Hi weltersys- does it, though, when one side of the horn path is combined?
The main reason I am going with a symmetrical path is because earlier on in the thread it was noted that a high aspect ratio mouth would create a largely varied velocity near the edges (if I understand correctly). As well with a higher aspect ratio mouth covering the width of my desired exterior dimension (39w x 25h x 38d) would require heavy bracing as he mouth would be nearly 38w x 12h.
The main reason I am going with a symmetrical path is because earlier on in the thread it was noted that a high aspect ratio mouth would create a largely varied velocity near the edges (if I understand correctly). As well with a higher aspect ratio mouth covering the width of my desired exterior dimension (39w x 25h x 38d) would require heavy bracing as he mouth would be nearly 38w x 12h.
Yes he is right. Maybe not fully twice as much wood but definitely more. Both of your most current models (the one I drew up and the one you extrapolated on) are both symmetrical and both use more wood than a single path horn would. Drawing out one path uses less wood than two half paths. But in the symmetrical layout since there is more wood and it's spaced closer together you might get away with less bracing. You'd have to do that math to see how much wood each requires, including adequate bracing in each.
The disadvantage to the single path would be both driver would have to be side to side (no room in your 20 inch height restriction so you'd have to go back to the high aspect design again) or they have to be end to end which means your minimum L12 is a lot longer. Here's what a dual driver single path with a small aspect ratio would look like. L12 does not equal the length of the last segment in this drawing.
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If he's referring to 1V as large signal, then yes we were talking about two COMPLETELY different things. It never even occurred to me that he thought I meant anything other than REAL high power thermal considerations. This is the post he was responding to, it specifically says "hundreds of watts" and "thermal compression". Not sure how that was unclear to him.
Boundary friction causes the air closest to the boundaries (including bracing) to resist moving as freely as the air in the middle of the duct. As velocity increases the boundary friction layer becomes thicker, so more and more air in the duct has a tough time moving freely.
Ideally the horn would be a circular profile and infinitely strong so no bracing is required. That way there is the minimum possible amount of air in contact with the horn boundary. Once you start making the horn square (or rectangular shaped) and adding a bunch of bracing there is a lot more boundaries that the air is in contact with.
You can draw it out with a high aspect ratio or a low aspect ratio flare, add in the bracing and calculate how much wood surface area is in the horn at any given point.
Here's an example. This is a snapshot of the cross sectional area of a horn at the mouth with two different aspect ratios but each horn mouth area is 1 sq ft. On the left is a mouth with dimensions of 1 x 1 ft. On the right is a mouth with dimensions of 2 feet x 6 inches. Bracing has been added to both so that there is no unbraced panel area over 6 inches long. Both mouths (including bracing area) have exactly the same amount of boundary area, both will be equally affected by boundary layer friction.
High or low aspect ratio makes no difference in this example, both have the same amount of boundary area.
If we did NOT consider the bracing, the low aspect ratio example has the benefit. It's circumference is 4 ft, while the circumference of the high aspect ratio is 5 ft. When people say high aspect ratio causes problems they are usually not considering the bracing, or they are talking about an unbraced duct or a stick or dowel braced duct (because those bracing methods have very little surface area) or areas that can't be braced like the beginning part of the horn where the driver is.
An externally hosted image should be here but it was not working when we last tested it.
To make a long story short(er), if your duct is adequately braced and you are using solid (or almost solid) bracing then aspect ratio doesn't matter much (if at all) except in areas that can't be braced. If you have no bracing or use bracing with very little surface area like sticks or dowels then aspect ratio matters more and in these situations an extremely high aspect ratio can be a problem at high velocity.
Flare It is a nice little program that can be used to evaluate how high is too high for velocity vs duct area.
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I don't mind having to add a little bracing, plus it looks cool.
And, the whole thing about adding mouths together = a bit of bass extension. I'll take it!
I'm working on a new sim/model with slightly lower F3. Outer box dims are 38.5x25x38.5. Really pushing the limits of what I can fit back there. It's a very tight fit
And, the whole thing about adding mouths together = a bit of bass extension. I'll take it!
I'm working on a new sim/model with slightly lower F3. Outer box dims are 38.5x25x38.5. Really pushing the limits of what I can fit back there. It's a very tight fit
The boundary layer in fluid mechanics refers to the region where the free stream velocity starts to go to zero. It is enforced by the boundary condition for viscous flows that velocity is by definition equal to zero at a solid wall or boundary due to the no-slip condition. The thickness of the boundary layer gets -thinner- with increasing velocity.
Drag increases with increasing velocity due to viscous and pressure drag. Often described phenomenologically as Drag-force = 1/2 Cd A V^2. Where A is the characteristic area and Cd is the drag coefficient and V is the flow velocity. There is a Cd for skin or wall friction and there is a Cd for pressure drag caused by solid flow blockages. There is a Cd for flow through corners, etc. They all vary as velocity squared. That is why drag increases - velocity squared (quadratic effect). Drag force varies linearly for special cases of very very slow flows and for non-Newtonian liquids. Flow of air in speakers is conventional viscous oscillating flow.
I don't understand any of that but I think you are trying to tell me that instead of the boundary layer getting thicker I should be saying drag increases with velocity. Other than that I haven't got a clue but I don't think you disagree with the general premise I laid down, so if I made any other mistakes let me know. I know about Reynolds number but I am not familiar with drag coefficient.
Is it worth going back to try the "high aspect ratio" mouth?
I'll let you decide, because I am pretty happy with this 😀
3:1 CR
model
38.5" x 25" x 38.5" outer box dims
brace detail
I'll let you decide, because I am pretty happy with this 😀
3:1 CR
model
38.5" x 25" x 38.5" outer box dims
brace detail
I don't like the high aspect version due to the driver sag issue. You can calculate if sag will be a problem in the short term (less than 5% of xmax is I believe the acceptable amount) but even if it passes that test I wouldn't trust it over the long term. If you want a single path horn (unsymmetrical) I'd lay it out like the Danley sub pic I posted. But again it's all up to you.
Anyway, I hope you are not done with drawing in bracing in that pic. You need lots of bracing everywhere, all down the horn length (IMO). That single vertical brace isn't going to cut it. Your panels are 20 inches high (or more now?) that's a huge area for an unbraced panel, especially in the high pressure parts of the horn near the beginning. Instead of doubling up that one panel in there you could use that wood for horizontal bracing in that part of the horn. And then add more horizontal bracing. And then some more.
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Gotcha. I guess bracing isn't much of an issue on the stadiumhorn because of lesser CR?
Btw, this is for a 22" box height (black) vs 25" (grey)
Btw, this is for a 22" box height (black) vs 25" (grey)
No you did not have anything else that wasn't right. If you know Reynolds number I am surprised you don't know the relation for drag. Reynolds number is much more abstract as it is the ratio of the momentum forces to viscous forces. A big Re number means turbulent fast flow and the Cd's I mentioned above have relationships that are a function of Re number. They are provided as charts and lookup tables from empirical data. So calculate the Re, lookup the Cd, then calculate drag.
I lied, one more comparison, I might end up building the 22"h one because it still kicks the crap out of the vented box. Though a 3.5:1 CR.. hmm...
Does compression ratio have an adverse affect on sound quality?
Does compression ratio have an adverse affect on sound quality?
I'm not familiar with the internal of the Stadiumhorn but all horns (all boxes of any type) should be well braced. In some forums they recommend that bracing should be applied so that there is no part of any panel that is unbraced for more than a 6 x 6 inch area. They also recommend doubling up that baffle and typically use 3/4 inch sheet products for construction. And they recommend that for small boxes for 5 or 6 inch woofers, usually two way fullrange speakers even if they are high passed and used with a sub. So there are varying opinions on how much to use.
No amount of bracing is too much unless it starts to eat up too much internal volume. But there is definitely a point of diminishing returns as Brian pointed out. And there are areas that need it more than others.
I would recommend stick or dowel bracing at least in the parts of the horn you can't see (your existing fancy brace has aesthetic appeal so there's no reason to change it. I would break up your 25 inch height AT LEAST once, at least ideally twice or 3x.
The internals of the stadiumhorn is zero bracing besides one at the bottom near the mouth.
I never really ran them at full blast, either, though (23V with lower 28hz HPF instead of 50V 35hz HPF).
Still, no panel flex that I could see or feel. Those suckers are huge, too. 24w x 48h x 36d
I will be using 3/4" arauco plywood for construction, same thing I used for the stadiumhorns and the vented box. Home depot carries the stuff, it is 7 layer and decent quality. ~35USD for a 4x8 sheet
I never really ran them at full blast, either, though (23V with lower 28hz HPF instead of 50V 35hz HPF).
Still, no panel flex that I could see or feel. Those suckers are huge, too. 24w x 48h x 36d
I will be using 3/4" arauco plywood for construction, same thing I used for the stadiumhorns and the vented box. Home depot carries the stuff, it is 7 layer and decent quality. ~35USD for a 4x8 sheet
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I "know" Reynolds number in that I have a Moody chart and I use a simple online calculator to find Reynolds number and then plot it on the chart. But with the Flare It program there's not much need to do that. Flare It obviously isn't as good as a more significant analysis obviously but it's close enough for quickly determining how much airflow is acceptable through a duct. It assumes a round duct used as a port, probably made of PVC, but should be well within reason for properly sizing most any duct (or horn flare segment) for enclosure design purposes.
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So, which method is the most accurate? If the furthest right is the most accurate, then taking a larger radius path around a corner actually increases path length. I am assuming a flow simulation program would be able to determine the true path length?
Advanced centerline is the one you want, the middle one. This post describes a method a bit more advanced than the advanced centerline method. AkAbak for Dummies 😉 - Page 2 - AVS Forum But it's a lot of work.
I don't know anything about flow simulation programs. There's probably some type of fluid dynamics software that can figure this out to a high degree of accuracy but the advanced centerline method should be more than adequate for horn folding.
I don't know anything about flow simulation programs. There's probably some type of fluid dynamics software that can figure this out to a high degree of accuracy but the advanced centerline method should be more than adequate for horn folding.
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Thanks! That does clear it up.
Had to go back to make a small adjustment: once CAD'd I rechecked my advanced centerline and it was a few cm short. I feel good about this next one though.
I think I'm going to be building a box tomorrow if all goes well 🙂
Also forgot to mention, when I checked my diaphragm pressure for the vented box it was much higher than any TH sim I have posted. I feel okay with running a slightly higher compression on the shorter box.
Had to go back to make a small adjustment: once CAD'd I rechecked my advanced centerline and it was a few cm short. I feel good about this next one though.
I think I'm going to be building a box tomorrow if all goes well 🙂
Also forgot to mention, when I checked my diaphragm pressure for the vented box it was much higher than any TH sim I have posted. I feel okay with running a slightly higher compression on the shorter box.