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Old 29th December 2009, 08:05 PM   #1
tomchr is offline tomchr  United States
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Default Vent hole in sealed subs?

Folks,

This has probably been debated ad nauseum, but I hope you won't mind giving the gist of the debate.

I am thinking to build a sealed sub based on Zapf's Dayton RSS315HF design. There is one thing that puzzles me: In a sealed sub enclosure, do you need a small weep hole so the air pressure can stabilize inside vs outside of the driver?

One would think that changes in atmospheric pressure would put strain on the driver membrane. Not to mention the strain from the pressure formed when mounting the front baffle to the rest of the enclosure. Are there normally enough leaks in a sealed enclosure to take care of this or do I need to drill a 1 mm (or something equally tiny) hole somewhere?

Thanks,

~Tom
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Old 29th December 2009, 08:11 PM   #2
Glowbug is offline Glowbug  United States
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Nope, don't put any holes in it - sealed really is sealed

I'm not really sure what you mean by pressure when mounting the front baffle.
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Old 29th December 2009, 08:17 PM   #3
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This thought has occurred to me as well. When I had sealed speakers that I built, I just used the smallest drill bit I had and put a tiny hole in them. I couldn't feel anything at the hole with my finger when I played them. I just did it because they were in a car and I figured there may be some rapid pressure changes.

I think usually there is always some kind of slow leakage that would allow compensation for barometric pressure changes.
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Old 29th December 2009, 08:18 PM   #4
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I always leave a slight gap between what i use to seal the driver to the enclosure, i might leave a 1mm gap in a sealing gasket. Your mention of 1mm would be ok. As you have realised, you need to make sure that the atmospheric pressure is always equalised on both sides of the driver. A tiny hole or a small gap in the seal between the driver & enclosure will keep the driver voice coil centered & allow maximum performance from the driver in a sealed box.

It does need to be tiny though
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Old 29th December 2009, 08:28 PM   #5
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Depending on how well a cabinet is sealed depends on whether an atmospheric relief hole is required or not.
I mostly port my cabinets so a hole isnt required.
On the ones I have sealed there is always a small hole where the jack socket goes.
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Old 29th December 2009, 09:03 PM   #6
tomchr is offline tomchr  United States
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Quote:
Originally Posted by Glowbug View Post
I'm not really sure what you mean by pressure when mounting the front baffle.
Let me rephrase. A sealed box is built to be air tight. Then the driver is mounted. The driver will displace some air and some of this air will be trapped behind the driver. My question is if this air should be allowed to seep out though a hole or not.

It seems the consensus is that the atmospheric pressure should be allowed to equalize. But of course, the weep hole should be small enough that it doesn't allow for air flow in the frequency range of interest.


Now for a second question: Down-firing vs front-firing. What are the tradeoffs of one vs the other?

Thanks,

~Tom
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Old 29th December 2009, 09:26 PM   #7
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Any air displaced by the driver will surely find it's way out while the driver is being mounted.

If you press a sealed-box woofer's cone in and it returns to center very slowly, there is still enough leakage to equalize atmospheric pressure changes they happen in a fixed locale.

Were your box traveling vertically at 0.5 mach or so, then I would recommend a vent hole.
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Old 29th December 2009, 09:48 PM   #8
tomchr is offline tomchr  United States
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Good points everybody. Thanks!!

I seem to have found an "answer" to my second question about front vs down firing. Also see This Audioholics Thread. At least according to The Internetz, front vs down firing doesn't matter much for a sound quality perspective, though, there are some concerns about shag carpet eating up the sound quality. But down firing subs are supposedly easier to place.

Ya' know... I think I'll build a box with a driver in it and play around with it.

Thanks for your help guys (and gals).

~Tom
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Old 29th December 2009, 10:31 PM   #9
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tsmith1315 gets it right. He understands that no driver is sealed, not even a PR system, so there never will be a difference between the inside and outside. Seal 'er up tight.
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Old 30th December 2009, 02:45 AM   #10
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suspension sag can be a problem for up or down firing subs, I don't think its a big deal unless its alum or other heavy cone with a large x-max *soft suspension for cone mass*
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