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Re: Fans

Michael wrote: >
> Subject: Fans
> 
> You can get quiet, inexpensive AC "muffin" fans from Radio Shack! 
> When
> the fan in my CustomSealife fixture started making noise almost 2
> years
> ago I tried one for a bit, but eventually wound up just disconnecting
> it.  The intake and exhaust ports in the fixture provide enough
> ventillation that I've experienced no heat gain or related
> bulb/balast
> degradation.  DC fans run much quieter, but require a transformer to
> convert AC to DC power.
>  
There is nothing about the design of DC brushless fans that makes them
inherently quieter than their AC counterparts.  While the noise level
depends on a number of factors (type of bearing and specific bearing
design, amount of wear, blade shape, size, speed, airflow, etc.)
generally noise correlates with airflow for a given basic type of
design.  I.e., more powerful fans are generally noisier.  But between
any two fans there can be exceptions to this due to the variety of
other factors.   For a given output for a specific DC fan, you stand a
good chance of finding an AC fan of the same size that is quieter. The
same could be said for an AC fan of a given size and output vis-a-vis
DC fans.  It's like, gasoline engine cars are not quieter than diesel
engine cars -- you have to say which diesel car and which gasoline car.
 

I looked at an assortment of 3.15" and 4.7 inch tubeaxial fans of
various outputs.  The average db per cfm for 3.15 inch fans was 1.17
for DC fans and 1.2 for AC fans and the average db level per fan was
30.8 for DC and 32.7 for the ACs. In the 4.7 inch size, the DC fans
averaged 0.69 db/cfm and the AC fans averaged 0.54 db/cfm and the
average db-level per fan was 45 for the DCs and 43 for the ACs. The
data is tabulated below.

When you shop for a fan, consider the noise level you desire and the
airflow you need, then find the fan that best fits your needs.

DC Fans
Size	CFM	DB	DB/CFM
3.15	19.8	25	1.26
	27	32	1.19
	27	32	1.19
	32.4	35	1.08
	19.8	25	1.26
	27	32	1.19
	32.4	35	1.08
Avg.s	26.49	30.86	1.18

Size	CFM	DB	DB/CFM
4.72	54	39	0.72
	64.8	46	0.71
	79.2	50	0.63
	54	39	0.72
	64.8	46	0.71
	79.2	50	0.63
Avg.s	66	45	0.69

AC Fans
Size	CFM	DB	DB/CFM
3.15	32	38	1.19
	32	38	1.19
	29	37	1.28
	26	31	1.19
	21	26	1.24
	21	26	1.24
Avg.s	26.83	32.67	1.22

Size	CFM	DB	DB/CFM
4.69	105	50	0.48
	105	50	0.48
	55	35	0.64
	65	38	0.58
	78	42	0.54
Avg.s	81.60	43.00	0.54


Scott H.

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