Do Speaker Enclosure proportions matter...Fibonacci numbers

[Akira]

I know some will say that only the 'air space' interacting with a given driver matter. The actual shape of the enclosure is of little consequence.
I have always believed that dimensional ratios play into design. (and please don't quote me the inverse square law-- that is really rudimentary)

I came accross an article on Fibonacci numerical sequences which I found fascinating. http://en.wikipedia.org/wiki/Fibonacci_number
In simplest terms it is a mathematical sequence that appears in nature, art, music, studio design, architecture and dare I say "snake oil" speaker wire. http://goldennumber.net/acoustics.htm

I know by instinct and past experience the the Fibonacci ratio of 1 : 1.618 is a natural choice for studio design. And apparently the dimensions of a Stradivarius violin.

Does this apply to enclosure design?

[4313B]

Over twenty five years ago I determined that the 1.62 : 1.00 : 0.62 ratio wasn't all that great for a loudspeaker box (unless you use the 0.62 edge as the baffle instead of the side). Boxes with narrow baffles, curved or non-parallel sides and 0.80 or better depth to width ratios seem to sound significantly better. For subwoofers I usually try and use 1.25 : 1.00 : 0.80

[1audiohack]

I know some will say that only the 'air space' interacting with a given driver matter. The actual shape of the enclosure is of little consequence.
I have always believed that dimensional ratios play into design.

From the statement above I take it that you are concerned with the internal dimensions of the enclosure. If that is the case then the dimensions are of little consequence as long as the enclosure is acoustically small. As an example if you are building a subwoofer that is cut off at 80Hz, it would have to have at least one internal dimension of 7.06 feet to support a standing wave at 80Hz and would be incapable of any type of constructive or destructive interferrence below 80Hz, build a cube if you want to. The problem comes at you fast with increasing frequency however, at 500Hz your first problem shows up at only 1.13 feet.

Two of the "preferred" dimensions I see quoted most often are, the "Golden Ratio" of 0.618 X 1.0 X 1.618, and the "Acoustic Ratio" of 0.7937 X 1.0 X 1.2599. If you do the math on frequency wave lengths with these ratios you find the Golden Ratio will support standing waves at 2/3 octave intervals while the Acoustic Ratio will support standing waves at 1/3 octave intervals. The rules of Small Room Acoustics apply to these enclosures as well.

I agree with 4313B, the Acoustic Ratio sounds better to me as well.

[Akira]

A box that seems to fit the Golden ratio is the 4315. Great sounding box-- my fav speaker.
Your argument favoring the Acoustic ratio is sound, so perhaps dimensional proportions do make a difference.

In a recording studio, you are talking about large rooms. A control room requires a minimum 18' of clearance to reproduce an unbroken 60Hz wave length. That doesn't mean a smaller room will not work or even sound good. It just means constructive or destructive wave lengths will add or subtract to the main fundamental.

[1audiohack]

I don't mean to infer that one ratio is superior to all others. The baffle size and arrangment has effect as well.

Manfred Schroder basically defines a large room for wide range music room at 250,000 cubic feet or greater. The "acoustical" size of a room is a frequency dependent phenmenon right? So we are dealing with room modes rather than a statistical reverberant sound field, small room acoustics apply here.

When I work out the dimensions for a listening room or a loudspeaker enclosure without the aid of a computer program I use lined paper and create a Horizontal 1/3 octave scale in the range I am interested in. Take the dimensions of the space you are working within and find the first modes, Fo equals 1130/2L in feet. Draw a vertical line from the apropriate point on your octave scale three lines high, unless you're in a cube or sphere you now have three vertical lines, X2 each frequency for mode two and draw a vertical line
two lines tall, X3 the original modes for mode three and draw them one line high. You can go on but I consider this far enough for a loudspeaker enclosure, you're just getting started for a critical listening space as you know. What you
don't want is for them to pile up anywhere, if they do you get to start changing dimensions to scatter them out for better distribution.

[Soloford]

I wonder if you can give me some guidance on my project? I have a set of 4343B's...I have rotated the upper baffles 90 degrees...have mounted the speakers sideways...up close to the ceiling...on special shelves that keep the enclosures away from the walls and toed into the room. I'm considering cutting 5 inches off of the 41 inch dimension of the stock cabinets...reducing the cabinets to 36 inches wide by 25 inches tall by 14 inches deep. The box around the mid's remains stock, as does the bass enclosure.

Any idea how will this affect the sound of the speaker? And if so, is there a way to adjust for it...like adding a sealed box on the back to add back the loss in volume and putting a port on the high frequency side to that new box?

I'm limited in the width and height profile of the speakers...but I could add more depth....

Any help you could give would be appreciated...Thanks!

[1audiohack]

Hey there Soloford;

I'll jump in but need some more information. Should we jump this back to your original thread?

[Ian Mackenzie]

Common sense will always prevail but I have read one foremost loudspeaker engineer say just fill the enclosure with fibreglass and the acoustic issues go away. There's logic to that when you understand how much sound energy the fluff absorbs.

Have a look inside the 4344 and its loaded.

I would suggest it depends on how critical you are..I mean some drivers and box construction are so poorly implemented that it matters not.

The more complex the system, the more these things matter.

A while back there ended up being a war of words when one member made some changes to an L200. The signal to noise ratio of that thread go so bad I can't recall of the box was at fault or not.......

[4313B]

A while back there ended up being a war of words when one member made some changes to an L200. The signal to noise ratio of that thread go so bad I can't recall of the box was at fault or not.......

Yep. That's why it's best to just not get involved, especially on the Internet. The man himself actually got involved in that one with the end result being "It's the box. No one here at JBL ever liked that system anyway." L200b

[Ian Mackenzie]

Yep. That's why it's best to just not get involved, especially on the Internet. The man himself actually got involved in that one with the end result being "It's the box. No one here at JBL ever liked that system anyway." L200b

Then there's the guy who looses it because nobody cares.

The wrong box was actually the title of a funny movie.

I guess we should now move on to coffin couplers.