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sub box math, am i doing it right?


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ncc74656 
Copper - Posts: 71
Copper spacespace
Joined: April 27, 2011
Posted: February 21, 2013 at 6:33 PM / IP Logged  
i want to build a new box to give me more frequency on the lower end with out sacraficing much on the high end and to add more volume. i run a ZX1500.1 now and plan to upgrade to a 2500.1 with the new box.
vehicle: 2500 dodge ram, quad cab.
sub: Fi BL 18"
current box: https://imgur.com/jsn9ChP,kOPnk4V
looks like this: http://www.cumminsforum.com/forum/attachments/98-5-02-non-powertrain/55589d1360778641-stereo-installs-uploadfromtaptalk1360778640211.jpg
my idea for a new box: https://imgur.com/HTTQEGy
looks like this: https://i.imgur.com/mwytek3l.jpg
does this math look correct?
does it matter if i have a slanted side to my box? i read that any angles are a bad thing for sub boxes.
should i leave the bottom of the port open like that or should i baffle it with a bottom at the same distance as the port hight?
soundnsecurity 
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Location: Louisiana, United States
Posted: February 21, 2013 at 7:20 PM / IP Logged  
your pictures dont work
ncc74656 
Copper - Posts: 71
Copper spacespace
Joined: April 27, 2011
Posted: February 22, 2013 at 9:01 AM / IP Logged  
i just tried them and they do work. for what ever reason it did not allow a URL in the post so you need to copy and past them into the URL bar.
ncc74656 
Copper - Posts: 71
Copper spacespace
Joined: April 27, 2011
Posted: February 22, 2013 at 9:07 AM / IP Logged  
new box math
new box looks like this
current box math
current box picture
i tried to edit my last reply but it wouldn't let me. so ive asked this question on a couple forums now and i have zero replies. am i not asking it right or doing something wrong that no one wants to point out?
DYohn 
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Joined: April 22, 2003
Location: Arizona, United States
Posted: February 22, 2013 at 9:42 AM / IP Logged  
Please read the forum rules for information on why you cannot yet edit your posts. If you want help with math it might be better if you just type out what you're doing rather than try to post pictures that may or may not tell us anything useful., Thanks!
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ncc74656 
Copper - Posts: 71
Copper spacespace
Joined: April 27, 2011
Posted: February 22, 2013 at 9:47 AM / IP Logged  
the pictures contain all the dimensions and information from torres tuning calc. this is why i am posting pictures as it is much easier to read a well laid out form than my chicken scratch. the basic numbers however would be:
tuning of 36.16hz, 29" high, 34" wide, 22.5" deep. port: 3.8" high, 32.5" wide, 21" long. the box has 1 extra baffel, .75" MDF, and a net volume of 7.93 cubic feet
DYohn 
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Joined: April 22, 2003
Location: Arizona, United States
Posted: February 22, 2013 at 10:04 AM / IP Logged  
And what do you want to know? If that is correct?
Subwoofer enclosure calculators
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ncc74656 
Copper - Posts: 71
Copper spacespace
Joined: April 27, 2011
Posted: February 22, 2013 at 10:30 AM / IP Logged  
my port extends straight into the box with a fair amount of space from its end to the bottom of hte box. should there be any kind of baffling at the end or is it allright for the port to be build in this way? for a 2500W sub is .75" MDF adequate for the job or should i double it up on more than just the front?
is it true that angles in sub boxes are bad for acoustic? such as an angled side?
would that foam padding be required at all? i believe its meant to increase the size of the box so id think it is not needed but maybe i dont understand it correctly.
should the corners inside the box be rounded off? with quarter round or with fiber glass?
my current box is much smaller (cubic foot wise) than my new one. my understanding is that the larger the box the more frequencies it will be able to obtain on the lower end. i do not want to loose all my high frequencies that i have now. is this correct?
i read that one should not use screws on these boxes but rather glue and braid nails, is that correct?
i tried to use winISD but its numbers are so far off from my subs spec sheet and nothing seems to add up so that program is a total loss for me.
also im looking for any input on questions that perhaps i have not asked and should as well as any tips for a first time sub box builder.
thanks
DYohn 
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Joined: April 22, 2003
Location: Arizona, United States
Posted: February 22, 2013 at 1:45 PM / IP Logged  
my port extends straight into the box with a fair amount of space from its end to the bottom of hte box. should there be any kind of baffling at the end or is it allright for the port to be build in this way? for a 2500W sub is .75" MDF adequate for the job or should i double it up on more than just the front?
A port does not require any sort of baffling, and 3/4" MDF is fine. Doubling the front baffle is a good design choice as it helps support the woofer.
is it true that angles in sub boxes are bad for acoustic? such as an angled side?
No, it is not true. Subwoofer enclosures can be any shape.
would that foam padding be required at all? i believe its meant to increase the size of the box so id think it is not needed but maybe i dont understand it correctly.
Foam padding? If you mean acoustic foam, it is never a bad idea to line your enclosure with it as it helps deaden the baffles and prevent vibration.
should the corners inside the box be rounded off? with quarter round or with fiber glass?
Not necessary.
my current box is much smaller (cubic foot wise) than my new one. my understanding is that the larger the box the more frequencies it will be able to obtain on the lower end. i do not want to loose all my high frequencies that i have now. is this correct?
This is not correct. A larger enclosure will generally have a lower system resonance and be less subject to "boom." But the woofer will reproduce the same frequency range.
i read that one should not use screws on these boxes but rather glue and braid nails, is that correct?
No. In fact, I normally glue and screw. Just be sure you drill pilot holes for your screws so you don't split the MDF.
i tried to use winISD but its numbers are so far off from my subs spec sheet and nothing seems to add up so that program is a total loss for me.
WinISD is a completely accurate program and is one of the best design tools you can use, but it is only as good as the information you give it. If you don't have complete T/S specs for your woofer it will not be able to give you good results.
also im looking for any input on questions that perhaps i have not asked and should as well as any tips for a first time sub box builder.
If you are a first time builder I highly recommend keeping it simple. Build a sealed enclosure first and work your way up to a slot port design, as sizing is much more critical in a vented system. Also, how did you come up with the dimensions you list above? For what woofer?
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ncc74656 
Copper - Posts: 71
Copper spacespace
Joined: April 27, 2011
Posted: February 22, 2013 at 3:41 PM / IP Logged  
the sub is a fi bl 18. I tried putting all the values on the Fi website, this lead to a very large discrepancy in what fi says the subs spesifications are and what the program said the specifications are. In the end the program gave me complete jump results. Never showing any frequency curve about negative 2 decibel. I do not have the option to build a sealed enclosure as the subs for ported only. My goal in this is to get a greater frequency response on the low end. Currently it has a great deal of volume on high end which I like. I intend to put an additional 1000 watts into this sub to help with the reduced SPL from the lower tune.   You mentioned that a larger box reduces the boom, do you mean that it lowers the overall volume?
In the end this sub is going to go from 1500 watt RMS to 2500 watt RMS with the new amp.
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