Question and assistance needed for ported enclosure

[cmarion1024 0]

I am new to the forum and I am trying to get help on something I just dont seem to be understanding. I have a Ford Explorer and I have two Lethal Injection 12's (4ohm/dvc model). I wanted to see how they sounded sealed, since I couldn't find anyone on the web. Only people asking has anyone done it. They are clean, crisp and loud being pushed with 800watts each. The sound quality is phenominal whether soft, medium or hard hitting. If I open the front doors only, its like a huge ported box turned up using old school SPL comp cd's. The pressure level is unreal for a sealed enclosure. I cannot say enough good things about these speakers. Best investment I made for not a lot of money! However, I want to also try ported to see which over all sounds better in the Explorer. I wanted to stick with a external measurement of 17"x41"x13.5" and 3/4mdf (height/width/depth) since I have to sometimes put in the double stroller if I have to take the kids somewhere in my car (And no I will not be cranking up the stereo with them in it). I am trying to understand everything for a ported enclosure. I have built numerous sealed enclosures out of different materials, hidden boxes,etc. But I have not built a ported enclosure. I would like to try and learn correctly as I know they are two different animals. I have read and read, but I am stumped on one part. In no way shape or form am I claiming to be a professional, but asking for professional help in understanding.

My problem is with these enclosure dimensions, I keep trying to figure out the port size using the-12volt(DOT)com calculator. On Incriminator Audio's website it recommends 25-40 inches of port. Does this mean the entire length of my port needs to be in this parameter (no matter what width or height of port) if I am trying to tune at 34Hz? Or can I just go off the port calculator? Obviously I dont have room for a huge long box with a double stroller. The dimensions mentioned above gives me 4.25cuft, but with the subwoofers up and port back I do not have that much area for that much port length (according to IA). Am I misunderstanding their recommendations versus what I am coming up with on the calculator? If I read correctly, I want the interior port end to be away from the subwoofer as far as possible. I read a nominal slot port size is 2.75" of opening and any smaller would be bad (please correct me if what I read was wrong). Using a port width of 14" and port height of 3", my total port length for 34Hz would be 17.96". Rounded to the nearest 1/4" is 18" (did I do this correctly?). This port I can do with the dimensions I have. I am trying to figure this out using these dimensions. In order for me to keep the interior end of the port away from the subs, my port would be towards the top portion of the rear wall in the middle facing the hatch. Then go down to the base and towards the back (like a backwards capital L). However, does this matter according to IA's recommended 25-40 inches of port? Or is this merely a number to fall back on. This is where I am stuck and just do not seem to be grasping the concept.

I tried different port sizes, but I can't get any that will work with these dimensions and stay within the supposed "25-40 inches of port". If I start zig zagging the port, I think I am in the realm of a "transmission line" box. And I am not remotely close to that skill level. I would appreciate any help or tips you could give me. I wanted to try and use the program I read about (WinISD Pro), but I do not have all the specifications for the subwoofer and it gives me an error when it auto calculates the other boxes left blank. To get a visual of the difference between the two boxes and if it is worth the time.

Edited April 1, 2012 by cmarion1024

[cmarion1024 0]

Or would I be better off using a round port inside the box to save the space? As in a 4" Precision Port with flared ends or a 6"? The calculator advises 4.478289" of port length using one 4" port, and 12.27065" of port length for a 6".

[dbsupra 69]

Welcome!

I see your confusion. They are talking about port AREA not port length.

Port area is length x height for a slot port. A 14 x 3 would be 42 sq inches. Once you determine that you calculate the length accordingly to tune the frequency.

I recommend Torres calculator. If you do a Google search you can download it for free. I use it to design all my enclosures.

[cmarion1024 0]

Thank you very much! That I understand. So if the "average" according to IA is 2.0cuft per 12 and 30" of port 'area', I would want to do a width of 10" and height of 3", giving a length of 12.13 and an area of 30" for 34Hz. Is that a better combination since it minimizes my port length, but stays within the specified port 'area'?

Help section in the program you suggested:

#7 - Port length uses the box wall or baffle(s) as part of the port length. So a port that is 10" long with one baffle using .75"

wood will only need to be 9.25" long as the box wall or baffle(s) will account for the other .75". If using two baffles,

then it would be 8.5" long as the baffle will account for 1.5" of port length.

So by using the numbers above from 12-voltDOTcom, it actually raises the Hz to 35 in this program. If I make the width 9", height 3" gives a length of 10.697" and area of 27" which brings the tune to 34Hz. I also entered into the box for number of wall baffles to two, since the top and rear wall would be part of the port. It shows physical port length as 6.95", does this mean I still need to have the port near the top of the rear wall and 90* down which means the part of the port going down is 6.95"? Now in that link I read it said it automatically figures in the correct port end math. There for I should be good if I make my port using these dimensions I entered into the calculator. Right? Forgive me, as I am trying to understand everything that I have read for the last three days and apply it the first time. I am hoping that if I build this, it will not sound horrible and waste my time.

I liked the idea of the round ports with the flared ends, but it seems to be a debate or personal interest on which is better. As it only requires the hole in the box and the tube (plus ends) for the given calculated length versus constructing a slot inside the box. However, it seems to be a personal preference and different sound for each application.

Before I begin, I will wait for a response from you or someone else that these numbers are correct.

Edited April 1, 2012 by cmarion1024

[dbsupra 69]

No problem!

Using a flared round port isn't too hard to build, you just have to be sure you have enough length since it isn't near as easy to 90*.

To determine port area for a round port:

Radius x Radius x Pi

Example: 6" port is 3 x 3 x Pi = 28.26 sqin

Round ports are lighter weight if that is a concern, but cost a lot more than a couple pieces of wood. Aero ports (flared) are a little more efficient than a standard round port so you can get away with a little less port area. But you have to take into account the flare end in tuning the length. You have to add 1" per port if using flared on both ends.

Also, I assume the port area suggested is per sub, so keep that in mind. You may want to double check that.

[cmarion1024 0]

Ahh! The spec's sheet just says :

Lethal Injection Series 12

Sealed .8 cubes - 1.4 cubes

Ported 1.75 cubes - 2.5 cubes, 25 - 40 Inches of Port, 28-35 Hz

Average: 2.00 cubes, 30 inches, 28-35 Hz

So, I too would assume per sub. There for I need to make two ports with these dimensions. Thanks, that never crossed my mind. For a first time attempt, figuring the correct math is difficult. It seems easier and more feasable to make one large port, which then would need to be 60 inches of area to accomodate two subwoofers. What I cannot seem to get right is a port length the will fit in this box for my available dimensions. I must not be looking at my situation correctly, I have a feeling I am missing something in the design area that would accomodate what port I need in this box for one large port.

I am about to just give up on trying this. I can read till my head explodes, but I am just not grasping what I can and can't do for this to work.

Edited April 1, 2012 by cmarion1024

[cmarion1024 0]

error

Edited April 1, 2012 by cmarion1024

[cmarion1024 0]

Here is what I am working with to give you a visual. Maybe this will help in figuring out the best way to do 60" of port area and be at 34Hz. I can also flip it to where the top/bottom is 17" and the front/back is 13.5". My max from front to back outside is 17". And my width is maxed at 41" to sit on the floor for outside measurement. Can I do two ports at the rear? My problem is getting my Hz to match the port area.

Edited April 1, 2012 by cmarion1024

[duanebrow 6]

Now you see why people just pay someone to design a box for them. Don't forget that you must subtract the port from the box volume. As far as port size/area it depends on how much air will be moving through the port. This will change with how much power is applied.

I am a big fan of winISD, if you can list the specs you have for the drivers I will see what I can do to find the rest. Modeling the enclosure will show you how the tuning and box size will change your output. This can be directly compared to your current sealed box. I think this will go a long way to help you understand what is going on with the different enclosures. This will help you to be able to build better ones in the future.

[duanebrow 6]

http://www.incrimina...udio.com/li.htm I found T/S specs here. I don't know if they are correct. Is this the model you have?

Ok that is old. I found them at SSA. Anyway 12x4 port would be about 31.5" long in a 3cf box. See if you can get move space after you subtract the port. That is plenty of port area if you are giving them 1200watts total.

Also for the latest version of WinISD: http://www.facebook.com/WinISD

Edited April 2, 2012 by Duane

[cmarion1024 0]

Yes, the Lethal Injection 12 (x2) 4ohm DVC. Depending on the port, I am looking at an overall net volume of 3.8cuft. Which is ok, the dimensions give me .2 cuft extra to take in account for the port to drop down where I need it. Just a hair under. I downloaded WinISD originally, but it kept crashing. It may not like my Win764. Also, IA doesn't list all the specifications that WinISD asks for and it fills in the blanks with its own calculations. Then it gives an error when you try to load that subwoofer because the parameters don't match up. I got irritated with it because I couldn't even load my subwoofer. Not its fault, just missing specs. I see why people do pay to have an enclosure made, but I don't want to pay for a sweet design and box if I end up not liking it. It may be a pain to learn, but I enjoy learning new things and the pleasure of building something yourself.

Any assistance would be awesome and grateful. I am not asking for someone to do all the work, just point me in the right direction or show me where I am making the mistake. I'm confident in the wood work and matching the dimensions it says to do. I just can't get the port to tune to 34Hz (anywhere from 32-34Hz would be great) and the port area to match IA's specs. The sweet spot seems to be 34Hz, 2.0cuft and 30in2 port area per sub.

[aBrokeNinja91 4]

hey i used the 12volt calculator for all my builds so far and what you should do is:

1. input the length/width/height that youre willing to use, and get the gross volume (without port, sub, and brace displacement)

2. calculate port length with desired port area, when you do this input the desired net volume (air space)

3. figure out how much volume the port, sub, bracing takes up and subtract it from step #1

4. this number will be off from your desired net volume, so youre gonna adjust port area in small incriments while repeating steps 2 and 3.

usually my ports take up anywhere from 1/4 to 1/3 of my gross volume. so with your 4.25 cu.ft. gross volume (your inside dimensions 15.5x39.5x12) you should be able to get within the recommendations for the sub.

my first box took awhile to plan so just take your time man. if you do decide to make the box bigger, increasing the shortest lengths will yeild the most gain in volume.

[cmarion1024 0]

I can make it 17x17x41. That is as big as I can go. Unless I make a capital T, the base width cant be bigger than 41 due to the wheel wells. 17" deep is my max to still fit the double stroller, if need be. And 17" high is at the top of the seat. On SSA for the specs, they are not all there either. I read a thread about people emailing the company over the specs. Why not give them all then? Not that difficult, at least I dont think it is.

ABrokeNinja; I am doing that now to see what it comes up with. I guess it doesnt like the size I wanted to use?! I see many enclosures that use one big port. However, when do you figure in the air movement speed? As in is a 10" wide by 4" high port that is 12.8" long be big enough for these two subwoofers? Or would it be better to use two ports that give me the needed port area, length and tune?

Edited April 2, 2012 by cmarion1024

[CHRIS 323 12]

im glad you got help cause i haven't gotten none lol

[duanebrow 6]

I will help you get WinISD going. The specs you need to enter are - re (just enter 4 in this case.), SD, qes, qms, fs, and Vas. (WinISD will calculate all the other specs for you at this point.) Then you should also enter xmax and pe.

[duanebrow 6]

Using your max box size I came up with 4.5cf net. I would suggest using this size box. Tuning to 34hz (15.5 x 3 x 18L) gives you a nearly 5db boost in the low 40's. This could make the box sound boomy. I like the look of a lower tuning for this sub. Tuned to 29 hz (15.5 x 2.75 x 24L) lowers the boost at 40 to 3db and it is only 2db below that peak at 30 hz.

[cmarion1024 0]

I deleted the WinISD I dowloaded and used the link you provided for v7. This one doesnt crash. I entered in all the specs I could find on the Lethal Injection and the speaker dimensions. After designing a sealed enclosure to match what I built vs IA Specs sealed vs IA sweet spot ported, here is the graph. The ported I seem to be stuck at getting a port to correctly match the Hz and port area. The dark blue is my box volume, light blue is IA spec volume. Green is ported, at least the best I could do.

Edited April 2, 2012 by cmarion1024

[cmarion1024 0]

Here is the graph using the box and port dimension's you just posted for 29Hz and 34Hz vs my sealed. Does that look right compared to yours? 34Hz starts off lower.

Looking at the graph, in your opinion, would it be worth it ""SQL"" wise to go ported? It will be louder, but is it going to ruin the sound quality? This I dont know by looking at a graph, I am not a pro.

Edited April 2, 2012 by cmarion1024

[cmarion1024 0]

I ask since I "read" the best of both worlds is in the 33-35Hz range for a ported enclosure compared to sealed to have a clean frequency band. However, looking at the graph it appears it is not so here. The 29Hz looks very clean and an even flow. On the 29Hz box, the port comes out to 42.63 in². Is that okay if it is recommended to be between 25-40" of port area per sub? Again, I am assuming that is per sub since it does not say.

[duanebrow 6]

I'm on my phone, but that looks right. When you add cabin gain the sealed will be the flattest. But if you like that or ported is a matter of opinion. As far as the ported box I like the the lower tuned one better. If you will be listening to anything that goes down to 30 Hz I would go with that one.

As far as the port area I used 1200 watts rms as the system power. With this much power the ports are big enough. If you go with a lot more power then you might get some port compression.

[cmarion1024 0]

Im currently running 1700 watts at 1 ohm to both. How much bigger do you recommend? I listen to a variety of music such as rock, heavy metal, rap, dubstep, and techno. Im currently having issues with my head unit, so I cant test music non stop. My stupid Kenwood kdc-mp745u keeps shutting down even with the internal amp switched off after a minute or so of music no matter the volume. I have to pull the unit out, pull the rear fuse and put back in to restart. Amazing how the majority seem to start failing right outside of the one year warranty. Bastards. Never again will I get a Kenwood, this is ridiculous.

[dbsupra 69]

Keep in mind the winisd plot isn't exactly representative of actually inside a car.

Also with your headunit I've had that problem before. I wired the power directly to the battery and ground to chassis. It solved the problem on mine. Might be worth a shot.

[cmarion1024 0]

That much I understand. After Duane mentioned "boominess", I didnt want it to sound like complete crap after building another box. Some think the "crap" bass sounds good, can't say I am a fan. But I wont know until I build it. I will pick up the materials this weekend. I just want to confirm and reconfirm the port measurements.

Was this a Kenwood? After it began I googled this situation and found a plethora of people with the same issue, but no one said they found a cure. Im thinking it is either caused by my door speakers, or power drop to the unit. I am getting a four channel amp to power my doors, but hell I thought this would atleast be able to run them kinda okay. I didnt expect it to be phenominal for the Polk Momo components, just work until I get the amp next week. I will try the wiring first. If it dont fix it then we will see with the external amp.

Edited April 3, 2012 by cmarion1024

[duanebrow 6]

I will check on the air speed @ 1700 watts. I don't think that it will be a big deal. Going with a 3" wide port will require about an extra 5" of port length. This should fit fine. Do you know how low you want to go? I was aiming at 30 Hz when I modeled the lower tuned box. It should be fine down to about 25 Hz. If you want to go lower, tuning should be lower.

[cmarion1024 0]

Down to 25Hz should be good. So the 29Hz dimensions would be good (15.5 x 2.75 x 24L). Would it be better to make a backwards capital L for the port or start at the lower rear wall and go towards the front, then back towards the rear to get the full length?