air flow through plexi window

Below is a pic of a sub box I've made to house 2- 10" subs that will be given 500WRMS each. Still have a little finishing up to do before wrapping it, but had a question on the viewing window portion.



Each chamber is sealed from eachother with approx .80 cubic feet of air space. Now the opening above the subs is 18"x13" and the plan is to insert a 1/2" thick plexi "viewing window" in the opening and have our club logo, or some other design cut into the plexi allowing air to pass through.

My question is how big of an opening in the plexi would I need to avoid any tuning problems/freq changes? The subs/box are designed to work in a sealed application, so I don't want the plexi changing the box to a bandpass style cause there isn't enough space for the air to pass through freely.

Unfortunately, that is exactly what you will be doing, looking at the room you have to work with. Personally, I would make the "window" a lot bigger, and make the logo thing out of plexi and have it hang out in mid air (that is, instead of cutting the logo out of plexi and having the resulting hole be the pass through for air movement, do the reverse)

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Wherever I go, that is where I end up......

I second the motion. I find that restricting more than 70% of the combined surface areas of the cones tend to make a slight restriction on the woofers. SLIGHT, but in some cases it is enough to affect the sound.

I'm not concerned about the window size, but if you must put something there, I would look at doing a floating logo rather than a pane of a window. Your other option would be to cut out the back area and put a recessed wall there to give more area for hte air to move out and make your club logo as large as possible for the window. The key here is to give as much space as possible for air to move with as little restriction as possible.

Ganbatte ne!

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Never send your ducks to eagle school.
The difference between ordinary and extraordinary is that little extra.
The 3Ls of life: Learn from the Past, Live for the Present, Look to the Future.

first off, the enclosure looks great!

I agree with gus and mrs.racer! do floating plexy instead. You could also think about placing some LED's in the 1/2" pocket you cut for the glass and have it light up the plexi. Just a thought.

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...don't crush the weasel...

Thanks for the heads up everyone! Before building the box I had figured that each 10" sub would have a surface area of 95 square inches, so two of them would be 190 square inches. I had made the opening 234 square inches thinking that it would give some room to play with, but could of made it a little bigger I think. Gonna have to make some mock ups of floating designs to see what things look like and how much open space there's left. So is there any general rule as far as how much space to leave open to avoid air restriction problems. For example 80, 90, or 100% of the speaker's surface area is = how much space is needed for air flow?

Tubbs: Read my mind with the LED's Also was going to rout out some slots on the bottom of the top to hid some LED strips in too.

nice! I'm in the middle of fiberglassing some 3 way pods for my front door and working on a sub box as well... when it's finished i'll post a thread on it...

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...don't crush the weasel...

I've been keeping in eye on your thread on fiberglass forums. It's shaping up nicely!

In your opening you can restrict up to 85 square inches and still be fine for most subs...Some subs may still be affected, so be aware of that during the rest of your install. Shape doesn't matter for the most part, but large planes and/or small holes will act as a slight restricter, so any holes smaller than 1.5 in2, I would consider as a "blocked" area.

Assuming your surface area is correct and going with a typical xmax for 10s, you need to keep about 150 square inches available in the window to minimize restrictions, any more than that, and you'll have the beginnings of a bandpass... not a large effect, but still an affect.

Ganbatte ne!

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Never send your ducks to eagle school.
The difference between ordinary and extraordinary is that little extra.
The 3Ls of life: Learn from the Past, Live for the Present, Look to the Future.

mrpurple wrote:

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I've been keeping in eye on your thread on fiberglass forums. It's shaping up nicely!

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thanks. once I finish the build I'll post a thread here on it from start to finish. I lack glassing the outside, body filler and paint (if it turns out worthy enough for paint that is... lol) if not, I'll cover it in matching suede or vinyl.

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...don't crush the weasel...