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SneakoBaggin 14th January 2013 12:12 PM

Best design program
 
I saw this project and really liked it: http://www.diyaudio.com/forums/full-...-w3-881si.html

It's super simple and seems fun (not to mention cheap). I would like to challenge myself a little from a woodworking perspective though, see what I'm able to do. What would be a good program that would allow me to take that project and add a lot of complexity to the box with good modeled results still. I'd like to be able to angle the front baffle, maybe protrude it out a bit, add internal bracing, mess with port size and location.

I have vaguely read that some programs don't calculate ports very well, so that's why I'm asking.

xrk971 14th January 2013 12:40 PM

For modeling bass reflex cabinets, WinISD works well. In the case of Cogitech's nanotower, there is some accidental mass loaded transmission line (MLTL) effects happening. To model that properly, you will need to use Martin J King's Mathcad worksheets which can account for fairly complex geometries and include effects of damping using stuffing. You can also model a lot of the simpler box or horn geometries with HornResp. For really complex geometries, really, the only program is Akabak. Akabak is very powerful but takes some finesse and expertise to use and can do a lot. All except the MJK programs are free. I would play around with HornResp first if you are interested in getting started and want to do more than a bass reflex.
Good luck.

SneakoBaggin 20th January 2013 01:15 PM

So I downloaded all of those programs, and WinISD was quite easy to get the hang of, but MathCAD is much more complex and I found myself quite lost.

I wanted to make a few simple changes to the Nano-tower design to better fit my needs and design likes (that sounds weird but you get it).

Anyways I modeled up what I'm thinking for a cabinet. I did my best to make the model as similar looking to the actual cuts of wood I'd make as possible, although Maya isn't really designed for that.

Basic dimensions are - width: 4.5" - depth: 9.5" - height in front: 42" with a slope down in the rear. I'm not completely sure the amount of slope, although similar to the model. The slope is created cutting arches that are the width of the mdf, 3/4". I'll stack and glue the arches, then sand them smooth. The plan was to just leave the bottom side of them stepped. It's a bit hard to see in the pics. That's a decision MathCAD or your guys experience could help with.
And the port was moved to the front. It will be 3" not 3.5", and I was planning on just using the sides and bottom of the cabinet as 3 of the walls.

Anyways, I was hoping for some experienced thoughts and ideas before I start cutting the wood. Is the cabinet narrow enough for it to not matter or do I need some cross bracing? Will the arch on top create problems? Does the port need to be different?
If somebody is feeling super extra nice some decent guides to help me learn how to input this data into MathCAD would be great, or maybe even specific help :)

http://i91.photobucket.com/albums/k2.../Ventedbox.jpg
http://i91.photobucket.com/albums/k2...SpeakerCab.jpg

xrk971 21st January 2013 10:30 AM

Nice work on the design and in downloading all the programs. Is there a reason you have it so tall? This will make the speaker very tippy unless you put wide legs or weight the bottom. The WinISD is giving you Bass Reflex behavior only, in reality it will go much lower. If you want to try this out quickly and cheaply, make it out of foam core board first before cutting wood. You will get an idea of the sound and how deep the bass is.

SneakoBaggin 21st January 2013 10:45 AM

The reason for the height is that it puts the driver exactly at ear level in my office chair. I was planning on adding some molding to the bottom that would stick out about 1/2" all the way around and I already have spikes that i would place in that. I'd think tipping wouldn't be an issue with that on wood floors, don't plan to bump into them too much

planet10 21st January 2013 10:58 AM

That simulated response is REALLY ugly. But it is not accurate as the height + the vent at the bottom make it an ML-TL. With that much height you will be tuning the poor little driver too low. And in an ML-TL, especially of that height (given the driver), you should really be taking advantage of offset.

If you want the box that tall you'd be much better making a false bottom and fill it with sand.

I'd also use good plywood.

MatCad is vry complex, but its purpose is to run Martin's worksheets.

dave

SneakoBaggin 21st January 2013 11:22 AM

I am quite new at all of this Dave, so go easy on me. By offset you are referring to not centering the driver horizontally, in order to reduce issues with diffraction? My thoughts were that since the cabinet was so narrow, and with a good 1/2" roundover on all front edges I wouldn't have any issues with that. Or do you mean vertical offset, lowering the driver in the cabinet?

I was thinking since you say that tuning the driver that low is not good, I would reduce the depth from 9.5" to 6", which reduces the volume from .52 ft^3 (measured incorrectly above) to .29 ft^3. In keeping the same .75" x 3" port, making it 3.75" deep I get the same basic shape of the frequency response curve, but much flatter with a 2.5db rise, but no dip like above. Puts the tuning frequency at 62hz

planet10 21st January 2013 07:15 PM

Quote:

Originally Posted by SneakoBaggin (Post 3335683)
By offset you are referring to not centering the driver horizontally, in order to reduce issues with diffraction?

No. Offset the driver vertically to kill the 1st undesirable harmonic in the TL, allowing for less damping and more bottom. In a line like this typically near a 1/3 of the way down (exact placement is fairly important)

Quote:

I was thinking since you say that tuning the driver that low is not good, I would reduce the depth from 9.5" to 6", which reduces the volume from .52 ft^3 (measured incorrectly above) to .29 ft^3.
Because the aspect ratio of the cabinet is so tall, the tuning of the driver is dominated by the boxes' height. Anything you do in WinISD will not tell you what is happening, as it assummes a box that is much closer to a cube... once one dimension starts becoming significantly larger then the others the box starts transforming from a BR to a mass loaded transmission line.

Another thing to consider is that it is not really a good idea to tune a driver to less than 0.71 x the Fs = 75 Hz with this driver. Also keep an eye on excursion.

dave

planet10 21st January 2013 07:28 PM

Doing some sims, and ignoring what might be possible with a TL or horn, there is no vented enclosure that works (Qt is too high), 3 to 4 litre sealed is what i'd do. Also no matter what i do, with 1 W in, xMax is exceeded at 300 Hz.

dave

tuxedocivic 21st January 2013 07:42 PM

If you have the budget, I added a woofer from 300hz and down with this little Tang Band. Now that I've proven it with an active cross over, I was going to start working on a passive to free up my minidsp and some amp channels. But that would make the enclosure way wider. But it would also solve the issues Dave has pointed out with that little guy wanting a sealed box and a 300hz lower limit.


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