That density of bracing in the center seems like a waste of material and cabinet volume when the outer most side panels are almost unbraced by comparison 😉Or both.
dave
Outer side panels are unbraced?
Besies the bracing that attaches to the side, the sides are 3 layers, there construction of an iBeam-like structure.
dave
Besies the bracing that attaches to the side, the sides are 3 layers, there construction of an iBeam-like structure.
dave
Very nice analysis. I am also a bit surprised that a constrained edge makes enough difference that the double thickness panel benefits so much. But thinking about it, it makes sense.
The single and double stick brace that you modelled is what I would consider a barely effective bracing. The photo below is more what I have in mind when I talk about well-designed bracing. The upper and lower bulkheads react the primary bending of the front baffle and shear the load out to the side panels. The middle bulkhead constrain the sides and back. This is a woofer cabinet
Planet10's graphic in post 29 shows a highly effective bracing strategy. I employ a similar approach to midrange cabinets
j.
Attachments
That graphic reminded me of my first serious sub enclosure, 160 liters, side and back wall only 19mm mdf, baffle 36. Well braced every 20cm in every direction. Quite solid, at high levels everything in the room contributed but the enclosure itself. That was back in the late eighties 😊.
Midrange enclosures benefit a lot from driver decoupling, less so from extensive bracing. Unless you’re able to push resonances outside the passband (Celestion SL600, remember?). In general a small enclosure and well damped construction betters bracing alone. Think of the damped braces Earl Geddes and KEF (amongst others of course) apply.
My first experience with this technique, KEF 105, had us finding that the speaker sounded better, had greater DDR, when the decoupling gaskets were removed.
In my situation, with a single driver, tightly coupling the driver to the mass of the box maxiizes DDR but it does require that you build a good box or you will here it.
A similar result, anecdotally, occurs when the midBasses in Thor variants are tightly coupled to the box mass improves midrange DDR/detail.
dave
The assumption being made that the bracing is done in the MIDDLE of the panel being braced and broken into two equal halves.
IMHO, you'd be much better off putting the brace at an offset from the middle, ie: splitting the panel into a 60/40 or 55/45 ratio. That way you spread out the resonant frequencies of the panel and introduce a lower amplitude, but broader frequency, resonance from the cabinet.
A proper German would both brace and triple the wall thickness. Ay! Perhaps add some active cancellation as well.
Something i was clear to mention earlier on.
Ignoring the thickness of the brace, one in the middle does not suppress even harmonics very well. Braces should be assymetrica in their placmentl.
Can make a HUGE difference if well done at the lower frequencies, removing some (est) 90% of the enrgy flowing into the box structure that excites the (potential) resonance.
dave
Yes, shifting the brace from the middle will change the harmonic frequency of the panel but as I said I'm a structural engineer and thus only really know how to deal with static forces on structures. Correct me if I'm wrong but i would imagine a golden ratio or division by the square root of two would be optimal as these numbers are irrational and won't create harmonics like in Planet 10's post #47.
You would definately get an even stiffer box by employing three braces or more like Planet10 and Hifijim's boxes. In a simplified model you can say by halving the length between two fixed points, the deflection will be 16 times smaller, as the length goes into the equation with a power of 4.
Irratuonal numbers are your friends when working out cabinet dimensions. Be carefuk using root(2) twice.
dave
Keep the irrationality to the imagination of the electrical reactance of the crossover for the driver.
Follow a Fibonacci series... 1 2 3 5 8 13 21 34 Might want to bypass 1. Go with a 2 3 5 8 sequence.
This is, divide the length of the panel by 18 ( 2+3+5+8) and lay out the braces at 2, 5 and 10. That will give you panel segments of 2, 3, 5 and 8.
No harmonics!
BTW, my living room (stereo) and den (HT) are 21 x 14 x 8 which are also very close to 8, 13, 21. With some large openings here and there, the acoustics are really good.
I'll post this again, since it seems few people read it... and this being DIYAudio, I find this very apropos..
https://www.passdiy.com/project/speakers/the-legend-of-el-pipe-o
A square cabinet with 90 degree borders is not very optimal for sound... just cheap to build.
As far as the Golden Ratio, just follow a Fibonacci series as I described earlier.
Where are you?
Would a mini El Pipo be called an El Bongo? ;-)
I thought about building a pair, about 7 feet tall and a foot wide. With a single 8 inch facing down. But I don't want to push it... because these would go into the living room to provide a back up to the Maggies. Maybe if I painted them to match the walls?
The other thing... what if the El Bongo had a 12 inch cube box somewhere along the pipe, as in T set up. instead of being at the bottom, with the woofer facing forward into the room. Place the box about a foot off the short end with a six foot sticking out the other way. Make it so that one end of the pipe could be closed. Or perhaps, have the woofer shoot internally down either leg of El Bongo. In this case, it could be done with a round plate somewhere along the length of thebong ,err!, pipe tube (dang!). I don't know how mechanically strong that might be though.
Would a mini El Pipo be called an El Bongo? ;-)
I thought about building a pair, about 7 feet tall and a foot wide. With a single 8 inch facing down. But I don't want to push it... because these would go into the living room to provide a back up to the Maggies. Maybe if I painted them to match the walls?
The other thing... what if the El Bongo had a 12 inch cube box somewhere along the pipe, as in T set up. instead of being at the bottom, with the woofer facing forward into the room. Place the box about a foot off the short end with a six foot sticking out the other way. Make it so that one end of the pipe could be closed. Or perhaps, have the woofer shoot internally down either leg of El Bongo. In this case, it could be done with a round plate somewhere along the length of the
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I am in Victoria BC (the Highlands).
These are 8” pipes, about 7 foot tall with 7” Easttech woofers. 2 EnABLed and a spare since one of the treated drivers might be pooched. And somehwere the terminus vent needed to make it into a proper ML-TL.
The pipe in the middle. On the sides 2 of the other 3 woofers for giveaway if you can pick-up. 2 of them veered, just add woofers and XO. The little white boxes are basic 4th order active XOs (free, the could use a bit of work)/ 3 are available to go out with the woofers. 2 ML-TLs, one vented shaped to fit a corner (2 each of the same woofer as the tall pipes), and an isobarik pair tht use a total of 8 12” drivers (i have 9 more woofers but i want modest money for them)
dave
These are 8” pipes, about 7 foot tall with 7” Easttech woofers. 2 EnABLed and a spare since one of the treated drivers might be pooched. And somehwere the terminus vent needed to make it into a proper ML-TL.
The pipe in the middle. On the sides 2 of the other 3 woofers for giveaway if you can pick-up. 2 of them veered, just add woofers and XO. The little white boxes are basic 4th order active XOs (free, the could use a bit of work)/ 3 are available to go out with the woofers. 2 ML-TLs, one vented shaped to fit a corner (2 each of the same woofer as the tall pipes), and an isobarik pair tht use a total of 8 12” drivers (i have 9 more woofers but i want modest money for them)
dave
Why? If the walls are thin it will not be stiff, just like a rectangular tube. Only a sphere has inherent stiffness due to its curvature (mathematically a cylinder has zero curvature, which is why you can roll one up from a flat sheet). With a sphere any flexing of the thin wall has to also stretch or compress in the plane of the sheet somewhere else, which involves much more energy than flexing a sheet.
Or put another way a cylindrical wheel needs spokes, a spherical one doesn't.
Time for physics, not mathematics. ( We drive mathematicians nuts...).
Assume a cylinder standing up.
The stiffness is along the horizontal plane. The cross section is a circle and, as you have guessed correctly, is very stiff and resists stress and strain.
The vertical plane is linear so, on first thought, it will be subject to in and out displacement... BUT, and here's the trick, as the pressure waveform moves along the vertical plane it attempts to expand and contract the horizontal plane... but... but... guess what? It can not because the cross sectional circle resists both stress and strain forces.
So, the cylinder is the strongest.
The sphere, btw, is not desirable at all because it resonantes terribly... think about it.
The wheel example is not applicable. The reason a wheel needs spokes is to support the hub. A hula hoop has no spokes, huh?
Because of the shape. The walls on the PVC pipes above is something like 5mm and will be much more resonance immune than the same in a rectangualr pipe.
I also wanted to add the comment, ref an earlier post about only having to worry about the caps at the ends, the push-pull push-push isobarik in the pic above has drivers as end plates so it will not be an issue.
dave
I am in Victoria BC (the Highlands).
These are 8” pipes, about 7 foot tall with 7” Easttech woofers. 2 EnABLed and a spare since one of the treated drivers might be pooched. And somehwere the terminus vent needed to make it into a proper ML-TL.
The pipe in the middle. On the sides 2 of the other 3 woofers for giveaway if you can pick-up. 2 of them veered, just add woofers and XO. The little white boxes are basic 4th order active XOs (free, the could use a bit of work)/ 3 are available to go out with the woofers. 2 ML-TLs, one vented shaped to fit a corner (2 each of the same woofer as the tall pipes), and an isobarik pair tht use a total of 8 12” drivers (i have 9 more woofers but i want modest money for them)
dave
Nice but you are really far away.... I was in Victoria once, late July, took the high speed ferry from Port Angeles... saw flowers (Bouchard Gardens?), drank excellent beer, had oysters, smoked a cubano, wife did some shopping, etc...
About 1400 miles North from my listening rooms.
:^)
I have lived here since 1976 and never been to Buchart Gardens. There is a longish hike from my place to there, so i am fairly close as the crow flies.
dave
I have lived here since 1976 and never been to Buchart Gardens. There is a longish hike from my place to there, so i am fairly close as the crow flies.
dave
Interesting... the El Pipo was not isobaric, it was opened at the top too...
Perhaps what the World needs is an Isobaric El Bongo design. So, take an 8 inch column, 6 feet tall, put two 6 inch woofers at either end in isobaric configuration (*) and add some Falcon 9 like legs to hold them up.
We need to create an Isobarico El Bongo thread. I think I want mine to look like two Falcon 9 models. Someone surely will come up with the equations to describe the resonance and tuning. Driver design, crossover, filters and power required.
(*) In concept you could say that being 6 feet apart it will affect their in-phase coupling, but since they are low frequency drivers dealing with long wavelength signals their phase shift should be minimal.