Inputs on enclosure design

[jrs]

I was hoping to get some basic input on a design I'm thinking about.

I wanted something other than the typical rectangular box. I recalled a Spica Angelus (sp?) that were amazing performers, but a bit too dramatic design for my wife.

I was hoping to achieve a blend of form/function, but of course function being number one. I know any design would "work" but would it "work well"?

I want very thin front-back (I have seen some full-range enclosure designs that are only 4 inches deep, but considerably wider). I also want a flared bottom.

Question - is it the overall volume that makes the most difference or is it there some minimum front-back thickness needed for a specific driver to perform well?

In this design I would vent the bottom back, with a reflector plate as shown (dotted line on the side view). I would also block out the sharp inside corners, making it more trapezoidal s-s. Finally, if worse comes to worse I could channel the inside so it's straight on the sides, leaving just the front curve to add volume.

The second side-view is a thought to curve the back a bit...just for esthetics as much as anything else...likely wouldn't go that far.

(hopefully my image will show up)...

Thoughts? (or laughs, with explanation of the punchline appreciated?.

[Svante]

There are three main things to think about when deciding the shape of the box.

1. Baffle diffraction. The shape of the front baffle and the placement of the drivers affects the response quite a lot. The worst shape possible is a round circular baffle with the driver in the middle, but there are other shapes and placements that are bad too. Typically a tall narrow baffle is better that a wide one. The baffle step affects the range ~400-3000 Hz, typically.

2. The volume of the box. Affects the low frequency response, ~20-150 Hz. Depends on the seleced driver and box type (bass-reflex/closed etc)

3. Resonances in the air inside the box. A wery tall and narrow box tends to get a pronounced first resonance in the up-down direction. This has to be handled with an appropriate amount of damping material inside the box.

There are loudspeaker simulators around that manages 1 and 2, but typically not 3. Get one.

Edit: I just noticed that esthetics was not one of my three points... Add if you wish .

[AndrewT]

Hi,
would you consider a 3way?
Then you could make the top half an open baffle handling just mid and treble.
The lower half could be a boxed volume for the bass only, cutting off around 200 to 300Hz.

[Inductor]

Originally posted by Svante

3. Resonances in the air inside the box. A wery tall and narrow box tends to get a pronounced first resonance in the up-down direction. This has to be handled with an appropriate amount of damping material inside the box.

A tall box will ressonate on the quarter wave harmonics. True? For that (to cancel it), jrs, break the interior in two or three different parts, you can brace it well in those places and use some kind of acoustics insulation. For the inside dimensions you can use also an optimizer software, if not following any specific design:

Standing Wave Calculator (Box Dimensions/internal)
http://www.vikash.info/audio/standing_wave_calc/

Calculate Enclosures (OUTSIDE dimensions)
http://www.mhsoft.nl/CalculateEnclosures.asp

New Driver / box calculator (fast graphics from LinearTeam, this only to show main difference between a sealed box and bassreflex or vented, don't use the optimum alignment because it's only one of them depending on box size and damping)
http://www.linearteam.dk/default.aspx?pageid=newdriver

(note that it's also very easy to model the front baffle output component with Svante software, either of them.)

[Svante]

Originally posted by Inductor


A tall box will ressonate on the quarter wave harmonics. True? For that (to cancel it), jrs, break the interior in two or three different parts, you can brace it well in those places and use some kind of acoustics insulation. For the inside dimensions you can use also an optimizer software, if not following any specific design:

Mja...

A closed or BR box will resonate on multiples of f=c/(2*h). I am not sure if that is what you are saying, but the way to get rid of the resonances is to use stuffing. For the BR box, the stuffing should be kept away from the port, maybe bracing wiould help to keep the stuffing in place, yes.

Otherwise, the effects of the resonance is that it affects the movement of the cone at the resonance. It can almost always be seen as a little notch in the frequency response on tall boxes with too little stuffing.

[Inductor]

Thanks Svante.
I refer to a tube effect (lenght or height?) with a dominant in frequency showing as a peak (or more, if you say multiples) in it's output.
Best way to check with the Standing wave modes calculator, I guess.
Maybe you can also help here and say what should be the "Standing Wave Threshold" (Hz), what is it for(?), in case #1 on previous post "Standing Wave Calculator/Dimensions".