Golden Ratio Q's

[johndavis]

Again, I must thank everyone for the advice on crossover construction and the veneer tutorials! My next question is hopefully a basic one.

The "Golden Ratio"...

.62:1:1.62

It sounds interesting. In the Noah's 8s DIY project, can I apply that ratio to the construction of the cabinet without throwing everything off-kilter? What I was going to do was to make the top "square" at .62 of the original 10" x 12" (as I remember the measurement), the bottom "square" at 1.62 of the original 10" x 12" and then match the facia boards to the proper angles to the bottom and top. In essence I'd be making a thin, flat-topped tetrahedional pyramid versus the original rectangular "cuboid"-type enclosure.

Am I thinking about this ratio correctly in reference to the actual box construction?

Thoughts?

[Dirk]

> Again, I must thank everyone for the advice
> on crossover construction and the veneer
> tutorials! My next question is hopefully a
> basic one.

> The "Golden Ratio"...

> .62:1:1.62

> It sounds interesting. In the Noah's 8s DIY
> project, can I apply that ratio to the
> construction of the cabinet without throwing
> everything off-kilter? What I was going to
> do was to make the top "square" at
> .62 of the original 10" x 12" (as
> I remember the measurement), the bottom
> "square" at 1.62 of the original
> 10" x 12" and then match the facia
> boards to the proper angles to the bottom
> and top. In essence I'd be making a thin,
> flat-topped tetrahedional pyramid versus the
> original rectangular "cuboid"-type
> enclosure.

> Am I thinking about this ratio correctly in
> reference to the actual box construction?

> Thoughts?

IMHO, the issue of the golden ratio is thrown out of proportion...especially if the interior of the box is properly lined with damping material. Look at Curt C's Exclamations. The midrange is a sphere! This should be the worst possible box shape for the excitation of internal reflection icky-ness. Borrowed shamelessly from Curt's site (http://www.geocities.com/cc00541/index.html):
The detriments of spherical enclosures:
Theory states that enclosures develop standing waves of frequencies dependent on their internal dimensions, and much has been said about the golden ratio providing the best enclosure for mitigating those effects. Since a sphere has the same dimension in all directions, conventional wisdom suggests it would exhibit a single standing wave frequency, and represent the worst possible case for standing waves. Well, I.ve not found that to be the case. Take for example the sphere of the Exclamation, which as an internal diameter of roughly 14 inches. This should result in a fundamental standing wave of approximately 485 Hz. Clearly it should be audible, especially if the sphere is only lightly stuffed. Interestingly enough, this has not been my experience, and any audible effects of standing waves in the sphere.s I.ve auditioned appear to be subtle, if they exist at all.

[killerkowalczyk]

I think you have it all wrong. The golden ratio applies specifically to a rectangular shaped box.

Box dimensions are measured X(.62) Y(1) Z(1.62) (width,depth,heighth).

Say you needed a front face
width = 10" (x)0.62)

your depth would be = 16.13" (y)1)

your depth would be = 26.13" (z)1.62)

now this would give you a volume of 2.5cuft

if you needed a larger or smaller volume you would have to adjust all panel sizes accordingly while keeping the "golden ratio"

The golden ratio is supposed to reduce standing waves in boxes, just incase you didnt know or were unclear on the subject.

hope this helped.

KILLER

> Again, I must thank everyone for the advice
> on crossover construction and the veneer
> tutorials! My next question is hopefully a
> basic one.

> The "Golden Ratio"...

> .62:1:1.62

> It sounds interesting. In the Noah's 8s DIY
> project, can I apply that ratio to the
> construction of the cabinet without throwing
> everything off-kilter? What I was going to
> do was to make the top "square" at
> .62 of the original 10" x 12" (as
> I remember the measurement), the bottom
> "square" at 1.62 of the original
> 10" x 12" and then match the facia
> boards to the proper angles to the bottom
> and top. In essence I'd be making a thin,
> flat-topped tetrahedional pyramid versus the
> original rectangular "cuboid"-type
> enclosure.

> Am I thinking about this ratio correctly in
> reference to the actual box construction?

> Thoughts?

[killerkowalczyk]

This may sound like a stupid question, but is the inside of the sphere, spherical? BTW, I also think that the whole Golden Ratio thing is blown out of proportion. Probably just another audiophile gimick.

> IMHO, the issue of the golden ratio is
> thrown out of proportion...especially if the
> interior of the box is properly lined with
> damping material. Look at Curt C's
> Exclamations. The midrange is a sphere! This
> should be the worst possible box shape for
> the excitation of internal reflection
> icky-ness. Borrowed shamelessly from Curt's
> site
> (http://www.geocities.com/cc00541/index.html):
> The detriments of spherical enclosures:
> Theory states that enclosures develop
> standing waves of frequencies dependent on
> their internal dimensions, and much has been
> said about the golden ratio providing the
> best enclosure for mitigating those effects.
> Since a sphere has the same dimension in all
> directions, conventional wisdom suggests it
> would exhibit a single standing wave
> frequency, and represent the worst possible
> case for standing waves. Well, I.ve not
> found that to be the case. Take for example
> the sphere of the Exclamation, which as an
> internal diameter of roughly 14 inches. This
> should result in a fundamental standing wave
> of approximately 485 Hz. Clearly it should
> be audible, especially if the sphere is only
> lightly stuffed. Interestingly enough, this
> has not been my experience, and any audible
> effects of standing waves in the sphere.s
> I.ve auditioned appear to be subtle, if they
> exist at all.

[killerkowalczyk]

and by the way, width, depth, and heighth can also be juggled around (say you needed a really wide front baffle and a short height and front to back, then you might want to make the 1.62 ratio apply to the width, 1 to height and .62 to depth.

KILLER

> I think you have it all wrong. The golden
> ratio applies specifically to a rectangular
> shaped box.

> Box dimensions are measured X(.62) Y(1)
> Z(1.62) (width,depth,heighth).

> Say you needed a front face
> width = 10" (x)0.62)

> your depth would be = 16.13" (y)1)

> your depth would be = 26.13" (z)1.62)

> now this would give you a volume of 2.5cuft

> if you needed a larger or smaller volume you
> would have to adjust all panel sizes
> accordingly while keeping the "golden
> ratio"

> The golden ratio is supposed to reduce
> standing waves in boxes, just incase you
> didnt know or were unclear on the subject.

> hope this helped.

> KILLER

[robertcottiers]

> and by the way, width, depth, and heighth
> can also be juggled around (say you needed a
> really wide front baffle and a short height
> and front to back, then you might want to
> make the 1.62 ratio apply to the width, 1 to
> height and .62 to depth.

> KILLER

And the winner by 2nd round TKO..and new Light heavyweight champion.

Just my .02 cent prediction

Bob C.

[killerkowalczyk]

am I wrong? do I sound like an idiot or something?

> And the winner by 2nd round TKO..and new
> Light heavyweight champion.

> Just my .02 cent prediction

> Bob C.

[Dirk]

> am I wrong? do I sound like an idiot or
> something?

Meh. No more than normal. ;-)

You're right that all 3 would have to be adjusted in unison. And in doing so, you'd be changing the width of the front baffle, which is MUCH more likely to cause detrimental effects.

[killerkowalczyk]

I was saying a wide baffle might be needed for space constraints, or a large diameter woofer that only needs a small cabinet would only be able to fit on that particular side.

> Meh. No more than normal. ;-)

> You're right that all 3 would have to be
> adjusted in unison. And in doing so, you'd
> be changing the width of the front baffle,
> which is MUCH more likely to cause
> detrimental effects.

[DaveBurke]

quite simply the ratio was determined to break up the cabinet vibrations into the most effective frequencies to break up peaks. Since each cab has walls usually of different sizes and shapes you can assume it's not a corrective measure but an very general idea, or another "tool" so to speak. For instance, I've used the principle for internal bracing, dividing the bracing and spacing according to the ratio with good results. As far as just going a "golden ratio" cab I think your results will be minimal compared to a well designed cab and bracing. Of course with a thin walled cab and no bracing you may see some noticible improvement but I'd sumise you have other worse problems in that case. Your "Q" (or total box Q) is a direct result of your driver in combination with your cab design, damping, etc and this golden ratio won't change or effect total Q just by it's shape.

Hope this helps

Dave

[unknownuser]

you will be doing worse to manipulate the baffle to accomadate the golden ratio. As the box is right now:
H= 176Hz
D= 645Hz
W= 753Hz

All of these can be fairly well midigated with damping material on the walls except the standing wave of the hieght. I suggest a shelf in the midle of the enclosure to push the standing wave of the hieght up to were you can deal with it using damping material. Make sure air can pass thru the shelf.


(Originally posted by: new guy)

[unknownuser]

> This may sound like a stupid question, but
> is the inside of the sphere, spherical? BTW,
> I also think that the whole Golden Ratio
> thing is blown out of proportion. Probably
> just another audiophile gimick.

Its not a gimick. As far as speakers go, its a much smaller scale and not so noticable.
The idea behind the GR is to spread all the modes of an enclosed area out evenly instead of piling up at certain frequencies (dependant on distance). This is no more a gimmick than saying music will sound better in a larger room than smaller. Larger roomes spread the modes out more , whereas smaller rooms have the modes bunched together in a narrow part of the audio band.


(Originally posted by: new guy)

[unknownuser]

(Originally posted by: new guy)

[curt_c]

IMO, the golden ratio is not as important as other good enclosure practices. As the standing waves can be easily mitigated with judicious use of stuffing, I'd suggest moving the port to low on the back (or front) baffle and adding a small amount of polyfill in the center of the enclosure and behind the woofer. This will go a long ways to eliminate the inherent standing waves, and will not audibly affect the port output.

Proper bracing is always important. Using the bracing to also push the standing wave frequencies above the passband of the woofer would be advantageous as well, but probably not easily accomplished on this design.

C

[damkor]

>Since a sphere has the same dimension in all >directions,

No.

This discussion was had some time ago. With a rectangular box, there are 6 definable parallel planar surfaces, so we talk of three dimensions.

In a sphere, you might THINK that the single most important analogous dimension is the diameter, (after all, there are an infinite number of lines, each exactly one diameter long inside the sphere).

BUT, there are an infinite number of lines of ALL dimensions inside a sphere, that a sound wave can take! Picture a circle with a dodecahedron drawn inside and you can picture this. Sound does not resonate only between diameters, going through the center of the sphere.

Therefore the inside diameter of a sphere is NOT the important dimension that L, W or H inside a rectangular box is. So, it is an error to predict that standing waves inside a sphere would be bad. So, the contrary result does not challenge the importance of internal dimension.

[Dirk]

> No.

> This discussion was had some time ago. With
> a rectangular box, there are 6 definable
> parallel planar surfaces, so we talk of
> three dimensions.

> In a sphere, you might THINK that the single
> most important analogous dimension is the
> diameter, (after all, there are an infinite
> number of lines, each exactly one diameter
> long inside the sphere).

> BUT, there are an infinite number of lines
> of ALL dimensions inside a sphere, that a
> sound wave can take! Picture a circle with a
> dodecahedron drawn inside and you can
> picture this. Sound does not resonate only
> between diameters, going through the center
> of the sphere.

> Therefore the inside diameter of a sphere is
> NOT the important dimension that L, W or H
> inside a rectangular box is. So, it is an
> error to predict that standing waves inside
> a sphere would be bad. So, the contrary
> result does not challenge the importance of
> internal dimension.

If I read you right, you're saying that spheres have an infinite number of resonances? Or that spheres excite all frequencies more-or-less evenly? I can conceed that point.

However, I still firmly believe that proper damping materials can make these "internal reflection" issues quite moot.

[johndavis]

It seems that I have overestimated this "golden ratio" idea.

What I was going to do instead of polyfill was use egg-crate foam...of which I have a good amount left from a purchase a couple years ago from PE.

The idea of using an internal brace with larger holes in it (like a screen) that doesn't inhibit air flow seems like a good idea. Where should that brace be put? In between the tweeter and woofer, below the woofer and above the port or somewhere else?

Thanks again for all the advice!

[damkor]

> If I read you right, you're saying that
> spheres have an infinite number of
> resonances? Or that spheres excite all
> frequencies more-or-less evenly?

Both. Makes them good for internal volume shape as well as external baffle shape.

I agree that the dimension thing may be overstated. I like the "acoustic ratio": 0.78 : 1: 1.2599. Golden ratio makes things quite long and narrow.

More important is the size: Make the volume big.

[curt_c]

> It seems that I have overestimated this
> "golden ratio" idea.

Not at all...

In this design, I'd suggest either a couple of windowpane type braces, one below the woofer, and the other further down, or... a single windowpane brace running vertically down the sides, and a couple of broomstick type braces tying the front and rear baffles together.

Here's where the GR comes in... You don't want to space the braces so that there are equal distances between the unsupported enclosure panels. -So use the GR, or some odd multiple such as 2/3/5, etc. to determine the bracing distances from each other. The broomstick braces should be offset on the panels as well...

C