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post #91 of 302 Old 12-10-2012, 03:16 PM
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Originally Posted by diy speaker guy View Post

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?

Annnnd what we are telling you is that you will create more problems than make.


BUILD A SEALED ALIGNMENT.


Gosh.

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post #92 of 302 Old 12-10-2012, 03:17 PM
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One more point and I guess I might be wrong in even trying to offer this. I find that generally a port is utilized to help the driver in about the same way passives do. You gain a good 1/2 octave below the driver's resonance frequency and then it rockets down. The port not so much, but the port is still just as difficult to design because of size shape and so forth. I know more about passives than anyone I have spoken to because I took the time to actually "see" them in action as I was testing them, not just reading about them and spouting off. That being said, I would expect the port to be somewhat limited in the octaves of improvement that they can achieve. I hope you do not get mad, but I am only saying this because my design is like a port but with out a hole. There are limitations to all designs and it took my actual tests to show me that. I did not believe that a driver could actually excite a passive when on the outside of the cabinet, but it does. At tuning, the driver stops and as I held the passive, it swung like crazy. I would expect the port to act the same. The lower you go, the more air you move regardless of velocity. I can liken this to a 200 mph backpack plower or a 74 mile per hour hurricane. that 2 inch port blowing at 200 miles per hour is still not going to move as much air as the little 74 mph hurricane.

Is that better?

getting the velocity correct still does not account for the huge "slug" of air that has to be moved at full tilt. Mark, Josh, Scott John, Bosso and I and right on this. We may be wrong about your build working or not, but a 2 inch port is too small to work at full tilt in your sub
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post #93 of 302 Old 12-10-2012, 03:23 PM - Thread Starter
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Quote:
Originally Posted by Mark Seaton View Post

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.

Thanks Mark, I really appreciate your answers. It's refreshing in a sea of mindless dismissal with no supporting evidence. Your first two sentences make sense and are the ONLY sensible arguement provided so far. I think others might have been alluding to this but if so no one has been able actually say it.

Do you have any hard info on how extremes affect things or are you just speculating here? Like I said, oil and water pipelines are not at all the same thing but they can be thousands of miles long and not be extrmely wide diameter pipe. Is there a program that will take aspect ratio into account? I'm sure NASA or similar has something but is there anything you have that I could get?

I'll do the excercises you suggested.
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post #94 of 302 Old 12-10-2012, 03:27 PM - Thread Starter
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Originally Posted by N8DOGG View Post

I do have to know, have you ever built anything?

Forgot to answer this. Yes I build. But (like most people, I thnk) I simulate a lot more than I build. My first tapped horn was documented online in early 09 (?), by my count at the time it was one of the first 5 diy tapped horns that were built AND measured. In fact, IIRC it might have been one of the first 5 diy AND commercial models that I could find measurements for at the time, but that was long ago and I can't remember the exact details. I've built a whole pile of stuff you can pm me if you like because it's got nothing to do with this thread.

But I fully admit I have no experience whatsover with something like this proposed design. But no one else here does either.
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post #95 of 302 Old 12-10-2012, 03:30 PM - Thread Starter
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Originally Posted by Scott Simonian View Post

Annnnd what we are telling you is that you will create more problems than make.
BUILD A SEALED ALIGNMENT.
Gosh.

Yeah, but if you are convinced it won't work you should be able to use your words and explain why. Mark is the only one even attempting to do that. (LTD's contributions were useful too.)
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post #96 of 302 Old 12-10-2012, 03:32 PM
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I will build this and use test it. I have all the gear. I hope I have the skills to actually assemble it correctly so that it will function as designed. One question.

Would you mind if I just allowed the pipe to hang out of the box and not fold it inside, because you obviously know what problems that is going to open up. If you are ok with this. I will start working on it now and as soon as The drivers ship it will be done.
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post #97 of 302 Old 12-10-2012, 03:41 PM
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Originally Posted by diy speaker guy View Post

Yeah, but if you are convinced it won't work you should be able to use your words and explain why. Mark is the only one even attempting to do that. (LTD's contributions were useful too.)

A guy with the same idea as this comes by every year. I'm tired of explaining every little detail. All the important stuff you really need to know has been said already by several members.

We are genuinely trying to help you get whatever you end result is. You say you want to do some odd alignment to remove some port nasties or something? This alignment is creating MORE! Why bother with lower frequence issues when you are creating a 78hz port resonance?!? It's insane. A simple sealed alignment will be smaller by a huge amount and have none of the issues that your alignment is creating all while having the same or better response because you are not making an non-linearities that the port will absolutely create.

This isn't exactly a groundbreaking design. This conversation has been had before. It won't work, it's not worth the effort. You want crazy SPL for the cheap? I was there, man. I build BOTH my LLT's (which measure flat to about 8hz) for $1,200. I specifically designed my system to stretch the extremes of what a vented alignment was capable of doing while at the same time avoiding the bad stuff. It is simply impracticable to go any further. It's been a few years and now I want more SPL and more extension. Where else is there to go than build a proper sealed system? No where. If all you need is 10hz extension and you want to save some bucks and not have to use a bunch of amps? Build my LLT's. If you want lower extension? Go sealed.

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post #98 of 302 Old 12-10-2012, 03:55 PM
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Quote:
Originally Posted by diy speaker guy View Post

Quote:
Originally Posted by Mark Seaton View Post

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.

Thanks Mark, I really appreciate your answers. It's refreshing in a sea of mindless dismissal with no supporting evidence. Your first two sentences make sense and are the ONLY sensible arguement provided so far. I think others might have been alluding to this but if so no one has been able actually say it.

Do you have any hard info on how extremes affect things or are you just speculating here? Like I said, oil and water pipelines are not at all the same thing but they can be thousands of miles long and not be extrmely wide diameter pipe. Is there a program that will take aspect ratio into account? I'm sure NASA or similar has something but is there anything you have that I could get?

I'll do the excercises you suggested.

Varying Q related to exact geometries are separate from compression effects. Simple fact: A large diameter port that is a fraction of its diameter in length behaves rather differently at tuning than a port that is 5-20x its diameter in length. In general you will also see that real world losses mean that boxes which appear to have very high Q peaks at tuning never have peaks as high as the model.

The fact that we see a bunch of different programs showing different Q to the driver excursion minimum and port velocity points to the Q and loss assumptions I'm referring to. As with any model, the best use always comes from understanding the assumptions it was built on and variables involved. In this case we have at minimum Ql, Qa & % fill of the box to contend with, and then the effects of the end terminations which will all affect the sharpness or Q of the behavior, as well as losses.

It's not that the box won't work, it's that it is unlikely to be demonstrably/significantly better than the same driver in a sealed box of the same or bit smaller size. If you aren't leaving sine waves on for minutes at a time well below 16Hz, more power than the rating is not a problem thermally. For real listening without running hard into clip limits, it's unlikely to ever be a problem. The bigger concerns come down to real world excursion limits in a given box after suspension stiffening, BL drop and mechanical clearances are considered.

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post #99 of 302 Old 12-10-2012, 03:59 PM - Thread Starter
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Quote:
Originally Posted by Scott Simonian View Post

A guy with the same idea as this comes by every year. I'm tired of explaining every little detail. All the important stuff you really need to know has been said already by several members.
We are genuinely trying to help you get whatever you end result is. You say you want to do some odd alignment to remove some port nasties or something? This alignment is creating MORE! Why bother with lower frequence issues when you are creating a 78hz port resonance?!? It's insane. A simple sealed alignment will be smaller by a huge amount and have none of the issues that your alignment is creating all while having the same or better response because you are not making an non-linearities that the port will absolutely create.
This isn't exactly a groundbreaking design. This conversation has been had before. It won't work, it's not worth the effort. You want crazy SPL for the cheap? I was there, man. I build BOTH my LLT's (which measure flat to about 8hz) for $1,200. I specifically designed my system to stretch the extremes of what a vented alignment was capable of doing while at the same time avoiding the bad stuff. It is simply impracticable to go any further. It's been a few years and now I want more SPL and more extension. Where else is there to go than build a proper sealed system? No where. If all you need is 10hz extension and you want to save some bucks and not have to use a bunch of amps? Build my LLT's. If you want lower extension? Go sealed.

The endgame here is to understand the simulation in post 1 as fully as possible and explore it's validity. This is an intellectual excercise, as I've stated several times I'm probably not going to build this anyway but this seems like an interesting concept.

If this has been discussed every year like clockwork why hasn't anyone posted links to threads where this was discussed in detail? That may (or may not) have saved everyone a bunch of time and frustration.

The goal of the simulation is to increase xmax limited max spl down near tuning using a massively undersized port and accepting the fact that there is NO CONTENT in any recorded media low enough to cause velocity problems.

To be honest I like horns and don't really have any need for any response at all below 35 hz in my daily life, but as I mentioned in post 1 I've never been able to afford high xmax drivers before so I've never simulated them in much detail to find out what's possible. I came up with what seemed like a good idea, I felt like discussing it, I posted it. The only reason I'm even considering building it is because it might be cool, although I'd probably never use it.

So you are not "saving me from myself" here, I'm just trying to learn about the validity of simulations when pushed to an extreme like this.
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post #100 of 302 Old 12-10-2012, 04:01 PM
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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.

Quote:
Originally Posted by diy speaker guy View Post

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.

Sentence 1, 2 and 3 are all true. I am not off the cuff guessing. I don't know where you got that. Flare it is well known around these parts too. Mark gave you plenty of clues with his hints about comparing smaller systems scaled up in frequency. Your simulations at the beginning of this thread are not accurate or there is some information entered wrongly. Otherwise they bend the laws of physics and the known ways that ports work. I don't know how much more plainly it can be put. You are assuming that no one has experience with this type of design but plenty of people have experience with vented designs and there is reams of data on it. The basics of port operation are well established and will not change just because it is tuned lower than normal. You seem to be claiming that they will. If a 2 Hz tuned system is giving effective gains in performance at 20Hz at 10x tuning then one would expect performance gains from a 20Hz tuned system all the way up to 200Hz. This is not what happens. Bass reflex only gives effective gains over a limited bandwidth. By 2 octaves above tuning the port is not providing advantage anymore.

Basically you do get some reduction in excursion and increased sensitivity by using a port. No one is disputing that. However ports are only effective over a limited bandwidth of about 2 octaves. Also in order to make them effective over that range and remain linear they must have enough port area to cope with the air flow. Ports chuff easier and overload sooner the lower in frequency you go. Smaller ports overload at lower air speeds than larger ports. A 10" port will be much more linear at 25 m/s than a 4" port. If you tune to 2 Hz you can get some gain in sensitivity and reduction in excursion up to about 7-8Hz that is the extent of the bandwidth it will help with. Unfortunately a 2" port just cannot handle the air flow needed in that 2-8Hz range to realize the gains there on paper. This type of system would be much better realized in an IB install with a ton of back space so a large 8 or 10" port that will cope with the airflow can be used and a slightly higher tuning. These reasons are why you don't see builds like this. The super low tuning does not help with any of the content that truly matters and the port size and enclosure volumes needed to avoid noise and compression over the range that the port is effective are huge.

What bandwidth are you trying to realize gains from the port over? Ports only give gains over 2 octaves. 2-4 Hz is an entire octave. Tuning to 2 Hz means all of your excursion reduction and port output is below 8Hz. Is it really worth the trouble to use a tiny port for changes in performance below 8Hz where the content is of limited importance anyway? I would argue no personally. If you want solid gains in output and excursion reduction over the 10-20Hz octave I would suggest tuning in the 8-12Hz range and increase your port area as much as feasible.
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post #101 of 302 Old 12-10-2012, 04:07 PM
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10-26-10: Drew_eckhardt
A ported enclosure can be 3dB more efficient at the same size or play a quarter octave lower at the same efficiency.

The same driver excursion will net you perhaps an extra 1/3 octave of extension with a ported speaker.

You'll have higher excursion limited output in the bottom of a ported design's pass-band so you can use smaller + less expensive drivers.

Distortion will also be lower in the bottom of the speaker's pass-band with the port because of the reduced excursion.

Ported enclosure+driver combinations have four poles in their high-pass function for an eventual 24dB/octave roll-off function while sealed ones have just two for 12dB/octave. With sufficiently shallow roll-off room gain (12dB/octave in an infinitely rigid room below its fundamental resonance at 1130 / 2 / the longest dimension) can keep the speaker flat below its roll-off.

Ported enclosures do not load the driver once you get below the port tune, with excursion increasing to what it would be in free air. Where too much low frequency energy is present below the speaker's pass-band you'll have distortion (including midrange IM distortion on 2-way speakers) and may even run the drivers into their mechanical limits resulting in damage (some very nice drivers will bottom the voice coils on the back plate). For a given input level sealed speaker excursion remains constant with decreasing frequency.
Drew_eckhardt (System | Answers | This Thread)


I hope Drew does not mind me posting this here. I hope this helps.

I do not have winisd on my new computer, so I would ask if you could model the sealed version of the same enclosure and then compare the two and post them here. That might help some.
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post #102 of 302 Old 12-10-2012, 04:08 PM - Thread Starter
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Originally Posted by Ricci View Post

The basics of port operation are well established and will not change just because it is tuned lower than normal. You seem to be claiming that they will.

I know how ports work but as Mark is pointing out (I think) this may be an issue that the software does not accurately reflect. I've got no problem with that but he's the only one giving any kind of reasonable explanation. Anyway, all the simulations I posted show there is no problem with my design. If there is a problem it's not reflected in the graphs in post 1.

I'm not claiming anything other than what the simulations are showing me, you can check the graphs I posted in post 1. I also included all the user inputs so you can verify or deny that I entered somthing wrong.

All the graphs in all the softwares say the same thing so I'm not sure why you think they are all wrong.
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post #103 of 302 Old 12-10-2012, 04:12 PM - Thread Starter
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10-26-10: Drew_eckhardt

I do not have winisd on my new computer, so I would ask if you could model the sealed version of the same enclosure and then compare the two and post them here. That might help some.

Ricci already posted this data a few posts back, but like I said, I'm going to go over his data, make my own, and I'll post it as well if you like.
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post #104 of 302 Old 12-10-2012, 04:18 PM
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Sorry, I did not read Josh's post. I kind of know his thoughts on this,hence the redundancy.
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post #105 of 302 Old 12-10-2012, 04:21 PM - Thread Starter
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Quote:
Originally Posted by Mark Seaton View Post

Varying Q related to exact geometries are separate from compression effects. Simple fact: A large diameter port that is a fraction of its diameter in length behaves rather differently at tuning than a port that is 5-20x its diameter in length. In general you will also see that real world losses mean that boxes which appear to have very high Q peaks at tuning never have peaks as high as the model.
Ok, but in your first post of this thread you said compression was the problem. I already mentioned q and losses way back on page 1 or 2 when I explained the WinISD velocity spike at 75 hz made me nervous but was likely not real. So what is the exact problem here? Q, compression, velocity? Where exactly does the model break down?
Quote:
The fact that we see a bunch of different programs showing different Q to the driver excursion minimum and port velocity points to the Q and loss assumptions I'm referring to. As with any model, the best use always comes from understanding the assumptions it was built on and variables involved. In this case we have at minimum Ql, Qa & % fill of the box to contend with, and then the effects of the end terminations which will all affect the sharpness or Q of the behavior, as well as losses.
It's not that the box won't work, it's that it is unlikely to be demonstrably/significantly better than the same driver in a sealed box of the same or bit smaller size. If you aren't leaving sine waves on for minutes at a time well below 16Hz, more power than the rating is not a problem thermally. For real listening without running hard into clip limits, it's unlikely to ever be a problem. The bigger concerns come down to real world excursion limits in a given box after suspension stiffening, BL drop and mechanical clearances are considered.

Thanks. In your first post, you mentioned that if I use a program that could simulate compression I would see this design can't handle more than 250 watts or so. Which program do you recommend?
Quote:
I'm pretty certain that real world testing and any program which simulates port compression will show that this situations only exists at very low power.
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post #106 of 302 Old 12-10-2012, 04:43 PM - Thread Starter
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... ports are only effective over a limited bandwidth of about 2 octaves.

I'm trying not to dispute every single thing point by point but finding it difficult to resist...

WinISD (with port resonances turned off) might agree with you but that's a very simple model.



That's just a random model I pulled up, first graph is summed response, second graph is port vs driver contribution that makes up the summed response in graph 1. This port response should be remarkably accurate if you do an accurate port near field measurement. Ports are not restricted to a single massive spike. They have a big influence way up high. In fact that's exactly why they visually contribute to spikes up high in frequency way above the port tuning. I don't know what software you use (I assume WinISD with port resonances turned off) but it doesn't seem to accurately reflect reality.

I've seen at least a couple of examples of people doing a near field port measurement and being completely confused about what they see. Then I model it for them with 1/4 wave software and it's clear to see why the port has significant output way above where WinISD says it should.

Hornresp and Akabak will also show the same thing as shown in this pic. WinISD with port resonances turned off will not, it shows a single spike with much higher q. This 1/4 wave model simulation software shows the generally accepted way that ports work and it's pretty easy to measure if you don't believe it. Just be very careful to only capture the port output.


(blue dotted line in graph 1 is IB response, just disregard that.)
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post #107 of 302 Old 12-10-2012, 04:52 PM
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I haven't used winisd in a looooong time until today. I'm basing that 2 octave effective from measurements. I don't consider the resonances or less than 1dB as effective FWTW.
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post #109 of 302 Old 12-10-2012, 05:03 PM - Thread Starter
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If you like I can attempt to find the threads where people measured their port output, which I then simulated and showed a remarkable similarity. (They all look just like the same thing as the pic I just posted.) I don't know what you measured but from what I've seen MJK's software is incredibly accurate. Not perfect but way better than you could reasonably expect a simple simulation to be.

I don't mean to be nitpicky but port output in my design visually helps up to 10 hz at least in my simulations with accurate software, that's why I posted.
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post #110 of 302 Old 12-10-2012, 05:15 PM
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700 liters with a 2x90inch port mounted external to box. Is that correct? Does the port have to be on the same face as the driver. so it could be wrapped around the box and come out in the same direction as the woofer. Hey, I will get NEO Dan to sketch this for me so that I have something to actually go by that you agree on. If you can do sketchup, then I will follow your plans. As you wish, I will build. I hope you find my building skills up to the task.

Thanks,

Robert
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post #111 of 302 Old 12-10-2012, 05:24 PM - Thread Starter
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700 liters with a 2x90inch port mounted external to box. Is that correct? Does the port have to be on the same face as the driver. so it could be wrapped around the box and come out in the same direction as the woofer. Hey, I will get NEO Dan to sketch this for me so that I have something to actually go by that you agree on. If you can do sketchup, then I will follow your plans. As you wish, I will build. I hope you find my building skills up to the task.
Thanks,
Robert

It's been mentioned that this can be tested on a scale model, I wouldn't bother doing a full scale if there is any doubt that this will work. (I still think it will do exactly as the simulations in post 1 show but I'm willing to admit I could be wrong. Mark has me half convinced that I'm missing something but I'm waiting for him to provide a link to software that will back up what he said in his first post - he said there is software that will prove me wrong but hasn't stated what software).

Anyway, the design details are not important, just tune to 2 hz and see what happens. Or else do a scaled model and see what happens. Just make sure you model what you build accurately.

But the problem is that you need some pretty decent measuring equipment to set this up properly to match the simulation assumptions and measure accurately unless all you want is subjective impressions, and I don't know of any way to test port velocity so the results aren't going to mean much anyway. (Unless you happen to notice massive chuffing even at 10 hz at the specified power input, which would obviously prove me fantastically wrong about all of this.)
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Ever since my dad bought a car when I was a kid I remember something he told the saleman. The salesman told him that the car he was showing him had a V6 and my dad said he wanted a V8. The salesman replied" It acts like a V8. To that, my old man says "I don't want something that acts like a V8, I want a V8. Needless to say, he bought a Crown Vic in short order.

So, I will build the exact thing and let it rip.
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post #113 of 302 Old 12-10-2012, 05:37 PM
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Well, I do not even think I will get to the need for the measuring equipment beyond what I have. I think the port will be a non issue and I will see a nice rolloff as in a sealed alignment. Just my thoughts, but I am probably wrong. But, if I do build it and just use the woofer tester on it. The tuning should be really low at least as low as my mic goes? I can easily get a nice microphone shipped to me for little and reduce that problem.
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I have aBryston amplifier that is just laying around. I think it can reach fairly deep in the spectrum. Will that help?
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post #115 of 302 Old 12-10-2012, 05:41 PM
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It's been mentioned that this can be tested on a scale model, I wouldn't bother doing a full scale if there is any doubt that this will work. (I still think it will do exactly as the simulations in post 1 show but I'm willing to admit I could be wrong. Mark has me half convinced that I'm missing something but I'm waiting for him to provide a link to software that will back up what he said in his first post - he said there is software that will prove me wrong but hasn't stated what software).
Anyway, the design details are not important, just tune to 2 hz and see what happens. Or else do a scaled model and see what happens. Just make sure you model what you build accurately.
But the problem is that you need some pretty decent measuring equipment to set this up properly to match the simulation assumptions and measure accurately unless all you want is subjective impressions, and I don't know of any way to test port velocity so the results aren't going to mean much anyway. (Unless you happen to notice massive chuffing even at 10 hz at the specified power input, which would obviously prove me fantastically wrong about all of this.)

Wow. I just read this through and I think you are second quessing yourself or again insulting me and my stuff. I offer to pay and build this thing and you again insult me. Do all the other guys see this or am I just reading this wrong?
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Wow. I just read this through and I think you are second quessing yourself or again insulting me and my stuff. I offer to pay and build this thing and you again insult me. Do all the other guys see this or am I just reading this wrong?

Not at all. The problem is that I couldn't do this myself, I'm not sure how you can. I don't think even Ricci can test velocity.

I don't have a mic that will go that low. I don't have a source that will go that low. I don't have any amps that will go that low. Aside from the ashley amp that's been mentioned I don't know of any equipment that can run or measure this down to tuning (which I might mention was the whole point of the design in the first place - it's tuned so low that the supporting equipment is not able to pass any signal in the frequency band that is problematic.) Maybe from 5 hz and up if you have really pricey equipment and mics but you probably won't get any usable and accurate results below that. So good luck with that, I wouldn't even want to try to set up and measure this accurately. You can get subjective impressions pretty easily but accurate measured info that you can share with confidence is another thing.

Anyway, I'm not second guessing myself either, from the beginning I was willing to admit that I could be wrong but I have not yet been convinced. Mark is doing a good job but hasn't proven his point yet, IMO. I wouldn't push it, but he specifically said there is software that will prove me wrong, I've asked for it several times and I'm content to wait as long as it takes to get that link. Until then all I know for sure is that all the software I have access to says the same thing and I've reported nothing besides what the software says.
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post #117 of 302 Old 12-10-2012, 05:53 PM
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I apparently need this written in crayon for me, but why tune so low, effectively eliminating any useful gain from the port? As previously stated by me, the large SLLT designs looked to be effective at boosting the <10hz content, but were tuned more than an octave higher than what you want to do, and used a port large enough to not be problematic. So instead of tuning low enough to push port problems into some mystical realm of 1hz, why not just eliminate those problems?

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post #118 of 302 Old 12-10-2012, 06:02 PM - Thread Starter
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I apparently need this written in crayon for me, but why tune so low, effectively eliminating any useful gain from the port?

Please reread post 1, especially the simulations. This design does not effectively eliminate any useful gain from the port. It wastes a lot down low, but above 3 hz or so and up until 10 hz the port is contributing significantly.

This is all part of the design. If it wasn't tuned so low (and much of the port output wasted) there is no way you could ever get by with such an incredibly small port. But just because part of the port output is wasted doesn't mean it doesn't contribute significantly above that.

This design is designed specifically to chuff like crazy (that's what happen when you use a small port) - but only below 3 hz, and since there is no output down there you can completely disregard the graphs below 3 hz. What you are left with is significant port contribution above 3 hz up to about 10 hz.

I've explained this completely in post 1 and probably a dozen times since. I'm not sure where the confusion is. Do you have any specific questions?
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I do not think that will be an issue. What I think is that as that slug of air is moving into the chamber, it will compress and resist. For the frequencies to eminate, the air has to exit the cabinet. If the volume cannot get out and I do believe a large volume of air will move at the tuning, The cabinet will just act like a sealed cabinet with a leak. I was asking you to model the system as a sealed in order to see what the Fb would be and the F3. Those are around where I think this system would measure. I do not believe this driver in a huge ssealed box can take the power you are going to give it. I think it will fail. I have seen drivers of greater lineage turned to scrap under less demanding situations. 1000 watts to the coil may be fine, but the mechanical limits on this, what may turn out to be an essentially sealed box, may be too much. Easy to find out by powering it up. I do not need measuring equipment to watch the following trailer turn a driver inside out.





http://www.thx.com/consumer/movies/7458473

I have seen it done and it is not pretty. So, if this system will work, it will work one way or the other and should handle anything I throw at it. At least that is what the model says. If I pump Bass I love You through this, it should not hesitate to perform at 1000 watts of input. Afterall, Bass I love You only goes down to about 8 Hertz- More than 1/2 octave over your 5 Hertz guarantee where the port will do most of the work.

I think that the system will see a final tune of a large sealed box and the driver will unload down in the single digits. Just my thoughts.
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post #120 of 302 Old 12-10-2012, 06:15 PM - Thread Starter
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I do not think that will be an issue. What I think is that as that slug of air is moving into the chamber, it will compress and resist. For the frequencies to eminate, the air has to exit the cabinet. If the volume cannot get out and I do believe a large volume of air will move at the tuning,

This is what the software is for, it simulates all these things for us.
Quote:
The cabinet will just act like a sealed cabinet with a leak. I was asking you to model the system as a sealed in order to see what the Fb would be and the F3. Those are around where I think this system would measure. I do not believe this driver in a huge ssealed box can take the power you are going to give it. I think it will fail. I have seen drivers of greater lineage turned to scrap under less demanding situations. 1000 watts to the coil may be fine, but the mechanical limits on this, what may turn out to be an essentially sealed box, may be too much. Easy to find out by powering it up. I do not need measuring equipment to watch the following trailer turn a driver inside out.
http://www.thx.com/consumer/movies/7458473
I have seen it done and it is not pretty. So, if this system will work, it will work one way or the other and should handle anything I throw at it. At least that is what the model says. If I pump Bass I love You through this, it should not hesitate to perform at 1000 watts of input. Afterall, Bass I love You only goes down to about 8 Hertz- More than 1/2 octave over your 5 Hertz guarantee where the port will do most of the work.
I think that the system will see a final tune of a large sealed box and the driver will unload down in the single digits. Just my thoughts.

If you already know what's going to happen what's the point in building and measuring? Your predictions do not match any of the software currently available.

Anyway, as I mentioned earlier, MJK's software simulates RMS deflection so I simulated with probably too much power, as WinISD shows well past xmax at that point. I can adjust to actual xmax if you like but haven't bothered to correct that yet since it's not really important to the conversation and no one that has done their own sims has mentioned it. But yes, my prediction is that you can play Bass I Love You at somewhere approaching 1000 watts with no problems from the port.

I'm going to do the simulations you suggested but you guys are keeping me pretty busy here trying to reply to everyone.
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