Re: Revealed: Re: Audio Shootout - Aluminum vs. Paper Cones


"Brian Running" <brunning@xxxxxxxxxxxxxxxxx> wrote in
message
news:I0kJh.7385$FG1.4888@xxxxxxxxxxxxxxxxxxxxxxxxxxxxx
:> For the third time with added enthusiasm ( and link)
: >
http://www.amazon.com/Loudspeaker-Design-Cookbook-Vance-Dickason/dp/1882580109
:
: Thanks. I'll add more emphasis to my questions. I
am only aware that
: vented-box systems have a roll-off at 24 dB/octave
below the port tuning
: frequency. I am not an expert on speaker design, and
don't claim any
: special knowledge -- however, I have never seen a
reference to anything
: other than a 24 dB/octave roll-off for vented
designs, and if there is
: an authority that states to the contrary, I would be
curious to see it.
: Does Vance Dickinson state that there are vented
designs with other
: than a 24 dB/octave roll-off?

This is true. A vented box is analagous to a 24dB per
octave high pass filter. It may have a variety of
shapes in the passband ( where it goes from not rolling
off to rolling off at 24 dB/octave) while it always
terminates at 24dB/octave. The shape of the passband
will be sensative to the tuning and will color the
sound to that tuning. Getting it tuned right for the
sound you want is not trivial and can not be done by
looking in a book or a computer screen it needs to be
heard.


:
: Secondly, I am aware of a speaker's power-handling
capacity only in
: terms of the electrical power that it can physically
handle -- i.e., the
: limiting factor is the voice coil's capacity to
absorb and dissipate
: heat. I am not aware that this can be affected in
any way by the design
: of the box, it's a physical attribute of the driver.
I am aware of the
: peaks and valleys in a speaker's impedance curve
being affected by the
: tuning of the box, but this doesn't have anything to
do with the
: speaker's physical ability to absorb and dissipate
heat. Is there an
: authority which states that the box tuning will
affect the voice coil's
: heat capacity?

This is confusion based on what power really is and how
the audio industry has dumbed it down so apples and
oranges can be compared with something called
"sensitivity".


Engineering speak~~~~~~~~~~~~~~~~~~~~~~~~~
power = the square of the input voltage divided by the
complex impedance of the load.

The impedance of the load is different at all
frequencies therefore the power at each frequency is
different. If you take the output of an amp it is rated
into a constant 2-4-8 ohm load. If the amp can put out
a hundred watts at 8 ohms it can put 28.8 volts across
8 ohms. If the speaker is perhaps a closed box and you
are at Fc the impedance at resonance will be maybe 40
ohms so putting 28.8 volts across the speaker at that
frequency will only take 20 watts from the amp. The
reduction in power input will not affect the output of
the system so much since the speaker is still moving
thanks to the mechanics of resonance.

At resonance power handling is up so long as you do not
exceed xmax and blow the cone out of the basket.

Marketing speak~~~~~~~~~~~~~~~~~~~~~~~~~~~
So to make life easy for everyone they come up with
sensitivity to equalize the impedance curve of the
speaker and let people say that with a certain voltage
applied to this unknown load the sound pressure level
will be ----- some number that throws power out of the
equation --------- so speakers with lower impedance (
suck more power) may play louder than ones with higher
impedance just by swapping the leads for one speaker to
another at the amp ----- just like at the stereo store
assuming the amp can handle the load and phase angle of
it.



peace
dawg


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