucket subs. I used the Peerless 8” driver that was spec’ed and joint compound buckets that I sanded down and painted black. I did not use concrete on the inside because concrete has a habit of shrinking and I did not want it to loosen inside the bucket. I used USG brand Dura-Bond instead, reinforced with long screws zipped through the sides and used three 2” hard rubber feet for the base.
I was thoroughly impressed when I fired them up! They will not rock the house for home theater use but they have a nice musicality about them for regular music. Great project for not a lot of money
Thanks for chiming in Vunce. They actually look pretty professional, still not sure swmbo will tolerate em?
Did you make any measurements? What are you driving them with? Using much eq?
And thanks Everyone else for your input.
So it seems we have a stiff enclosure (once the ends are taken care of) and no chance of standing waves occurring. Good stuff so far.
Here's my question.
Most subs have very thick heavy enclosures. Given the thin walls of the bucket will a lot of the rear radiation from the driver actually get transmitted through them and cause cancellation issues or do the stiff walls resist this transmission of energy?
This area of physics is not something I know much about.
So it seems we have a stiff enclosure (once the ends are taken care of) and no chance of standing waves occurring. Good stuff so far.
Here's my question.
Most subs have very thick heavy enclosures. Given the thin walls of the bucket will a lot of the rear radiation from the driver actually get transmitted through them and cause cancellation issues or do the stiff walls resist this transmission of energy?
This area of physics is not something I know much about.
Hello ewollowe,
I had to look up swmbo
That’s why I tucked them in the corners behind the main speakers, lol!
No fancy measurements, I used the dsp settings in my Anthem pre/pro for the filtering, phase, etc...
I built a class D amplifier based on a pair of Anaview modules to drive them.
They added a pleasant fullness to the music, never calling attention to themselves. All in all, I’d say they have a high ‘Bang for the Buck’ ratio.
Good luck with your project and convincing swmbo
Cheers,
Vunce
Subs often have thick walls because that is what is needed to make them stiff. Stiff is what is important… not thick or heavy.
To prove a point i made my dual 10” push-push subs out of 15mm plywood. Even well braced the flat panels are not near as stiff as even a thin walled cylinder.
dave
Correct me if I'm wrong, but here's how I think of it.
The stiffness of a cylinder is easy to comprehend if we take a sheet of paper.
When it's flat out in vertical position, it can't support any weight. (Well it can't even stay up in vertical position, but just in theory)
When it's rolled to a cylinder, it can support quite a bit of weight on top of it. It will give in if you press the sides with your fingers but in speaker enclosures the pressure distributes evenly from the inside.
Thanks Nenola,
I understand the concept of the stiffness of the cylinder, it's just that it feels somewhat counter intuitive that a thin stiff wall can prevent the rear output of a sub interfering with the front wave better than a thick heavy one?
So thinking out loud, the thin stiff wall resists flexing at lower frequencies and so doesn't "sing" when the sub is in use?
Correct me if I'm wrong?
I understand the concept of the stiffness of the cylinder, it's just that it feels somewhat counter intuitive that a thin stiff wall can prevent the rear output of a sub interfering with the front wave better than a thick heavy one?
So thinking out loud, the thin stiff wall resists flexing at lower frequencies and so doesn't "sing" when the sub is in use?
Correct me if I'm wrong?
When more pressure is put into a circular shape, there is nowhere the circle can flex to increase it's volume. It might stretch microscopically because it's plastic, but nothing that would affect the sonic output. All that can happen is the increase in pressure, because it's already at it's maximum volume. This is why pressure vessels are usually spherical or cylindrical, so they won't flex under the pressure. The only force on the walls is tension, which most common structural materials resist well.
As Dave said, the disc ends are the only part of this sub that can flex - but one end is reinforced against flexing by the concrete, and the other end is mostly the steel loudspeaker frame. There is a type of concrete that does not shrink, actually expands.
Because the wavelengths of the sound are much smaller than the dimensions on the bucket, there will be no echoing inside the bucket. All surfaces of the interior will feel the pressure pulse expansion at the same time. It will try to swell, but it can't because it's a cylinder.
FYI, 7 gallon buckets do exist, maybe available in AUS? Amazon.com: Letica 7 Gallon HDPE Bucket, White: Home & Kitchen
As Dave said, the disc ends are the only part of this sub that can flex - but one end is reinforced against flexing by the concrete, and the other end is mostly the steel loudspeaker frame. There is a type of concrete that does not shrink, actually expands.
Because the wavelengths of the sound are much smaller than the dimensions on the bucket, there will be no echoing inside the bucket. All surfaces of the interior will feel the pressure pulse expansion at the same time. It will try to swell, but it can't because it's a cylinder.
FYI, 7 gallon buckets do exist, maybe available in AUS? Amazon.com: Letica 7 Gallon HDPE Bucket, White: Home & Kitchen
This is really fascinating
0ne thing, I thought the frequencies in the sub where longer than the dimensions of the bucket?
It is all in the shape… take a geodesic dome for instance… it is amazing how much spindly little struts can support.
dave
Has any 3rd party verified this design as "essentially flat from 25 Hz to 100Hz". Seems far fetched for a 8" in just under 19L, without EQ. PE lists a F3 of 58Hz in a slightly larger sealed enclosure. Modeling it in winisd and bassbox6, 25hz is at -16db, doesn't seem like room gain can account for that. I'm also showing a peak around 60-70hz, so not really flat.
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Bigun, a sealed woofer operating below Fs needs EQ (2nd order circuit to flatten the FR), huge xmax and a very big amp. One of the Pro compannies did/does this with their woofers.
Given the dominance of the room, it is unlikely any (sub)woofer is flat 25-100 Hz (without EQ and rarely even then).
dave
Given the dominance of the room, it is unlikely any (sub)woofer is flat 25-100 Hz (without EQ and rarely even then).
dave
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