# the 1:3 rule of cabinet dimension?

#### contessa

I was trying to build a fullrange sealed box with the volume of 30cm*30cm*115cm.

However, I have found threads on enclosure dimensions, pointing out:

'if the length of an edge is excessively greater (3 times as a rule of thumb) than the others, the box will act as an ML-TL, instead of behaving as a sealed box.'

is this phenomenon caused from standing waves within the enclosure?

as a humble hobbyist, I am quite not sure if I have understood it correctly...

if it is, would my enclosure design work properly as a sealed box, if I put in enough stuffing, to suppress the standing waves?

judging by the Boxnotes simulation, I assume that fully (in theory, as bass absorption would be a tough task) absorbing sound waves within the enclosure from 176hz and up would eliminate any unwanted resonances caused from standing waves... but I am again unsure of whether I understand how all this works.

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#### planet10

Paid Member
!:3. Not a rule AFAIK. It is not really enuff to push a BR to an ML-TL.

But one should try to avoid dimensions that are the same (ie 30x30), and integer (3) multiples should be avoided. Irrational numbers are your friend.

dave

1 user

#### contessa

!:3. Not a rule AFAIK. It is not really enuff to push a BR to an ML-TL.

so, 30*30*115cm wouldn't turn a sealed enclosure into an ML-TL...

what a relief!

I will redesign the width and depth according to your comments however.

#### planet10

Paid Member
No. Actually given it is a sealed box it can never morph into an ML-TL which is a quarter-wave resonance (ie has a hole in the box). It can morph into a sealed half-wave transmisison line. A half-wave line needs to be 2x as long as a quarter-wave line.

I would change the 30x30cmto soethign less square.

dave

1 user

#### contessa

A half-wave line needs to be 2x as long as a quarter-wave line.

then my box will definately keep acting as a sealed box.

I will also take account of enclosure shapes' effect, as you suggest.

Thank you very much!

#### GM

Yes, and no in that a sealed or vented box program assumes it has an air mass 'plug' of uniform particle density, but as its aspect ratio increases it begins to develop eigenmodes (open pipe in this case) with peaks/dips in the response modulating the driver(s), which in your case begins at ~34400/2/115 = ~150 Hz.

You can sim it in Hornresp where you can even find the ~ideal driver offset and amount of stuffing density to quell them.

#### WhiteDragon

Golden Ratio works out well too.
Which will make the baffle slightly wider. Depth shorter
And Height will appear pleasing and not odd looking.
Since the ratio is found rather pleasing aesthetically.

No sides will be equal. less likely for resonance
Ironically when doing diffraction sims
flattest response is almost or directly lined up to
smaller divisions of same ratio. And wider baffle
usually flatter response anyways. all good

You can use exact 1.618 ratio.
or just round to no decimal.
I just make it close to even numbers
so finding center is easy.

Base the ratio off widest speaker on the baffle.
So 10" around 255mm

37
60
97
158
- 255-
413
668
1081
1749

413 wide by 668 tall
or 413 wide by 1081 tall

depth 255 or 413 whatever yields needed volume.

or as mentioned 412 so finding center is easy

1 users

#### planet10

Paid Member
Golden Ratio works out well too

An oft used irrational number. I use it in these boxes.

The basic math is:
1/ take the cube root of the volume.
2/ multiply one dimension by 1.618
3/ divide another one dimension by 1.618

Gives you a 0.618:1:1.618 (note 1/1.618 = 0.618)

dave

2 users

#### WhiteDragon

rather beautiful isn't it
AKA Golden Mean, Golden Section.... or = Divine Proportion.

I remember overthinking baffles for designs.
I can start design / and sim instantly.
Since the largest driver defines the width
and everything else.

everything now , all done, 1 minute
use largest driver or plywood thickness
So no cuts are weird or off.

Like 18mm ply =

7
11
18
29
47
76
123
199
322
521
843
1364
2207

numbers are rounded to nearest decimal
tends to look better with largest driver as the ratio
start point

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#### Richard Ellis

Another aspect that I like to do is offset the drivers location on the horizontal axis...IE , not centered on the 30cm width...say an offset of 0.618 ...I read somewhere that the rearward traveling acoustic pressure wave can "reinforce" itself if the distance traveled inside is equal from any other, off the cone & reflected back, trying to induce a vibration. This applies to the vertical axis as well.

-------------------------------------------------------------------------------------------------------------------------------------Rick...

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#### planet10

Paid Member
Another aspect that I like to do is offset the drivers location on the horizontal axis

Me too. You will note that the wide CGR shown above the driver is offset (vertically & horizontally) based on the Golden Ratio.

dave

#### WhiteDragon

Another aspect that I like to do is offset the drivers location on the horizontal axis...IE , not centered on the 30cm width...say an offset of 0.618 ...I read somewhere that the rearward traveling acoustic pressure wave can "reinforce" itself if the distance traveled inside is equal from any other, off the cone & reflected back, trying to induce a vibration. This applies to the vertical axis as well.

-------------------------------------------------------------------------------------------------------------------------------------Rick...
yep ironically it just proves itself over and over.
Even in Sim.
Flat response will fall on or close to the ratio numbers.

300mm baffle offset would be close to smaller numbers of ratio.

44
71
115
185
300

vertical horizontal tweeter etc etc.
will fall on those
with diffraction tools now.
you see it or find it easily in sim

#### contessa

I didn't know that hornresp could simulate enclosures other than horn. Should look into it...

and also thank you all for introducing priceless tips, such as using the golden ratio

#### AllenB

Paid Member
would my enclosure design work properly as a sealed box, if I put in enough stuffing, to suppress the standing waves?
Yes, this is the key.

The common view may be that even if you make the box bigger by making it wider you still have the long dimension standing waves. Some see this as OK because if you have more resonances they can possibly do a better job of evening each other out.

However, they can still be non minimum phase. It is still preferrable to damp them unless you want to use them.

#### wdyn1

Indeed! There are some amazing examples in design and nature of various irrational numbers (everywhere!). The history of it is also fascinating and has some interesting theories of its own.

A short primer on the construction of useful irrationals:

1.618... (phi, the golden ratio, etc.)

2. Find the midpoint of AB (let's call it point E)
3. Using a compass, find the distance from E to D or C
4. Trace an arc of length EC (or ED) from point E
5. Extend AB to intersect the arc (point F)
6. Construct a rectangle AFGD

If you work out the math of length AF vs the length of AD, you'll find that it is (1 + sqrt(5)) / 2 which is approximated by 1.618

1.414... Square Root of 2

2. Using a compass, find the distance between AC or BD
3. Trace an arc of length AC (or BD)
4. Extend AB to insect the arc (point F)
5. Construct a rectangle AFGD

Continue ad infinitum using the previous rectangle to replace the square in step one (e.g. square -> sqrt(2) -> sqrt(3) -> sqrt(4) -> (sqrt(5)...)

#### mdpaudio

The guy that invented math must have been real smart! Lol
nature apparently studied the math guys stuff because these ratios are all over the place. Nature was smart to listen to the math guy because it makes stuff work. Some guy named Fibonacci tried to take credit for what nature already knew. Basically, look to nature for good ideas, it’s been doing it for a long time and outside of the platypus has gotten it right!

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#### wdyn1

The guy that invented math must have been real smart! Lol
This is a question mathematicians are sometimes asked: Do you invent or discover?

A lot of them feel that they fall on the discovery side, but admit that there is room for invention. Then there's applied mathematics which is more my bag.

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#### wchang

... discover theorem, invent algorithm

#### planet10

Paid Member
This is a question mathematicians are sometimes asked: Do you invent or discover?

A lot of them feel that they fall on the discovery side, but admit that there is room for invention. Then there's applied mathematics which is more my bag.

In my experience math is discovery that sometimes uses clever tools invented by somebody. Liebniz/Newton -> Calculus,

My only mathematical “invention” was a clever proof for a differentail equation problem (2nd year) using some topology theories (4th year course). I hadn’t paid much attention in class and din’t have a clue how to do it the conventional way. Prof siad it was very creative. It gave me a comfortable pass.

dave

1 user