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Sealed enclosure -- golden ratio?
Sealed enclosure -- golden ratio?
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Old 13th September 2017, 09:50 PM   #81
33Polkhigh is offline 33Polkhigh  United States
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Originally Posted by AllenB View Post
The aim is the same, keep the bass and get rid of the rest. Since it was discovered that an optimal transmission line gives a similar response to a closed box I've stopped building them.
I would assume that a t-line gives a 3db+ increase over a closed box in the bass. So then it has to be converting sound energy to do that. But with equalization and powerful amps sealed makes a lot of sense.
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Old 13th September 2017, 10:27 PM   #82
planet10 is online now planet10  Canada
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Sealed enclosure -- golden ratio?
TL-space covers a lot of design options… how much gain in the bass (plus or minus) depends heavily on the options chosen.

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Old 14th September 2017, 12:35 AM   #83
gedlee is offline gedlee  United States
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Originally Posted by 33Polkhigh View Post
Yeah, not a scientific study. I have to say that there is something less musical about a stuffed speaker. A lot of experienced builders use minimal stuffing. Maybe its just that the stuffing filters out higher frequencies so much better and so has a muffling effect on the sound emanating from the box.
I would assume that sound energy takes a path of least resistance and so something that blocks or slightly impedes the waves can affect the behavior of the source but idk.



This has been my experience. In my first build I tried foam on the walls and fully stuffed and liked neither. No stuffing was okay, but when I tried a flattened pancake of stuffing behind the drivers (horizontally) it was the best sound.

I would think a round beehive of stuffing or f-glass in the middle would break up the axial modes which I assume is a good thing. Then the internal sound would dissipate better with less distortions. Also a ball or slug in the middle would make the internal shape itself less important.

Honestly, I can't think if anything good about the back wave of a driver, so, to me, absorbing it is the best thing to do, high or low freqs, its all un-useful.

Damp the cabinet and some internal absorption and don't worry too much about box shape and where and what amounts of damping. Its all too low the significant range to be of much bother. Its what happens outside that matters, not what happens inside. And yes the two are pretty well independent one hardly affects the other.
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Old 14th September 2017, 04:53 AM   #84
Brett is offline Brett
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^^ Agreed.

It also makes example #11407 of trivialities audiophiles obsess about.
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Old 14th September 2017, 08:41 AM   #85
keithj01 is offline keithj01  United Kingdom
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Originally Posted by gedlee View Post
Shape and placement of the sound absorbing material will have a big effect on its effectiveness. This is because sound is absorbed only when there is particle velocity. At the walls the particle velocity goes to zero so absorption on the walls does little. I always place the absorption in the middle of the box, not on the walls. The box shape will affect the mode shape and move the locations of maximum particle velocity around. A long tube with absorption on the walls won't see so much sound attenuation because the wave motion is normal to the walls. Place it in the middle of the tube and it becomes very effective. So shape is a factor, but any shape can be optimized if you know what you are looking for - hence no shape is any better than any other. Only the implementations vary.
Quite agree.

On the subject of the internal walls, the velocities are low and the pressure high, as you've said. But, it's a very convenient place to put some sort of damping material, so it's just a question of choosing the most appropriate in this situation. Usually cited as being effective as a lining is carpet or thick, dense felt. To be used in addition to stuffing the box, of course.

As much as possible needs to be done to absorb rear radiation, as a speaker cone isn't much of a barrier at middle frequencies...
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Old 14th September 2017, 09:06 AM   #86
AllenB is offline AllenB  Australia
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Originally Posted by 33Polkhigh View Post
and so something that blocks or slightly impedes the waves can affect the behavior of the source but idk.
It can, but it needs to be fairly close. Ordinarily higher frequencies will gain independence from the source, then become chaotic in the larger box and resonate, and thus not be very useful. To me this suggests that absorbing them isn't a bad thing.
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Old 14th September 2017, 09:58 AM   #87
lcsaszar is offline lcsaszar  Hungary
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We are talking about two different resonances here:

1. The box walls could behave as vibrating plates, they could be excited by the speaker driver at various "eigenfrequencies". This effect can be reduced by setting the width/length of each surface a golden ratio. Also the thicker is the wall, the higher is the eigenfrequency, and more energy is stored - more difficult to dampen. Bracing will also push the frequency up. This kind of vibration can be reduced by bitumenous felt or similar attached to the internal walls.

2. Standing waves. Golden ratio also helps, and this kind of resonances can be reduced by stuffing (long haired wool, mineral wool, other stuff with high specific heat, since sound energy will be absorbed through friction).

General concensus is that stuufing is good for closed boxes, but not good for ported boxes (and obviously not for horns).
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Old 14th September 2017, 05:43 PM   #88
gedlee is offline gedlee  United States
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I never make ported boxes so I was referring to closed ones.

The structural damping case is the more important but that snot what was being discussed. Stiffer construction is not harder to damp, it is easier. Stiff and undamped is a bad idea however.
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Old 14th September 2017, 08:19 PM   #89
33Polkhigh is offline 33Polkhigh  United States
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Originally Posted by Brett View Post
^^ Agreed.

It also makes example #11407 of trivialities audiophiles obsess about.
You can't just throw stuffing in a box. You need a cylindrical enclosure built around a f-glass beehive.

Seriously though I've found the quality and quantity of box noise matters more than a lot of things including electronics. It depends to on listening volume, size of box, the crossover point etc. There is a nice natural ring that adds space and depth to the sound. Works with room as well.

Bracing is key, the right sound absorption, and probably avoiding obvious axial modes, though modes can be equalized out.
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Old 14th September 2017, 08:44 PM   #90
33Polkhigh is offline 33Polkhigh  United States
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Originally Posted by gedlee View Post
Honestly, I can't think if anything good about the back wave of a driver, so, to me, absorbing it is the best thing to do, high or low freqs, its all un-useful.
Out of curiousity, has anyone here heard an infinite baffle set-up? Does it sound strange not hearing any box or backwave.
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