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2 hz tuning - pros and cons - Page 3

post #61 of 302
12/10/12 at 12:56pm
Quote:
Originally Posted by diy speaker guy View Post

Yeah, see, I agree with you completely that ports can only handle so much velocity. But PLEASE look at the velocity graph in post #1, shown at 1000 watts. You can clearly see port velocity is below 10 m/s until below 5 hz. And please explain why this is not accurate. Several people now have said it's not accurate but no one can give a reason why this might be so. This has never ever been questioned before as far as I know. Why is it different now? Port velocity is port velocity, the model doesn't break down. If you think it does, please explain why.

I was scratching my head as to how the port velocity could be so low at such a low freq; I think the answer is the ~70 dB of output..
Quote:
Originally Posted by LTD02 View Post

that is interesting and probably has something to do with the transition frequency of the enclosure.

Definition please
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post #62 of 302
12/10/12 at 12:57pm
Quote:
Originally Posted by diy speaker guy View Post

Quote:
Originally Posted by Ricci View Post

Mark and John pretty much covered the reasons that you do not see enclosures like this. The port is far too small to cope with 18" drivers and very low frequencies. It will compress very quickly essentially turning this into a large sealed enclosure. Actually even if a much larger 10" port could be used for example with an IB sized space, it wouldn't matter much as the system basically acts like a sealed enclosure above 10Hz anyway. With the 2" x 90" long port ( 90" is 7.5 feet of port BTW) you will have to get 7.5 ft of port length in the enclosure and I'm not so certain that the port resonance won't be a little more dramatic than shown in the sims. That is a VERY long tuned pipe. With any of the worthwhile port effects taken place primarily below 10Hz I would be very surprised if you could tell a difference between the 2Hz tuned design and sealed. Content that low is very limited and what happens above 10Hz is far more important. A better proposition would be to tune to 12 or 13Hz and forget about the <10Hz content. You will gain a ton of output where it makes a much more noticeable difference.If you must have <10Hz go sealed or IB.

Yeah, John and Mark said the same thing (at least I think they did, who is John?). But the software clearly says otherwise so I guess there's no point in going any further with this conversation. No one can give any reason why the software might be wrong (I'm talking about both the acoustic simulators AND the Flare It program.

I'm not educated in fluid (or gas) flow but I do know there are similarities and I do know that pipelines carrying water and oil have been and are being built that are several thousand miles long. If what you guys were saying was even reasonably true, these pipelines would have to be almost infinitely large to be effective at all.

I expected more from avsforum than a bunch of guys dropping by to drop the "you are wrong" bomb without providing any proof at all besides what they think might happen in a situation they have no practical experience with. To be fair I have no experience either but I do have the common sense to trust software that is much better at predicting this stuff than anyone who has commented here.

Mark has not posted here again, I have to assume he has no rebuttal to the Flare It program output, so unless ANYONE can give ANY reason the software might be incorrect I have to assume I am correct in trusting it but there's not much point in discussing it further I guess.

Actually I've been working on 5 separate custom subwoofer designs over the course of the weekend while trying to pretend I have a social life. I'd wager you will be staring at various models for quite a while before making any sawdust or having parts in hand. The laws of physics aren't going to change between then and now. Chill out.

Only in you more recent posts did you clarify that your hope/intent is to in essence not expect the sub to get worked much at the 2Hz tuning, and to take advantage of some excursion reduction above tuning where the port velocity is still low. That can work so long as the port airflow isn't pushed high at ANY frequency. Just like driver excursion, just because it might only take 4mm of xmax in the middle of the bandwidth to produce high SPL, if a 16Hz signal is asking 40mm at the same time, both get distorted. In other words, any signal which pushes too much airflow through the port will affect the entire range of operation of the port. The limited electrical throughput at 2Hz greatly reduces this risk, but it brings us back to how great is the realized advantage vs. the same driver in a sealed box? I'd argue you will see much more variation in the port linearity than the amount of compression at the power and excursion levels you are concerned about.

For most any overly large or particularly complex design, I start with a quick sanity check to determine what the idea offers vs. some reasonably comparable solution such as a simple sealed system with EQ. IMO, the real world behavior of a long port won't be worth the added construction hassle. Instead build something simpler, possibly smaller, and add save some money on the project to add a second driver at a later date. You don't need any more power to see a benefit in a pair of sealed drivers by comparison, and you leave yourself some room to upgrade whenever you can justify a little more power down the road.

There could be some cases you might find where a huge box volume and very low tuned port could benefit much more over a sealed alternate, but I'm not seeing the benefit for this comparison.

Finally, if you really want to test what will happen, build a box scaled by 10x higher frequency with a similar response shape. You can use electronic filters in a MiniDSP or similar to see what the real world operation will be at 10x the frequency and in a much more manageable package.
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post #63 of 302
12/10/12 at 1:00pm
I'm surprised no one brought up Steve C and the SLLT design. For those that don't know, it was essentially a ported IB, tuned around 5hz, but used a port large enough in diameter to minimize port compression. It worked at boosting the <10hz area and kept excursion in check, so more power could be applied.
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post #64 of 302
12/10/12 at 1:22pm
Thread Starter 
Quote:
Originally Posted by Mark Seaton View Post

Actually I've been working on 5 separate custom subwoofer designs over the course of the weekend while trying to pretend I have a social life. I'd wager you will be staring at various models for quite a while before making any sawdust or having parts in hand. The laws of physics aren't going to change between then and now. Chill out.

Thanks so much for responding. To be clear, I didn't think you were going to, that's why I was not chilled.
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Only in you more recent posts did you clarify that your hope/intent is to in essence not expect the sub to get worked much at the 2Hz tuning, and to take advantage of some excursion reduction above tuning where the port velocity is still low.

Ok, I'm sorry I didn't mention this earlier but I thought it was more than obvious by looking at the graphs in post 1, combined with the fact that there is no useful content at 2 hz in any media, and even if there was it would probably have to be 140 db to even perceive it and you would need a specialized signal chain to pass that signal along to the sub.
Quote:
That can work so long as the port airflow isn't pushed high at ANY frequency. Just like driver excursion, just because it might only take 4mm of xmax in the middle of the bandwidth to produce high SPL, if a 16Hz signal is asking 40mm at the same time, both get distorted. In other words, any signal which pushes too much airflow through the port will affect the entire range of operation of the port. The limited electrical throughput at 2Hz greatly reduces this risk...

Yes, of course this is all true. If for example, a massive 1 hz blast did somehow come through the system it would mess up the port output through the port's entire passband. That is exactly why I tuned it so low that this will never ever happen because it simply isn't pssible.
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but it brings us back to how great is the realized advantage vs. the same driver in a sealed box?

Probably the same as ANY driver compared in a sealed vs ported box - except for the fact that I'm willingly and purposefully throwing out the entire lower half of the port output.
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I'd argue you will see much more variation in the port linearity than the amount of compression at the power and excursion levels you are concerned about.

Again, all the 3 softwares I've shown show my port velocity is lower than 10 m/s above 5 hz, and that the core velocity of a 2 inch pipe is 10 m/s. That says to me this design is good to go with no linearity problems above 5 hz. But if you don't agree with that please explain why. I'm not saying you are not wrong, I just don't see it from your perspective and if there's something to learn here I want to learn it. What point exactly do you think the model breaks down?
Quote:
For most any overly large or particularly complex design, I start with a quick sanity check to determine what the idea offers vs. some reasonably comparable solution such as a simple sealed system with EQ. IMO, the real world behavior of a long port won't be worth the added construction hassle. Instead build something simpler, possibly smaller, and add save some money on the project to add a second driver at a later date. You don't need any more power to see a benefit in a pair of sealed drivers by comparison, and you leave yourself some room to upgrade whenever you can justify a little more power down the road.
There could be some cases you might find where a huge box volume and very low tuned port could benefit much more over a sealed alternate, but I'm not seeing the benefit for this comparison.
Finally, if you really want to test what will happen, build a box scaled by 10x higher frequency with a similar response shape. You can use electronic filters in a MiniDSP or similar to see what the real world operation will be at 10x the frequency and in a much more manageable package.

This is all very good advice and I've thought about a scaled test model (I have a Tang Band 6 inch driver with 13 mm xmax) but I'm not sure where to find a port material small enough in diameter and rigid enough to make a true scale model. I don't have anything like that at home

At least with this post we are gaining some common ground on this subject. This response clearly tells me that you think this idea has merit even if reality might throw a small wrench into the works at some point. I'm not sure if that was your point, but I'm not feeling so cranky anymore at least.

Please understand though, (everyone) I've tried to provide as much evidence and context as possible, I posted a bunch of pics of different software that all agree with each other. I've tried to answer questions that weren't even asked (although they were implied by saying I was wrong). I've tried to keep this on topic (THIS IS NOT A CONVERSATION ABOUT TUNING PREFERENCES, it's a conversation about a single proposed design and the validity of the simulation software. So please forgive me if I seem a bit cranky. It's only because I am.
Edited by diy speaker guy - 12/10/12 at 1:38pm
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post #65 of 302
12/10/12 at 1:30pm
Thread Starter 
Quote:
Originally Posted by noah katz View Post

I was scratching my head as to how the port velocity could be so low at such a low freq; I think the answer is the ~70 dB of output..

Yes, exactly (although it's showing closer to 82 db at 2 hz, not 70). There's not much velocity because there's really not much going on. (But at the same time, please remember that at 1 hz there actually is REALLY high velocity, but it's so low in frequency that it makes no difference.

This brings up a good point though, in terms of a scale model. Spl needs to be scaled too, not just frequency. Since the scaled model will be able to put out a LOT of spl at the scaled frequency, you have to limit spl to reflect the fact that even dual 18 inch drivers can't push much air at 2 hz.
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post #66 of 302
12/10/12 at 1:32pm
Thread Starter 
Quote:
Originally Posted by Looneybomber View Post

I'm surprised no one brought up Steve C and the SLLT design. For those that don't know, it was essentially a ported IB, tuned around 5hz, but used a port large enough in diameter to minimize port compression. It worked at boosting the <10hz area and kept excursion in check, so more power could be applied.

I'm not familiar with it but it sounds like the opposite of what I'm doing. I'm deliberately undersizing the port and throwing out the entire lower half of the port resonance, instead of making the port large enough so it won't chuff.
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post #67 of 302
12/10/12 at 1:40pm
http://www.fohonline.com/home/20-features/6031-tech-feature-subwoofer-ports.html

Give this one a read. It might help. I am sorry I did not realize you were just trying to build a vented box. I thought you were trying to improve on an already designed tapped horn. So, my mistake. I still agree with Mark and John though. Simulations are great, but as I told you before, when you build it and test it out you will either be right or wrong- just do not spend a whole lot of money and time building a specific design without first just "slapping" one together to see what happens.

Good luck,

Robert
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post #68 of 302
12/10/12 at 1:42pm
Quote:
Originally Posted by diy speaker guy View Post

I'm not familiar with it but it sounds like the opposite of what I'm doing. I'm deliberately undersizing the port and throwing out the entire lower half of the port resonance, instead of making the port large enough so it won't chuff.

No, it is really exactly what you are trying to do except they are actually built and they work but the ports are large like the 10 inch port I told you to model last night
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post #69 of 302
12/10/12 at 1:44pm
Quote:
Originally Posted by robertcharles View Post

No, it is really exactly what you are trying to do except they are actually built and they work but the ports are large like the 10 inch port I told you to model last night

Steve is really the KING as far as SLLT goes, so ask him and if you do not believe him then there is really no point after that.

Good luck,

Robert
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post #70 of 302
12/10/12 at 1:44pm
Thread Starter 
Quote:
Originally Posted by robertcharles View Post

http://www.fohonline.com/home/20-features/6031-tech-feature-subwoofer-ports.html
Give this one a read. It might help. I am sorry I did not realize you were just trying to build a vented box. I thought you were trying to improve on an already designed tapped horn. So, my mistake. I still agree with Mark and John though. Simulations are great, but as I told you before, when you build it and test it out you will either be right or wrong- just do not spend a whole lot of money and time building a specific design without first just "slapping" one together to see what happens.
Good luck,
Robert

Um... I still don't know who John is but assuming you are talking about LTD, both those guys seem to be agreeing with me now (in principle if not in exact detail).

Everyone agrees (I hope) at this point that the core velocity of a 2 inch pipe is 10 m/s, and my design does not exceed that until below 5 hz. In other words the concept works, at least on paper.
Edited by diy speaker guy - 12/10/12 at 1:50pm
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post #71 of 302
12/10/12 at 1:46pm
Thread Starter 
Quote:
Originally Posted by robertcharles View Post

Steve is really the KING as far as SLLT goes, so ask him and if you do not believe him then there is really no point after that.
Good luck,
Robert

Don't start this again please, you made a big mess of this thread and wasted a lot of my time last night. If you can't point out a problem with my simulations or ideas with math please don't tell me what to do. I know who Steve is and I also know what I am doing. We are not doing the same thing. Instead of providing more links, please read through the thread and try to understand what's going on here.
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post #72 of 302
12/10/12 at 1:48pm
Quote:
Originally Posted by diy speaker guy View Post

I'm not familiar with it but it sounds like the opposite of what I'm doing. I'm deliberately undersizing the port and throwing out the entire lower half of the port resonance, instead of making the port large enough so it won't chuff.


http://www.hometheatershack.com/forums/members-stevecallas-263/
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post #73 of 302
12/10/12 at 1:58pm
I am sincerely trying to offer help here. I know you want a larger sized box tuned low and use a port to do it. Right? Nothing exotic?

I will offer what I know and I think I have a handle on the problem if you could just allow a simple dialoque. Ok?
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post #74 of 302
12/10/12 at 1:58pm
You came onto AVS and are mad because people don't agree with you? biggrin.gif Not sure what you expected but sims are not always right, it's been proven time and time again, they will be a great ballpark but are not an perfect. Build your design, what you obviously want to do no matter what and take your measurements. You can argue with people on here all day but until you actually build something, no one is going to give to craps I'm afraid because it happens all the time. There is a good reason everyone is saying it's not a great idea but you don't want to hear it. Just build the damn thing and try prove everyone wrong! If you keep up the arguing with everyone, no one will want to help you.

The proof is in the sawdust! for $100 you could build one of you cabs.... get at it!!
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post #75 of 302
12/10/12 at 2:14pm
Thread Starter 
Quote:
Originally Posted by robertcharles View Post

I am sincerely trying to offer help here. I know you want a larger sized box tuned low and use a port to do it. Right? Nothing exotic?
I will offer what I know and I think I have a handle on the problem if you could just allow a simple dialoque. Ok?

I appreciate what you are trying to do but it's not working. You made about 40 posts last night that basically all said the same thing. I responded to all of them, and after a couple of hours of that it became clear that you did not understand what I was simulating in the first place. Post 1 clearly said it was a simple ported box, the pics show all the software inputs that clearly show a simple ported box. And the whole time it's been clear that you don't understand why I'm doing what i"m doing.

If you can't read and understand the info in post 1 I don't think you have anything to offer me here. I'm really trying not to be condescending but you are either in a little too deep here or simply are not paying attention to to the details in post 1.
Edited by diy speaker guy - 12/10/12 at 2:25pm
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post #76 of 302
12/10/12 at 2:18pm
Well, I guess I do not have or want to go further.

I hope it works for you,

Merry Christmas,

Robert
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post #77 of 302
12/10/12 at 2:19pm
Thread Starter 
Quote:
Originally Posted by N8DOGG View Post

You came onto AVS and are mad because people don't agree with you? biggrin.gif Not sure what you expected but sims are not always right, it's been proven time and time again, they will be a great ballpark but are not an perfect. Build your design, what you obviously want to do no matter what and take your measurements. You can argue with people on here all day but until you actually build something, no one is going to give to craps I'm afraid because it happens all the time. There is a good reason everyone is saying it's not a great idea but you don't want to hear it. Just build the damn thing and try prove everyone wrong! If you keep up the arguing with everyone, no one will want to help you.
The proof is in the sawdust! for $100 you could build one of you cabs.... get at it!!

I'm not mad because people don't agree with me. I brought this converstion here (of all places I could have gone) specifically for the knowledge base here and I WELCOME disagreement. It leads to learning.

I AM mad when people tell me my goals are wrong (which is OT and not helpful) and I do get upset when people disagree but don't provide any details, especially when I've spent considerable time presenting a balanced arguement with plenty of supporting evidence.

Other than my posts there's maybe 5 posts in this entire thread that are on topic. Wouldn't that bother you if you were honestly trying to share and learn?

Simulations should be incrdibly accurate as long as you actually build exactly what you simulate (which does not happen A LOT, as soho54 used to point out with his incredibly complex and accurate 50+ segment horn models) and are mindful of things that the software does not consider, like power compression. I've seen dozens of measurements overlayed directly overtop of sims showing far greater agreement than is actually necessary - but you are right, none of them are a perfect overlay.

As far as I can tell, the 3 people (Mark, LTD, Noah) that have actually stayed on topic and read my posts in detail and maybe done some of their own simulations are not disagreeing with me on the broad strokes. We might have some differences of opinion in the small details but I think we are still working on that.
Edited by diy speaker guy - 12/10/12 at 2:29pm
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post #78 of 302
12/10/12 at 2:31pm
I don't have a lot of time right at the moment but that simulation is not accurate. You gain only 1dB at 10Hz (EDIT: Not even that actually. )versus a sealed enclosure and that is assuming that content that low will not compress the port which it will with any appreciable level as Mark notes. Your excursion reduction only takes effect below 10Hz as well. Of course any real output that low will overload the port in very short order nullifying any real gains in the sub 10Hz area. This is what Mark was talking about. There is no advantage offered 10-200Hz. Additionally you have a 78hz pipe resonance to deal with. Simply adding one more driver to a sealed system would improve the performance much more meaningfully.
Couple of simulations that show no notable advantage until below roughly 7Hz. Vent speed gets up to about 12m/s for the little improvement at 7Hz and it is doubtful that a 2" port will support that much air at such a low frequency.





Edited by Ricci - 12/10/12 at 2:51pm
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post #79 of 302
12/10/12 at 2:34pm
Quote:
Originally Posted by diy speaker guy View Post

As far as I can tell, the 3 people (Mark, LTD, Noah) that have actually stayed on topic and read my posts in detail and maybe done some of their own simulations are not disagreeing with me on the broad strokes. We might have some differences of opinion in the small details but I think we are still working on that.

Sorry but they are just humoring you and the idea. tongue.gif

The rest of us know better.

This system would not work. Look at the system in my sig for a proper LLT and about the most one could squeeze out of a resonant alignment without going to unbuildable extremes.
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post #80 of 302
12/10/12 at 2:42pm
Thread Starter 
Quote:
Originally Posted by Ricci View Post

I don't have a lot of time right at the moment but that simulation is not accurate. You gain only 1dB at 10Hz versus a sealed enclosure and that is assuming that content that low will not compress the port which it will with any appreciable level as Mark notes.

Go back and read his last post, that's not what he said at all. The port will only compress below 2 or 3 hz where there is NO CONTENT IN ANY RECORDED MEDIA and even if there was the signal chain wouldn't pass it to the sub. So it will not ever chuff. Above 5 hz (where there is content in recorded media) velocity is 10 m/s or less, completely acceptable according to Flare It.
Quote:
Your excursion reduction only takes effect below 10Hz as well. Of course any real output that low will overload the port in very short order nullifying any real gains in the sub 10Hz area. This is what Mark was talking about. There is no advantage offered 10-200Hz. Additionally you have a 78hz pipe resonance to deal with. Simply adding one more driver to a sealed system would improve the performance much more meaningfully.

I agree with the first sentence 100 percent. Sentence 2 is completely untrue. Sentence 3 is kinda true, but we just discussed this, there is no content in the frequency band of port chuffing problems so it's really not an issue. Sentence 4 is mostly correct. We already discussed the 75 hz resonance, and while it makes me a bit nervous, WinISD shows high q peaks that the other software in post 1 does not show. As for the last sentence, as I said about 10x now, I can't afford sealed boxes and power for them. If you want to send me stuff I'll be happy to go that way.
Edited by diy speaker guy - 12/10/12 at 2:50pm
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post #81 of 302
12/10/12 at 2:45pm
Thread Starter 
Quote:
Originally Posted by Scott Simonian View Post

Sorry but they are just humoring you and the idea. tongue.gif
The rest of us know better.
This system would not work. Look at the system in my sig for a proper LLT and about the most one could squeeze out of a resonant alignment without going to unbuildable extremes.

I doubt they are humoring me. I was spectacularly wrong about something last week and no one humored me then. (I wasn't wrong because I was stupid, I understood the physics just fine but was incorrect in my understanding of the layout of the internal workings of a device that I didn't have a picture of at the time.)

Unless the build in your sig is tuned to 2 hz it has nothing whatsoever with this conversation. It may be a good design but it's not even close to the same thing.
Edited by diy speaker guy - 12/10/12 at 2:54pm
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post #82 of 302
12/10/12 at 2:46pm
Hey guy, I will actually send you the money to build this thing if you actually build it. If it works you can feel like you win both ways, if it does not, I want an apology. OK?
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post #83 of 302
12/10/12 at 2:46pm
Quote:
Originally Posted by diy speaker guy View Post

I'm not mad because people don't agree with me. I brought this converstion here (of all places I could have gone) specifically for the knowledge base here and I WELCOME disagreement. It leads to learning.
I AM mad when people tell me my goals are wrong (which is OT and not helpful) and I do get upset when people disagree but don't provide any details, especially when I've spent considerable time presenting a balanced arguement with plenty of supporting evidence.
Other than my posts there's maybe 5 posts in this entire thread that are on topic. Wouldn't that bother you if you were honestly trying to share and learn?
Simulations should be incrdibly accurate as long as you actually build exactly what you simulate (which does not happen A LOT, as soho54 used to point out with his incredibly complex and accurate 50+ segment horn models) and are mindful of things that the software does not consider, like power compression. I've seen dozens of measurements overlayed directly overtop of sims showing far greater agreement than is actually necessary - but you are right, none of them are a perfect overlay.
As far as I can tell, the 3 people (Mark, LTD, Noah) that have actually stayed on topic and read my posts in detail and maybe done some of their own simulations are not disagreeing with me on the broad strokes. We might have some differences of opinion in the small details but I think we are still working on that.

No man, that would not bother me, I'd expect it. Getting worked up over a few posts on a forum? common man, grow a thicker skin.
And no sims are not always accurate, try out some real world testing vs your sims.

I do have to know, have you ever built anything? You seem pretty sure about your design, I can't for the life of me understand why you don't try it out and see for your self.
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post #84 of 302
12/10/12 at 2:49pm
Quote:
Originally Posted by diy speaker guy View Post

I doubt they are humoring me. I was spectacularly wrong about something last week and no one humored me then. (I wasn't wrong because I was stupid, I understood the physics just fine but was unsure of the layout of the internal workings of a device that I didn't have a picture of.)
Unless the build in your sig is tuned to 2 hz it has nothing whatsoever with this conversation. It may be a good design but it's not even close to the same thing.


Well... mine is real and I'm using it. It also works properly.

Good luck with .... whatever this thing is. confused.gif

See.... I've had flat to just below 10hz extension since 2007. Now I want more. Guess what I have to do? Build a proper sealed system and get my signal chain right. You can do all you want trying to make this alignment work but do you even know if your signal chain will support flat to 2hz? Cuz pretty much no one on Earth can get flat that low with with all their equipment.

Heh. Good luck. wink.gif
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post #85 of 302
12/10/12 at 2:55pm
Thread Starter 
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Originally Posted by robertcharles View Post

Hey guy, I will actually send you the money to build this thing if you actually build it. If it works you can feel like you win both ways, if it does not, I want an apology. OK?

No, I'm not going to take your money. But all the same if I do find out I am wrong about any aspect of this I will seek you out to apologize.
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post #86 of 302
12/10/12 at 2:59pm
Quote:
Originally Posted by diy speaker guy View Post

Go back and read his last post, that's not what he said at all. The port will only compress below 2 or 3 hz where there is NO CONTENT IN ANY RECORDED MEDIA and even if there was the signal chain wouldn't pass it to the sub. So it will not ever chuff. Above 5 hz (where there is content in recorded media) velocity is 10 m/s or less, completely acceptable according to Flare It.

I agree with the first sentence 100 percent. Sentence 2 is completely untrue. Sentence 3 is kinda true, but we just discussed this, there is no content in the frequency band of port chuffing problems so it's really not an issue. Sentence 4 is mostly correct. We already discussed the 75 hz resonance, and while it makes me a bit nervous, WinISD shows high q peaks that the other software in post 1 does not show. As for the last sentence, as I said about 10x now, I can't afford sealed boxes and power for them. If you want to send me stuff I'll be happy to go that way.

You are not listening to what we are trying to tell you. This idea has come and gone many times before.

Go back and look at the simulations I posted. There is zero as in ZERO gain anywhere above 7Hz. That is assuming the port responds in a linear fashion which it will not. We have already covered that the port will not support the airflow needed for 2-7Hz ULF at even modest levels. A 2" port simply can't. Where is your gain then if there is none above 7Hz and really none below 7Hz since the port cannot support it? Where is the advantage to this idea? Tuning to 12-15Hz will be a much better use of the drivers.
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post #87 of 302
12/10/12 at 2:59pm
Thread Starter 
Quote:
Originally Posted by Scott Simonian View Post

Well... mine is real and I'm using it. It also works properly.
Good luck with .... whatever this thing is. confused.gif
See.... I've had flat to just below 10hz extension since 2007. Now I want more. Guess what I have to do? Build a proper sealed system and get my signal chain right. You can do all you want trying to make this alignment work but do you even know if your signal chain will support flat to 2hz? Cuz pretty much no one on Earth can get flat that low with with all their equipment.
Heh. Good luck. wink.gif

I'm sure your sub is very nice, well designed, well built and perfect for your needs (at the time). But it's simply not the same thing so it doesn't matter in this conversation.

I've made it clear several times now that the purpose of this is NOT to have 2 hz output, It won't. That should be clear and if that's your only arguement I agree with you. But it's more than likely (according to the sims) that there will be good output from at least 5 hz and up.

The low tuning is NOT to get 2 hz output, it's to push the problems of a massively undersized port below 5 hz. How can I make this more clear?
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post #88 of 302
12/10/12 at 2:59pm
Fair enough. But, the offer still stands. And by the way, I bet you did not know I was one of the first to order that little sub you are talking about. That is why I was curious. I will put the box together and test it myself. I have all the port material and ply laying around, so to do it myself would be no problem if you would not mind me using your design.
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post #89 of 302
12/10/12 at 3:10pm
Quote:
Originally Posted by diy speaker guy View Post

Quote:
Originally Posted by Mark Seaton View Post

but it brings us back to how great is the realized advantage vs. the same driver in a sealed box?

Probably the same as ANY driver compared in a sealed vs ported box - except for the fact that I'm willingly and purposefully throwing out the entire lower half of the port output.
Quote:
I'd argue you will see much more variation in the port linearity than the amount of compression at the power and excursion levels you are concerned about.

Again, all the 3 softwares I've shown show my port velocity is lower than 10 m/s above 5 hz, and that the core velocity of a 2 inch pipe is 10 m/s. That says to me this design is good to go with no linearity problems above 5 hz. But if you don't agree with that please explain why. I'm not saying you are not wrong, I just don't see it from your perspective and if there's something to learn here I want to learn it. What point exactly do you think the model breaks down?

Short answer: As ports get to any sort of extreme, the Q can deviate greatly from assumptions in the model. Those extremes can be short/long, small/large, high Q/low Q alignments, etc. I suspect your cases will lower the Q a bit, which further lowers the port contribution and excursion reduction. As an example, programs like LspCAD and some others will show noticeably different driver and port behavior beyond upper resonances with say a 2" vs. 6" diameter port for the same box size and tuning frequency. The total response looks very similar, but the relative contribution changes, and that's the entire purpose of your effort. My question is what % excursion reduction are you expecting at 5, 8 & 10Hz vs. the same driver, same box size, same SPL?

Homework:

Overlay the excursion plot of a single driver in your intended box size with 500W input. One curve sealed, one curve ported as you intend.
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post #90 of 302
12/10/12 at 3:14pm
Thread Starter 
Quote:
Originally Posted by Ricci View Post

You are not listening to what we are trying to tell you. This idea has come and gone many times before.
Go back and look at the simulations I posted. There is zero as in ZERO gain anywhere above 7Hz. That is assuming the port responds in a linear fashion which it will not. We have already covered that the port will not support the airflow needed for 2-7Hz ULF at even modest levels. A 2" port simply can't. Where is your gain then if there is none above 7Hz and really none below 7Hz since the port cannot support it? Where is the advantage to this idea? Tuning to 12-15Hz will be a much better use of the drivers.

Flare It is the only trustworthy source of core velocity info that I know of, and it says 10 m/s for 2 inch pipe. My design doesn't exceed that until below 5 hz. I don't understand your argument here, the software clearly shows a passing grade for the design above 5 hz. Am I supposed to trust that your off the cuff guess about what will happen is more accurate than Flare It? I respect you and the work you do but I'm sorry, I don't trust your guesses about something you have no experience with more than software made specifically for this purpose.

Your sims don't look like there is much to gain, I'll admit that. But I haven't done the exact same comparison you have (no even sure exactly what you modeled) but I will look at your info in depth and do my own sims of the same situation. But notice in post 1 graph 2, it clearly shows excursion reduction (vs IB) benefits all the way up to 20 hz.
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