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Old 26th February 2014, 08:18 PM   #1
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Default sealed design prevent sagging?

I plan to do build a small enclosure sealed sub in the near future. I wish to do down firing. My only concern is gravity pulling on the cone all the time when it is off. I am inclined to think however that a properly and completely sealed enclosure will keep the driver centered as the vacuum created as the cone falls will counteract the gravity and keep it in place. Thoughts or experiences regarding this?
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Old 26th February 2014, 10:04 PM   #2
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Good thinking but wrong - lol

The fact that the enclosre is sealed has nothing to do with how much the driver will sag.

It really depends upon a number of factors and some drivers are more suitable for down firing than others here's a LINK to a good article on how to see if the drivers you are considering would be good candidates for down firing
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Old 26th February 2014, 10:18 PM   #3
sreten is offline sreten  United Kingdom
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Hi,

A small and sealed subwoofer is very unlikely to have cone sag issues.

FWIW though a driver that does sag can be built with an offset coil
to make it specifically optimised for downfiring, and / or some cheap
drivers are notably assymetrical when tested, and a bit of sag is OK.

A lot of basic drivers tend to to move towards the magnet as
average position under heavy drive, due to magnet assymetry,
and downfiring can counteract that effect somewhat.

Some drivers are simply not sealed enough for the air to act
as a spring short term, some are, but long term sag is not
affected by the air in the box, air diffuses through surrounds
and paper cones, just like your car tyres going down.

rgds, sreten.
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Last edited by sreten; 26th February 2014 at 10:39 PM.
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Old 26th February 2014, 10:26 PM   #4
tinitus is offline tinitus  Europe
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the forward drive may be slightly stronger
with that in mind, maybe consider mount with magnet side down

btw, how long do expect to keep it (just curious) ?
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Old 26th February 2014, 10:31 PM   #5
laplace is offline laplace  Australia
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Air diffuses slowly through the driver, so there's no such thing as truly airtight sealed. The air will support the cone at audio frequencies but not over days or weeks.
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Old 26th February 2014, 10:33 PM   #6
tinitus is offline tinitus  Europe
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I like to use hard felt as gasket behind the driver frame, so ...
or even better, aperiodic
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Old 26th February 2014, 10:49 PM   #7
sreten is offline sreten  United Kingdom
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Quote:
Originally Posted by tinitus View Post
the forward drive may be slightly stronger
with that in mind, maybe consider mount with magnet side down
Hi,

Generally there is more field inside the magnet than in front. Which
tends to move the driver towards the magnet under heavy drive.

rgds, sreten.
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When your only tool is a hammer, every problem looks like a nail - Abraham Maslow

Last edited by sreten; 26th February 2014 at 11:01 PM.
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Old 27th February 2014, 02:56 AM   #8
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Thanks everybody, I will be moving with downfiring. I plan to keep it for a long time (years and years) but using the formulas provided in the link above (thanks by the way), both provide under 2% sag. The leakage will be as minimal as I think it can be as the driver has a one piece poly cone and heavy rubber half roll surround. Thanks for all the points of view!
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Old 27th February 2014, 08:12 PM   #9
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Quote:
Originally Posted by dutchess View Post
I plan to keep it for a long time (years and years) but using the formulas provided in the link above (thanks by the way), both provide under 2% sag. The leakage will be as minimal as I think it can be as the driver has a one piece poly cone and heavy rubber half roll surround. Thanks for all the points of view!
I have a down firing one piece poly cone neoprene half roll surround sub in my kitchen.

After around 14 years, it appears to have around 2mm sag, probably half of it's Xmax.
That said, it still seems to sound OK, though I'm not paying much attention in the kitchen .
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Old 28th February 2014, 01:53 AM   #10
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Quote:
Originally Posted by weltersys View Post
I have a down firing one piece poly cone neoprene half roll surround sub in my kitchen.

After around 14 years, it appears to have around 2mm sag, probably half of it's Xmax.
That said, it still seems to sound OK, though I'm not paying much attention in the kitchen .
I wish I had a sub in my kitchen..

This has 14mm one way, so I have a little room for sag anyway. Thanks!
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