Re: How much power do I really need?

On 11/30/03 12:24 AM, in article [EMAIL PROTECTED],
"normanstrong" <[EMAIL PROTECTED]> wrote:

> "Michael Scarpitti" <[EMAIL PROTECTED]> wrote in message
> news:[EMAIL PROTECTED]
>> [EMAIL PROTECTED] (CCSman) wrote in message
> news:<[EMAIL PROTECTED]>...
>>> My room is 14 x 24, and the back, ie, listening area, open up into
> a dining
>>> room.  Using a Radio Shack SPL meter, it seems that I rarely get a
> reading of
>>> 85 dB, let alone 80 dB (at the listening position).  So, let's say
> max, average
>>> listeing level, 85 dB.  Speakers are listed at 87 dB efficiency,
> at 6 ohms,
>>> dropping to a low of 3 ohms.  How much power is adequate for my
> needs, assuming
>>> I also want some margin and not run an amp at the limit?
>>> 
>>> Thanks in advance!
>> 
>> I'd say at least 150WPC.
> 
> First of all, it's not a matter of opinion, it's a matter of
> calculation.  Secondly, "87db efficiency, at 6 ohms, dropping to a low
> of 3 ohms" doesn't make any sense.  Is that exactly the way the
> manufacturer stated it?  Efficiency is a dimensionless quantity that
> is very difficult to measure, and of little importance.  The number
> you gave is probably the voltage sensitivity.
> 
> Second, how long does the impedance linger around 3 ohms, and where in
> the frequency range does this occur?  It sounds to me like a 4 ohm
> speaker--not 6.

There are a *lot* of speakers that are specified that way - partly because
if you see the actual impedance plot of the speaker, you would reveal your
idea about the crossover design style.

If I had a amplifier that was sensitive to load (like a tube amp) and had a
4 and 8 ohm tap - I would start with the 4 ohm tap, like you said, and then
try the 8 ohm and figure out what would sound better.