Go Back   Home > Forums > Loudspeakers > Full Range

Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 16th February 2014, 09:59 AM   #1
diyAudio Member
 
Join Date: Dec 2010
Location: North, lakes region
Default Open baffle Nautilus: the Fibonacci solution to edge diffraction

Wondering about open baffle from the last couple of months, I finally decided to give them a try, so I bought a pair of Fostex FF85wk and put inside a rectangular baffle 20" height and 12" wide, very close to the golden rectangle

As soon as I connected the two raw test article to my Trends Audio 10.1, it became immediately clear to me that I love the open baffle sound vs boxed speakers, in this case further enhanced by the coherence of the little fullrange

Bass, below 200Hz, was compromised of course, but the rest of the spectrum was soooo clear, sweet, open and detailed, only sound stage and imaging suffered a bit, I thought due the wide baffle

So I decided to try different baffle shapes and test how the edge diffraction affects imaging and sound signature

First I simply moved the fostex off center in the same rectangular baffle, using the Fibonacci sequence to determine the exact offset from one side edge, then the upper and finally the other side.

Things audibly improved, a bit

Then I cut the upper half of the baffle following the Fibonacci spiral shape, the same golden spiral present in nature in many life form, with the fostex in the spiral center

Click the image to open in full size.

Bingo!!

Things improved further, this time a lot !!!

Imaging improved dramatically, but also sound signature changed for the better, all traces of peak and dip along the spectrum due to edge difraction disappeared completely

To make sure it wasn't a placebo, I compared the spiral to other two shapes

First the same 12"x20" rectangle with the upper edge rounded, with the fostex placed centered in the baffle but off the circle center: this sounded reasonably good, but not as good as the spiral and less focused

Second, I cut away other material, narrowing the baffle to a bullet shape: imaging improved, but the lower mids became thinner, unbalancing the frequency response to the upper mids

Click the image to open in full size.

Tried again the golden spiral, yeah, that one sound right in every aspect, I stay with it

Next step was to add the right weight to the bass, so I added an Eminence Alpha 8a, cut at 150Hz with a passive second order LC filter

The eminence proved to be the right partner for the little fostex, giving to these loudspeakers the right balance all over the spectrum; bass will be never shaking or kicking, but wonderfully crisp and natural, without any boominess tipical of boxed speakers

That's it, we have the Nautilus

Click the image to open in full size.

Click the image to open in full size.

Click the image to open in full size.

Probably would be better biamped with an active crossover, but for the moment I'm happy with the result
Attached Images
File Type: jpg Golden Mean Complete.jpg (41.3 KB, 932 views)
File Type: jpg 20140215_104742.jpg (662.6 KB, 1060 views)
File Type: jpg 20140215_105004.jpg (854.8 KB, 986 views)
File Type: jpg 20140216_114220.jpg (804.3 KB, 974 views)
File Type: jpg 20140215_104851[1].jpg (959.3 KB, 991 views)
  Reply With Quote
Old 16th February 2014, 02:36 PM   #2
diyAudio Member
 
MITsound's Avatar
 
Join Date: Jul 2013
Location: Burnaby
Blog Entries: 1
Nice job!
I settled on two golden ratio rectangles, one stacked sideways.
This pretty much gives a 1-4-9 ratio, the first evenly square rootable numbers.
Also the 2001 Space odyssey monolith's ratio.
  Reply With Quote
Old 16th February 2014, 05:11 PM   #3
diyAudio Member
 
Join Date: Dec 2010
Location: North, lakes region
Interesting...

Sometimes I feel we music lover are quite disturbed People

But... I can't exactly figure out what do you mean for stacked sideway, can you provide a picture?
  Reply With Quote
Old 16th February 2014, 05:19 PM   #4
diyAudio Member
 
Join Date: Sep 2008
Nicely done! What is the significance of the Fibonacci spiral shape you mention? How far down in frequency do you think this effects your design?
  Reply With Quote
Old 16th February 2014, 06:08 PM   #5
diyAudio Member
 
MITsound's Avatar
 
Join Date: Jul 2013
Location: Burnaby
Blog Entries: 1
:smash
Can't load photo at this time. But if you start with a 24" wide baffle measurement, multiply it by 1.618. This is 38.832.
Multiply 24 x0.618. This is 14.832.
So there are two golden ratio rectangles, 24x14.832", and 24x38.832".
When these are stacked long axis of the big one with the short axis of the small one, a 24x 53.664 panel is created.
With the addition of 5 1/4" "wings behind the sides of the baffle, this is very close to a 1-4-9 ratio of depth to width to height of my horned open baffle.
Sorry I'm not able to send a diagram or photo.
Most people like the looks of this panel ratio.
And it wastes very little from a 4x8 plywood sheet, with the off cuts well suited to supply the base, top wing, and nice brace for the woofer motor.
Attached Images
File Type: jpg image.jpg (504.3 KB, 132 views)
  Reply With Quote
Old 16th February 2014, 06:09 PM   #6
diyAudio Member
 
Join Date: Dec 2010
Location: North, lakes region
Quote:
Originally Posted by pcb121055 View Post
What is the significance of the Fibonacci spiral shape you mention? How far down in frequency do you think this effects your design?
Honestly, the Fibonacci sequence and then the golden spiral were just an enlightenment without any scientific basis.

I was just thinking about how to reduce the edge diffraction, and to me an asymmetric shape with a curvature that spread continuosly the distance from speaker to edge (and hence wavelenght) would have been the right solution, and suddenly golden spiral came to mind.

Why not? It was just a bet, and to my ears was the right one

Moreover, why we continue to stick to squared loudspeakers (boxed or open baffled) when I can recall no one music instrument with squared shape?

Unfortunately I can't provide any measurement, I just can tell you that is the most musical piece of wood with speaker that I've ever heard, just try yourself, is quite easy and I'd like to know more opinions
  Reply With Quote
Old 16th February 2014, 06:10 PM   #7
diyAudio Member
 
MITsound's Avatar
 
Join Date: Jul 2013
Location: Burnaby
Blog Entries: 1
I guess the photo went through. Sometimes it's better to be lucky than good.
  Reply With Quote
Old 16th February 2014, 06:14 PM   #8
diyAudio Member
 
Join Date: Dec 2010
Location: North, lakes region
Ok MITsound, I see now, thank'you for the explanation
  Reply With Quote
Old 16th February 2014, 06:22 PM   #9
diyAudio Member
 
Join Date: Mar 2007
Location: California
Deriving the baffle shape from a famously-named spiral is not doing anything special in this case. Anytime you place a driver near an edge of an open baffle you get the benefit that much of the amplitude of the dipole oscillations is reduced, especially in the case of your small fullranger. This is the same whether your baffle is spiral, ziggurat, pyrimidal, rectangular, or whatever shaped.

The proximity of the driver to the edges of the baffle is influencing the dipole radiation pattern. That is all. Enjoy.
  Reply With Quote
Old 16th February 2014, 06:33 PM   #10
diyAudio Member
 
Join Date: Dec 2010
Location: North, lakes region
Quote:
Originally Posted by CharlieLaub View Post
This is the same whether your baffle is spiral, ziggurat, pyrimidal, rectangular, or whatever shaped
Hello Charlie, thanks for the valuable technical contribute, but I have to disagree with the above statement

I tried many different shapes, both curved or squared, centered or near the edge, and every one does sound different, and to me, the spiral gives the most correct and natural presentation

Maybe it's a placebo induced by the nice looking woodwork , but for sure, as you said, I enjoy
  Reply With Quote

Reply


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Any open baffle Edge experts help with a redesign Pls webby Full Range 37 5th January 2014 12:59 AM
Baffle Edge Diffraction has been extensively discussed - what about Grills? Nvr2manybikes Multi-Way 19 28th June 2013 07:14 PM
Edge diffraction: large, rounded baffle, or narrow square baffle fortyquid Multi-Way 23 12th February 2013 02:23 AM
Edge ? full range open baffle pforeman Full Range 3 12th June 2010 11:47 AM
Will this take care of edge diffraction? amo Multi-Way 6 14th June 2004 05:08 PM


New To Site? Need Help?

All times are GMT. The time now is 02:53 PM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright 1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2