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Old 8th January 2013, 07:28 AM   #11
GM is offline GM  United States
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An inverse tapered TL is best for a low Qt driver where its specs dictate a very long vent to get a low vent mach, so try simming an expanding, mass loaded [vented] one similar to MJK's original ML-TQWT if you want a low tuning, otherwise a simple [straight] TL tuned to Fs/Qts to get a maximally flat impedance alignment.

GM
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Old 8th January 2013, 01:17 PM   #12
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@GM: I can't figure out how to simulate any TL designs right now. I'm using a free software stack (GPL free, not no cost), and have no idea how to use MJK's sheets. Any suggestions?
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Old 8th January 2013, 02:41 PM   #13
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No clue what you're referring to, but you can download MathCad's demo 8 freeware on MJK's site to run his software, you just can't save the results except by copy/pasting into WORD or similar AFAIK, but I'm mostly computer illiterate, so might want to ask about other options on his forum.

WRT using his software, it's beyond simple for basic simming as all you need to do is input the driver specs and the cab's various dimensions by highlighting each one and typing in the new. He also has a tutorial: http://www.quarter-wave.com/Back_Doo...al_7_03_09.pdf

Even easier is using Hornresp's Loudspeaker Wizard to 'slide' your way to a design that looks promising, then inputting the results into MJK's to see how damping will affect its response.

GM
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Old 8th January 2013, 04:12 PM   #14
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Originally Posted by justinzane View Post
As far as the driver goes, it is a cheap driver for a first attempt and was picked based on a number of "models" as the most likely to be useful. I do very much like your suggestion, though. I just might get one for the next project.
This kinda sounds like you already have the driver. Do you?

Here's some graphs. The Goldwood driver is in 3 cubic metres volume, sealed. The MCM woofer is in 30L ported tuned to 28Hz, with a small amount of series resistance to raise Qts to ~0.3.

The -3dB point is similar, but the Goldwood (even in the massive enclosure) has a peaky output due to the >0.7 Qts.

With adequate power, the MCM woofer will do >6dB more SPL than the Goldwood, with a flatter frequency response, in a cabinet 1/100th the size.

Given cabinets the same size, the Goldwood will stand more power to hit Xmax, but, as you can see, its no use as a subwoofer.


I could fire up Hornresp and simulate something more exotic, but I suspect the outcome will be similar.

Chris
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Old 8th January 2013, 04:52 PM   #15
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@GM: I do not use proprietary software, by choice. I value freedom greatly, and, for the same reason I love this forum -- the free exchange of ideas and opinions between interested people -- I use free software. The link in my signature gives a good explanation of what this means. The other link in my sig is to a discussion here about creating truly free acoustics tools.

Since I almost exclusively use free software, Flash Player and nVidia's binary driver to watch Hulu with my wife being the only exceptions, I do not have any Windows licenses nor is it worth it, to me, to purchase or pirate a copy simply for speaker design tools that are also closed source.

I hope I did not sound critical of you, as I am not. I just wanted to let you know, in more detail, why I can't use MJK's stuff as is. I'd really love it if someone could show me how to port MathCAD to something open.
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Old 8th January 2013, 05:08 PM   #16
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@chris661: I've put the driver you suggested into gspeakers and got similar results. I'm pretty sure I'll order one soon. For now, I'll experiment with the GW-212-4 and see what box and role it sounds best in. One of the reasons that I picked it was because it was cheap enough that I'll have no regrets even if it thoroughly sucks. After all, it cost about as much as 3 "indestructible" chew toys that our little pit-mix destroys in a day.

I really appreciate the thoughtful advice and guidance!
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Old 8th January 2013, 05:59 PM   #17
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Originally Posted by justinzane View Post
@GM: I do not use proprietary software, by choice. I value freedom greatly.........I do not have any Windows licenses nor is it worth it, to me, to purchase or pirate a copy simply for speaker design tools that are also closed source.

I hope I did not sound critical of you, as I am not. I just wanted to let you know, in more detail, why I can't use MJK's stuff as is. I'd really love it if someone could show me how to port MathCAD to something open.
I value freedom also, but it's my understanding that the MC demo is in effect very old freeware, so are you saying it's not?

Anyway, if I'm understanding you, seems like you could find out from MC's owner how to port it plus would have to buy a relatively expensive licensed copy, otherwise you would be pirating MC. In my ignorance of such things, your repeated request to get help for this is how it seems to me.

Specific to MJK's software, his underlying math is proprietary and not available at all AFAIK, though of course that hasn't stopped some folks from trying to hack it.

WRT Hornresp, IIRC it can be run in a Widoze emulator for mac owners, so does this help?

What about these early DOS programs? Bullock and White's Home Page

GM
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Old 8th January 2013, 06:46 PM   #18
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Originally Posted by justinzane View Post
@chris661: I've put the driver you suggested into gspeakers and got similar results. I'm pretty sure I'll order one soon. For now, I'll experiment with the GW-212-4 and see what box and role it sounds best in. One of the reasons that I picked it was because it was cheap enough that I'll have no regrets even if it thoroughly sucks. After all, it cost about as much as 3 "indestructible" chew toys that our little pit-mix destroys in a day.

I really appreciate the thoughtful advice and guidance!
You're welcome.

Give the Goldwood a try in a really simple H-frame (or U-frame) dipole system.
It won't go very loud, but the dipole cancellation will flatten out the peaky response, which might give you something usable.

Take lots of pictures whatever you build - they're always appreciated.

Chris
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Old 8th January 2013, 08:37 PM   #19
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Quote:
Originally Posted by GM View Post
I value freedom also, but it's my understanding that the MC demo is in effect very old freeware, so are you saying it's not?
...
WRT Hornresp, IIRC it can be run in a Widoze emulator for mac owners, so does this help? What about these early DOS programs? Bullock and White's Home Page
It is free only with respect to price. Free software is something different. Please read the first link in my signature to get a better description that I could write.

Quote:
Originally Posted by GM View Post
Anyway, if I'm understanding you, seems like you could find out from MC's owner how to port it plus would have to buy a relatively expensive licensed copy, otherwise you would be pirating MC. In my ignorance of such things, your repeated request to get help for this is how it seems to me.
I have no interest in MathCAD. There are numerous very capable math and engineering programs that are free and open. What I am hoping for is that someone who is more familiar with these types of simulation than I am can suggest which one to use and perhaps how to do so with respect to this specific problem set.

Quote:
Originally Posted by GM View Post
Specific to MJK's software, his underlying math is proprietary and not available at all AFAIK, though of course that hasn't stopped some folks from trying to hack it.
His math cannot be proprietary, at least in the USA:
Quote:
From Wikipedia: Gottschalk v. BensonThe invention in this case was a method of programming a general-purpose digital computer using an algorithm to convert binary-coded decimal numbers into pure binary numbers. The Supreme Court noted that phenomena of nature, mental processes and abstract intellectual concepts were not patentable, since they were the basic tools of scientific and technological work. However, new and useful inventions derived from such discoveries are patentable. The Court found that the discovery in Benson was unpatentable since the invention, an algorithm, was no more than abstract mathematics. Despite this holding, the Court emphasized that its decision did not preclude computer software from being patented, but rather precluded the patentability of software where the only useful characteristic was an algorithm. The Court further noted that validating this type of patent would foreclose all future use of the algorithm in question.
That being the case, it is perfectly appropriate to ask for help in applying the algorithms that he has developed and published. What M. J. King can patent are his designs that he has developed using those algorithms. He can copyright software that implements the algorithms, but he cannot copyright formulas and equations.
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Old 8th January 2013, 09:52 PM   #20
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You can do pretty well with the DIY Panasonic capsule mic. See Linkwitz for details. Most of use have a Behringer calibrated mic. Pretty cheap.

There were a lot of TL papers in Speaker Builder in the old days.

I fully applaud designing away from the box, however the engineer side of me reminds me that a box works pretty darn well. Most of my speakers are painted, none of them black or white. My main subs look like Chinese chests.

Speakers are simple? Ah Grasshopper, soon you shall have the truth laid before you. In time you will find we don't actually know what to measure and the kind of repeatability you may be accustomed to is just not possible. Even the moment to moment changes in air pressure exceed basic test equipment. Mode, measure, think, then realize why we all do final voicing by ear. The TL is almost as miss-understood as the horn. Simple in concept, very complex in execution. You'll see.
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