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Old 25th August 2008, 10:50 PM   #1
mikee55 is offline mikee55  United Kingdom
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Default Driver has magnet vent, but not the dust cover?

Hi all, was just looking at my old Longmill 10" car woofer, and I ask myself, the magnet is vented, I can see a gauze, but the cone and dust cap are sealed. Is this right? What would happen if I put a hole in the dustcap? Reason I ask, is because of pressure relief in a Sealed Enclosure, is there a benefit?

Mike
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Old 25th August 2008, 11:05 PM   #2
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I think you'll find you vent one or the other or you'd have a "hole" in the cabinet right through the driver. It would probably make a lot of chuffing noise at higher levels as the driver moved in and out. You might also have cancellation issues, although in todays world of OB that seems trivial.
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Old 25th August 2008, 11:21 PM   #3
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If the dust cap was holed as well there would be no pumping action. As well as the cabinet having an effective hole in it.
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Old 26th August 2008, 12:31 AM   #4
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wouldn't it be creating a virtual port as well. It's tuning would vary depending the on the vent dimensions in the magnet and size of the hole, but lets say you removed the dust cap, the voice coil is say 2", that might mean say a 2" by 6" port. In a 1 cubic foot box that might be a roughly 35z tuning. My point would be, its no longer a sealed box but would instead would perform like a ported sub with an undersized port (i.e. probably chuffing at higher volumes).

Now if you mean just putting a tiny hole, say a 1/4" hole in the dust cap, which is what I suspect you are talking about, it still would be acting like a port in a way, but with a much different tuning, and because of the very tiny size, and the air going from the larger coil volume into the dustcap "chamber" and out that tiny hole, would have very bad chuffing, I would think. None the less, many speakers are not well sealed, especially in the proaudio world, where they are generally used in a ported, bandpass, or horn loaded enclosure, and where it won't matter as much.
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Old 26th August 2008, 07:27 AM   #5
mikee55 is offline mikee55  United Kingdom
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Default Thankss

I figured something like that. I read somewhere that, if you put a hole in the dust cover, it helps with cooling at high power levels. Perhaps it was bad info!

Thanks, again
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Old 26th August 2008, 11:43 AM   #6
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It was good info. A vented cap will help cool the motor. So does a vented pole piece. You're just not likely to see both on the same driver.
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