Sealed Speaker Enclosures
John Kodis
the speaker cones move in and out in response to changes in barometric
pressure? Wouldn't this allow audiophiles to dabble in weather
prediction, by examining the position of their woofer cones at the
start of a listening session?
Now, I can understand how with a paper-cone driver, or a driver with a
foam surround, there would be enough air leakage that the pressure in
the speaker enclosure would pretty quickly equalize with that of the
speaker's environment. But now we're seeing speakers built out of
polyurathane coated MDF, using speakers with rubber surrounds and
aluminum or kevlar cones, sealed in place with caulking compound.
I don't see much room for leakage in a system of this sort. And yet I
don't see speakers being produced that are able to double as
barometers, or that are supplied with vent-cocks on the back and
instructions to vent the speakers to ambient pressure before extended
listening sessions. How come?
-- John Kodis.
Arther Dent
>If a speaker were built so that it was completely air-tight, wouldn't
>the speaker cones move in and out in response to changes in barometric
>pressure?
>polyurathane coated MDF, using speakers with rubber surrounds and
>aluminum or kevlar cones, sealed in place with caulking compound.
>
>I don't see much room for leakage in a system of this sort. And yet I
>don't see speakers being produced that are able to double as
>barometers, or that are supplied with vent-cocks on the back and
>instructions to vent the speakers to ambient pressure before extended
>listening sessions. How come?
Interesting question, I belive it has to do with the binding posts, they
are not totaly air tight, the foam seal allows some air to get through.
(besides, the barametric pressure dosen't vary enough to cause any
visable change, I think <DP you wanna check this one out?> ) Oh, most
Kevlar drivers are fairly porous (the woven ones, at least)
Earlier I was worried about excessive temprature inside my speakers (home
build, totaly sealed) I then did some math and discovered that enough
energy would escape through the dirver cones as not to be a problem.
BTW, by amp puts out ~300 WPC into my speaker's 3.2 ohm load.
--
Arther.
Shankar Ramakrishnan
>ko...@access1.digex.net (John Kodis) wrote:
>>If a speaker were built so that it was completely air-tight, wouldn't
>>the speaker cones move in and out in response to changes in barometric
>>pressure?
> But now we're seeing speakers built out of
>>polyurathane coated MDF, using speakers with rubber surrounds and
>>aluminum or kevlar cones, sealed in place with caulking compound.
>>
>>I don't see much room for leakage in a system of this sort. And yet I
>>don't see speakers being produced that are able to double as
>>barometers, or that are supplied with vent-cocks on the back and
>>instructions to vent the speakers to ambient pressure before extended
>>listening sessions. How come?
There have been instances where tweeter domes get sucked in during
shipping by air. Long term leakage is a good thing. Amongst other things,
it ensures that the cones are always 'centered'.
>
>Interesting question, I belive it has to do with the binding posts, they
>are not totaly air tight, the foam seal allows some air to get through.
>(besides, the barametric pressure dosen't vary enough to cause any
>visable change, I think <DP you wanna check this one out?> ) Oh, most
>Kevlar drivers are fairly porous (the woven ones, at least)
Time and again, I come across drivers (even from reputed firms like
Audax) where the surround is not properly glued to the cone. I guess that
from the general slopiness exhibited by most manufacturers in this
regard, there is always bound to be a small leakage at the cone-surround
interface. Unfortunately, this could have a profound effect on performance.
Shankar
Lon Stowell
>If a speaker were built so that it was completely air-tight, wouldn't
>the speaker cones move in and out in response to changes in barometric
>prediction, by examining the position of their woofer cones at the
>start of a listening session?
The ordinary lab barometer uses a very similar mechanism...but the
absolute magnitude of the change is so small that an extremely
long off-center lever mechanism is needed to observe the deflection.
Worth thinking about if you live in a tornado area...if the low
pressure in the funnel hits your house, very likely your woofer
would explode--as they begin their long flight from Kansas to Oz.
However, the small change is something new for audiocultists to
worry about. Maybe they can prevail on the manufacturer's to
include small pressure guages on the enclosures? Then a new
trend in listening rooms to include the ability to pressurize
the listening environment to the optimal levels? Along with a new
epedimic of bends cases in overly avid 'philes?
Richard D Pierce
Shankar Ramakrishnan <sha...@vlibs.com> wrote:
>
>There have been instances where tweeter domes get sucked in during
>shipping by air.
Nope. Name one air carrier whose cargo hold is unpressurized, or has
pressure drops to less than about 8,000 ft equivalent.
If the dome is "sucked in," it's simply due to bad packing and mechanical
damage. Dome tweeters are the leakiest of drivers. I've shipped and been
shipped hundreds upon hundreds of tweeters and have never once seen a
dome "sucked in" by air pressure differences.
>Long term leakage is a good thing. Amongst other things,
>it ensures that the cones are always 'centered'.
Centered how?
--
| Dick Pierce |
| Loudspeaker and Software Consulting |
| 17 Sartelle Street Pepperell, MA 01463 |
| (508) 433-9183 (Voice and FAX) |
Shankar Ramakrishnan
>In article <shankarD...@netcom.com>,
>Shankar Ramakrishnan <sha...@vlibs.com> wrote:
>>
>>There have been instances where tweeter domes get sucked in during
>>shipping by air.
>
>Nope. Name one air carrier whose cargo hold is unpressurized, or has
>pressure drops to less than about 8,000 ft equivalent.
>
>If the dome is "sucked in," it's simply due to bad packing and mechanical
>damage. Dome tweeters are the leakiest of drivers. I've shipped and been
>shipped hundreds upon hundreds of tweeters and have never once seen a
>dome "sucked in" by air pressure differences.
This is not my explanation, but rather that of someone at A&S Speakers.
He showed me a couple of damaged Scan Speak D2905s. Maybe there was some
kind of depressurization that occured during that particular shipment.
>
>>Long term leakage is a good thing. Amongst other things,
>>it ensures that the cones are always 'centered'.
>
>Centered how?
In the direction of the cone motion. I spoiled your day, didn't I?
Shankar
S.M.S.
: In article <shankarD...@netcom.com>,
: Shankar Ramakrishnan <sha...@vlibs.com> wrote:
: >
: >There have been instances where tweeter domes get sucked in during
: >shipping by air.
: Nope. Name one air carrier whose cargo hold is unpressurized, or has
: pressure drops to less than about 8,000 ft equivalent.
Sorry Dick, but you're wrong. I worked for a major air carrier for 2
years and there are "bins" (not "cargo holds") that are unpressurized and
unheated. It all depends on the type of aircraft. Boeing 727's, 737's
and 757's have both heated/pressurized and un heated/pressurized bins.
Same goes for the MD-80, and many other aircraft.
You might want to verify your facts before spouting them off as gospel.
Some people might actually get the idea that you always know what you are
talking about.
Steve
--
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Richard D Pierce
Richard D Pierce <DPi...@world.std.com> wrote:
>In article <476o8e$s...@news.netusa1.net>,
>Ted A. Weber <twe...@mail.netusa1.net> wrote:
>>In article <476gkc$c...@shore.shore.net>, sla...@shore.net (S.M.S.) wrote:
>>
>>>Sorry Dick, but you're wrong. I worked for a major air carrier for 2
>>>years and there are "bins" (not "cargo holds") that are unpressurized and
>>>unheated. It all depends on the type of aircraft.
>>
>>myself, how does a diaphram or cone in a speaker get permanently damaged or
>>biased as a result of being shipped in one of those areas? I'm confused (=:
>>The area around the VC isn't aneroid is it?
>
>Well, despite claims and counterclaims about what the pressure inside
>aircraft at altitude may and may not be, there are facts to be had here.
>
>The pressure required to collapse a dome is not that great, on the order
>of a few inches equivalent water column (about 1/4 lb/sq in). So, it
>would seem that it really doesn't take much to cause the damage that
>another person asserted. Why, then, does Dick Pierce assert that it
>couldn't possibly happen?
<an experiment>
>The result? Not a single dome showed ANY evidence of distortion or
>collapse of the dome. Why? Because not a single one of them had enough of
>a seal to prevent equalization of pressure between the front and rear
>surfaces of the dome.
I have subsequently disected several of the tweeters used for the test.
As yet another piece of evidence gainst the notion of aircraft-
depressurization-induced damage, two of the tweeters I used in my tests
have ferrofluid in the gap. Neither showed ANY evidence whatsoever that
the fluid had migrated under the influence of differential pressure,
suggesting that there are plenty of leakage paths available for rapid
normalization of pressures.
Beakman
: In any case, I would think that a depressurization of the cargo hold
: would not result in a dome that was sucked "in", rather, wouldn't the
: higher internal pressure of the sealed enclosure tend to blow it "out"?
Quite true, though you probably wouldn't see many problems in tweeters
without ferrofluid, but possibly in some tweeters which did use
ferrofluid, as the ferrofluid would help seal the airspace behind the
dome.
I would imagine that Dick has been lucky, or that in shipping small
numbers of tweeters the packages were placed in pressurized bins. Driver
manufacturers like Seas and Vifa generally ship by boat because it is much
more economical - so again, no problem.
The only time I ever had a problem was when I needed a rush shipment of
Vifa tweeters with ferrofluid. These were air-freighted to the States,
and many of the tweeters arrived damaged. As you suspected, the internal
pressure behind the dome caused the aluminum dome to move outward - so
much so that, in this case, it pressed up against the plastic diffuser,
leaving an imprint of the diffuser in the aluminum. If the tweeter
didn't have a diffuser, the dome would have just returned to it's
original position, undamaged, upon landing.
David Fokos
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Richard D Pierce
Ted A. Weber <twe...@mail.netusa1.net> wrote:
>In article <476gkc$c...@shore.shore.net>, sla...@shore.net (S.M.S.) wrote:
>
>>Sorry Dick, but you're wrong. I worked for a major air carrier for 2
>>years and there are "bins" (not "cargo holds") that are unpressurized and
>>unheated. It all depends on the type of aircraft.
>
>Interesting. Thanks for that input. Now, for the uninformed neophytes like
>myself, how does a diaphram or cone in a speaker get permanently damaged or
>biased as a result of being shipped in one of those areas? I'm confused (=:
>The area around the VC isn't aneroid is it?
Well, despite claims and counterclaims about what the pressure inside
aircraft at altitude may and may not be, there are facts to be had here.
The pressure required to collapse a dome is not that great, on the order
of a few inches equivalent water column (about 1/4 lb/sq in). So, it
would seem that it really doesn't take much to cause the damage that
another person asserted. Why, then, does Dick Pierce assert that it
couldn't possibly happen?
Because the assertion that shipping tweeters in unpressurized aircraft
causes damage is completely ludicrous, that's why. It simply can't happen
as described, for a variety of reasons.
The first, an MOST obvious, is that the claimed damage to the dome is
precisely the opposite of what one would expect (as someone else pointed
out, I should add). Reducing the external pressure will cause a pressure
differential that MUST exert a force OUTWARDS on the dome, NOT INWARDS,
as originally asserted. The damge claimed was that the dome was pushed
inwards, completely contrary to what the physics should allow.
Let's ignore THAT fatal flaw, and investigate more thoroughly.
In order for there to be sufficient pressure differential between the
front and the rear of the dome requires a rather special set of
circumstances: A tweeter shipped in its sipping carton has no mechanical
seal between the volume in the rear of the chamber and the outside air
other than that afforded by the mechanical design of the tweeter. Thus,
that seal MUST be airtight OR that seal must have a leak time constant
that is slower than the rate at which the pressure would likely change in
ANY aircraft cargo hold.
So, to prove the point, I just performed an experiment today. I have a
large vessel (actually, an old industrial pressure cooker, made out of
1/2 inch thick cast and machined aluminum) that I use for a variety of
tasks related to my work (for example, when I cast some component in a
resin, I'll place it in the cooker and pull a vacuum on it: this pulls
the majority of the bubbles out of the resin before it sets).
I placed 8 dome tweeters from various manufacturers in the chamber, models
from Audax, Seas, Vifa, Peerless, DynAudio and a couple of others. I then
proceeded to reduce the pressure inside the cooker to about 4 lb/sq in,
equivalent to the pressure found at about 10 km (6 miles) up. It took
approximately 10 minutes of pumping to reach this pressure. The pressure
was held there for about 10 minutes, and then reduced over a period of 20
minutes (through a small needle valve back to sea-level pressure.
The result? Not a single dome showed ANY evidence of distortion or
collapse of the dome. Why? Because not a single one of them had enough of
a seal to prevent equalization of pressure between the front and rear
surfaces of the dome.
There was I could cause damage of the kind described:
If the pressure inside the chamber was brought back to atmospheric
pressure quickly enough, then distortion occurred. So what's quickly
enough? The time to reach atmospheric pressure from about 1/4 atmosphere
had to be on the order of 5-10 seconds! This is the equivalent of the
plane plunging from 32,000 ft to ground level in 5-10 seeconds. At the end
of such a descent, I would suspect that damage to a couple of tweeter
dones would be the least of our worries, yes?
However, it's not clear WHY the damage occured. The inrushing air stream
was enough to cause at least two tweeters to actually move: it's
altogether likely the damage was due as much to the force of the incoming
air as it was to simple pressure changes.
So, my friend, it's extraordinarily unlikely that the damaged described,
a collapsed dome, had ANYTHING to do with air pressure changes in an
airplane. In all likelihood, it was probably caused by incorrect packing,
rough handling when unpacking, inquizitive finger-poking, and the like.
Richard D Pierce
Scott Maclean <scott_...@arthor.cais.com> wrote:
>
>>In any case, I would think that a depressurization of the cargo hold
>>would not result in a dome that was sucked "in", rather, wouldn't the
>>higher internal pressure of the sealed enclosure tend to blow it "out"?
>
>somewhat permeable under pressure. Commercial aircraft are typically
>pressurized to 8,000 feet. At this point, the interior of the speaker
>will be under pressure, as the surrounding pressure will be
>significantly lower. Try it with a bag of potato chips the next time you
>fly somewhere if you want to see what I mean.
A bag of potato chips is constructed in a rather different fashion than a
loudspeaker, would you not agree?
>In any case, under pressure, some of the air inside the speaker leaks
>out.
Fine, so the external pressure is lower than the internal pressure at
altitude, yes? So, you claim, the air leaks out and the inside pressure
attains equilibrium with the outside pressure, as you claim.
Then you say:
>Then the airplane returns to the ground, and the ambient pressure
>increases to the normal ground-level pressure. However, the remaining
>air inside the speaker is at a much lower pressure, as it tried to
>equalize itself at altitude. The result is that the cone collapses.
And finally, you end with the admonition:
>Basic physics, guys.
Right, Scott, basic physics, no disagreement. But...
WHY is the basic physics unsymmetrical, as you assert? You claim that if
the air pressure outside is less than the air pressure inside, the air
leaks out until the pressure is equalized. THEN you claim, that, if the
pressure outside is greater than the pressure inside, the system achieves
equilibrium by collapsing the cone. Where's that leak? Why doesn't IT play
a role in achieving equilibrium? How come we have a DIFFERENT basic
physics on arrival then we do on departure?
Let's perform something of a reductio ad absurdum. To do that, we'll
assume the following:
1) The speaker, driver, whatever, is PERFECTLY sealed: no air can
enter or escape, and equilibrium MUST be achieved by moving the
cone, dome, whatever.
2) The cargo holds of planes ARE NOT pressurized, and can achieve
pressures ranging from sea level (1 atmosphere, 14.7 lbs/sq in)
to that at 33,000 ft (about 1/4 atmosphere, about 3.7 lbs/sq in).
Let's look at the consequences of these assumptions.
A) A system with a 12" woofer has a cone area of approximately 80
square inches. At 33,000, assuming the system is sealed, the net
outward pressure on that cone will 1 atm - .25 atm or .75 atm.
The resulting force experienced by the cone will be some 882 pounds:
The cone will be destroyed.
B) A 1" dome tweeter has an area of about .8 sq in. At 33,000 feet,
it will experience a net outward force of almost 9 pounds. It, too,
will be destroyed.
Both of these phenomenon MUST occur ALL the time if the two assumptions are
true. Since they do NOT occur 100% of the time, and since, in the few
isolated instances where they DO occur, there exists other, satisfactory
and plausible explanations, then at least one of the necessary
assumptions MUST be false.
While I will admit that I may not have ALL the dat on the pressure
maintained in cargo holds, I will, however, based both on arguably
extensive experience AND direct measurement of systems AND the mechanical
data for a rather large number of drivers and systems, I will counter
assert that NO driver and NO system is, in fact, devoid of leaks capable
of equilizing pressures. (There is ONE exception in the case of a driver
that I am aware of, a rather specialized and VERY expensive dome tweeter
that has the rear chamber permanently pressurized to maintain tension on
the dome material.)
Yup, basic physics, but the SAME physics all around, please.
Scott Maclean
Subject: Sealed Speaker Enclosures
Reply-To: DPi...@world.std.com (Richard D Pierce)
RDP>WHY is the basic physics unsymmetrical, as you assert? You claim that if
RDP>the air pressure outside is less than the air pressure inside, the air
RDP>leaks out until the pressure is equalized. THEN you claim, that, if the
RDP>pressure outside is greater than the pressure inside, the system achieves
RDP>equilibrium by collapsing the cone. Where's that leak? Why doesn't IT play
RDP>a role in achieving equilibrium? How come we have a DIFFERENT basic
RDP>physics on arrival then we do on departure?
Because a pinhole leak is not instantaneous. When the air is leaking OUT
of the speaker, it happens over a given amount of time, after a
sufficient pressure differential has built up. If there were some sort
of mechanism that could be crumpled up to equalize the pressure, and
that happened at a lower pressure than that at which air is forced out
through the pinhole, it would happen. But there isn't, so air just leaks
out.
However, when the process is reversed, there is a very soft, pliable
dome which can be easily crumpled to help equalize the pressure - much
more easily than by forcing air through a pinhole. So it crumples. Air
may still leak back into the speaker through the pinhole, but not until
after the cone has already collapsed.
Scott MacLean CASMEL-I Artificial Horizons BBS
art...@cais.com Aviation! (301) 417-9341
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Scott Maclean
Subject: Sealed Speaker Enclosures
Reply-To: DPi...@world.std.com (Richard D Pierce)
RDP>WHY is the basic physics unsymmetrical, as you assert? You claim that if
RDP>the air pressure outside is less than the air pressure inside, the air
RDP>leaks out until the pressure is equalized. THEN you claim, that, if the
RDP>pressure outside is greater than the pressure inside, the system achieves
RDP>equilibrium by collapsing the cone. Where's that leak? Why doesn't IT play
RDP>a role in achieving equilibrium? How come we have a DIFFERENT basic
RDP>physics on arrival then we do on departure?
Because a pinhole leak is not instantaneous. When the air is leaking OUT
of the speaker, it happens over a given amount of time, after a
sufficient pressure differential has built up. If there were some sort
of mechanism that could be crumpled up to equalize the pressure, and
that happened at a lower pressure than that at which air is forced out
through the pinhole, it would happen. But there isn't, so air just leaks
out.
However, when the process is reversed, there is a very soft, pliable
dome which can be easily crumpled to help equalize the pressure - much
more easily than by forcing air through a pinhole. So it crumples. Air
may still leak back into the speaker through the pinhole, but not until
after the cone has already collapsed.
RDP> 2) The cargo holds of planes ARE NOT pressurized, and can achieve
RDP> pressures ranging from sea level (1 atmosphere, 14.7 lbs/sq in)
RDP> to that at 33,000 ft (about 1/4 atmosphere, about 3.7 lbs/sq in).
Cargo holds of airplanes are pressurized to 8,000 feet, just like the
cabin is. Otherwise you'd see dead animals every time they off-loaded
people's pets upon landing.
Richard D Pierce
>RDP>the air pressure outside is less than the air pressure inside, the air
>RDP>leaks out until the pressure is equalized. THEN you claim, that, if the
>RDP>pressure outside is greater than the pressure inside, the system achieves
>RDP>equilibrium by collapsing the cone. Where's that leak? Why doesn't IT play
>RDP>a role in achieving equilibrium? How come we have a DIFFERENT basic
>RDP>physics on arrival then we do on departure?
>
>Because a pinhole leak is not instantaneous. When the air is leaking OUT
>of the speaker, it happens over a given amount of time, after a
>sufficient pressure differential has built up. If there were some sort
>of mechanism that could be crumpled up to equalize the pressure, and
>that happened at a lower pressure than that at which air is forced out
>through the pinhole, it would happen. But there isn't, so air just leaks
>out.
And, Scott, do you have an idea what the time constant of those leaks
are? How long would it take to reach equilibrium? In order to cause the
effects claimed, those time constants MUST be on the order of many
minutes when, in fact, they ARE on the order of several seconds to a
dozen seconds.
Thusm the assertion fails in the face of the factual realities of domes
and loudspeaker cabinets.
>However, when the process is reversed, there is a very soft, pliable
>dome which can be easily crumpled to help equalize the pressure - much
>more easily than by forcing air through a pinhole. So it crumples. Air
>may still leak back into the speaker through the pinhole, but not until
>after the cone has already collapsed.
And here we heap more and more complex and highly unlikely explanations
ontop of an already rickety heap of the same.
No one has presented a single piece of unequivocal evidence that the
problem even exists. Rather, we have this ridiculous chain of assertions
and assumptions attempting to uphold something that may even be
non-existant.
Look, I have personally handled hundreds of tweeters shipped by air. Not
a single one has shown damage that could ONLY be explained by air
pressure issues, and every single one of those that were damaged can be
explained by far more liekely, far simpler processes.
>RDP> 2) The cargo holds of planes ARE NOT pressurized, and can achieve
>RDP> pressures ranging from sea level (1 atmosphere, 14.7 lbs/sq in)
>RDP> to that at 33,000 ft (about 1/4 atmosphere, about 3.7 lbs/sq in).
>
>Cargo holds of airplanes are pressurized to 8,000 feet, just like the
>cabin is.
Scott, be fair and quote the ENTIRE section of the post. I was making a
"reductio ad absurdum": assuming a set of absurd assumptions, what
conclusion can we draw? Well, the conlsuioons are absurd, and we never
see reality mirroring such conclusions, so the assumptions, the premises
MUST be incorrect.
John Kreskovsky
Why bother to try and educate the ignorant. If I am to believe some of
the argument I would have to believe that planes approach for landing from
altitude at velocities greater than terminal velocity. And these little pin
holes in cabinets, you know the one way ones ( ;-) )? Haven't you
recognized them??? There are the infamous invers anal retentive pin holes.
They blow out but they don't suck! But there is a little bit of truth here.
Of course, Dick, some one is out there right now designing a sealed dome
tweeter, just to prove you wrong. Next week they will attack with new and
conclusive evidence. By the way, I congratulate you on your pressure cooked
experiment. I got a kick out of it.
--
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Senior Research Scientist Phone: (860) 659-0333
Scientific Research Associates, Inc. Fax: (860) 633-0676
<<<<<< Opinions expressed are often my own, and occasionally correct! >>>>>>
Arther Dent
>The result? Not a single dome showed ANY evidence of distortion or
>collapse of the dome. Why? Because not a single one of them had enough of
>a seal to prevent equalization of pressure between the front and rear
>surfaces of the dome.
>
Did any of these tweters use ferrofluid? Ferofluid tweters are sealed
much better than those with air around the voice coil.
>So, my friend, it's extraordinarily unlikely that the damaged described,
>a collapsed dome, had ANYTHING to do with air pressure changes in an
>airplane.
But the rate of drop in your expirment is 25ft/sec. Many planes drop much
faster than that, I belive. (could the guy that knows correct me?) and,
25ft/sec was, by your own admission, enough to move two of the domes
noticably. say, the plane hits a pocket of hot air, it would drop at
close to 30ft/sec/sec. say it lasts three seconds, the plane is falling
at close to 90ft/sec when it comes out of the air pocket. (this is all
very rough, the plane would be hard presssed to find a pocket of air that
low in density, and it does have air resestance too) that would accound
for a sifgicent pressure change to occur in an un-pressurised hold.
Enough to probally dent in the domes of some ferofluid tweters.
The assertion that "this damage could not have occured by changes in air
pressure." is, in fact wrong.
--
Arther.
Richard D Pierce
>DPi...@world.std.com (Richard D Pierce) wrote:
>
>>collapse of the dome. Why? Because not a single one of them had enough of
>>a seal to prevent equalization of pressure between the front and rear
>>surfaces of the dome.
>>
>much better than those with air around the voice coil.
Yes, several did, and showed no problems.
>>So, my friend, it's extraordinarily unlikely that the damaged described,
>>a collapsed dome, had ANYTHING to do with air pressure changes in an
>>airplane.
>
>But the rate of drop in your expirment is 25ft/sec. Many planes drop much
>faster than that, I belive. (could the guy that knows correct me?) and,
>25ft/sec was, by your own admission, enough to move two of the domes
>noticably.
Uh, do the math again, Arthur, the equivalent rate of descent was on the
order of 3,200 ft/sec: Once again: three THOUSAND, two HUNDRED FEET PER
SECOND. That's THREE TIMES the speed of sound. That's going from crusing
altitude to see level in ten seconds or so. How many cargo planes descend at
that rate AND survive?
>say, the plane hits a pocket of hot air, it would drop at
>close to 30ft/sec/sec. say it lasts three seconds, the plane is falling
>at close to 90ft/sec when it comes out of the air pocket. (this is all
>very rough, the plane would be hard presssed to find a pocket of air that
>low in density, and it does have air resestance too) that would accound
>for a sifgicent pressure change to occur in an un-pressurised hold.
>Enough to probally dent in the domes of some ferofluid tweters.
Nope, do the math again, the drop is NOWEHERE near as precipitous as
that. In order for that to happen, the lift on the wings must drop to 0.
>The assertion that "this damage could not have occured by changes in air
>pressure." is, in fact wrong.
No, Arthur, it is not. The test I ran accounts for air pressure drops at
rates that are AT LEAST 100 TIMES that found in even less-than-routine
flights.
Again, people are engaged in trying to support an extremely shaky
"theory" to explain something that a) occurs infrequently and b) is FULLY
explained by far more likely, far simpler causes.
Now, if, indeed, the problem was as asserted, then why isn't this a far
mopre prevelant problem. Why wasn't EVERY tweeter in the alledged
shipment similarily damaged? Why, in fact, did we EVER see these
tweeters, as the carrier is, in all likelihood, liable for the damage?
It's not a problem simply because no one has yet to provide ANY
incontrovertable evidence that it occured.
PETER LARSEN
RP> >This is not my explanation, but rather that of someone at A&S
RP> Speakers. >He showed me a couple of damaged Scan Speak D2905s. Maybe
RP> there was some >kind of depressurization that occured during that
RP> particular shipment.
RP> And the flight crew survived? :-)
RP> If that's their explanation, I might suggest that a) either they
RP> made it up or b) that's what they believe, but it's still an
RP> erroneous belief.
The 'luggage compartment' or - in a combined freight and passenger
flight the 'freight compartment' may not have been pressurized, mostly I
think it isn't.
Kind regards
Peter Larsen
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PETER LARSEN
Hi John,
References: <476rp0$s...@nnrp2.news.primenet.com> <46kdns$q...@nntp.crl.com> <shankarD...@netcom.com> <DHA7HE.Hy
JD> In any case, I would think that a depressurization of the cargo hold
JD> would not result in a dome that was sucked "in", rather, wouldn't
JD> the higher internal pressure of the sealed enclosure tend to blow it
JD> "out"?
and if the compartment the enclosure is in is not pressurized, then just
what will the sequence of air pressure changes be?
PETER LARSEN
RP> >This is not my explanation, but rather that of someone at A&S
RP> Speakers. >He showed me a couple of damaged Scan Speak D2905s. Maybe
RP> there was some >kind of depressurization that occured during that
RP> particular shipment.
RP> And the flight crew survived? :-)
RP> If that's their explanation, I might suggest that a) either they
RP> made it up or b) that's what they believe, but it's still an
RP> erroneous belief.
The 'luggage compartment' or - in a combined freight and passenger
flight the 'freight compartment' may not have been pressurized, mostly I
think it isn't.
PETER LARSEN
Hi John,
References: <476rp0$s...@nnrp2.news.primenet.com> <46kdns$q...@nntp.crl.com> <shankarD...@netcom.com> <DHA7HE.Hy
JD> In any case, I would think that a depressurization of the cargo hold
JD> would not result in a dome that was sucked "in", rather, wouldn't
JD> the higher internal pressure of the sealed enclosure tend to blow it
JD> "out"?
and if the compartment the enclosure is in is not pressurized, then just
what will the sequence of air pressure changes be?
Richard D Pierce
>>faster than that, I belive. (could the guy that knows correct me?) and,
>>25ft/sec was, by your own admission, enough to move two of the domes
>>noticably.
>
>Uh, do the math again, Arthur, the equivalent rate of descent was on the
>order of 3,200 ft/sec: Once again: three THOUSAND, two HUNDRED FEET PER
>SECOND. That's THREE TIMES the speed of sound. That's going from crusing
>altitude to see level in ten seconds or so. How many cargo planes descend at
>that rate AND survive?
It was just pointed out to me that my original figure was that I
increased the pressure from 6 km equivalent to sea level equivalent in 10
minutes. That was a typo on my part. The reduction took place over about
10 SECONDS, not 10 minutes.
I apologize for any confusion I may have caused by my typo.
Chris Christensen
Dick Pierce is a top professional in the speaker world. He has posted
several responses and done an experiment. For this work he would have
probably collected over a thousand dollars...... And _we_ got it for free.
Now don't confuse this posting as a defense of Dick Pierce... He is very
capable of that! Just think about what I have said. People pay him for
what he knows and understands. Oh and _please_ stop preaching physics...
Not until you get your "facts" straight! :-)
--
Just My opinion, worth the price paid and not a reflection of my employer.
D.R. "Chris" Christensen chr...@shasta.gvg.tek.com
Grass Valley Group Inc. 916-478-3419 Voice 916-478-3887 FAX
P.O. Box 1114 Grass Valley, California, 95945
Steve Gray
says...
>
>When are you guys gonna get it?
>
FYI, so is Ken.
Steve