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Old 18th December 2009, 12:45 PM   #1
jmar is offline jmar  United States
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Default Sealed enclosure -- golden ratio?

I need a lesson on the importance (or not) of the L-W-H dimensions of a sealed enclosure.

I've read in the past about the "golden ratio" but I've seen box enclosures that are "all over the place" since the 1970's

It seems that the more recent boxes have the depth longer than the width.

In the past, I've seen the opposite.

I'm sure it may be a function of the driver parameters? BUT generally what should you shoot for? (and why? -- please teach me).

After all, air is moved with more force from the front and back so in a sealed enclosure it would seem that making the depth longer would make sense.

I'm interested at the moment in building a simple system using the Pioneer B20 full range in a sealed enclosure and I again see dimensions (width and depth) that are inconsistent.

One plan calls for a 10" wide, 6" deep, 40" high?

THANKS.
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Old 18th December 2009, 12:56 PM   #2
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Having the longest dimension as the depth helps to reduce the intensity of rear wall reflections back through the cone. Also there has been a tendency towards narrower baffles for improved imaging in more recent years (this works well with transforming the box to have what would previously have been the width become the depth and vice versa.

As far as golden ratio's are concerned, it doesn't hurt because it ensures you don't make a box that is prone to pipe resonances. A rule of thumb is that no internal dimension should be more than 3 times that of any other. If you stick to that you should be ok. Another rule of thumb would be that you shouldn't have any two internal dimensions the same (or very close to the same).

One of the main reasons you don't see too many golden ratio boxes these days is because they tend to be ugly

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Old 18th December 2009, 01:00 PM   #3
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Attached is a chart I worked out many years ago. It shows plots of the depth (left one), width (center one) and height in inches vs box volume. It's based on the 0.62: 1: 1.62 golden mean ratio used by artists for centuries.

You just need to decide on what your box volume needs to be based on your driver's T/S parameters. You can use a free box calculator program available on the WWW. Just Google search.
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File Type: jpg Speaker box dims vs box volume w golden ratio.jpg (604.4 KB, 786 views)
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Old 18th December 2009, 03:43 PM   #4
jmar is offline jmar  United States
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Well certainly as you say a deeper cabinet (although an eyesore) would be better than the dimensions for this Pioneer B20 project.

It shows 9.75" wide and only 5.5" deep.

For an 8" woofer I would think that would be a problem (and even have some audible negatives?)

I'll copy that graph for future reference.
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Old 18th December 2009, 07:52 PM   #5
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None of the internal dimensions should be a multiple of another to avoid reinforcing standing waves.
Ideally none of the internal walls should be parallel but that makes building them a fair deal more complex.
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Old 18th December 2009, 09:21 PM   #6
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Let me tie some of these comments together.

1/ internal box ratios are best if they are multiples of irrational numbers so that a standing wave across one set of opposite box walls does not reinforce any of the others. Be careful with the square root of 2.
2/ the golden ratio (phi) is an appealing irrational number. Due to one of its properties it is easy to calculate the internal box dimensions. Take the total required gross volume (ie includes volume of back of driver & all bracing) and find the cube root. That is D1. Then multiply D1 by phi for D2. Take D1 and divide by phi to get D3. Choose any side for the driver. Each has it's advantages and disadvantages. A Classic GR, sets D1 to width and D2 to height. Rotating it such that D1 is now depth fits today's aesthetic better.
3/ if one dimension starts to become significantly larger than the others (wintermute mentioned 3x) then the box becomes a quarter-wave resonator (ie a TL) if it has a hole/port/terminus in it, and a half wave resonator if sealed.

Click the image to open in full size.

dave
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Old 19th December 2009, 01:47 AM   #7
gedlee is offline gedlee  United States
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Quote:
Originally Posted by jmar View Post
I need a lesson on the importance (or not) of the L-W-H dimensions of a sealed enclosure.

THANKS.
"Not" really, as long as there is enough damping material inside to dampen any standing waves. I like my enclosures "near" cubic, but not exactly cubic. The cube has the greatest internal volume with the least surface area. This will minimize the potential for box reradiation through stuctural resonances.
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Old 19th December 2009, 02:16 AM   #8
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IMHO the golden ratio looks nice but has little to do with speaker building. Build an irregular box. Angle the front. Or something. Irregular boxes, IMO, tend to have fewer high Q resonant modes of the panels.

CH
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Old 19th December 2009, 02:27 AM   #9
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Quote:
Originally Posted by Conrad Hoffman View Post
Irregular boxes, IMO, tend to have fewer high Q resonant modes of the panels.
If a panel is going to resonate, a high Q one is preferable to a low Q one as it will be less audible.

dave
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Old 19th December 2009, 05:39 AM   #10
gedlee is offline gedlee  United States
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Quote:
Originally Posted by Conrad Hoffman View Post
IMHO the golden ratio looks nice but has little to do with speaker building. Build an irregular box. Angle the front. Or something. Irregular boxes, IMO, tend to have fewer high Q resonant modes of the panels.

CH
I'm sorry but this is not correct. The shape of the box cannot have any effect on the Q of a resonance. It also doesn't have any effect on the modal density, that depends only on the total volume. Thats why as far as the internal box effects are concerned shape doesn't have much of an effect.

Quote:
Originally Posted by planet10 View Post
If a panel is going to resonate, a high Q one is preferable to a low Q one as it will be less audible.

dave
Are you saying this because of Floyd Tooles work? because I don;t think that applies here. And if not then what are you basing this on because it seems to me that the effect would be the opposite.
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