You could put in a 24v fan and as long as 12v would kick it on it would spin at 1/2 speed. Anything lower than a 12v fan could burn out from the extra voltage.

www.bigfootcomputers.com has a good selection of 12v fans, some really quiet ones too. If noise is a concern I would look into spending 5-10 bucks instead of a cheapo $2 fan that probably won't be much quieter.

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Alpine IVA-W200
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Blade SE6175
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Sony XM2000R
MTX 12" 7000 x 3 freeair

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