2 hz tuning - pros and cons - Page 7 - AVS Forum
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post #181 of 302 Old 12-11-2012, 10:17 AM
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I must say I can understand diy's frustration.

I think this thread has gone 'round and 'round because of the dozens of comments on port compression, when the simulations have shown, and not been refuted that I can see, that there won't be any, except maybe with a track or two, like F'in Irene which I believe has some strong 5 Hz rotor blade noise.

It's also been pointed though that such a small port can't add significant useful output, and this is borne out by the simulations as well, which show an increase of a couple of dB.

Going off on a tangent, sort of, many times I've puzzled over why is that a couple of dB is not a lot?

That represents about a 60% increase in efficiency, which anywhere else in engineering is huge.

I think the answer is that it may very well be significant if that's the difference between loud enough and not quite loud enough, or loud enough with a hotter VC and more compression than if you didn't have the extra 2 dB.

To those who say 2 dB isn't a big difference in loudness, I guess that's personal, as many times the 1 dB steps on my volume control seem too coarse.

OTOOH, the above applies to midrange freq but perhaps not the low freq we're talking about here.

Noah
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post #182 of 302 Old 12-11-2012, 10:18 AM
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Not to go too off topic, but 'they' told Columbus that the world was round but the shore of India was too far away and he'd never make it, because even back then there was a consensus on the circumference of the Earth and the journey was seen as being too long. Columbus disagreed, but he was in fact the one who was wrong... but he was lucky. Possibly as lucky as anyone in all of history. He'd be dead if the America's weren't there. http://www-spof.gsfc.nasa.gov/stargaze/Scolumb.htm

I don't think there's an undiscovered country hiding somewhere inside the physics that define the workings of a conventional subwoofer. If you want 2 Hz, you need a fan-based design whereby displacement naturally (and dramatically) increases as the frequency decreases... or you'll have to build out your entire wall with subs (and still likely not match the fan).
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Originally Posted by ack_bk View Post

Well they told Christopher Columbus that the world was flat, and the Wright Brothers that they would never fly, so OP, if you truly believe in your simulations (and clearly you do, even when very knowledgeable people tell you that it is waste of time) I say build it and prove them wrong if you are that confident.
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post #183 of 302 Old 12-11-2012, 10:23 AM
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Originally Posted by LTD02 View Post

noah, by transition frequency, i meant the point where the air transitions from behaving like a compressible gas to more like an incompressible gas.

Why do you think the air in a port ever behaves as compressible?

Oh, and diy, about you're analogy between port air and fluids in pipelines:

I don't really see the comparison, as the point of a port is to get some extra energy with resonance, and the point of a pipeline is to transfer material without much importance to the energy required.

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post #184 of 302 Old 12-11-2012, 10:26 AM - Thread Starter
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Originally Posted by LTD02 View Post

hi again.
from collo's experimental port site and built into flareit, we know that ports go turbulent (i.e. completely fail to any longer act like ports) when the air speed in m/s is 5 times the port diameter in inches. in this case, that is 10 m/s.

Not true sir. Both the red line and the blue line in Flare It show the ONSET of turbulence, not the complete failure point. Like I said many posts ago, I don't expect audible chuffing until the core get up to 20 m/s or higher.
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post #185 of 302 Old 12-11-2012, 10:27 AM - Thread Starter
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Originally Posted by Ricci View Post

Exactly what I've been saying. Cut everything below 7Hz and look at what is left. Virtually no difference at all.
The gains in the simulation are not really there at high power because the 2" vent can't cope without compressing and going turbulent. What you might gain is what is shown above 7Hz which is next to nothing.

See post 137. Significant gains. Nothing you have said yet undermines the validity of my simulations.
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post #186 of 302 Old 12-11-2012, 10:29 AM - Thread Starter
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Originally Posted by Looneybomber View Post

It's already been covered, but all I am asking is why tune so low, when you can tune an octave or more higher and get a lot more benefit from the port, without "wasting" as much. Efficiency is what you're going for, so why not increase your efficiency and tune to 5, 6, or 7hz?
I'm not gonna ask a 5yr old to help me move, I'll ask a 20yr old to get more benefit/help from them. Same with the port, I'll tune a little higher to get more benefit/help from it.

The only reason (and it super super simple) is because that is simply not the stated goal. I'm not saying it's not a good idea, I'm not saying it won't match your (or anyone else's) goals much much better.

It just simply is not the stated goal of this conversation.
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post #187 of 302 Old 12-11-2012, 10:33 AM - Thread Starter
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name="Ricci" url="/t/1444329/2-hz-tuning-pros-and-cons/150#post_22689248"]
They are not real though. Simulations are only as good as the data entered and the complexity allowed. At 1w or maybe 10w the simulation would be valid. At the maximum power levels and frequencies used the port will not produce the output shown. There is no possibility. Even 8 and 10" heavily flared ports with 15 to 20x the area compress a little at the air speeds shown.

Ok, let's go round and round again. One more time just for fun. I've asked at least a dozen times where you guys think the model breaks down. I've received no answer at all. I've been told to simulate things with different programs and show the results. I've done that and now the arguement is that the models are not correct. If they are not correct, why did you do your own models and talk about both our models extensively?

IMO the model does not break down. No one has shown any reason why it might.
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I'm not arguing against being frugal and getting the most out of your money. This just isn't the way to do it IMHO. If you are going to make room for extra large enclosures and pay more for the materials. (Yes I understand that you have free wood, but not everyone does.) don't you want a return on investment from that? For a moment let's assume that the 2" port somehow can produce it's contribution without issue and all of the gains in the simulation are still there at full volume. Do you think it would give a better experience than a simple sealed system? Would you be able to tell under blind circumstances if someone plugged the port? Keep in mind all of your gains are below 7Hz. I am confident you would never be able to tell a difference. If you cannot then what are the big enclosures and ports for?
If I had free wood and wanted to get maximum potential out of a couple of drivers on the cheap I would forget about everything below 10Hz right at the outset.

Thank you for your opinion.
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post #188 of 302 Old 12-11-2012, 10:42 AM - Thread Starter
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Originally Posted by ack_bk View Post

Well they told Christopher Columbus that the world was flat, and the Wright Brothers that they would never fly, so OP, if you truly believe in your simulations (and clearly you do, even when very knowledgeable people tell you that it is waste of time) I say build it and prove them wrong if you are that confident.
Nothing ventured, nothing gained.

Yes, most of the people here have shown they are knowledgable but the problem here is they are not smarter than a simulation when it comes to predicting port compression, although they seem to think they are.

I thought this was all settled yesterday (except for a couple people). If the simulations are incorrect, can ANYONE point out the flaw? I've shown WinISD, MJK's Mathcad and Flare It, all of which say the design is fine and these programs were made for just this purpose (especially Flare It) but suddenly no one has faith in any of these programs anymore. For some reason they are used and recommended by everyone here... until right now.

Use your words people, use math or pictures or any other communication device you have at your disposal to explain and show why the simulators are incorrect. If you feel they are not accounting for something tell me exactly what it is. Otherwise you are just blowing a LOT of hot air.
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post #189 of 302 Old 12-11-2012, 10:45 AM - Thread Starter
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Originally Posted by noah katz View Post

Why do you think the air in a port ever behaves as compressible?
Oh, and diy, about you're analogy between port air and fluids in pipelines:
I don't really see the comparison, as the point of a port is to get some extra energy with resonance, and the point of a pipeline is to transfer material without much importance to the energy required.

At the time I thought the major reason people thought the port would compress was boundary layer friction, which the oil and water pipes also have.

I know it's a bad analogy but I was pulling my hair out trying to get ANYONE to give ANY reason the models I've shown might not be accurate.
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post #190 of 302 Old 12-11-2012, 10:53 AM
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"I've asked at least a dozen times where you guys think the model breaks down. I've received no answer at all."

chuffing is where turbulence begins.

turbulence is where you get complete compression. the port fails and for all practical purposes, you have a sealed enclosure.

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post #191 of 302 Old 12-11-2012, 10:55 AM
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"Not true sir. Both the red line and the blue line in Flare It show the ONSET of turbulence, not the complete failure point."

blue line is the onset of turbulence aka chuffing.

red line is failure of the port.

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post #192 of 302 Old 12-11-2012, 10:56 AM
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"Yes, most of the people here have shown they are knowledgable but the problem here is they are not smarter than a simulation when it comes to predicting port compression, although they seem to think they are."

your model isn't prediciting compression. it is a t/s model.

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post #193 of 302 Old 12-11-2012, 11:00 AM
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"Like I said many posts ago, I don't expect audible chuffing until the core get up to 20 m/s or higher."

well, there is your major failure point.

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post #194 of 302 Old 12-11-2012, 11:06 AM - Thread Starter
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Quote:
Originally Posted by LTD02 View Post

"Yes, most of the people here have shown they are knowledgable but the problem here is they are not smarter than a simulation when it comes to predicting port compression, although they seem to think they are."
your model isn't prediciting compression. it is a t/s model.

What are you talking about? There's no where to enter t/s into Flare It.

If you are correct about the red line in Flare It being the complete failure point - well that changes everything. Like I said, I don't think it is but I'll look into it. If you can provide a link to the info to save me some time that would be appreciated, but please don't expect me to just trust you. Within about 2 minutes of downloading the program for the first time I was already pointing out that you were reading the info below 20 hz wrong.
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post #195 of 302 Old 12-11-2012, 11:07 AM - Thread Starter
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Originally Posted by LTD02 View Post

"Like I said many posts ago, I don't expect audible chuffing until the core get up to 20 m/s or higher."
well, there is your major failure point.

Yes, ok, that's what I said in the first place, many many posts ago. But then you said the red line was the complete fail point.
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post #196 of 302 Old 12-11-2012, 11:09 AM - Thread Starter
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Originally Posted by LTD02 View Post

"I've asked at least a dozen times where you guys think the model breaks down. I've received no answer at all."
chuffing is where turbulence begins.
turbulence is where you get complete compression. the port fails and for all practical purposes, you have a sealed enclosure.

Turbulence begins way way before chuffing. Chuffing is simply turbulence so bad it sounds like a fart. Complete port failure is way way past the audible chuffing point.

So it goes like this - minor turbulertnce (which is distortion but not chuffing), then chuffing, then really bad chuffing, then complete port failure.
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post #197 of 302 Old 12-11-2012, 11:40 AM
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"Turbulence begins way way before chuffing. Chuffing is simply turbulence so bad it sounds like a fart."

there is your problem right there.

"Increasing velocity even further, the air in the "core" of the port becomes turbulent. Flares are unable to help with this problem, which represents the limiting velocity for the port. By this stage the port is beginning to present a different load to the system, resulting in de-tuning and subsequent loss of output, known as compression."

http://www.subwoofer-builder.com/flare-testing.htm

this is what is meant by core limit. chuffing is just where you begin to hear some noise but the port is still functioning.

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post #198 of 302 Old 12-11-2012, 11:47 AM
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This effect can be observed with a kitchen funnel and rice grains, but also in freeway traffic. Go to 2:20 in this video:
Quote:
Originally Posted by LTD02 View Post

"Turbulence begins way way before chuffing. Chuffing is simply turbulence so bad it sounds like a fart."
there is your problem right there.
"Increasing velocity even further, the air in the "core" of the port becomes turbulent. Flares are unable to help with this problem, which represents the limiting velocity for the port. By this stage the port is beginning to present a different load to the system, resulting in de-tuning and subsequent loss of output, known as compression."
http://www.subwoofer-builder.com/flare-testing.htm
this is what is meant by core limit. chuffing is just where you begin to hear some noise but the port is still functioning.

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post #199 of 302 Old 12-11-2012, 11:47 AM
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"Wouldn't that be analogous to including Flare It results directly within the program? I admit that would be cool for ALL the simulators to have but since we can use Flare It separately I don't see any need."

sure, but you asked why the software was a failure. my answer was that it is based on t/s parameters only. t/s parameters don't include collo's work on port chuffing. as a result, relying on the simulation software only can fake one out.

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post #200 of 302 Old 12-11-2012, 11:49 AM - Thread Starter
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Originally Posted by LTD02 View Post

"Increasing velocity even further, the air in the "core" of the port becomes turbulent.

Yes, exactly what I said. Core velocity limit (red line) is the ONSET of compression, not the failure point.

I agree with this whole post, since it's basically exactly what I just said especially this quoted part. (Granted, there is a difference between core limit and boundary layer limit represented by the red and blue lines, but passing either the red or blue line is where compression will begin as minor turbulence - NOT the fail point - the fail point is when you drastically and dramatically surpass the red or blue line.)

(I think this is the third time now that you've linked to info that clearly proves my point and not yours, so thanks for that.)
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post #201 of 302 Old 12-11-2012, 11:53 AM - Thread Starter
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Originally Posted by LTD02 View Post

"Wouldn't that be analogous to including Flare It results directly within the program? I admit that would be cool for ALL the simulators to have but since we can use Flare It separately I don't see any need."
sure, but you asked why the software was a failure. my answer was that it is based on t/s parameters only. t/s parameters don't include collo's work on port chuffing. as a result, relying on the simulation software only can fake one out.

Yes, this is true but that's why you suggested using Flare It in the first place. I did, and it says there's no problem with my design until below 5 hz, which is the point that turbulence is just starting to begin. It won't be bad enough to chuff until below 4 (or maybe even 3) hz with a decent roundover and it won't completely fail until below that.
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post #202 of 302 Old 12-11-2012, 12:02 PM - Thread Starter
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Quote:
Originally Posted by imagic View Post

This effect can be observed with a kitchen funnel and rice grains, but also in freeway traffic. Go to 2:20 in this video:

Nice video. This is (very basically) what Flare It calculates. Unless Flare It is wrong, there's no problem with my design. Some people think my design will function like the plugged tube on the right but Flare It clearly says my design will act like the unblocked tube on the left until well below 5 hz. Chuffing will probably begin at 20 m/s and complete port failure will probably happen at about 40 or 50 m/s for the 2 inch tube in my design.

Just in case anyone missed it - the red line is Flare It is the ONSET of MINOR turbulence. It's not the fail point or even the chuff point.
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post #203 of 302 Old 12-11-2012, 12:03 PM
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"Yes, ok, that's what I said in the first place, many many posts ago."

i meant that your thinking that 20m/s was your failure point, not that 20m/s is your failure point. at 10m/s, you are at the core limit for a 2" port and will be compressing and de-tuning the sub. as such, the t/s models that have been posted along the way are no longer valid. in the latest one, that appears around 7hz. in my winisd model it is around 9hz. so somewhere in that region, the models are no longer valid.

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post #204 of 302 Old 12-11-2012, 12:17 PM - Thread Starter
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Originally Posted by LTD02 View Post

"Yes, ok, that's what I said in the first place, many many posts ago."
i meant that your thinking that 20m/s was your failure point, not that 20m/s is your failure point. at 10m/s, you are at the core limit for a 2" port and will be compressing and de-tuning the sub. as such, the t/s models that have been posted along the way are no longer valid. in the latest one, that appears around 7hz. in my winisd model it is around 9hz. so somewhere in that region, the models are no longer valid.

No, I'm thinking 10 m/s is the onset of minor turbulence, minor compression, minor detuning. 20 m/s is approximately where chuffing usually starts to just become audible. The complete fail point is well past 20 m/s. How fast is your vacuum sucking air? (I'm not sure myself but I think it's pretty quick.) Vacuum hoses are small and they do chuff but they certainly don't completely stop functioning due to massive turbulence unless you want to power it with a much larger motor and suck way faster.

When you sneeze how fast is that going? Your nose hole is pretty small and it's passing a lot of air very very quickly - the full capacity of your lungs in a fraction of a second. Does it stop functioning as a hole and back up into your brain? If you added a very narrow very long tube (same diameter as your nostrils) to the end of your nose, would the sneeze not come out?

These are silly analogies, but come on man. This compression issue is being way way overblown and Flare IT in particular says so.
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post #205 of 302 Old 12-11-2012, 12:23 PM
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Quote:
Originally Posted by diy speaker guy View Post

Ok, let's go round and round again. One more time just for fun. I've asked at least a dozen times where you guys think the model breaks down. I've received no answer at all. I've been told to simulate things with different programs and show the results. I've done that and now the arguement is that the models are not correct. If they are not correct, why did you do your own models and talk about both our models extensively?
IMO the model does not break down. No one has shown any reason why it might.
Thank you for your opinion.

I have not changed my stance on this. And I have attempted to explain multiple times why the simulation at high power is not representative of the real world result and also why this type of system doesn't really offer much of anything to justify its increased bulk and space occupied. Simulations scale in a perfectly linear manner. They do not for the most part attempt to address large signal deviations that occur in the system due to a large variety of factors. They do not simulate driver thermal compression, impedance rise, motor and suspension non linearities, vent compression, etc. You go from 1 volt input to a 10v input and you get a perfect increase of 20dB and then increase it from 10v to 100v and get another 20dB increase in output. This does not happen in the real world. Any speaker measured at high power will start to show shifts in the response and compression or even expansion of output as the parameters shift and with vented systems vent compression occurs. Simulations are very basic representations of much more complex and varied real systems. The more output you ask from the system the further the result deviates from the model due to these unaccounted for factors.

The model is fine and works as predicted at low power.

This one breaks down anywhere that the port is going to be pushed past 10m/s airspeed where significant vent compression is going to occur. How much we cannot know exactly with out having the actual system built and measured but all evidence points to there being compression. There are plenty of compression tests of vented subs available from Illka, Avtalk, myself and others. It is not being overblown. What is being overblown is the extra 1 maybe 2dB if we are generous of output all of it below 10Hz mind you, from a system many times the size of a comparable performing sealed system while ignoring things like vent noise and pipe resonances. It just doesn't make sense to build anything like this unless you have an IB sized space available.
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post #206 of 302 Old 12-11-2012, 12:27 PM
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Solution is simple. Build it, and present your findings smile.gif
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post #207 of 302 Old 12-11-2012, 12:31 PM - Thread Starter
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http://wiki.answers.com/Q/What_is_the_speed_of_the_average_sneeze

That's the first google hit for average velocity of a sneeze.

40 - 100 mph. Approximately 45 m/s at the high end (if I did the math right).

Flare It says core limit for 1 inch dimater is 7 m/s, and thats conservative since your nose hole is nowhere near 1 inch diameter.

If what you are saying is true a big sneeze would be theoretically impossible.
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post #208 of 302 Old 12-11-2012, 12:33 PM - Thread Starter
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Quote:
Originally Posted by Ricci View Post

Simulations scale in a perfectly linear manner. They do not for the most part attempt to address large signal deviations that occur in the system due to a large variety of factors.

Never mind the t/s models. What about Flare It? This is EXACTLY what Flare It is for.
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This one breaks down anywhere that the port is going to be pushed past 10m/s airspeed where significant vent compression is going to occur.

Flare It says this is dead wrong. AGAIN, please explain why you think Flare It is wrong. The model does not break down, minor compression starts to happen at that point.

YOU are the guy that measures things and shows that the curve goes up in a completely linear fashion with increasing power up until right around the point that Flare It predicts it will not act linear anymore (or thermal compression sets in).

I cannot understand why you would trust Flare It for more conventional applications but think it does not apply here.
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post #209 of 302 Old 12-11-2012, 12:34 PM
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"I'm thinking 10 m/s is the onset of minor turbulence, minor compression, minor detuning."

for practical purposes, the point of onset of minor turbulence is where the port begins to audibly chuff. once the port is audibly chuffing, you are already getting minor compression and minor detuning, but it is usually acceptable. you are talking about exceeding the core limit, so you are talking about significant compression and detuning.

this is what all the other guys have been trying to say from the beginning.

"How fast is your vacuum sucking air?"

you do realize that electric motors make little to no sound and that most all the noise from a vacuum cleaner is related to all the various air turbulences?

Listen. It's All Good.
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post #210 of 302 Old 12-11-2012, 01:04 PM - Thread Starter
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Quote:
Originally Posted by LTD02 View Post

for practical purposes, the point of onset of minor turbulence is where the port begins to audibly chuff.

Again, not correct. Chuffing is massive turbulence, not minor turbulence. The onset of minor turbulence is what Flare It is showing, not the chuff point. It actually says so in the quote you posted a few posts back.
Quote:
"How fast is your vacuum sucking air?"
you do realize that electric motors make little to no sound and that most all the noise from a vacuum cleaner is related to all the various air turbulences?

Yes I fully realize that. But the point is that it does not become so turbulent that it ceases to function as a hole, which is what many people are implying with my design.

Round and round we go.

Let's talk about the sneeze since we can't agree on my simulations. It's a verified fact that sneezing at high velocity is possible and we all have experience, so let's talk about that. The fail point of your nostrils is clearly way higher velocity than you can sneeze, right? Otherwise the sneeze wouldn't come out. Flare It says the core velocity of your nostrils is somewhere below 7 m/s, probably closer to 5 depending on the dimensions of your anatomy. So we're pushing 45 m/s through a very small duct (which is also long by the way, it extends several inches down to your lungs). Basically the same thing as my design, a very small hole in a very long pipe. If the Flare It model breaks down and the port ceases to function completely and reverts to sealed at relatively low velocity as some of you are insisting, how is a big sneeze possible?

This compression issue is way overblown.
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