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Frequency response, mass vs. inductance



 
 
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  #1  
Old July 6th 05, 11:34 PM
Todd H.
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writes:
> I have a question. Someone on a message board I usually post on talked
> about woofer speed. I assume what this translates to is frequency
> response (ie 1/time=frequency). He also posted a link, which I read:
>
http://www.adireaudio.com/Files/Tech...ooferSpeed.pdf

Interesting paper. Written apparently by a high school graduate?
Maybe.

> At the end of the page it shows a graph, with the frequency response of
> the speaker they used. To me, inductance would have little or no effect
> on a speaker unless, it were a midrange or a tweeter. And from this
> graph, mass still seems to dampen the signal more throught the
> frequency range than does the inductor, which is should I would think.
> (ie xl=2(pi)(f)(l)) When it does eventually does get to the higher end
> the inductor does not seem to cut the signal all that much.
> So what I would like to know is, if the inductance is the most
> important part, why not make it small, and increase your frequency
> response of the speaker? This probably would not effect a woofer all
> that much if the woofer was used for bass only or would it? I find it
> hard to believe that the mass of the cone has nothing to do with this
> at higher frequencies, which is why you cannot use a tweeter for a
> woofer.
> And by cutting down the inductance would also mean a smaller coil and
> maybe larger wire? Wouldn't that be a problem?


Ding! It's a juggling act and there are tradeoffs. Want less
inductance, use fewer turns of wire, but... oops, now you need more
current to achieve the same force to move a given mass with a given
transient response, and ah crap, also need bigger wire to achieve the
now-great power handling requirement, so you use a better magnet, but
that adds cost and/or heft, perhaps more than your target market will
be willing to pay. And so on on.

The paper seems to want to debunk the thought that moving mass isn't
an issue at all in terms woofer transient response, but instead lower
H is more important. I'm guessing this manufactuer's driver have more
mass and less inductance than their competitors--just a wild guess!

Marketeering at work.


However, reviewing the transient response graph on page 5 -- I don't
see significant reasons to draw much of any useful conclusion from it.
And as you tacitly suggested, using a steady state frequency response
analysis, pointing to unaffected high frequency response, and using
that to draw a conclusion on transient response of a given low
frequency driver is hocus pocus science.

And adding mass to the dust cap of a speaker... and ... I don't think
you should trust this paper to draw any sort of useful conclusions at
all.

Trust thy ears.

Best Regards,
--
/"\ ASCII Ribbon Campaign | Todd H
\ / | http://www.toddh.net/
X Promoting good netiquette | http://triplethreatband.com/
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  #2  
Old July 7th 05, 12:04 AM
[email protected]
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Default Frequency response, mass vs. inductance

I have a question. Someone on a message board I usually post on talked
about woofer speed. I assume what this translates to is frequency
response (ie 1/time=frequency). He also posted a link, which I read:
http://www.adireaudio.com/Files/Tech...ooferSpeed.pdf
At the end of the page it shows a graph, with the frequency response of
the speaker they used. To me, inductance would have little or no effect
on a speaker unless, it were a midrange or a tweeter. And from this
graph, mass still seems to dampen the signal more throught the
frequency range than does the inductor, which is should I would think.
(ie xl=2(pi)(f)(l)) When it does eventually does get to the higher end
the inductor does not seem to cut the signal all that much.
So what I would like to know is, if the inductance is the most
important part, why not make it small, and increase your frequency
response of the speaker? This probably would not effect a woofer all
that much if the woofer was used for bass only or would it? I find it
hard to believe that the mass of the cone has nothing to do with this
at higher frequencies, which is why you cannot use a tweeter for a
woofer.
And by cutting down the inductance would also mean a smaller coil and
maybe larger wire? Wouldn't that be a problem?

  #3  
Old July 7th 05, 12:54 AM
Richard Crowley
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"Todd H." wrote ...
> Ding! It's a juggling act and there are tradeoffs. Want less
> inductance, use fewer turns of wire, but... oops, now you
> need more current to achieve the same force to move a given
> mass with a given transient response, and ah crap, also need
> bigger wire to achieve the now-great power handling requirement,
> so you use a better magnet, but that adds cost and/or heft,
> perhaps more than your target market will be willing to pay.
> And so on on.


Which is why JBL took ordinary (round) magnet wire and ran it
through a home-made kludge that flattened it into a ~rectangular
shape. They pointed out this device on a tour of the factory I took a
couple decades ago. They claimed this exercise allowed them to...

1) Pack more turns (mean cross-sectional area) in a given space
by more efficiently using the space (filling in the corners, etc.)

2) Make self-supporting voice-coils so they didn't have to use
the fiber (paper) coil forms seen in other drivers. I believe they
claimed this allowed smaller gaps (increasing flux) and made
the coils better at shedding heat (no insulating coil form on the
inside of the solenoid).

They had a lathe-like device where they would edge-wind
long solenoids of coil, slathering them with something that
held them together. Then heating the coil and allowing it to
cure (overnight). After that, they could take the big coils
and chop off just the amount needed to make a voice coil
with a bit extra to bring out the leads.

At least that is the way I remember it.


  #4  
Old July 7th 05, 11:23 AM
Arny Krueger
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> wrote in message
oups.com
> I have a question. Someone on a message board I usually

post
> on talked about woofer speed. I assume what this

translates to
> is frequency response (ie 1/time=frequency). He also

posted a
> link, which I read:
> http://www.adireaudio.com/Files/Tech...ooferSpeed.pdf
> At the end of the page it shows a graph, with the

frequency
> response of the speaker they used. To me, inductance would
> have little or no effect on a speaker unless, it were a
> midrange or a tweeter. And from this graph, mass still

seems
> to dampen the signal more throught the frequency range

than
> does the inductor, which is should I would think. (ie
> xl=2(pi)(f)(l)) When it does eventually does get to the

higher
> end the inductor does not seem to cut the signal all that
> much.


> So what I would like to know is, if the inductance is the

most
> important part, why not make it small, and increase your
> frequency response of the speaker?


Because frequency response isn't everything. Dispersion is
also important. Dispersion is largely based on the diameter
of the radiating surface. The larger the diameter of the
speaker, the less dispersion at high frequencies. As a rule,
people don't want beamy-sounding speakers, speakers that
beam sound like tight laser beams, speakers that have a
sweet spot the size of a dime.

>This probably would not
> effect a woofer all that much if the woofer was used for

bass
> only or would it?


Exactly. A very high proportion of all woofers in 2-way
speakers have additional inductance placed in series with
them. The inductance is part of the speaker's crossover, and
the goal of the woofer crossover is to further limit the
high frequency response of the speaker.

The idea of fast woofers is a fallacy because almost all
woofers are driven through low-pass filters that reduce the
high frequency response and slow down the transient response
of a woofer even more than the mechanical limits thusfar
described.

Another reason why electrical circuits are used to slow down
woofers and reduce frequency response well below mechanical
the mechanical limits of the driver relates to the
smoothness of frequency response. Just because a speaker
responds to some higher frequency doesn't mean that the
response is smooth in that area. The extreme case relates to
bandpass woofers that often have peaks in their response at
relatively low frequencies like 250 Hz or less. These
speakers are going to sound pretty honky in the lower
midrange unless an electrical network is used to roll-off
the woofer's response below this peak.

>I find it hard to believe that the mass of
> the cone has nothing to do with this at higher

frequencies,
> which is why you cannot use a tweeter for a woofer.


You've got that reversed. The mass of the cone has a lot to
do with low frequency response, which is why you can't use a
tweeter for a woofer. When you add mass to a speakers cone
and retune the enclosure for the new massier woofer, you get
greater bass extension at the cost of lower efficiency.

> And by cutting down the inductance would also mean a

smaller
> coil and maybe larger wire? Wouldn't that be a problem?


Voice nductance is usually relatively unimportant in woofers
because it is common to put even larger external inductors
in series with their voice coils.


  #5  
Old July 10th 05, 08:53 AM
James Lehman
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Posts: n/a
Default

No one has made the observation that all things the same, a woofer cone
driven by a sine wave of a given frequency will have a greater velocity at a
higher excursion. I think that is what "fast woofer cone" really is all
about. Also consider the fact that at low frequencies, a woofer tends to
move much like a piston, while at higher frequencies, the force from the
coil tends to propagate from the center of the cone to the edge as a
transverse wave in the cone material, otherwise known as ripple.



"Arny Krueger" > wrote in message
...
> > wrote in message
> oups.com
> > I have a question. Someone on a message board I usually

> post
> > on talked about woofer speed. I assume what this

> translates to
> > is frequency response (ie 1/time=frequency). He also

> posted a
> > link, which I read:
> > http://www.adireaudio.com/Files/Tech...ooferSpeed.pdf
> > At the end of the page it shows a graph, with the

> frequency
> > response of the speaker they used. To me, inductance would
> > have little or no effect on a speaker unless, it were a
> > midrange or a tweeter. And from this graph, mass still

> seems
> > to dampen the signal more throught the frequency range

> than
> > does the inductor, which is should I would think. (ie
> > xl=2(pi)(f)(l)) When it does eventually does get to the

> higher
> > end the inductor does not seem to cut the signal all that
> > much.

>
> > So what I would like to know is, if the inductance is the

> most
> > important part, why not make it small, and increase your
> > frequency response of the speaker?

>
> Because frequency response isn't everything. Dispersion is
> also important. Dispersion is largely based on the diameter
> of the radiating surface. The larger the diameter of the
> speaker, the less dispersion at high frequencies. As a rule,
> people don't want beamy-sounding speakers, speakers that
> beam sound like tight laser beams, speakers that have a
> sweet spot the size of a dime.
>
> >This probably would not
> > effect a woofer all that much if the woofer was used for

> bass
> > only or would it?

>
> Exactly. A very high proportion of all woofers in 2-way
> speakers have additional inductance placed in series with
> them. The inductance is part of the speaker's crossover, and
> the goal of the woofer crossover is to further limit the
> high frequency response of the speaker.
>
> The idea of fast woofers is a fallacy because almost all
> woofers are driven through low-pass filters that reduce the
> high frequency response and slow down the transient response
> of a woofer even more than the mechanical limits thusfar
> described.
>
> Another reason why electrical circuits are used to slow down
> woofers and reduce frequency response well below mechanical
> the mechanical limits of the driver relates to the
> smoothness of frequency response. Just because a speaker
> responds to some higher frequency doesn't mean that the
> response is smooth in that area. The extreme case relates to
> bandpass woofers that often have peaks in their response at
> relatively low frequencies like 250 Hz or less. These
> speakers are going to sound pretty honky in the lower
> midrange unless an electrical network is used to roll-off
> the woofer's response below this peak.
>
> >I find it hard to believe that the mass of
> > the cone has nothing to do with this at higher

> frequencies,
> > which is why you cannot use a tweeter for a woofer.

>
> You've got that reversed. The mass of the cone has a lot to
> do with low frequency response, which is why you can't use a
> tweeter for a woofer. When you add mass to a speakers cone
> and retune the enclosure for the new massier woofer, you get
> greater bass extension at the cost of lower efficiency.
>
> > And by cutting down the inductance would also mean a

> smaller
> > coil and maybe larger wire? Wouldn't that be a problem?

>
> Voice nductance is usually relatively unimportant in woofers
> because it is common to put even larger external inductors
> in series with their voice coils.
>
>



 




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