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View Full Version : A 4th order I designed



husker77
07-11-2012, 09:01 PM
for my pair of 15 ti's. Thinking about building this to put in my 91 lesabre daily driver. I know most of you are thinking "he's gotta be full of crap, no way his kid has a 86 s-10 and him a 91 lesabre, no one rolls that deep". But I assure you we have both of those fine automobiles in our fleet. The lesabre has a huge trunk, but to do this I would have to build it in 3 sections and assemble it in the trunk. The sealed sections and the ported section would all be separate, then bolted or screwed together in the trunk. I just kind of like playing around on sketchup, I'm not very good at it but like learning. I wish I could figure out how to move components you import, more practice.

I have no idea how good this box would be but I figured it would be a learning experience more than anything.

http://img822.imageshack.us/img822/1167/topview4thorderh.jpg (http://imageshack.us/photo/my-images/822/topview4thorderh.jpg/)


It is right at 1.7 ^3 on each sealed section and then right around 6.5 on the ported(kinda hard to figure with the little air diverted I put in). So a little over a 3:1 ratio. I could make the sealed a little bigger, therefore shrinking the ported section. Then I figured use 2 6" aero ports up through the rear deck of my car, should even be able to hide them in the original speaker area. I thought I would start at about 8" long, which should be right around 40 hz if I am doing anything right. I thought I could make them adjustable so I can play with the tuning.

Like I said I want to learn and the only way is to do. Any advise or criticism is welcome.

RAM_Designs
07-11-2012, 09:09 PM
It'd actually be less than a 2:1 ratio since you have 3.4ft^3 sealed and 6.5ft^3 ported.

husker77
07-11-2012, 09:18 PM
It'd actually be less than a 2:1 ratio since you have 3.4ft^3 sealed and 6.5ft^3 ported.

Math fail, wth was I thinking, long day I guess. So it isn't really going to work, since I wouldn't think going smaller on the sealed portion would be to good.

Blue Fury
07-11-2012, 09:23 PM
First thing I see- ditch those fancy braces and just put window bracing. Save yourself some time because no one will see it anyway.
Next- What design program did you use? You think 1.7cft sounds really small for a 15, then again, they're TI's.
2 6" aeros seems small.
And 40hz? For music? Yikes. You'd bee doing a hell of a lot of adjusting for it to sound good on music.

husker77
07-11-2012, 09:33 PM
First thing I see- ditch those fancy braces and just put window bracing. Save yourself some time because no one will see it anyway.

I didn't know if I would keep those or not, seeing what I could do on sketchup. I have a lot of tools, making them really wouldn't take to long. I would see them.;)


Next- What design program did you use? You think 1.7cft sounds really small for a 15, then again, they're TI's.

Not really small, just smallish. windisd and some box tuning calculator I downloaded. Just free stuff I find, it probably *****. I kinda came up with the cubic feet from some suggestions from an earlier thread.


2 6" aeros seems small.

6" is the biggest diameter I could use, but I could use more than 2, or could use a slot, like 6" by up 2 24" wide. I just thought the aeros would be easier. I just used the ported size in the calc and came up with 2 6" @ 7.5" long for 40hz.


And 40hz? For music? Yikes. You'd bee doing a hell of a lot of adjusting for it to sound good on music.

What would you suggest?

Like I said I'm learning.

Blue Fury
07-11-2012, 09:42 PM
What would you suggest?

Like I said I'm learning.

I use winISD and my hx2 6th order box was designed with it. I didn't design it, but the guy 'fallen' did an amazing job modeling it.

Tune as low as you can go but you probably wont be able to go <30hz with the amount of room you have. And do a kerfed slot port. Start a new model and see what the program suggests for that sub to take into consideration.

mazdakid
07-12-2012, 10:38 AM
I use winISD and my hx2 6th order box was designed with it. I didn't design it, but the guy 'fallen' did an amazing job modeling it.

Tune as low as you can go but you probably wont be able to go <30hz with the amount of room you have. And do a kerfed slot port. Start a new model and see what the program suggests for that sub to take into consideration.

You dont need to tune as low as you can go in a 4th order. the sealed side will take care of the lower bass. Lower 30s is pretty low for a 4th order.

husker77
07-12-2012, 04:26 PM
I like it and would like to see more.

Thanks, hopefully get some advice and start building it in a couple of weeks.


This is exactly right. Mine is tuned to 45 and its gets down into the mid 20s on tones. I mean not that you will ever really truly listen to anything in the low 20s anyway.

I want to get down to single digits! j/k


But yes, the sealed section should compensate for alot of teh low end. Also, remember the smaller the sealed side you have, the more you may lack in low end output. For 15s i have heard many theories but the majority of what ive seen is for 15"s subs try to stay in the 2cf region if possible,

Eclipse specs on the tis is small sealed, so maybe I will be okay. Maybe just have to compensate with more power.

Micksh
07-12-2012, 04:41 PM
Figure out the resonance of the subs in the sealed enclosure and tune to that....that is your most efficient way....and 30's tuning is WAY too low for a 4th order. The Astro we built is tuned at 46hz and plays well below 20hz without a problem.

husker77
07-12-2012, 04:57 PM
Figure out the resonance of the subs in the sealed enclosure and tune to that

So let me see if I understand correctly. Since I have to build this in 3 pieces, 2 sealed sections and the ported section, I could build the sealed parts first. Then I can test to see what the resonance frequency of the car is with the 2 sealed sections playing, then tune and build the ported section to match?

Micksh
07-12-2012, 05:36 PM
Correct...You build the ported section to whatever you are planning it to be, (whatever ratio you prefer) then tune it at that sealed resonant frequency. There's a good thread over on CACO about all of it (over 1000 posts) that explains it all, though there's a lot of reading to get through to find it...here's the link though... 4th orders why are some people so quiet with them? - Car Audio Classifieds (http://www.caraudioclassifieds.org/forum/general-car-audio-discussion-questions/123066-4th-orders-why-some-people-so-quiet-them.html)

husker77
07-13-2012, 03:01 PM
Okay I ran it through winISD. The teal is basically the way I have it drawn in the first post, and the peach/orange is moving some displacement from the sealed to the ported section to try and get closer to the 3:1 ratio. Both seem very peaky. By making the sealed section smaller and the ported section bigger it looks like it would play a little louder, but not quite as low. But it looks like it would probably be inaudible.

The other two are regular ported boxes with the area I have. The gray one is tuned to 34hz and the magenta to 28. They seem like they have better response curves than the 4th order. I don't know if I can go as big on a ported box because I have to have someplace to put the subs, if I fire them up they would hit the trunk lid, back and forward would also hit the trunk walls. So I would have to compensate for that somehow. I would gain some internal volume back from not having to mount the subs inside the box, or some of the walls for mounting the subs.

I read through some of that link given earlier(only on page 14 of 100 and some), but it seems my subs may not be suited all that well for a 4th order, especially with the size constraints of the box.


http://img703.imageshack.us/img703/525/winisdplots.jpg (http://imageshack.us/photo/my-images/703/winisdplots.jpg/)