"Richard Kuschel" wrote in message
...

If and ONLY IF you exceed the power handling of the driver. If the power
ratings are actual then a 300W amp is not going to burn out a 1000 watt
driver. Even at severe clipping you could maybe get 600 watts out of it.
Not
enough to burn out a true 1000 watt driver.




Richard H. Kuschel
"I canna change the law of physics."-----Scotty

I agree, unfortunately most audio myths have some background in physics
that
has just been slightly twisted to make sense, at least until you examine
them closely.

Les



It's pretty easy to burn up a driver by feeding it DC and still not exceed
the
power handling of the system.

Sure, but if your amp is sending DC to the speaker then you have a faulty
amp. The discussion is based on a properly functioning driver and amp. I
could burn out voice coils in many creative ways, but they are not relevant.

The heat doesn't disapate from the voice coil and the voice coil warps
destroying the speaker.

Sine Waves can also have a very fast deleterious effect on speakers.

What deleterious effects are you reffering too? Sure if you play a low sine
wave, say 30Hz for example, to loud you could make the driver take a leap of
faith out of its basket. But unless you exceed the power limits of the
driver you don't "burn out" the VC.

Fortunately music isn't DC or sine waves.

Yep. Good thing too, listening to music made from sine waves would get old
real quick.

I have seen lots of guitar amp speakers destroyed by amplifiers that had
less
power than the ratings of the speakers.

What destroyed them?


Les

"Richard Kuschel" wrote in message
...

I have seen lots of guitar amp speakers destroyed by amplifiers that
had
less
power than the ratings of the speakers.

What destroyed them?


Les

Usually sustained feedback., basically full power sine waves.

The VC does not care if your playing full power sine waves or music. What
matters is that you do not exceed the power handling of the driver. From
what I have seen, guitar amplifiers are generally more powerful than thier
speakers. Celestion greenbacks are only 25 watts, yet are highly regarded. I
still don't see how a sine wave is going to burn up a VC without exceeded
the power limits.


Occasionally, using limiters allowed enough current without cooling to
loosen
up the windings on the voice coils . Crest factor is diminished which is
the
difference between the average leve of a signal and peak level. Almost all
modern music has been squashed in this manner on CD mastering.

It may be, but the fact still remains that X number of watts is X number of
watts. And if your amp is capable of X and the driver is capable of 2X then
it doesn't matter is its a mastered CD, a live band, or a sine wave. If you
don't exceed the power limits then your driver is fine.


On our bigger PA systems the magnets get really hot after a night of use.
Lots
of heat to dissapate. Over time, the magnets would get hot enough that the
cooling effect would be negated.

That is why the average power handling of the driver is important. But
depending on the manufacture it can be achieved different ways. I have seen
it expressed on several Pro cabinets as a 20Hz-20Khz noise played at X watts
for 4 or 8 hours.

Not necessarily related to too much power, but woofers can self destruct
if the
speaker is run at a frequency that is below what the cabinet can support
the
cone.

Right. That is why it is important to be sure you high pass below the tuning
frequency. The cone has no damping below that.

When this happens, Spiders rip and surrounds can fall apart, the voice
coil may
bottom out or jump the gap--Same result- no more good sound.

Been there, really sucks too.

Now that said I generally use amplifiers with almost twice the power
rating as
the speaker. No distortion and better sound.

I agree. I like the headroom to know that I can go that extra volume without
my amps distorting. With too little power you always run out of gas.


Richard H. Kuschel
"I canna change the law of physics."-----Scotty

Les

\
Now, in reality ... an amplifier receives signal from the pre-amp (head
unit) and amplifies that signal. That's it, no magic involved. The amplifier
could care less what speaker(s) may be wired to it.
Here is a simplistic scenario:
A given amp has the gain set to saturate with a 2V input signal (maximum
output given a 2V input) This amp is rated to produce 350W RMS x 1 @ 4ohm.
A
4ohm sub is wired to it. It doesn't matter what the rated power handling
of
the sub is, when a signal comes down the line at 2V strength, the amp will
be pushing 350W into the sub. If the sub can only handle 200W RMS then it
will bottom out because of the excessive power going through the coil. If
the sub can handle 1200W RMS then it will barely move with only 350W
applied.

300 watts is definitely enough
to drive any 12" sub.

More stupidity ... if a sub is designed to handle 1000W RMS, it's not going
to go very far with only 300W pushing it. Where are you getting this
information?

Where are you getting your information?

A speaker that can handle 1000 watts is only going to be aabout 5dB quieter at
300 watts And that is going to be pretty loud even with the least effecient of
speakers

Drive that amplifier into distortion and the speaker will over heat and
eventually burn out even if the speaker is rated for 1000 watts.


What matters is the type of enclosure, is it a sealed
box or a more complex enclosure like a bandpass? P.

Why does the enclosure type matter?



An enclosure does matter, it radically modifies the effeciency and frequency
response of a speaker.

Richard H. Kuschel
"I canna change the law of physics."-----Scotty

If and ONLY IF you exceed the power handling of the driver. If the power
ratings are actual then a 300W amp is not going to burn out a 1000 watt
driver. Even at severe clipping you could maybe get 600 watts out of it. Not
enough to burn out a true 1000 watt driver.




Richard H. Kuschel
"I canna change the law of physics."-----Scotty

I agree, unfortunately most audio myths have some background in physics that
has just been slightly twisted to make sense, at least until you examine
them closely.

Les



It's pretty easy to burn up a driver by feeding it DC and still not exceed the
power handling of the system.

The heat doesn't disapate from the voice coil and the voice coil warps
destroying the speaker.

Sine Waves can also have a very fast deleterious effect on speakers.

Fortunately music isn't DC or sine waves.

I have seen lots of guitar amp speakers destroyed by amplifiers that had less
power than the ratings of the speakers.
Richard H. Kuschel
"I canna change the law of physics."-----Scotty

Richard Kuschel wrote

Where are you getting your information?

Admittedly small amount of personal experience. However, by nature of it's
design, a driver that can handle copious amounts of power is not terribly
efficient.

A speaker that can handle 1000 watts is only going to be aabout 5dB
quieter at
300 watts And that is going to be pretty loud even with the least
effecient of
speakers

True enough, but 5dB is less then half the volume (almost a third). It will
probably be very loud, but not even close to what it could be.

Drive that amplifier into distortion and the speaker will over heat and
eventually burn out even if the speaker is rated for 1000 watts.

It seems that you think I would believe otherwise?

An enclosure does matter, it radically modifies the effeciency and
frequency
response of a speaker.

I was questioning the relevance of the statement that Peter Klein made. He
is talking about speakers drawing power from amps, and then asserts that it
is the enclosure that makes the difference. Or was I misinterpreting his
thoughts? I understand that the enclosure affects the "performance" of a
speaker (power handling drops of viciously below the tuning frequency in
ported) but this information isn't really keeping score with the original
train of thought in his post.

I have seen lots of guitar amp speakers destroyed by amplifiers that had
less
power than the ratings of the speakers.

What destroyed them?


Les

Usually sustained feedback., basically full power sine waves.

Occasionally, using limiters allowed enough current without cooling to loosen
up the windings on the voice coils . Crest factor is diminished which is the
difference between the average leve of a signal and peak level. Almost all
modern music has been squashed in this manner on CD mastering.

On our bigger PA systems the magnets get really hot after a night of use. Lots
of heat to dissapate. Over time, the magnets would get hot enough that the
cooling effect would be negated.

Not necessarily related to too much power, but woofers can self destruct if the
speaker is run at a frequency that is below what the cabinet can support the
cone.

When this happens, Spiders rip and surrounds can fall apart, the voice coil may
bottom out or jump the gap--Same result- no more good sound.

Now that said I generally use amplifiers with almost twice the power rating as
the speaker. No distortion and better sound.

Richard H. Kuschel
"I canna change the law of physics."-----Scotty

Where are you getting your information?

Admittedly small amount of personal experience. However, by nature of it's
design, a driver that can handle copious amounts of power is not terribly
efficient.

That depends, on the design and weight of the cone, magnet structure and a
number of other things.

If you have a speaker wound with really heavy coil wire just to get power
handling, it won't be very effecient,
We saw a lot of this in the 18" speakers in Bass cabinets for theAcoustic 360
Bass amps. The JBL 18" was more effecient and would play louder even though
the power handling wasn't quite as high.


I understand that the enclosure affects the "performance" of a
speaker (power handling drops of viciously below the tuning frequency in
ported) but this information isn't really keeping score with the original
train of thought in his post.

I realize this has drifted, but hey, it's been fun.

True enough, but 5dB is less then half the volume (almost a third). It will
probably be very loud, but not even close to what it could be.

Twice as loud is 10 dBSPL which requires 10x the power to obtain.

6dB is 2x the voltage.
2x the power will give you a 3dB increase in SPL

You run into limits pretty quickly.

Assume a speaker(quite effecient)
100dBspl @1w/1Meter
2W=103dB
4W=106dB
8W=109dB
10W=110dB
16W=112dB
160W=122dB
1600W=132dB
16,000W=142dB
We run out of power pretty quickly because the speaker can't handle it.

Also as the speaker heats up, the amount of SPL that it ca nput out degrades
because the resistance becomes higher Richard Kuschel wrote




Richard H. Kuschel
"I canna change the law of physics."-----Scotty

Now that said I generally use amplifiers with almost twice the power
rating as
the speaker.

Well right there is the source of your confusion. You're mistakenly
supposing that power RATINGS accurately predict the actual power handling
capabilities of the driver.

No distortion and better sound.

In a guitar amp? Blasphemy I say!

"Richard Kuschel" wrote in message
...
. I
still don't see how a sine wave is going to burn up a VC without exceeded
the power limits.

Try putting a 15kHz signal into a speaker for an extended period of time.
The
speaker doesn't move enough to cool. It will heat up and fry
Richard H. Kuschel
"I canna change the law of physics."-----Scotty


Your sig line says that the laws of physics does not change. If this 15kHz
tone is not exceeding the true rating of the VC then how can it fry, that's
physics. Not only that but I don't know any woofers that will go that high
and tweeters and compression drivers are designed to handle a certain amount
of power for a given time in thier freq range, which 15k would be in. If you
don't exceed their limits then how can it fry? Why does physics change with
a sine wave vs music vs live? I'm sure if you left it there long enough it
would burn up, as power handling has a time limit associated with it, I am
also sure if would burn up if you exceeded the power limits. But given that
a driver can handle so much power in a freq range (sometimes denoted, other
times common sense; tweeters don't play 80Hz and woofers dont play 15khz)
then it shouldn't matter what the source is as power is power is power.

Les

On Wed, 16 Jun 2004 11:08:50 -0400, "Daniel Snooks"
wrote:

Admittedly small amount of personal experience. However, by nature of it's
design, a driver that can handle copious amounts of power is not terribly
efficient.

Hate to say this but you're incorrect on your assumption that drivers
that can handle copious amounts of power are inefficient by nature.

Perhaps you should have a look at the better professional sound
reinforcment drivers (JBL, Fane etc) for low frequency operation,
Typical SPL ratings are around 100-103 dB SPL with 1Wrms drive at 1
meter in free air for professional grade drivers in the size range
from 10-18". That equates to roughly 10-14dB SPL louder, or at least
twice the apparent volume level per Watt over most HiFi and car audio
drivers of equal diameter. HiFi / car audio drivers tend to be between
89 and 93 dB SPL at 1Wrms at 1m.

I was questioning the relevance of the statement that Peter Klein made. He
is talking about speakers drawing power from amps, and then asserts that it
is the enclosure that makes the difference. Or was I misinterpreting his
thoughts? I understand that the enclosure affects the "performance" of a
speaker (power handling drops of viciously below the tuning frequency in
ported) but this information isn't really keeping score with the original
train of thought in his post.

Sounds like someone's confused here!

Ian

. I
still don't see how a sine wave is going to burn up a VC without exceeded
the power limits.

Try putting a 15kHz signal into a speaker for an extended period of time. The
speaker doesn't move enough to cool. It will heat up and fry
Richard H. Kuschel
"I canna change the law of physics."-----Scotty

Try putting a 15kHz signal into a speaker for an extended period of time.
The
speaker doesn't move enough to cool. It will heat up and fry

What do you mean by "doesn't move enough to cool"? Why wouldn't it be
moving enough? What kind of speakers are you talking about specifically?

"Alan Gilchrist" wrote in message
news:MPG.1b3d218053245e62989686@nntp...
In article , rickpv8945
@aol.com says...

Sine Waves can also have a very fast deleterious effect on speakers.

Fortunately music isn't DC or sine waves.

And you think a audio signal isn't a form of sine wave ?!, Just be
glad it isn't square or triangle waves that your playing thru your amp
!.

Well Alan, music is a form of a sine wave, not a perfect one, which is what
the discussion was about. Next time try reading the thread before replying,
you might be able to add something to the discussion rather than missing the
point.

Les

"Les" wrote in message
...

"Richard Kuschel" wrote in message
...
. I
still don't see how a sine wave is going to burn up a VC without
exceeded
the power limits.

Try putting a 15kHz signal into a speaker for an extended period of
time.
The
speaker doesn't move enough to cool. It will heat up and fry
Richard H. Kuschel
"I canna change the law of physics."-----Scotty


Your sig line says that the laws of physics does not change. If this 15kHz
tone is not exceeding the true rating of the VC then how can it fry,
that's
physics. Not only that but I don't know any woofers that will go that high
and tweeters and compression drivers are designed to handle a certain
amount
of power for a given time in thier freq range, which 15k would be in. If
you
don't exceed their limits then how can it fry? Why does physics change
with
a sine wave vs music vs live? I'm sure if you left it there long enough
it
would burn up, as power handling has a time limit associated with it, I am
also sure if would burn up if you exceeded the power limits. But given
that
a driver can handle so much power in a freq range (sometimes denoted,
other
times common sense; tweeters don't play 80Hz and woofers dont play 15khz)
then it shouldn't matter what the source is as power is power is power.

Les



The speaker is cooled by air movement as the air heats around the vc it is
not being "bathed" in cool air. Yes it will burn up even the best of them
even with advanced VC cooling. As a reconer I have seen this alot when the
amps oscillates for some reason.

It can also be seen or understood in gearhead terms. You MUST fan cool an
air cooled engine when it's on a dyno. Wonder why? Gotta have that cold
air to wick heat away.

Chad

Ian W wrote
Hate to say this but you're incorrect on your assumption that drivers
that can handle copious amounts of power are inefficient by nature.

Perhaps you should have a look at the better professional sound
reinforcment drivers (JBL, Fane etc) for low frequency operation,
Typical SPL ratings are around 100-103 dB SPL with 1Wrms drive at 1
meter in free air for professional grade drivers in the size range
from 10-18". That equates to roughly 10-14dB SPL louder, or at least
twice the apparent volume level per Watt over most HiFi and car audio
drivers of equal diameter. HiFi / car audio drivers tend to be between
89 and 93 dB SPL at 1Wrms at 1m.

That is wonderful information ... what are typical power handling ratings
for those pro drivers? I am just curious, it seems that if you could safely
put 700 - 1000W RMS into a driver that is rated at 100 dB/W @ 1m you would
end up with some really insane output (for a single driver) What kind of
excursion can you typically get from these pro drivers?
The JL 13W7 comes to mind regarding my assumption. 1000W RMS and 86.3 dB
SPL, and the Orion H2 15.2 with 2000W RMS and 90.4 dB.
Come to think of it, going by the numbers (which I know is never a good
idea) it would seem that the Orion would out-perform the JL. Being poor, I
haven't ,and probably never will, used either of them, but I did get the
impression from people I talked to that the JL W7 drivers are considered top
of the heap, especially for SPL. Any thoughts on all of that?

Sounds like someone's confused here!

Yes I am !!! I am wondering what his statement regarding enclosures has to
do with his belief that speakers "draw" power from amps.

Dan

In article , rickpv8945
@aol.com says...

Sine Waves can also have a very fast deleterious effect on speakers.

Fortunately music isn't DC or sine waves.

And you think a audio signal isn't a form of sine wave ?!, Just be
glad it isn't square or triangle waves that your playing thru your amp
!.

In article , dsnooks70
@sympatico.ca says...

True enough, but 5dB is less then half the volume (almost a third). It will
probably be very loud, but not even close to what it could be.

That is incorrect, adjusting your volume just a slight increase (or
decrease) amounts to about 3db, so 5db is not far off.

That is incorrect, adjusting your volume just a slight increase (or
decrease) amounts to about 3db, so 5db is not far off.

Indeed. On my previous Alpine HU, a CDM-7834, each volume "number"
amounted to 2 dB. Going from 24 to 22 is not a deal breaker as far as
loudness is concerned...
--
Eric (Dero) Desrochers
http://homepage.mac.com/dero72

Hiroshima 45, Tchernobyl 86, Windows 95

The speaker is cooled by air movement as the air heats around the vc it is
not being "bathed" in cool air.

This is the claim, but it's not entirely accurate for all cases. In fact,
I'd question whether or not it's accurate even for MOST cases, especially
drivers that aren't designed with a vented polepiece or some other mechanism
to take advantage of this. What motion DOES do though is it increases the
*effective* surface area with which the coil can dissipate heat. In other
words, if the coil is 1 inch and the excursion is +/- 1/4", then you've
essentially increased the heat dissipation area by roughly 50%. But if the
coil is longer, and the excursion isn't much different under your restrained
case vs. normal, then the power handling capacity shouldn't change by much.

And you think a audio signal isn't a form of sine wave ?!, Just be
glad it isn't square or triangle waves that your playing thru your amp
!.

Ever look at the signal produced by a violin playing something absent
vibrato? It looks just like a triangle wave. So do I have to write an
article now entitled "Violins don't blow speakers"?

In article ,
"MZ" wrote:

And you think a audio signal isn't a form of sine wave ?!, Just be
glad it isn't square or triangle waves that your playing thru your amp
!.

I regularly play sine, square and triangle tones at varying frequencies
for testing. Try a sawtooth at 7hz through a capable setup

If your drivers/amps/etc. don't live through it, you now have an excuse
to get better gear.

Ever look at the signal produced by a violin playing something absent
vibrato? It looks just like a triangle wave. So do I have to write an
article now entitled "Violins don't blow speakers"?



Not to mention the square and triangle waves that alot of electronic
instruments make use of.

How 'bout "Moog synthesizers don't blow speakers"?

--
cyrus

*coughcasaucedoprodigynetcough*

Not to mention the square and triangle waves that alot of electronic
instruments make use of.

How 'bout "Moog synthesizers don't blow speakers"?

I wouldn't be surprised if Audiophile published an article called "Gary
Numan is hazardous to your speakers."

"MZ" wrote in message
...
The speaker is cooled by air movement as the air heats around the vc it
is
not being "bathed" in cool air.

This is the claim, but it's not entirely accurate for all cases. In fact,
I'd question whether or not it's accurate even for MOST cases, especially
drivers that aren't designed with a vented polepiece or some other
mechanism
to take advantage of this.

A vented pole peice cools the magnet assembly more than the voice coiil.
The movement of air around the voice coil happens more from spider leakage
and the dust cap causing low/high pressure variances. if the dust cap is
removed then the spider caused the pressure variances. Tale a look at the
JBL VGC assembly, now there's some venting. The old 1000, 1200, and 1500
GTI 's are the same basket as the JBL Professional 2206, 2226, 2241. These
drivers have vents around the pole peice to keep the VC cool.

I have seen a Crown Macrotech 1200 go into HF ocsillation and destroy this
type of woofer in more than one occasion. That amp puts out 325 W/ch into 8
ohms. Ther driver is rated at 600W 1200Max. The amp was not clipping. I
have seen the same amp banged into clip or limit all night and no problems
arrised. The coil just got damn hot because it was not moving. What you
are saying is that you can hang a VC in the air, not move it and apply it's
rated power and it will not burn up. This is false, it will burn up
quickly. Even with music that has a large crest factor. Do it, I have.

It's not actually the cool air that's cooling the VC its the fact that cool
air is wicking the heat away from the vc and transferring it to the basket
assembly, it's the laws of thermodynamics.

http://www.jblpro.com/pub/technote/tn_v1n22.pdf -- VGC explanation



What motion DOES do though is it increases the
*effective* surface area with which the coil can dissipate heat. In other
words, if the coil is 1 inch and the excursion is +/- 1/4", then you've
essentially increased the heat dissipation area by roughly 50%. But if
the
coil is longer, and the excursion isn't much different under your
restrained
case vs. normal, then the power handling capacity shouldn't change by
much.

Agreed. But if it ain't moving air inside the assembly it ain't gonna work
long. It is a well known fact in the audio circles that I work in. You
gotta move air to make sound, and you gotta move air to keep things cool.

Look at the Community Air Corp, compression drivers. They pump air thru the
driver to keep it cool. why because it can't do it itself. Many compression
drivers have 4" vc's with a pretty deep wind. sometimes as deep as a mid or
woofer. Can it handle as much power, no, wonder why?

Now I totally agree that this is all pretty much irrelavant because a
speaker that is designed to cool itself via excursion will not be used in an
application such as HF. BUT, HF can kill such devices even at lower than
their RMS power handling. I'll try to dig out pics of such VC's I have them
somewhere on an older PC, probably packed with my stuff to move as murphy
would have it

Best regards

Chad

snip
What you
are saying is that you can hang a VC in the air, not move it and apply
it's
rated power and it will not burn up. This is false, it will burn up
quickly. Even with music that has a large crest factor. Do it, I have.

No, that's not what I'm saying. I said that coil motion is indeed an
important aspect of cooling. But, as I pointed out in my prior post, this
is mostly due to the fact that high speed motion is (almost) equivalent to
simply extending the length of the coil, thereby increasing its effective
surface area. This serves to decrease the peak of the temp gradient. This
also gives rise to a heat dissipation dependence on excursion. This is much
more easily quantifiable than a sort of forced air convection mechanism,
which I'd argue is much less prevalent than you think. And I'd suspect then
that the variation of power handling with coil motion in most drivers could
be almost entirely accounted for by the theoretical gain due to increased
surface area (although this is entirely hand waving on my part). For
instance, look at tweeters. Also, based on your argument, low efficiency
drivers should then have *dramatically* lower power handling capabilities,
but this of course is not true.

snip
Now I totally agree that this is all pretty much irrelavant because a
speaker that is designed to cool itself via excursion will not be used in
an
application such as HF. BUT, HF can kill such devices even at lower than
their RMS power handling. I'll try to dig out pics of such VC's I have
them
somewhere on an older PC, probably packed with my stuff to move as murphy
would have it

One point I've tried to make in the past but have only alluded to in this
thread is that there really is no such thing as "RMS power handling." This
is a variable, dependent on too many factors - for example, ambient
temperature, playing time, enclosure effects (because of its effect on
motion), and so forth. Another influence should in theory be the waveform
itself. But my own experiments have failed to bear this out. Adding high
frequency content to subwoofers, for instance, while maintaining a state of
constant power dissipation (with a feedback routine custom written in
Matlab) failed to produce a significant coil temperature change in the
woofers I've tried. Essentially, my hypothesis was that the different
waveform would alter the cooling ability of the VC, but found the opposite
to be true. Anyway, the high frequency content I added was simply odd
harmonics of the fundamental (I was trying to simulate clipping by
approximating a square wave, but was generating the signal in the frequency
domain). I suspect you're referring to very high frequency content - well
above the primary breakup mode of the driver, where I'm guessing the first
possibility of a substantial decrease in efficiency would occur. But I'm
still not quite grasping your point here - if you get too high, the
impedance will just be too much for high freqs to be a contributing factor.

"MZ" pam
wrote:

.....snip to content.....
But I'm
still not quite grasping your point here - if you get too high, the
impedance will just be too much for high freqs to be a contributing factor.

Agreed. I recently measured the impedance of a single coil 12-inch woofer and
at 15 kHz its imedance was 66 ohms and rising.

"Nousaine" wrote in message
...
"MZ" pam
wrote:

....snip to content.....
But I'm
still not quite grasping your point here - if you get too high, the
impedance will just be too much for high freqs to be a contributing
factor.

Agreed. I recently measured the impedance of a single coil 12-inch woofer
and
at 15 kHz its imedance was 66 ohms and rising.

Not the case with all drivers, some have a pretty nice impedance curve up
there, it depends on the VC material and wind geometry.

But totally agreed, many "low efficiency" long excursion drivers have a
monstrous inductance.

I guess I have to get my head out of pro audio and back into car audio

Chad

"MZ" wrote in message
...
snip
.. I said that coil motion is indeed an
important aspect of cooling. But, as I pointed out in my prior post, this
is mostly due to the fact that high speed motion is (almost) equivalent to
simply extending the length of the coil, thereby increasing its effective
surface area. This serves to decrease the peak of the temp gradient.
This
also gives rise to a heat dissipation dependence on excursion.

I think we are kinda getting at the same point but in a diffeent manner, OK
by me!

This is much
more easily quantifiable than a sort of forced air convection mechanism,
which I'd argue is much less prevalent than you think.

Yes external methods of forced air are not prevalent, concept died in late
90's with the advent of smaller motor structures that don't hold as much
heat and advanced VC binding. But venting the GAP and forcing air around
the VC via excursion is very prevalent, almost standard in professional
loudspeakers. BTW we are shrinking magnets as car audio seems to grow them,
which is something I have never understood. Nothing like slowing your car
down with ferrite and chrome. We choose neo to reduce chiropractor bills,
Neo has advanced to the point where it is not as temp dependent.

And I'd suspect then
that the variation of power handling with coil motion in most drivers
could
be almost entirely accounted for by the theoretical gain due to increased
surface area (although this is entirely hand waving on my part).

I agree! If air were more dense (like water) our LF transducers would be
able to shrink, now if fish made music not Phish keep in mind that
the conducting medium has a response also, look what happens to the speed of
sound at different freq's as humidity rises.

For
instance, look at tweeters. Also, based on your argument, low efficiency
drivers should then have *dramatically* lower power handling capabilities,
but this of course is not true.

One of the reasons that they arent as efficient is because they have HUGE
motors on them. Copper weighs an awful lot and a big thick cone is heavy
also. If a speaker has to handle the power it has to have weight, weight
causes moving mass and we all know what that leads to. Also see above.


One point I've tried to make in the past but have only alluded to in this
thread is that there really is no such thing as "RMS power handling."
This
is a variable, dependent on too many factors - for example, ambient
temperature, playing time, enclosure effects (because of its effect on
motion), and so forth. Another influence should in theory be the waveform
itself. But my own experiments have failed to bear this out.

I couldn't agree more! Add to that power compression As for waveform I
have seen more mechanical damage than heating and electrical.

Adding high
frequency content to subwoofers, for instance, while maintaining a state
of
constant power dissipation (with a feedback routine custom written in
Matlab) failed to produce a significant coil temperature change in the
woofers I've tried. Essentially, my hypothesis was that the different
waveform would alter the cooling ability of the VC, but found the opposite
to be true. Anyway, the high frequency content I added was simply odd
harmonics of the fundamental (I was trying to simulate clipping by
approximating a square wave, but was generating the signal in the
frequency
domain). I suspect you're referring to very high frequency content - well
above the primary breakup mode of the driver, where I'm guessing the first
possibility of a substantial decrease in efficiency would occur.

Yep VHF.

But I'm
still not quite grasping your point here - if you get too high, the
impedance will just be too much for high freqs to be a contributing
factor.


Still blows 'em up, and remember I'm kinda OT here because I'm using
different drivers. I use 12's and 15's as mids in my paying job. And they
easily go up to 1.5K +

Single layer aluminum ribbon wound edgewise will have a different inductive
properties than multiple layers of round copper.

Chad

This is much
more easily quantifiable than a sort of forced air convection mechanism,
which I'd argue is much less prevalent than you think.

Yes external methods of forced air are not prevalent, concept died in late
90's with the advent of smaller motor structures that don't hold as much
heat and advanced VC binding. But venting the GAP and forcing air around
the VC via excursion is very prevalent, almost standard in professional
loudspeakers.

Perhaps I wasn't clear. I didn't mean that it wasn't prevalent. Many
speaker designs rely on this mechanism for standard operation. What I meant
was that it is less prevalent for this to be the dominant cooling mechanism.
In other words, it's not always vital, and loudspeakers can get along
without it. Disclaimer: of course a certain degree of air flow is necessary
in all designs, but it's passive (well, as passive as you can get in a
moving structure at least). Conversely, there are some designs which seem
to revolve around such a mechanism.

BTW we are shrinking magnets as car audio seems to grow them,
which is something I have never understood. Nothing like slowing your car
down with ferrite and chrome. We choose neo to reduce chiropractor bills,
Neo has advanced to the point where it is not as temp dependent.

It's quite simple. 99 out of 100 car audio buyers are under the impression
that bigger magnets = better speakers. Give the customer what they want.
They're just getting out of hand these days. Personally, I tend not to buy
that crap.


And I'd suspect then
that the variation of power handling with coil motion in most drivers
could
be almost entirely accounted for by the theoretical gain due to
increased
surface area (although this is entirely hand waving on my part).

I agree! If air were more dense (like water) our LF transducers would be
able to shrink, now if fish made music not Phish keep in mind that
the conducting medium has a response also, look what happens to the speed
of
sound at different freq's as humidity rises.

Good example.

For
instance, look at tweeters. Also, based on your argument, low
efficiency
drivers should then have *dramatically* lower power handling
capabilities,
but this of course is not true.

One of the reasons that they arent as efficient is because they have HUGE
motors on them. Copper weighs an awful lot and a big thick cone is heavy
also. If a speaker has to handle the power it has to have weight, weight
causes moving mass and we all know what that leads to. Also see above.

Right. After rereading what I wrote, I see that I could have expanded it to
"low efficiency system" rather than "low efficiency drivers". Basically,
what I was getting at is the ratio between excursion and electrical energy
dissipated in the form of heat. If speakers truly relied on air flow as
heavily as you've implied, there would appear to be a major departure from
the theoretical effects of increased surface area associated with excursion
as a function of input power, and this would be apparent by looking at two
speakers with similar VCs and geometries, but different efficiencies
(perhaps due to suspension or enclosure differences). In other words, take
the same speaker and put it in two very different sized boxes and you'll see
that in one case the cone moves a lot and in the other case it moves a
little, even with the same input power (of course, accounting for the
differences in back emf, etc). My argument is that any differences in VC
power handling that arise as a result could more closely be accounted for by
a decrease in effective VC surface area, rather than what you would predict
if the dominant mechanism was air flow. If the dominant mechanism was flow,
then the difference in power handling would probably be huge.

By the way, I have no data to back any of this up. It's just hand waving on
my part.



One point I've tried to make in the past but have only alluded to in
this
thread is that there really is no such thing as "RMS power handling."
This
is a variable, dependent on too many factors - for example, ambient
temperature, playing time, enclosure effects (because of its effect on
motion), and so forth. Another influence should in theory be the
waveform
itself. But my own experiments have failed to bear this out.

I couldn't agree more! Add to that power compression As for waveform
I
have seen more mechanical damage than heating and electrical.

I'm sure that's true. I don't know that power compression belongs on the
list though, because you're decreasing the power delivered to the coil due
to the increased DCR, even though the amplifier's output voltage remains
unchanged. So it's not really a power handling difference.

But I'm
still not quite grasping your point here - if you get too high, the
impedance will just be too much for high freqs to be a contributing
factor.


Still blows 'em up, and remember I'm kinda OT here because I'm using
different drivers. I use 12's and 15's as mids in my paying job. And they
easily go up to 1.5K +

Single layer aluminum ribbon wound edgewise will have a different
inductive
properties than multiple layers of round copper.

Got it.