Printer Friendly Forum Posts - sub box math, am i doing it right?

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: https://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?

your pictures dont work

-------------

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.

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?

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!

-------------
Support the12volt.com

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

And what do you want to know? If that is correct?
Subwoofer enclosure calculators

-------------
Support the12volt.com

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?

-------------
Support the12volt.com

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.

my goal is to gain more low end frequency as right now I can kinda hear it but not at any volume. its like its empty sound if that makes since. secondly I'd like to be able to see my sub as right now it fires into the seat. I want this sub to blow my tool boxes around., just crazy amounts of bass to the SPL side of things with out loosing to much quality. this is why I bought a BL as opposed to a Q. I am open to installing 2 18 BL's so long as it takes up no more than 1/2 of the back seat for storage.

Another question, I am thinking of removing the backseat of the truck and installing quarter inch plate to set the speaker on top of. Will this aid in the transfer of bass or does it not matter? 1 advantage of this either way is that it will give me about another 4 inches back and three inches down to install a larger box.

I ran your sub in WinISD and in 7.9 cuft vented at 31Hz you get a peak at 69Hz and the F3 is at 38Hz. The woofer has an Fs at 33Hz so it's never going to produce a lot of SPL at the lowest frequencies, it is more designed as a high SPL sub and works best between 70 and 100Hz. The Fi web site says it is rated for 1500 watts so I really can't recommend using more than that. By the way, to get good numbers in WinISD, try setting the power input at 500 watts or less.

If you really want high output in the first octave of 20-40Hz, you'll likely need a different woofer. But the Fi is a really well-made machine and will give you great output in the most musical subwoofer range.

-------------
Support the12volt.com

i was having such a hard time getting the specs into win isd, how did you end up getting yours to work? maybe i was trying to adhear to the fi's website specs to much? *shrug*

here is what i came up with for a box, its port length is 18.5" at 7.92 cubic ft, tuned to 36.46. people seem to think that fi can take much more than 1500 so im going to upgrade to a 2500W amp and take it up untill i find its max and pull it back a bit, we shall see. when i ordered teh sub i got all the cooling and spider extras.

the sub port would be pretty much at ear level, is that an issue? i am building this box as squar as i can get it so i can just rotate it to try different angles, top, bottom, front, and rear firing.

modle of new box idea posted_image

larger image, i accidently pasted in the small one... i gotta read these rules and figure out why i cant edit at some point >.<
large picture

Port at ear level? The port sound might dominate and you'll perceive the system much more like a one-note bandpass. I'd mount it with the port on the bottom. Also, with an enclosure that large I hope you have good bracing plans?

-------------
Support the12volt.com

my thoughts were some angled pieces of .75 on the edges and such. ive read some people place cross members across from wide to side and build a basket to hold the sub magnet. do you think that is necessary for this one?

BRACE IT!!! Yes, ANY flex in the cabinet wall translates to output loss. The less flex you have, the more accurate your response will be, AND you'll get more output. You're thinking that "It's a vented cabinet, the walls can't flex as much as a sealed cabinet..." You're dead wrong there! The internal pressure gradients inside a vented cabinet can be as much as TWO TO FOUR TIMES AS MUCH as a sealed cabinet! A vented cabinet relies FAR more on proper bracing than does an equivalently aligned sealed box... Additionally, EVERY box calculator assumes a theoretical "lossless" wall. If you have vibrations, you have loss.

If you're wondering what Dave considers the right amount of bracing is, check this out... You cannot overbrace a cabinet. Period.

-------------
It all reminds me of something that Molière once said to Guy de Maupassant at a café in Vienna: "That's nice. You should write it down."

ncc74656 wrote:

my thoughts were some angled pieces of .75 on the edges and such. ive read some people place cross members across from wide to side and build a basket to hold the sub magnet. do you think that is necessary for this one?

Oh yes, it is more than necessary, Please see Mr. Haemphyst's post above. :)

-------------
Support the12volt.com

so if i add much more bracing than i had intended i will need to increase the box size to make up for the loss in cubic feet. from there i could also use double walled thickness so id have 1.5" on all sides. that sound good?

doubling the thickness of the box all around is nice to have but you would be better served by running strong pieces of wood between opposite walls to keep them from flexing. a double wall can still flex although it is very hard to make them flex.

as far as my experience goes with big woofers and low tuning, bigger is usually better, this includes the port too. big slot port allows for the huge air flow you typically see in any "hair trick" video. the problem with big ports is that they need to be huge and long to keep a low tuning which in turn takes up valuable airspace and requires a much bigger box.

it will help your port to round the edges to have slightly better air flow but over all not necessary inside the box.

-------------

k, well i plan to start building this box some time this coming week. im picking up a new amp for my mids/highs tonight so with luck the sub wont over power everything...

i was thinking of using a sealed sub in my truck tomororw to find the optimal HZ that my cab resonates at and then tuning my sub box to that frequency. does that make since? is it worth doing?

na, if you want to measure the resonance of your cabin then you need to use a source with a known response so that you have something to compare it to. the sub woofer and box will have its own resonance peaks and you need to know which peaks came from which source.

-------------

ok, here it is. a fully built and reenforced box as i intend to build it. only missing routered edges and fiber glass in the cornors. what do we think of this guy? is it ready to build?

album of design

ncc74656 wrote:

ok, here it is. a fully built and reenforced box as i intend to build it. only missing routered edges and fiber glass in the cornors. what do we think of this guy? is it ready to build?

album of design

Dead link... No workie...

-------------
It all reminds me of something that Molière once said to Guy de Maupassant at a café in Vienna: "That's nice. You should write it down."

i just clicked it and it worked fine for me. ill post it again here:
https://imgur.com//a/Qgmbk#0
https://imgur.com//a/Qgmbk#0

That bracing is certainly better than none at all, but seriously... BRACE IT! Did you see the way I brace a 10" driver?!? You're using a MUCH larger driver, and a vented enclosure to boot! More bracing. Seriously. More.

-------------
It all reminds me of something that Molière once said to Guy de Maupassant at a café in Vienna: "That's nice. You should write it down."

I have no idea why your copy/paste process is adding additional slashes, but it is... Here's what he's trying to show...

::::EDIT::::
Never mind... the servers are filtering the address... Copy and paste this:

https://imgur.com/a/Qgmbk#0

-------------
It all reminds me of something that Molière once said to Guy de Maupassant at a café in Vienna: "That's nice. You should write it down."

Here are a few examples of bracing, most of it proper. Linky And as you scroll down, you'll see a few examples of very poor bracing, especially the carpet-covered pre-fab enclosures with none at all. Those are certain to disappoint.

-------------
Support the12volt.com

ok, so is the dynamics of air flow over the bracing an issue? it looks like nearly half of the space in the box is taken up by "bracing" what if i used steel mounted to the sides of the box instead of wood. i would need less of it to obtain the same rigidity right?

im just worried that ill have to double the size of the box seeing as id be taking up what seems to be close to 35% of its volume by wood. at that rate id be at 5.2 cubic feet instead of 8...

At the frequencies you'll be running, no. Air flow will be no issue at all. As far as using steel vs. wood? Ummm... Never tried that, but I can't say it wouldn't work. All you are really looking for is rigidity. Honestly, though...? I'm betting you'll see that if you use a space-frame like the pics are all showing, you'll be displacing FAR less than you think.

-------------
It all reminds me of something that Molière once said to Guy de Maupassant at a café in Vienna: "That's nice. You should write it down."

check out one of my threads that was discussed a while ago. you should find some good information about bracing boxes and over all design of a ported box.LINK

-------------

I forgot about that thread. That was a good discussion and something the OP should read through.

-------------
Support the12volt.com

im designing a new box tonight and ill post it once im finished. i cant get over what a difference putting a higher powered amp on my mids/highs has made for my sub. the new amp is only 11 times more powerfull than the old one.

ncc74656 wrote:

i cant get over what a difference putting a higher powered amp on my mids/highs has made for my sub. the new amp is only 11 times more powerfull than the old one.

"Only"... LOL posted_image

-------------
It all reminds me of something that Molière once said to Guy de Maupassant at a café in Vienna: "That's nice. You should write it down."

lol, i went from a 100W MTX 30A fuse X2 channel to a 1150W eclipse 4 40A fuses. my god its night and day! the tweets that i thought were maxing were actually clipping...

if the mtx has a 30A fuse then its at least a 200 watt amp at its max power. not quite 11X bigger but still a substantial boost. the eclipse is probably 300 watts per channel if the fuse ratings are correct. i dont know if you bought this amp new or used but sometimes when people want to sell a used amp they replace the normal fuses with bigger ones to make you think the amp is bigger than it really is.

-------------

both amps were used. the fuses match the factory docs so i think they are correct.

ok, here it is... the latest attempt. i will also be 45ing EVERY corner, i just did not care to draw all that out. assume all edges are routered as well and the 3 way corners are fiber glassed.

what do i need to change? if anything.

pics

https://imgur.com/a/d3ZrJ

honestly i think 45ing the corners would weaken the structure. its not like building a house with 2x4's, MDF is strange to work with because its not like other woods. when you shoot a screw through the 45'd corner the screw will want to pull through the first layer and its way easier if the corner is angled. for example it would be easier to grab the two pieces of wood and break them apart if the corners are angled than when you just leave them squared. the only time i see a box with angled corners is when the box is held together with only nails and glue. those boxes are usually not built to last.

plus its just extra work that isnt necessary at all.

-------------

k, then perhaps ill just use fiber glass to round off the inside corners. how does the rest of the box look? is this good to build? on a bit of a side note, subs have a min/max of cubic footage to use, what advantages or disadvantages would i have to a 7.99 cubic foot vs a 5 cubic foot? or maybe even a 7 cubic foot? and if i intend to over power the sub would i want to air on the side of more cubic footage?

also i read that 12-16 multiplier is the standard for port hight, i used 16 and took it back a tad. would i have any better or worse sound having a 3.55" hight on the port vs a 3" height or 3.8" height? my understanding is bigger is better to prevent port noise

I don't know where you got the idea that the inside corners of a subwoofer enclosure need to be rounded or angled or treated in any way, but they do not.

IN GENERAL, a smaller enclosure will increase the subwoofer's power handling slightly because it helps keep it from exceeding Xmax. But the effect is small, and the more likely effect from smaller systems is higher resonance frequency and a "bump" in the output often causing a boomy system. In a vented system, you are foolish to make it smaller unless you absolutely have to.

What "12-16 multiplier" are you talking about?

And lastly, did you decide how you plan to brace the enclosure?

-------------
Support the12volt.com

2 posts back i posted a new set of images from my redesign of the bracing. if you think that is good then ill go forward, let me know what needs to be changed.

the 12-16 is the multiplier. 8 cubic feet * 16 = 128 / port width (34.5) = 3.7" max port height. and *12 minimum port hight for its size.

here is a relink to the redesign: https://imgur.com/a/d3ZrJ
redesign

my thoughts were to try and keep the box as close to 8 cubic feet (max for this sub) as possible with out going over.

you mentioned the edges dont need to be cut in or rounded, ive seen many sub box videos where builders swear by this processes so thats what i was thinking of doing. they coat the inside with resin to add strength so i was planing to do the same, unless you feel its a waste.

i was planing to router every edge to a smooth rounded surface to help eliminate any rough air movement, is this a good idea?

Your links do not work. Use the forum's image up loader.

Coating the inside with resin is a great way to both add strength and seal the enclosure against air leaks. But rounding the corners or the edges is not necessary. "Rough air movement" is not an issue. Rounding the exit edge of a port can help reduce port noise (and it creates a small flare which changes the size of the port - makes it a bit longer.) Be sure if you do this you model your system with one flared end to make sure the port is the correct length.

You said: "the 12-16 is the multiplier. 8 cubic feet * 16 = 128 / port width (34.5) = 3.7" max port height. and *12 minimum port hight for its size." Where did you get that and what do you think it calculates?

-------------
Support the12volt.com

i just tested the links and they work, must be a browser issue on your end. *shrug*

i know how wide the port is given the width of the box, the formula calculates how high the port opening should be, it gives me the Y for X of the port surface area

here are the pics:
posted_image

The links work fine from your computer because you posted them, but the URL is incorrect in this forum. You are posting this: https://imgur.com/a/d3ZrJ but the IMG tag must end with a graphic file type descriptor.

In any case, sounds like you are calculating the area of the port opening. Fine.

The pics you did post correctly show a well-braced enclosure. Go for it.

-------------
Support the12volt.com

sweet, ill look to build it up this week. im picking up a ZX2500.1 in a swap for my current ZX1500.1. we shall see if the sub can handle the extra power, if so then great. if not then i suppose ill buy a second :P

Now, that's braced. Good job!

-------------
It all reminds me of something that Molière once said to Guy de Maupassant at a café in Vienna: "That's nice. You should write it down."

im glad you approve. this has been a long learning experience in just the design... cant wait to jump off the learning cliff during the physical build

PROTIP: pre-drill all screw holes or else you will split the MDF. use wood glue or liquid nails( i like liquid nails between my sides and it seals a box great)

also to answer your question about the port opening being 3" vs 3.5", considering the overall size of the port i dont think you would see a difference with any port noise, but keep in mind that going with a bigger port also means it must be longer to keep the same tuning. so the size you ultimately choose to use needs to take that detail into consideration. personally the biggest port ive made so far is for a box for two 18's that is 16 cubic feet and double layered the whole box. the port is 4" x 45" x 28"(not sure about the length). either way, its huge and the air that comes out of it is enormous. big ports definitely have a nice effect that comes with them.

-------------

well my plan is to follow tores tuning calcs and keep the back of the box only screwed on. then tune by adding varying lengths of wood brining the port down into the box and lowering my tune until i hit what i feel sounds best. i expect that a 36hz tune is going to be damn close to what im looking for according to my research.

i will predrill, use wood glue or gorilla wood glue and then resin the whole box. i have read that liquid nails has to much give to it and thus is a poor choice for heavy boxes with loads of power.

there is so much conflicting information and supposed "facts" around about car audio that this whole processes has been just one cluster F*** of opinions. it seems that for the most part you just have to get as close as you can in the middle ground and then try things out for your self. i cant tell you how varied the responses to questions ive gotten between car audio install forums, 12 volt forums, and SMD forums. not to mention the youtube box builder channels... then on top of that some craigs list audio installers have yet another recommendation and then car audio installers i worked with at circuit city install bay have even more "facts" that contradict.

quite the learning processes i have delved into here

box building is not really learnable from just reading and research, you just have to build boxes through trial and error unless you have someone directly teaching you. i had to learn the hard way and im still far from perfect, i too worked as an installer at circuit city and your friends probably dont know as much as they think they do. CC installers never got that heavy into custom boxes and they didnt receive any box building training from circuit city so anything they learn would have to come from somewhere else.

-------------

NCC, Most of the installers here at the12volt have been doing this for a long time. Many of us have owned our own shops and businesses. Some of them (like me) have been in this industry likely since before you were born. We do tend to know what we're talking about. posted_image

-------------
Support the12volt.com

Well I'm looking to build this guy up this week, so I suppose we'll see how much I've learned. By my math I need 5 sheets of 4 by 8 MDF. As for Circuit City our store had 1 installer that did competition audio but all the rest were just high school kids.

Just be patient and take your time. It will take several days to build something that complex.

-------------
Support the12volt.com

i intend to not only measure twice and cut once, but measure 4 times before cutting.

and then cut twice... posted_image

i have one final question. in this picture you see the port end and the bracing extending under the port. is this an issue? if so what needs to be changed?
posted_image

-------------
ZX2500.1 - SP4 18"
Eclipse 34320 - dual 10" mids
Audiobahn A275HC - tweets
KX3 xover
P7800HD deck
knukonceptz wire
custom 3/8" copper plate ANL fuse
4 group 31 1150CCA batteries

its hard for me to understand your picture. it looks like there are walls in places but they are see-through, like towards the top where it says 37" and on each side there are two vertical bars, what are the vertical bars? and one set of braces with the holes cut into them dont seem to connect with anything on their top side.

i think i know what you are trying to ask and from the look i dont know if that would affect the sound or port tuning. it might act like an extension of the port but that is just my guess

-------------