Why is woofer sensitivity +3dB

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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.
 
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On Sun, 25 Sep 2005 08:24:55 GMT, Morgan Ohlson
<morgan.ohlson@comhem.se> wrote:

>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?

It's not - it depends on your particular choice of drivers.

>Is it just to give a built-in loudness effect or is it something more
>sofisticated that is the motif behind?

IME, the tweeter is usually the one with the highest raw sensitivity,
among drivers intended for good quality domestic hi-fi. Generally, the
woofer is the *least* sensitive of the drivers in a 3-way system.
There are very good physical reasons why this would be so.
--

Stewart Pinkerton | Music is Art - Audio is Engineering
 
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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. :eek:)


"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.
 
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Morgan Ohlson wrote:

> 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?

It is easier to make high efficiency midrange units than high efficiency
bass units, but perhaps I don't really know what is "out there" anymore.

> Is it just to give a built-in loudness effect or is it something more
> sofisticated that is the motif behind?

You have to examine the conditions for the efficiency specs. All things
equal, and they rarely ever are, the woofer will play in full space and
the midrange unit in half space, assuming the loudspeaker is free
standing. The transition between full space and half space depends
largely on the width of the loudspeaker cabinet. Having that transition
take place around the cross-over between bass and midrange may make it
easier to compensate for it so you can not specify a cross-over without
also taking the box design, and MOST CERTAINLY the intended placement in
the room, into consideration.

This entire turf was covered in responso to your question about dual
bass units.

> Morgan O.


Kind regards

Peter Larsen

--
*******************************************
* My site is at: http://www.muyiovatki.dk *
*******************************************
 
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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. :eek:)

(+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.
 
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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. :eek:)




"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. :eek:)
>
> (+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.
 
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Archived from groups: rec.audio.tech (More info?)

On Wed, 28 Sep 2005 03:37:15 GMT, James Lehman wrote:


>>
>> (+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.

> 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. :eek:)

Does pads damge the sound?

....and also, by the way... how damageing are differnt kinds of covers for
the drivers?


Morgan O.
 
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>
> Does pads damge the sound?
>
> ...and also, by the way... how damageing are differnt kinds of covers for
> the drivers?
>
>
> Morgan O.

Hmmmm. That depends on who you ask, I guess. In theory, all it does is allow
less power to make it to the terminal of the speaker. There are different
kinds of resisters. You should use non-inductive power types for speakers.
You know what an L-pad is? Start with that. If you find a setting that is
perfect for your choice of speakers, then you can measure the L-pad and
replace it with fixed resisters.

The issue with not wanting to pad a woofer comes from the fact that the
woofer is the only driver in the system that is supposed to work down to -
and below it's resonance. Putting a resister in series with a woofer will
change its T/S parameters so much that your box calculation will be very
wrong. Besides that, you would be throwing away a lot of power / efficiency.
In most cases, the woofer covers the largest area of the spectrum. Just get
a mid and a tweeter that is at least or greater in efficiency and get on
with your life.

James. :eek:)
 
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