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Efficiency of radios

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Posted by JimChufff on January 24, 2009, 1:05 pm
 
Hi all,
  I live on a boat (off grid) and most of our electricity goes on
running an inverter that runs our stereo system. Does anyone know how
efficient car radios are? (we have 12v batteries) Or maybe the little
9v radios you get with mains adapters?

thanks in advance,

Jim Potter
UK

Posted by BobG on January 24, 2009, 2:11 pm
 
A digital multimeter is a must have for a boat owner. Efficiency is
power out/power in. Try measuring the current going to the inverter
with stereo on and off. Power is 12V x amps. Report back power used
with just inverter on, and with stereo on normal, Maybe the inverter
is not so efficient at low loads. Why use 100watts to produce 50watts?
In general, analog amps are 50% efficient, and they have linear power
supplies which are about 50% efficient. Any class-d amp will be much
more efficient... up to 80% These are used in battery equipment for
power saving reasons.

Posted by ransley on January 24, 2009, 4:45 pm
 
You might find info at Crutchfield on comparisons of units. Speaker
efficency varies greatly and is rated at crutchfields. Generaly a
smaller speaker requires more energy. I know some car speakers require
2x the power to get a certain volume.

Posted by Tim Jackson on January 24, 2009, 6:39 pm
 ransley wrote:

I'd agree that speaker efficiency is the main variable in DC powered
radios/amplifiers, and that any DC system is bound to be a lot more
efficient than running a mains system through an inverter, especially if
the inverter is sized to meet the peak demand of the stereo and so
mostly running at very low loading.  I'd guess better than half the load.

I'd also add that small hi-fi speakers will be less efficient than
larger lower quality units.  There is a trade off between efficiency and
sound quality, which in recent times of low cost amplifiers, has seen
speaker design trend towards the small size, heavily damped, low
efficiency route to sound quality.


Tim Jackson

Posted by ransley on January 25, 2009, 2:58 am
 
I think efficency is rated by, @ 1 watt speaker output level [spl]
rated by db at a certain inches distance. 6-8" speakers are usualy
fairly good, the 4" poor but they vary greatly by manufacturer that is
why Crutchfields listings will help. Remember 3db = a doubling of
power, Crutchfields rating is sensitivity at 1 watt. so even 1db makes
a difference. Get the greatest db number you can to reduce power
needed. Also reciever designs are changing to be more efficent you
need to compare numbers and talk to a pro.

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