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Old 24th December 2012, 06:54 AM   #1
abcdmku is offline abcdmku  United States
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Default quick question

I often wondered this, could a normal subwoofer be used as a passive radiator at its fs?
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Old 24th December 2012, 08:27 AM   #2
NEO Dan is offline NEO Dan  United States
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But generally it's not going to make a "good" passive radiator, once you stick it in the box the FS will go up. Passives are usually very soft suspension and heavy moving mass so when you stick them in a box they are still tuned low enough to be useful. You can always load the woofer cone with mass to lower the FS. There is a big YMMV on how well your woofer takes to this modification though.
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Old 24th December 2012, 06:42 PM   #3
abcdmku is offline abcdmku  United States
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Interesting, That makes sense and I feel like the extra weight might ruin the driver if it is not applied evenly, perhaps a heavy paint or something might work? I personally wouldn't use a passive radiator [or a normal driver as one] I was just curious.
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Old 24th December 2012, 07:07 PM   #4
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It's also possible to add various (usually passive) tuned electrical networks to the terminals of a speaker used as a passive radiator, even allowing you some tunable controls you can alter while listening. Can't remember where I read about doing this...Sorry I'm not more help...but you might get a PR with a network to avoid some common port problems. You might control the cone below tuning. You might lmiit excursion. I'd have to think about this more... And of course a PR might take less space than an equivalent port.

I've doped down many a driver; spraying or brushing on epoxy is one way, but others prefer lead weights or lengths of solder glued around the dust cap near where the coil former meets cone.
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Old 24th December 2012, 09:40 PM   #5
abcdmku is offline abcdmku  United States
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Not quite sure I understand the electrical network part, but couldn't the lead rip threw the cone after awhile, or is it attached to the voice coil?
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Old 24th December 2012, 09:49 PM   #6
sreten is offline sreten  United Kingdom
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Yes it can if it matches the other driver. A further step is to simply add
switchable resistances across the driver to affect the ABR/PR damping.

For a good adjustment range you want a high Qms, low Qes driver.

rgds, sreten.

Last edited by sreten; 24th December 2012 at 09:53 PM.
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