Does a sealed enclosure have laminar (linear) flow or turbulent flow?
If it is not linear, what would be the disadvantages and advantages of it?
If it is not linear, what would be the disadvantages and advantages of it?
Sealed has no flow. Molecules just compress when membrane moves in, and expand when membrane moves out. Air molecules get thinner or thicker, but they do not flow.
Only wave propagates. Its like wave on tribune. People stay in their seats.
https://www.gettyimages.com/detail/...vent-doing-the-stock-video-footage/1125654431
Only wave propagates. Its like wave on tribune. People stay in their seats.
https://www.gettyimages.com/detail/...vent-doing-the-stock-video-footage/1125654431
if the sealed enclosure is large enough, has any significant cross section reduction close to the driver opening up to a larger cavity volume, it will show as another smaller reactive resonant peak. This can be mistaken as a standing wave, but its in fact a separate small "tuned" system. Dual chamber reflex boxes have a similar small extra hump aside from the primary ones.
It will normally be unsteady laminar flow.
All flows are nonlinear because the convection of momentum includes the product of velocity components.
This is not strictly correct. There will be air motion around the moving cone that is not compression. The mechanical energy in the air motion through the pores of the stuffing that is converted to heat is not compression (on the scale of the pores). Etc...
If we want to linearize about fixed conditions in order to consider waves then in air there are five (2 acoustic, 2 vorticity and entropy) which follows from the 5 conservation equations governing the motion (mass, 3 momentum and energy). Although it can be done mathematically it won't be a good approximation in practice because in a typical speaker the variation in the thermodynamic state is going to be significantly nonlinear as may the velocity depending on details.
The assumption of no motion and polytropic compression of a single two phase lump of air and stuffing is a simple useful engineering one for sizing things. Detailed work though will require less assumptions which is why we are starting to see a few of the more engineering orientated speaker companies show some results of CFD simulations where the governing equations are solved in and around the speaker. It is a trickier CFD problem than one might expect and most commercial general purpose CFD codes are not geared up to do it well though one or two specialist codes likely are (no personal experience). This is likely to be a contributing factor to why CFD has been slow to be adopted for the detailed engineering of speakers compared to other engineering fields. As no doubt is the relative unimportance of detailed engineering to the success of home audio speakers in the market.
If we model the speaker as an ideal air pump producing a steady flow of particles perpendicular to the surface area, it would seem that the particles would tend to "spill over" and accelerate sideways in an arc if the shape of the cavity allows it. (A possible cause of harmonics?)
The interface between the cone and solid baffle would likely be a focal point with the tightest radii, where a 'tubular' or cylindrical radiation pattern begins its conversion into a hemispherical pattern.
The interface between the cone and solid baffle would likely be a focal point with the tightest radii, where a 'tubular' or cylindrical radiation pattern begins its conversion into a hemispherical pattern.
If we express the governing equations of motion as some constant background condition plus perturbations about that condition (i.e. waves) the rolling sideways motion would be vorticity waves. The problem is that the assumed background conditions around which the waves are perturbations isn't reasonably constant and will vary in a nonlinear way with overall compression/expansion inside the cabinet. So for significant cone motion there will be harmonics in reality but in the simulation these will have been assumed away by the background condition being constant. We can introduce terms to account for the nonlinearity/harmonics in several ways but these terms will require modelling assumptions and often empirical information in order to get to a solvable set of equations. Turbulence modelling is an example of this but something more like harmonic balance would likely be a more useful approach in our case.
Physics and research can be incredibly enjoyable, by the way.
Doing that while listening to good music is probably the peak of joy in this hobby.
Even with compression there is "flow" or a better way is to say that there are particles moving.
In the end it's nothing more than pressure differences between two points in space.
Otherwise things like turbulence and boundary layer effects could also not happen.
A better way of saying, is that there is no net flow when we look at it from a quasi static point of view.
Which works for calculations, but is not reality obviously.
Even less so when we go higher up in frequency, when we get all kinds of issues with standing waves, reflections and other stuff.
This is the danger of simplifying things.
It's not that they are wrong and don't work, but it's important to not forget the details and understand the significance of those details.
edit: I just realized that's basically what you just said as well 😀
Ah well, now it's there explained in two different ways, lol
To me, this sort of discussion in itself is enjoyable! Plenty of great input here. I have to admit that I often distract myself from the music by way of evaluation of all sorts of thoughts about what is happening in the audio system itself. A friend of mine is quite the opposite and I envy that sometimes. If I am fortunate enough both worlds collide and the effect is wonderful.
I have seen the opposite, which seems worse.
Not overthinking anything, wondering about myths and stories and the never ending comparing between plugs, cables, cork and snake oil, which you could avoid by just thinking a tiny little.
Idid some work awhile back with the idea of tapered resistance on the chamber behind the driver - an extension of the B&W little mid speaker - it surprised me at the amount of reduced internal interference and improvement in overall clarity of the wide range driver - an interesting exercise.
I must admit to a lot of "over-thinking" and "under-achievement" (aka, performance paralysis) and even been known to have tech conversations with myself instead of the dog! - prep for the onset of alzheimers?
Seasons greetings everyine and a better next year than this past one ...
I must admit to a lot of "over-thinking" and "under-achievement" (aka, performance paralysis) and even been known to have tech conversations with myself instead of the dog! - prep for the onset of alzheimers?
Seasons greetings everyine and a better next year than this past one ...
James, tapered resistance on the chamber behind the driver is dealing with back wave from the driver. Sure must be beneficial. Just like absorbing back wave behind the driver in closed box in general. We do not want back wave to bounce back. That's why i preffer open bafles.
I do not think this is what op is asking about.
He asked about air flow in closed box.
I do not think this is what op is asking about.
He asked about air flow in closed box.
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Just pressure, fill with absorption material
and all done.
Absorption helps with midrange frequency
non parallel walls slightly helps with low frequency
causing problems. More useful for very tall enclosures
like tower or floor stander. where parallel walls would be
significantly larger/longer.
Triangle /trapezoid.
Can make up mystical magical nonsense if you make
a spiral or magic artsy fartsy shape.
In the end not parallel, that is it.
Vented/ reflex
The port dont work magically by itself.
Still needs energy from the speaker.
That is the trade off.
Approaching resonance cone movement is
reduced. So reproduction and transients
get reduced near resonate frequency.
And movement is very little at resonance.
No accuracy, huffy puffy port
Causes 2 high impedance peaks.
Benefit of Sealed only one impedance peak.
Better transient response.
Less design time.
Easier to fill the box with absorption
material. Where its more effective
in the middle of the box.
Been noted transformer coupled amplifiers
seem to perform better with sealed.
In a very generalized description with a more
friendly impedance curve.
Brace , stuff and use non parallel walls.
As magic you can do.
As far as the rear of the speaker, or the box.
and all done.
Absorption helps with midrange frequency
non parallel walls slightly helps with low frequency
causing problems. More useful for very tall enclosures
like tower or floor stander. where parallel walls would be
significantly larger/longer.
Triangle /trapezoid.
Can make up mystical magical nonsense if you make
a spiral or magic artsy fartsy shape.
In the end not parallel, that is it.
Vented/ reflex
The port dont work magically by itself.
Still needs energy from the speaker.
That is the trade off.
Approaching resonance cone movement is
reduced. So reproduction and transients
get reduced near resonate frequency.
And movement is very little at resonance.
No accuracy, huffy puffy port
Causes 2 high impedance peaks.
Benefit of Sealed only one impedance peak.
Better transient response.
Less design time.
Easier to fill the box with absorption
material. Where its more effective
in the middle of the box.
Been noted transformer coupled amplifiers
seem to perform better with sealed.
In a very generalized description with a more
friendly impedance curve.
Brace , stuff and use non parallel walls.
As magic you can do.
As far as the rear of the speaker, or the box.
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