2 hz tuning - pros and cons - Page 6

Winisd transfer functions.pdf 26k .pdf file

apparent load.pdf 33k .pdf file

cone excursion.pdf 32k .pdf file

spl.pdf 30k .pdf file



port velocity.pdf 28k .pdf file

maximum power.pdf 32k .pdf file

Here they are. Open them and compare to your graphs. I used 1000 watts as was planned in the beginning.

Good luck,

Robert

Couldn't have said it better!

Notnyt have you ever taken a measurement of the electrical roll off of your signal chain to the subs as it comes out of the amps?

you are seriously twisted. What was entered wrong. I followed protocol just as stated. How did you enter your data?

What design are you talking about. You built a square box with a fence post hanging out of it. Not much design there.

It is essentially a sealed enclosure.
Edited by robertcharles - 12/10/12 at 9:52pm

Was this actually stated in this thread? I must've missed it if so. I would argue the "job" is a wasteful one. Either of materials, space or potential depending on how it is looked at. I guess I just don't get the point of gaining a minuscule amount of output in a bandwidth which will likely never be perceivable by increasing the enclosure volume to 3x the size and adding an 8 ft long tube..

my kids were doing homework at the time and the files were not saved correctly to the zip file. They are correct now as I saw on the winisd. No one but you is in disagreement here, so maybe you ought to check your graphs. Mine show extreme excursion, Steep rolloff. Extreme port velocity and so on and so on. And if you feed that thing more than a 100 watts down low the driver will go. Guaranteed.

Oh, and by the way, how do you know that you did not make a tiny mistake entering data? It had to be me. Well, my cabinets came out exactly like I wanted and I have the tune I could get with the most output. No port or radiator will get that low without potential damage. I bought 2 of these drivers because of the bang for the buck. They will not bang that hard.- period. Do you have any experience at all with vented cabinets. I can't see you insulting me when I have never been insulted on this forum before. All of these guys here in the last 2 days are knowledgable and in agreement. They may be wrong, but that is to be determined later, but, since you do not really have any experience one way or another other than a simulator, I say keep simulating and dreaming- it will work out.

Have you seen this my man. I spent years designing and building these1000 pound monsters. This is a design. Maybe not what everyone wants or needs, but it is a design, It models exactly like it was designed. No questions.And, if I wanted, it could destroy a good portion of my possessions. But, without a HPF, it could destroy itself. The model worked and was proven correct after the testing. 14.4 Hertz tuning as designed. But I did get different results at many points in time due to bugs in the program learning curve of win isd and just plain not paying attention to small things. You might not ever make a mistake, but in this case you need to have a little bit of something that you can show all these guys in order to prove your point. I could not have just been telling you the thing would look the same and get what I got by accident. I knew it and so does everyone else. The port will compress and it will be no benefit and maybe act like a sealed box and get excursion like a sealed and unload like in my excursion graph. Good luck,



Robert

[URL=http://s228.photobucket.com/albums/ee292/robertcharles123/?action=view&current=3.jpg][/URL]

Hey dude,

I guess you are right. I am wrong, Josh is wrong, Scott is wrong, John is wrong, Bosso is wrong, Mark is wrong, and you are right. You have found something. So, I will truly build your box and I am going to test it the best way I know how. Of course, when it fails, you will blame me. Maybe I will let Josh measure it. I think Josh might be able to be pursuaded to do that for me. Would you believe him if it did not work. Oh, maybe not because he does not have the expertise at measuring port velocity. It might be a great sealed box but 2 Hertz-never.

My 2 cents.

Can the concept of a box tuned to 2Hz in order to reduce xmax as you approach that low frequency work? Yes.
Is it worth building? No.
If I wanted to build it just for the heck of it, what would I change? Larger Diameter Port.

Why? Because of port compression.

from the graphs posted it looks like the design acts as a sealed box above 20Hz so for the real world this design may not get you what you are looking for tuned that low.
tuned to 10? might look better, would have to check the graphs to find out.

bottom line is port compression do to air speed is your enemy in all ported designs and you need something like flare it to help with selecting port sizes.

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.

i have attached your simulation with red dashed lines matching up the 10 m/s air speed to the three charts.

in the bottom chart, 10 m/s occurs at 7hz.

moving up to the middle chart, 7hz is right where the port is expected to help lower cone motion. but because below 7hz, the port will completely go turbulent and completely fail, the cone motion will just proceed up as though it were a sealed cab. so no benefit there.

moving to the top chart. again, the port provides less than 1db of gain above 7hz and because the port will completely fail below 7hz, there will be no spl advantage there.

so overall, no advantage to either spl or cone motion vs. sealed.



.....

noah, by transition frequency, i meant the point where the air transitions from behaving like a compressible gas to more like an incompressible gas. that is the only thought that i had on why there would be a cutoff frequency where turbulence is no longer a function of frequency in the port.
Edited by LTD02 - 12/11/12 at 3:54am

it might be interesting to send the guy who developed that software a note to include an algorithm that transitions the model from ported to sealed in the simulation when the port air velocity exceeds the critical threshold of complete turbulence, not just chuffing, but complete turbulent overload.

thiele and small did not include exceeding port turbulence thresholds in their equations.

i hope i'm not increasing anybody's blood pressure. it was an interesting idea and discussion.

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.

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.

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.

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.

Indeed they are, which is why I have ascertained that a 2,000 foot long, 22" wide vent tube would be sufficient to tune a large (300 liter) box to 2hz, using a typical 18" driver... with zero port-related issues. It would need to be an external port and feature a 180-degree bend, so it vents right next to the woofer itself instead of three or four blocks away. Makes sense because the wavelength of a 2hz tone is 562 feet.

Edited by imagic - 12/11/12 at 10:00am

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.

Because clearly this is on par with those two discoveries / inventions.