I realize this is probably an economic limitation, but it seems to me that a
few "price-no-object" driver manufacturers should be making something like
this:

I have some Dynaudio Acoustics woofers that are 8" and have 4" dia voice
coils. For their size, they sound incredible, big, deep, loud and very
responsive to transients, not to mention the power handling of 300W.

Now, I work with a lot of 18" woofers in sound reinforcement applications,
but the voice coil sizes are rarely larger than 3" or 4". I know there is a
British company called Precision that makes 21" woofer with 6" voice coils,
but if we consider the scale of things, an 18" woofer should do amazing
things if it had a 10" voice coil. The larger coil reduces the length of
unsupported piston area, provides enormously more power for accurate
transients, and has more rigidity against lateral movement. Plus with a
motor this large, the Xmax could be huge. Imagine an 18" woofer with a
redesigned skiver/suspension surround and the ability to stroke 8". Such a
driver would displace the volume of twenty 18" conventional woofers and be
capable of infrasonic low frequency extention.

In a sound reinforcement situation that is not a permanent installation,
such a driver would be the holy grail--just hook up a 10kW amplifier to it
and rock the house. While such a driver might have a 100lb magnet structure
(and if price is no object, we could make that a lighter weight neodymium
magnet), the benefit of having just one, heavy cabinet, over hauling two
dozen cabinets would be enormous.

And for the ultimate "Bass Pigs", such as this author :-) , this would be
the ultimate loudspeaker that could take over the neighborhood without
taking over the livingroom decor.

I've been thinking about this concept occasionally for the past 6-7 years.
It should be a reasonable progression. If Bob Carver can invent an 8"
subwoofer with a 2.35" stroke, then by golly, it should be possible to scale
this design up to an 18" driver.

I feel that 18" drivers have undersized voice coils. They could be larger,
both extending power handling, Xmax, upper frequency usefulness, transient
response and efficiency. Such drivers would really be useful for extreme low
frequency output, as of course, Doppler limits the maximum speed the piston
can move without causing audible pitch shifting.

Are we really at the technological limit with 5" voice coils on 18" drivers?


--
Best Regards,

Mark A. Weiss, P.E.
www.mwcomms.com
-

In article . net,
"Mark & Mary Ann Weiss" wrote:

I realize this is probably an economic limitation, but it seems to me that a
few "price-no-object" driver manufacturers should be making something like
this:

I have some Dynaudio Acoustics woofers that are 8" and have 4" dia voice
coils. For their size, they sound incredible, big, deep, loud and very
responsive to transients, not to mention the power handling of 300W.

Now, I work with a lot of 18" woofers in sound reinforcement applications,
but the voice coil sizes are rarely larger than 3" or 4". I know there is a
British company called Precision that makes 21" woofer with 6" voice coils,
but if we consider the scale of things, an 18" woofer should do amazing
things if it had a 10" voice coil. The larger coil reduces the length of
unsupported piston area, provides enormously more power for accurate
transients, and has more rigidity against lateral movement. Plus with a
motor this large, the Xmax could be huge. Imagine an 18" woofer with a
redesigned skiver/suspension surround and the ability to stroke 8". Such a
driver would displace the volume of twenty 18" conventional woofers and be
capable of infrasonic low frequency extention.

In a sound reinforcement situation that is not a permanent installation,
such a driver would be the holy grail--just hook up a 10kW amplifier to it
and rock the house. While such a driver might have a 100lb magnet structure
(and if price is no object, we could make that a lighter weight neodymium
magnet), the benefit of having just one, heavy cabinet, over hauling two
dozen cabinets would be enormous.

And for the ultimate "Bass Pigs", such as this author :-) , this would be
the ultimate loudspeaker that could take over the neighborhood without
taking over the livingroom decor.

I've been thinking about this concept occasionally for the past 6-7 years.
It should be a reasonable progression. If Bob Carver can invent an 8"
subwoofer with a 2.35" stroke, then by golly, it should be possible to scale
this design up to an 18" driver.

I feel that 18" drivers have undersized voice coils. They could be larger,
both extending power handling, Xmax, upper frequency usefulness, transient
response and efficiency. Such drivers would really be useful for extreme low
frequency output, as of course, Doppler limits the maximum speed the piston
can move without causing audible pitch shifting.

Are we really at the technological limit with 5" voice coils on 18" drivers?


--
Best Regards,

Mark A. Weiss, P.E.
www.mwcomms.com
-





IMO The moving mass would be too great, thereby decreasing the
sensitivity. This can be a bad thing for some, and negligible for
others. I too wonder what type of market large format drivers with
equally large vc's would have.

From what I understand, the large vc's are for simply cooling purposes.
And that the materials and assembly cost for motor structures would be
enormous.

There are however motor structures that can do 10"+ with simple 3" vc's
IIRC. The Adire Parthenon comes to mind.

IMO There's more to driver design than just the vc diameter.

--
Cyrus

*coughcasaucedoprodigynetcough*

Mark & Mary Ann Weiss wrote:

I realize this is probably an economic limitation, but it
seems to me
that a few "price-no-object" driver manufacturers should
be making
something like this:

I have some Dynaudio Acoustics woofers that are 8" and
have 4" dia
voice coils.

Figure that voice coil diameter if functional (not window
dressing) relates to voice coil power handling capacity.

For their size, they sound incredible, big, deep, loud
and very responsive to transients, not to mention the
power handling
of 300W.

Actually, Dynaudio woofers are the laughing stock of the
industry when they have substandard Xmax, and odd
Thiel-Small parameters.

Woofer power handling specs can be pretty crazy. There are
standards for measuring them, but are they being followed?

Now, I work with a lot of 18" woofers in sound
reinforcement
applications, but the voice coil sizes are rarely larger
than 3" or 4".

One thing you have to look at is the balance between
sensitivity and power handling. A woofer driver can have
sensitivity that ranges from about 83 dB/watt to 103 dB/watt
with some lying outside even this very wide 20 dB range. An
efficient woofer doesn't need a voice coil that can handle
megawatts in order to be suitably loud.

There is an iron law of physics that ties box size, low
frequency extension, and efficiency together. For example, a
big box allows higher efficiency for a given low frequency
extension. A small box means you either have low efficiency
or not much bass extension or both.

SR speakers tend to compromise low frequency extension (less
bass) and box size (larger) for efficiency (more efficient).

Studio monitors tend to compromise efficiency (less
efficient) for low frequency extension (deeper bass) and box
size (smaller).


I know there is a British company called Precision that
makes 21"
woofer with 6" voice coils, but if we consider the scale
of things,
an 18" woofer should do amazing things if it had a 10"
voice coil.

Depending on the context, such a large voice coil could be a
cosmic waste, and even limit the performance of the speaker.

More of some parameter that looks cool does not always give
better performance.

The larger coil reduces the length of unsupported piston
area,
provides enormously more power for accurate transients,
and has more
rigidity against lateral movement.

None of which may be issues in a particular system design.
Enough is enough if you have enough.

I also suspect that you didnt' mean to say that "The larger
coil provides enormously more power for accurate transients"
because the coil is not a source of power, the amplifier is.
Transients are minor issues when it comes to voice coil
heating because they are of short duration. The key
parameter relating to handling extreme transients relates to
strength, and its easier to make a smaller voice coil
stronger.

Plus with a motor this large, the Xmax could be huge.

I don't believe that voice coils are the major issue when it
comes to Xmax. My informants tell me that its easy to make a
voice coil long, but its hard to provide a cone suspension
that is compliant enough to allow large excursions, while
holding the cone in the proper path with enough precision to
avoid mechanical damage while the cone is stroking. A larger
diameter voice coil vastly increases the weight of the
magnet assembly for a given amount of flux density.

Imagine an 18" woofer with a redesigned
skiver/suspension surround and the ability to stroke 8".

There you go - you mentioned the cone suspension as being a
limiting factor for Xmax. Nice that we agree, eh? ;-)

Such a driver would displace the volume of twenty 18"
conventional woofers
and be capable of infrasonic low frequency extention.

In fact the justification for some exotic woofer designs
relates to beating the normal limits to Xmax due to
tranditional cone suspension systems.

In a sound reinforcement situation that is not a permanent
installation, such a driver would be the holy grail--just
hook up a
10kW amplifier to it and rock the house.

There's a trend towards powered speakers for SR. The weight
of the amp and the weight of the speaker are now combined
into a single parameter. It is very difficult to build a
long-stroke woofer that is also highly efficient.

While such a driver might
have a 100lb magnet structure (and if price is no object,
we could
make that a lighter weight neodymium magnet), the benefit
of having
just one, heavy cabinet, over hauling two dozen cabinets
would be
enormous.

The market and the designers are very sensitive to exactly
these issues. The better products on the market are no doubt
the result of careful work to optimize the weight/SPL
performance.

And for the ultimate "Bass Pigs", such as this author :-)
, this
would be the ultimate loudspeaker that could take over the
neighborhood without taking over the livingroom decor.

I've been thinking about this concept occasionally for the
past 6-7
years. It should be a reasonable progression. If Bob
Carver can
invent an 8" subwoofer with a 2.35" stroke, then by golly,
it should
be possible to scale this design up to an 18" driver.

AFAIK Bob Carver didn't invent the drivers his woofers use.
They were developed by a supplier. Bob Carver did have a
patent on subwoofers that he used to IMO extort money from
subwoofer manufacturers. The patent was found to be riddled
with errors and self-contradictions, and was eventually
invalidated in court. This left Carver exposed to damage
claims from the smaller companies that he had been holding
up for legally unjustified cash payments.

I feel that 18" drivers have undersized voice coils.

Thanks for using a word (feel) that denotes emotion, not
logic.

I think I know a thing or two about speakers, but I would
not want to tell speaker designers how to build better
speakers. I know a number of people who analyze and/or
design speakers who heartily agree with my lack of desire to
compete with their demonstrated abilities. ;-)

They could be larger, both extending power handling, Xmax,
upper frequency
usefulness, transient response and efficiency. Such
drivers would
really be useful for extreme low frequency output, as of
course,
Doppler limits the maximum speed the piston can move
without causing
audible pitch shifting.

Well, you can control Doppler by moving the high pass
frequency down.

Are we really at the technological limit with 5" voice
coils on 18" drivers?

All Science is subject to future discoveries and improved
analysis.

On Tue, 03 May 2005 07:08:56 GMT, Cyrus wrote:

In article . net,
"Mark & Mary Ann Weiss" wrote:

I realize this is probably an economic limitation, but it seems to me that a
few "price-no-object" driver manufacturers should be making something like
this:

I have some Dynaudio Acoustics woofers that are 8" and have 4" dia voice
coils. For their size, they sound incredible, big, deep, loud and very
responsive to transients, not to mention the power handling of 300W.

Now, I work with a lot of 18" woofers in sound reinforcement applications,
but the voice coil sizes are rarely larger than 3" or 4". I know there is a
British company called Precision that makes 21" woofer with 6" voice coils,
but if we consider the scale of things, an 18" woofer should do amazing
things if it had a 10" voice coil. The larger coil reduces the length of
unsupported piston area, provides enormously more power for accurate
transients, and has more rigidity against lateral movement. Plus with a
motor this large, the Xmax could be huge. Imagine an 18" woofer with a
redesigned skiver/suspension surround and the ability to stroke 8". Such a
driver would displace the volume of twenty 18" conventional woofers and be
capable of infrasonic low frequency extention.

In a sound reinforcement situation that is not a permanent installation,
such a driver would be the holy grail--just hook up a 10kW amplifier to it
and rock the house. While such a driver might have a 100lb magnet structure
(and if price is no object, we could make that a lighter weight neodymium
magnet), the benefit of having just one, heavy cabinet, over hauling two
dozen cabinets would be enormous.

And for the ultimate "Bass Pigs", such as this author :-) , this would be
the ultimate loudspeaker that could take over the neighborhood without
taking over the livingroom decor.

I've been thinking about this concept occasionally for the past 6-7 years.
It should be a reasonable progression. If Bob Carver can invent an 8"
subwoofer with a 2.35" stroke, then by golly, it should be possible to scale
this design up to an 18" driver.

I feel that 18" drivers have undersized voice coils. They could be larger,
both extending power handling, Xmax, upper frequency usefulness, transient
response and efficiency. Such drivers would really be useful for extreme low
frequency output, as of course, Doppler limits the maximum speed the piston
can move without causing audible pitch shifting.

Are we really at the technological limit with 5" voice coils on 18" drivers?


--
Best Regards,

Mark A. Weiss, P.E.
www.mwcomms.com

IMO The moving mass would be too great, thereby decreasing the
sensitivity. This can be a bad thing for some, and negligible for
others. I too wonder what type of market large format drivers with
equally large vc's would have.

From what I understand, the large vc's are for simply cooling purposes.
And that the materials and assembly cost for motor structures would be
enormous.

There are however motor structures that can do 10"+ with simple 3" vc's
IIRC. The Adire Parthenon comes to mind.

IMO There's more to driver design than just the vc diameter.

More to the point, it's a good commercial decision. As you've pointed
out, there are no significant excursion advantages to a huge VC, and
the cost of the magnet assembly would be horrific, for little or no
technical advantage.
--

Stewart Pinkerton | Music is Art - Audio is Engineering

Cyrus wrote:
In article . net,
From what I understand, the large vc's are for simply cooling
purposes.

No, they are not. Ignoring, for the moment, pure marketing driven
mis-designs, as one often sees, for example, in the car aduio market,
the gross voice coil diamter is driven by the requirement of obtaining
a sufficiently high Bl product required due to the higher moving mass
of larger drivers.

What "Bl product" means is the product of multiplying the length
"l" of the voice coil wire immersed in the magnetic field whose
flux density is "B." The Bl product is a very important factor
in determining the performance of the speaker. For example, the
efficiency of the driver is determined by the ratio of the Bl
product divided by the moving mass, whereas the electrical damping
is proportional to the moving mass divided by the square of the
Bl product.

So, very roughly speaking, the mass of the driver goes up at a rate
somewhere between the square and the cibe of the diameter (since it's
not only area, but the thickness of the driver, that increases). To
maintain the same efficiency, a driver of twice the diameter must
have at least 4 times the Bl product, all other things being equal.

There are two ways, theoretically, to increase the Bl product:

1. Increase the flux density, B
2. Increase the length of the wire in the magnetic field

You're stuck trying to increase the flux density, because magnets,
for best efficiency and stability, already run the gaps at or near
the saturation flux density at the gap, limiting the flux density
practically to 1 Tesla (10 kGauss). Adding more magnet will only
waste material: 10 kGauss is the limit.

You're left with increasing the length of the wire in the gap,
and there are three ways of doing that:

2a. Increase the depth of the gap, which has the disadvantage in
overhung coils, or reducing the voice-coil limited Xmax, or

2b. Increase the number of winding layers on the voice coil.
This requires an increas in the width of the gap, which
reduces the flux density and increases external leakage,
though generally, the tradeoff works in your favor.

2c. Increase the diameter of the gap. The problem you run into
here is that from the view point of magnet design, there is
an optimal ratio of pole-piece, gap, magnet diameter and
depth which essentially prevents you from arbitrarily increasing
the voice coil diameter. Consider the obvious limit: you make
the voice coil too large, and it results in magnet structure
whose diameter is bigger than the driver.

Designing a driver is all about optimizing conflicting requirements,
and, frankly, a 2-3" voice coil is just about the optimum size when
you've paid proper attention to ALL the important consderations.
Maybe some designs might dictate something as large as a 4", but
the circumstances are generally unusual to require that.

Performance DOES NOT, as the original poster hypothesised increase
without limit as you increase the voice coil diameter. Beyond a
certain point, the cost benefit ratio curves starts going sharply
negative, you start seriously compromising performance in many
aspects, and you end up with a design which is utterly impractical.

In article ,
"Arny Krueger" wrote:

Mark & Mary Ann Weiss wrote:
[snip]
Plus with a motor this large, the Xmax could be huge.

I don't believe that voice coils are the major issue when it
comes to Xmax. My informants tell me that its easy to make a
voice coil long, but its hard to provide a cone suspension
that is compliant enough to allow large excursions, while
holding the cone in the proper path with enough precision to
avoid mechanical damage while the cone is stroking. A larger
diameter voice coil vastly increases the weight of the
magnet assembly for a given amount of flux density.


Adire Audio used to have some discussions on high excursion subs before
they trashed their web site. They said that a major problem with high
excursions was that an oversized speaker surround would collapse or
invert itself from the air pressure. It would sound very bad and soon
tear.

Another problem is the area of the voice coil that is not in a magnetic
field. It does nothing but make heat. There's also terrible distortion
if the amount of the coil that is in the field doesn't remain constant
as the coil moves.

Adire can custom build a +/- 80mm excursion subwoofer motor called the
Parthenon for $3000. The cone/diaphragm is up to you.

I found a partial mirror of their old page:
http://www.acousticconcepts.com.au/Parthenon.html

On 3 May 2005 18:07:06 -0700, wrote:

You're stuck trying to increase the flux density, because magnets,
for best efficiency and stability, already run the gaps at or near
the saturation flux density at the gap, limiting the flux density
practically to 1 Tesla (10 kGauss). Adding more magnet will only
waste material: 10 kGauss is the limit.

Damn, nobody told Lowther............... :-)

--

Stewart Pinkerton | Music is Art - Audio is Engineering

Well, somebody DID tell Lowther. They don't use low-carbon steel in
their
magnet structures. Instead, they use an alloy that has a higher
saturation
magnetization. Seems a good fix to the problem, but it comes at a
significant
cost. These allows are far from cheap, they're hard to machine (they
tend
to be brittle and not kind to cutting tools) and they result in magnets
that
may not have the best temperature and shock stability.

It comes down, once again, to a matter of economics. Given the choice
between balance the cost of more copper vs more hard magnet material
vs more cheap steel vs more expensive exotic materials, which
combination
gives you what you need for your intended market?

Adire Audio used to have some discussions on high excursion subs before
they trashed their web site. They said that a major problem with high
excursions was that an oversized speaker surround would collapse or
invert itself from the air pressure. It would sound very bad and soon
tear.

Another problem is the area of the voice coil that is not in a magnetic
field. It does nothing but make heat. There's also terrible distortion
if the amount of the coil that is in the field doesn't remain constant
as the coil moves.

Adire can custom build a +/- 80mm excursion subwoofer motor called the
Parthenon for $3000. The cone/diaphragm is up to you.

I found a partial mirror of their old page:
http://www.acousticconcepts.com.au/Parthenon.html


Facinating discussions from all so far... and pretty much what I expected in
terms of answers. And yielding one radical product which seems to be THE
design concept I was after. I LIKE the idea of moving 16 cu ft of air with
one driver. Cute!

Getting back to some of the other replies in this thread, yes, I do observe
a correlation between optimal voice coil size and efficiency. I've noted
that the EVM 18B woofers with their smallish 2.5" coils seem to be
significantly more sensitive than offerings from JBL, Altec and others,
despite the 4" coils of the latter bunch. However, I don't think the
distortion levels are a match to the larger coils. The greater the piston
area is backed by motor power, the more faithful the piston can move. Small
coil, big piston, lots of breakup, modal resonances and other nasties.
I think that one of the reasons why my little Dynaudio woofers which I use
in some nearfield monitors move so much air and have amazing transient
response is due to the fact that a large area of the cone, not just a dot in
the center, is driven by the coil. I think there is a benefit there.

I've been thinking about a variety of loudspeaker designs, one of which was
similar to the Parthenon. I made some sketches 5-6 years ago, but never
persued it. I turned the skiver/surround 90º with respect to conventional
surrounds, and made it like an accordian hose, at the cone diameter. That
allows for lots of movement. The challenge was controlling lateral movement.

Years earlier, I was brainstorming a more radical design, where the air
molecules are excited directly by electrical energy. This Ion Loudspeaker
would have no diaphragm at all. Frequency response would extend literally
from DC to in the megahertz range. Drawbacks were high voltages and ozone
emissions. :-)


--
Best Regards,

Mark A. Weiss, P.E.
www.mwcomms.com
-

Servodrive.

On Sat, 07 May 2005 08:38:40 GMT, "Mark & Mary Ann Weiss"
wrote:

Adire Audio used to have some discussions on high excursion subs before
they trashed their web site. They said that a major problem with high
excursions was that an oversized speaker surround would collapse or
invert itself from the air pressure. It would sound very bad and soon
tear.

Another problem is the area of the voice coil that is not in a magnetic
field. It does nothing but make heat. There's also terrible distortion
if the amount of the coil that is in the field doesn't remain constant
as the coil moves.

Adire can custom build a +/- 80mm excursion subwoofer motor called the
Parthenon for $3000. The cone/diaphragm is up to you.

I found a partial mirror of their old page:
http://www.acousticconcepts.com.au/Parthenon.html

Facinating discussions from all so far... and pretty much what I expected in
terms of answers. And yielding one radical product which seems to be THE
design concept I was after. I LIKE the idea of moving 16 cu ft of air with
one driver. Cute!

You might think it's 'cute', but it will be much less cost-efficient
than using a bunch of 15" Tempests to do the same job. Note that the
Parthenon is not a driver, it's just a motor assembly. That 16cu ft
*theoretical* figure is for a non-existent extended motor with a
non-existant cone and suspension assembly, at an unmentioned total
cost - but figure say $15-20k ballpark, with a good risk that there'll
be something wrong with the first try. You can easily match that 16 cu
ft displacement with 160 Tempest drivers, which I'll bet you can buy
from Adire for less money, and they are known products which can be
driven as an array by a bunch of off-the-shelf amplifiers.

Getting back to some of the other replies in this thread, yes, I do observe
a correlation between optimal voice coil size and efficiency. I've noted
that the EVM 18B woofers with their smallish 2.5" coils seem to be
significantly more sensitive than offerings from JBL, Altec and others,
despite the 4" coils of the latter bunch. However, I don't think the
distortion levels are a match to the larger coils.

You don't 'think' the distortion levels are a match? If you don't
*know*, then don't speculate.

The greater the piston
area is backed by motor power, the more faithful the piston can move. Small
coil, big piston, lots of breakup, modal resonances and other nasties.
I think that one of the reasons why my little Dynaudio woofers which I use
in some nearfield monitors move so much air and have amazing transient
response is due to the fact that a large area of the cone, not just a dot in
the center, is driven by the coil. I think there is a benefit there.

Well, you're wrong. Transient response has *nothing* to do with coil
size, and neither does suspension travel. They do however handle large
power transients with little compression, and that does relate to
those oversized coils. Besides, those Dynaudio units are known to have
significant breakup in the 3-4kHz range, not true of several other
units with stiffer cones but smaller coils, as made by Focal,
Wilson-Benesch, and Wharfedale, among others. There's a reason why the
vast majority of top-class 4-6 inch drivers use 2-2.5 inch coils.

I've been thinking about a variety of loudspeaker designs, one of which was
similar to the Parthenon. I made some sketches 5-6 years ago, but never
persued it. I turned the skiver/surround 90º with respect to conventional
surrounds, and made it like an accordian hose, at the cone diameter. That
allows for lots of movement. The challenge was controlling lateral movement.

Note also the very first paragraph of this post............

Years earlier, I was brainstorming a more radical design, where the air
molecules are excited directly by electrical energy. This Ion Loudspeaker
would have no diaphragm at all. Frequency response would extend literally
from DC to in the megahertz range. Drawbacks were high voltages and ozone
emissions. :-)

No need for brainstorming, the IonoFane tweeter was a commercial
reality in the '60s and '70s.
--

Stewart Pinkerton | Music is Art - Audio is Engineering

In article ,
Stewart Pinkerton wrote:

You can easily match that 16 cu
ft displacement with 160 Tempest drivers, which I'll bet you can buy
from Adire for less money, and they are known products which can be
driven as an array by a bunch of off-the-shelf amplifiers.


Not anymore, for the old Tempests anyway.

The msrp pricing still looks scary for all of Adire's new lines, as msrp
does. Either way, I concur, one will get a good deal on drivers for an
order that big.. new Tempests or not.

--
Cyrus

*coughcasaucedoprodigynetcough*

Additionally, you should take a look at what sort of motor specs that
will result with the "long excursion" 8" vc that you propose. You may
find the weight to be ridiculously prohibitive, which will kill your
motor strength, and subsequently your ability to drive that 15" cone
structure to any sort of high performance level. You could go 2-layer,
but then that gives you less lines in the gap to build up your motor
strength. You could go with fine wire, but then your dcr may turn up
high and possibly your current handling capability/ultimate power
handling may become limited. Then there is the issue of will you
augment the magnet structure to achieve saturation in that *much*
larger 8" dia gap? If not, then you lose out on potential motor
strength and become more susceptible to motor modulation, as well. If
you do, then you will find your magnet structure will balloon quite
profoundly (bigger than the mounting flange, itself, was mentioned
earlier by someone, I believe). Going to neo will result in a rather
large slab and pot structure that may likely cost as much as a used car
(Crumax would love you, though- I'm sure). Then there's the issue of
acquiring a magnetizer that could actually charge magnet structures of
these sheer proportions (in either ferrite or neo scenario). Then
there's the issue of just practical handling and installation of such
heavy drivers (try moving one of those JL W7 drivers around and
handling it for installation to get an idea that there *is* a practical
weight/size limit for speakers that humans have to handle). Then there
is the inductance issue of such an extreme coil with essentially an
enormous iron core inside it- how well the cone handles on the upper
range may not even be an issue, if the motor is electrically
low-passing itself substantially well below that range.

You really need to get some modeling software and plug in your
hypothetical structure to really get an appreciation for the balance
between a sheer number of factors that comes into play. Then you will
understand much better how other motor structures in actual speakers on
the market become what they become to do the particular duties that
they do (and why they avoid certain extremes in their design). Just
picking certain parameters that you would like to accentuate while
hoping to maintain other parameters and observe extreme gains in still
other parameters is *really* stepping out on a limb. It's a HUGE
balancing act, and often requires rigorous and brute iteration to
actually hone in on your target w/o sacrificing too much in other
areas.

Mark & Mary Ann Weiss wrote:
Getting back to some of the other replies in this thread, yes, I do
observe
a correlation between optimal voice coil size and efficiency. I've
noted
that the EVM 18B woofers with their smallish 2.5" coils seem to be
significantly more sensitive than offerings from JBL, Altec and
others,
despite the 4" coils of the latter bunch. However, I don't think the
distortion levels are a match to the larger coils. The greater the
piston
area is backed by motor power, the more faithful the piston can move.
Small
coil, big piston, lots of breakup, modal resonances and other
nasties.
I think that one of the reasons why my little Dynaudio woofers which
I use
in some nearfield monitors move so much air and have amazing
transient
response is due to the fact that a large area of the cone, not just a
dot in
the center, is driven by the coil. I think there is a benefit there.

wrote in message
ups.com...
Servodrive.


Hell Yeah,

In article ,
"Chad Wahls" wrote:

wrote in message
ups.com...
Servodrive.


Hell Yeah,



Interesting it is. I wanna hear one.

Mr. Danley occasionally posts over at diyaudio.com.

--
Cyrus

*coughcasaucedoprodigynetcough*

Mark & Mary Ann Weiss wrote:

I've been thinking about a variety of loudspeaker designs, one of which was
similar to the Parthenon. I made some sketches 5-6 years ago, but never
persued it. I turned the skiver/surround 90º with respect to conventional
surrounds, and made it like an accordian hose, at the cone diameter. That
allows for lots of movement. The challenge was controlling lateral movement.

Well your other option is to look at entirely different motor designs
than the standard voice-coil-piston design. Someone else mentioned
ServoDrive. Several years ago Phoenix Gold licensed and adapted some of
their concepts for car audio as well.

For something REALLY different, check out their "rotary" driver design -
some good info from Tom Danley himself can be found he
http://www.diyaudio.com/forums/showthread/t-55122.html


---
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"Cyrus" wrote in message
...
In article ,
"Chad Wahls" wrote:

wrote in message
ups.com...
Servodrive.


Hell Yeah,



Interesting it is. I wanna hear one.

If you haven't then you should. Actually a single horn load is not that
impressive, need to have 4 mouth to mouth, and a pack of depends. (adult
diapers)

The best thing is their efficiency and lack of power compression. It does
not take much power to get them rockin and keep them there.

They are good for balls out bass, many have admitted that they are eithter
on or off and have stated that they suffer in low volume reproduction. But
good golly they do the loud stuff well.

Another thing to hear is an array of Bassmaxx horns or EAW KF940's

Chad

For what it's worth, the Precision Devices web page for the 21-inch driver
is he

http://www.precisiondevices.co.uk/showdetails.asp?id=16

They also make a 24-inch driver

http://www.precisiondevices.co.uk/showdetails.asp?id=17

Tim

In article ,
"Tim Martin" wrote:

For what it's worth, the Precision Devices web page for the 21-inch driver
is he

http://www.precisiondevices.co.uk/showdetails.asp?id=16

They also make a 24-inch driver

http://www.precisiondevices.co.uk/showdetails.asp?id=17

Tim



msrp? street prices?

--
Cyrus

*coughcasaucedoprodigynetcough*

"Cyrus" wrote in message
...

msrp? street prices?

here's one supplier's price list

http://www.bkelec.com/Pro/PD.htm

£430 for the 21-inch, £510 for the 24-inch.

Tim

would it be possible to solve the problem for the need of a huge
magnet by using an electromagnet instead of a permanent one.
obviously this would use up more power, but the strenght of your
magnet would be variable, and it would be relatively inexspensive

cpo wrote:
would it be possible to solve the problem for the need of a huge
magnet by using an electromagnet instead of a permanent one.
obviously this would use up more power, but the strenght of your
magnet would be variable, and it would be relatively inexspensive

No, for any number of reasons.

1. No matter how you energize the structure, you will
always be limited to the saturation magnetization
of the ferromagnetic magnet structure. 10-11 kG is
about the limit of affordable materials. Put a bazillion
amps through your electromagnet coil, and you won't
get another microgauss out of your magnet once
you're past the saturation magnetization.

2. Hard magnetic materials such as barium ferrite,
strontium ferrtie, even materials such as alnico or
some of the more exotic magnetic alloys are FAR
cheaper than a copper coil and the power supply
needed to energize it.

3. And what do you plan on doing with the rather large
amount of heat that WILL be dissipated by the ohmic
losses in your voice coil. There's enough of a problem
dissispating heat from the voice coil: in current magnet
structures, at least it's most of the time cooler than the
voice coil, the heat has someplace to go. Now you're
talking about rasing the temprature of the magnet
tructure all the time.

Basically, electromagnets are a bad idea, from a design,
efficiency, cost, size, thernal dissipatyion, performance
viewpoint. That's why the idea was abondoned quite
permanently 70 years ago.

On 9 May 2006 16:24:30 -0700, wrote:

Basically, electromagnets are a bad idea, from a design,
efficiency, cost, size, thernal dissipatyion, performance
viewpoint. That's why the idea was abondoned quite
permanently 70 years ago.
They were used in TV's and HiFi of the early 50's, so can we knock off
at least 20 years please.

"cpo" wrote in message
. ..
would it be possible to solve the problem for the need of a huge
magnet by using an electromagnet instead of a permanent one.
obviously this would use up more power, but the strenght of your
magnet would be variable, and it would be relatively inexspensive


No, electromagnets still suffer from core saturation.

The new approach to super woofer design is to use a pot core lined with
Neodymium magnets. Through finite element analysis, the flux density
throughout the gap can be made uniform over several inches.

New voice coil technology deals with heat and power compression issues by
utilizing:

Black body radiation
Extreme forced air ventilation
More efficient transfer of electric current to electro-motive power by
keeping the coil in the magnetic field at all times.
Anodized surfaces of voice coil instead of laquer insulation, enabling
operation above 500ºF without damage.

These and other emerging technology have allowed drivers of a given size to
move the same volumes of air as four or more commercially mass-produced
drivers of the same diameter, with the benefit of reducing the number of
cabinets needed to cover a given venue.

--
Take care,

Mark & Mary Ann Weiss

www.basspig.com The Bass Pig's Lair

Business sites at:
www.mwcomms.com
www.adventuresinanimemusic.com
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