new speaker baffle design concept...good or not?

[thadman 10+ year member]

I was thinking today about wide open baffles and narrow open baffles and the benefits of both (wide=later rolloff, narrow=less baffle reflections) and realized an idea.

I could place quarter wavelength foam on the front and rear of the baffle to eliminate all baffle reflections, but still maintain the low-roll off point of a wide open-baffle.

For a 3-way, It would be constructed like this.

I would build a compound tower, composed of 2 baffles (each 24" x 24"). The base baffle would be angled upwards slightly (5*-10*) and would house a 15" midbass driver crossed below 560hz (~24) as to eliminate all baffle reflections in its passband. The upper baffle would be a 24" wide x 24" tall x 9" deep structure. The baffle would be placed within this structure in the very middle (4.5" deep) and all unnecessary surface area would be cut away, as to minimize reflections and allow the waves to travel from the front sheet of foam to the rear. A sheet of 4" deep foam would be placed inside the structure in front of the baffle, and another 4" sheet of foam would be placed behind the baffle. The frequencies radiating from the front would extend through the front piece of foam to the rear and the rear wave would do just the opposite. The midrange and tweeter would be placed within the very center of this baffle and foam would be trimmed accordingly as to allow 30* of off-axis response. I would then cover the top baffle with grille cloth as to shroud the foam and make it aesthetically pleasing.

Hopefully, through the integration of the foam to the baffle, I can eliminate all baffle reflections.

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[thylantyr 10+ year member]

/curve ball

You can think of loudspeaker design as an artform where you make compromises to get the desired effect.

For instance, make a huge ugly box that takes up a chunk of the living room and

install speakers. Technically, it may perform flawlessly. When people come

to audition it, even before they listen, because it's so ugly in design, they will not even notice the sonic rewards because the ugly factor is too dominant

in their brain.

Take those same drivers and make a cute speaker box and people will

automatically say that it probably sounds as great as it looks in spite of any

technical shortcomings.

Moral of the story. Be a magician and create an illusion of sonic superiority

by making a pleasing design over a technical design. Then later, fix anomolies using

an electronic front end {EQ, etc.}. The reward will be greater in the long run as

the ugly duck will get annoying.

 

[thadman 10+ year member]

This isnt a design marketed towards consumers...this is a personal design that I would like to implement myself.

Does the concept itself work? Is it feasible?

The foam would be covered in grille cloth so I hardly think it would look appalling compared to other wide open baffle designs

 

[joetama 5,000+ posts]

Alright, I think that I am on the same page are you from reading your post there. So, this has been done in some PA speakers before. Foam has even been used in horns, JBL Line Arrays, to better time align the horn to the mid-range while deleting some standing waves in the throat of the horn. It does work; however make sure you keep in mind the displacement of any foam that you add in a baffle or in the box. The deadening factor of the foam or cloth can run you into having a bit too dead of a sound making the speaker system sound almost thin or hollow.

 

[thylantyr 10+ year member]

This isnt a design marketed towards consumers...this is a personal design that I would like to implement myself.
Does the concept itself work? Is it feasible?

The foam would be covered in grille cloth so I hardly think it would look appalling compared to other wide open baffle designs

Experiment and compare the sound to your idea to a normal design and

post your results.//content.invisioncic.com/y282845/emoticons/biggrin.gif.d71a5d36fcbab170f2364c9f2e3946cb.gif

 

[thadman 10+ year member]

Anybody have any clue where Id purchase some of this foam?

 

[thylantyr 10+ year member]

Look at mcmaster.com

 

[thadman 10+ year member]

Wow...theres a lot of types of foam over theremg:

Is there a type of foam thats been accepted as best for absorbing sound waves?

 

[thylantyr 10+ year member]

You need to study acoustical treatments {google} to understand the different materials and their sound absorption/diffusion/dampening/etc abilities.

One resource;

http://www.ethanwiner.com/acoustics.html

http://www.acousticsfirst.com/articles/ChurchProduction/primer.htm

 

[thadman 10+ year member]

Good Read

Owens-Corning 703 Rigid Fiberglass seems like the way to go!//content.invisioncic.com/y282845/emoticons/biggrin.gif.d71a5d36fcbab170f2364c9f2e3946cb.gif

Have you read any articles that deal with spacing? I've read in several articles the mention of spacing panels from the wall, which improved absorption substantially, but have never read any conclusive results or specific tests outlining how far to space and what the benefits are.

I've heard dense acoustic foam corresponds to 1/4 the wavelength, what does 703 RF correspond to?

Does this mean that 703 is 86% efficient at 250hz and 98% at 4000hz?