Archived from groups: rec.audio.tech (
More info?)
I believe that when a woofer is measured for efficiency (if it really is
measured and not just calculated), it is mounted in what is called an
infinite baffle. Imagine mounting a woofer right in the middle of a large
wall with no box behind it. The front of the cone is all that radiates out
into the room. All of the rear phase energy from the cone just radiates away
from the back of the cone, behind the wall and has no effect on the front
sound field.
If you have never designed and built a pair of speakers before, do yourself
a favor and get some cheap parts and experiment. Don't expect to build the
greatest speaker system in the world on your first try.
If you are so concerned about baffle effect, try moving your speakers around
in the room. You will notice they sound very different when they are out in
the middle of the room or up against a single wall or pushed into the
corners of the room. That's what it's all about!
Honestly, 3 to 5 dB variations in the total output of a wide range speaker
system is not a problem at all. If you can make a speaker system that is
within less than 5dB from some reasonable low frequency to some reasonable
high frequency, you've really got something!
What you need to watch for are gross mismatches from one driver to the next,
the phase relationship between the drivers and peaks or spikes in the
frequency response as these indicate resonance or ringing.
Also remember. You can easily pad down a mid or a tweeter to match a woofer.
It is not a good idea to pad down a woofer by putting a resister in series
with it.
James.
)
"Morgan Ohlson" <morgan.ohlson@comhem.se> wrote in message
news:1gj9a9tdxv5dc.pjpyrbtwrrqs$.dlg@40tude.net...
> On Sun, 25 Sep 2005 20:37:49 GMT, James Lehman wrote:
>
> >
> >
> > "Morgan Ohlson" <morgan.ohlson@comhem.se> wrote in message
> > news:iln6821gzshp.1dzx03sh20vcq.dlg@40tude.net...
> >> Balanced woofer and mid choice for 3-way system.
> >>
> >> Why is woofer sensitivity in most designs that is called balanced /hifi
> > etc.
> >> almost allways + 3-5dB above the mid? Shouldn't it be the same?
> >>
> >> Is it just to give a built-in loudness effect or is it something more
> >> sofisticated that is the motif behind?
> >>
> >>
> >> Morgan O.
>
>
>
>
> > This *might* be because the designer of the system wanted to compensate
for
> > the effect of the baffle. The higher the frequency of sound, the shorter
the
> > wavelength is. Usually, the woofer puts out sound that has wavelengths
that
> > are much greater than the width of the baffle. So the baffle has no
effect
> > on separating the space that the woofer is radiating into. In other
words, a
> > lot of the energy put out by the woofer is going off to the sides and
even
> > behind the box. As frequencies get higher, their wavelengths get
shorter, to
> > the point where the baffle effectively separates the space that the
speaker
> > is radiating into, such that almost all of the energy is radiating only
> > forward. This means that the energy from the speaker is radiating into
about
> > half of the space (+3dB). As a matter of fact, when the frequency gets
high
> > enough that the wavelength is as short or shorter than the diameter of
the
> > speaker, then it really starts to beam the sound right out in front of
the
> > speaker. So, to answer your question: it's not so much a matter of the
total
> > amount of energy that a speaker puts into a room. It is more about how
much
> > energy effectively radiates out from the front of the baffle towards the
> > listening area.
> >
> > James.
)
>
> (+3-5dB often occures in kit-designs and ready to buy speakers.)
>
> So when looking into driver sensitivity ratings there is no baffle effect
> taken into account?
>
> The reasoning could then be turned around. ??? I.e to say that a mid
driver
> mounted in a box usually deliver a higher percentage of output to the
> listening area and that the woofer sensitivity must (could?) be
compensated
> for that.
>
> Wouldn't a reasonable guess then be that the tweeter delivers almost
exaktly
> the same in practise as in a sensitivity meassurement because of less
> reflections?
> ...and therefore should be perhaps 1dB less then the mid?
>
> Morgan O.
/www.muyiovatki.dk
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