Enclosure help

[KC90]

I am designing a square ported box that goes over my wheelwells. I was hoping someone could look over my design and see if I did it properly or not (PandorasCustoms I believe you have a bit of enclosure knowledge?)

3/4" MDF (Maglios Building calls it Ranger board here)
Box is split into 2 chambers - each 2.1474cu.ft. including subwoofer displacement and excluding port displacement.

The port should be 35hz

Here is the actual measurements of the box:
= (total measurement)
= (internal measurement)

Top - Height = 12.75"
= 12"

Width = 51.85"
= 50.35"

Depth = 12"
= 10.5"

Internal Volume = 3.671'

Bottom - Height = 5.25"
= 4.5"

Width = 41.25"
= 39.75"

Depth = 12"
= 10.5"

Internal Volume = 1.087'

Combined Internal Volume = 4.758'

Internal Volume after split = 4.6828' = 2.3414' x 2chambers

Sub displacement = .194' = 2.1474' x 2chambers

I'm having problems sorting out the port...

Port - H = 4.75"
= 3.25"
W = 4.75"
= 3.25"
D = 8.14"
Now, I used a square port Calculator http://www.carstereo.com/help/Articles.cfm?id=31 (The bottom one "Calculate Your Vent Length.") I inputted 3.25" H & W, 35hz, 2.1474 Volume and got 8.14" Length. What do I do about the ports Displacement? If I work it out I get 2.0414cu.ft. after port displacement. Wouldn't that change the tune of the port because the internal volume has changed? :scratch:

I am sorry if this is confusing. This would be my first square port enclosure I designed from scratch, second enclosure overall. My first was with the help of the REAudio LPort Calculator( nice box but its just so big..)

Another question, about flaring.. Would I add the flares to the length of the port or include it? (Include meaning the flared ends plus the length of the port equals the 8.14")

But yeah please if someone could look over my design and help me out that would be great. If additional info is needed please ask.

Thanks,
KC

 

[KC90]

OK I have corrected some numbers. I end up with 3.435cu.ft. with the top half and 1.268cu.ft. on bottom - combined to 4.703.

I changed the internal measurements of the top to: Height 11.25, Width 50.25, Depth 10.5. Bottom: H 5.25, W 39.75, D 10.5.

The only thing I changed externally was the Top width to make measuring easier. From 51.85 to 51.75".

I still cannot figure out what to do about the port. I want about 35hz but the internal volume changes after I add the port, which changes the port tuning(?) This is a square port, not slot "L"port

EDIT: Forgot to mention each chamber now has 2.1199cu.ft. after sub displacement

 

[Blacksheep Josh]

Hey man, I saw this earlier, can do you me a favor, I'm good with numbers, but can you do a simple diagram on microsoft paint with the measurements on it? So I can see something visually? I'll crunch them through a few different calculators I have and let you know what's up.

 

[Blacksheep Josh]

nevermind, i sketched it out. Read the manual for the subwoofers, I know with my Kicker CVR's it says to NOT subtract the subwoofers displacement from box size when building an enclosure.

Also, I would just use a router on both ends of the port so air can enter/exit the port at both ends with as little disturbance as possible. The easier air can escape supposedly the better it'll sound.

Now I just crunched a few numbers for my own situation and figured out that the RE Enclosure calculator was subtracting the displacement of the port when giving me my final "cubic feet" measurement. Without teh port displacement I was roughly 4 cubes, after figuring up the port displacement it was giving me 3.5ish, and the RE enclosure was giving me that I had about 3.7...

Unless you're a human audio meter, I say just build the box with what you have now, and then test it and see where you're at, cause you can always redesign.

 

[Blacksheep Josh]

Here is a good page to look at as well, play around with that calculator, it's a LOT better. Read through the firs tpost and it'll tell you what all you need to do. Like you can enter in teh total volume and figure out the port length and all... This is waht I would use if I didn't have a Mac

 

[KC90]

Alright heres what i made up ( Ive got nothing for artistic skills here lol)

Red is the board Im using to split the box into 2 chambers.
Green lines are to split between upper and lower half of the box ( it not actually going to be split, its just to make my calculating easier by doing each individually then adding afterwards).
Blue is the port.

The numbers I put in the pic are internal measurements. The port (I changed measurements of it) is 3" high, 3.25" wide internally, 4.5"x 4.75" external (including boards.) I put ? because IDK how long it should be, displacement is confusing me.

 

[PandorasCustoms]

KC90...
Hey got your PM, and I actually made an Excel Spreadsheet that modifies the internal volume to include your port displacement.

It is posted under....
Port Enclosure Calculator

You should be able to figure everything out there by just punching in the numbers.
(make sure to select Port Type: Square)
And, since you are doing two chambers, put the measurements for one chamber with one port.

Just as a test, I ran what you have listed above and for this:

• Gross Internal Volume: 2.3414 Cu' (4045.9392 Cu")
• Port Length: 3.5"
• Port Width: 3.5"
• Port Depth: 8.25"
• Net Internal Volume: 2.26 Cu' (3896.92 Cu")
• Tuning Frequency: 35.08 Hz

Another thing you may want to consider (I don't see you have it up here yet) is the Rear Port Air Velocity. This varies dramatically with Port Size changes. The bigger the better, but the bigger, the more displacement, so it is all up to you. I personally do not know how to calculate this number, and have relied on WinISD to help me calculate this number. You usually want to keep it under 50 ft/s. Depending on where the ports are, you can play with that number a little bit. It just means that you might end up with a little bit of port noise.

If you don't have Excel, let me know. I have another version of that that can run as a solo program on a Windows Console.

 

[PandorasCustoms]

Well, sorry, I didn't read everything through.
I now see that the internal volume changed...

The corrected numbers I have are...

• Gross Internal Volume: 2.12 Cu' (3663.1872 Cu")
• Port Length: 3.5"
• Port Width: 3.5"
• Port Depth: 7.75"
• Port Displacement: .08 Cu' (139.98 Cu")
• Net Internal Volume: 2.04 Cu' (3523.20 Cu")
• Tuning Frequency: 35.10 Hz

I wouldn't worry about flares specifically, what I usually do is take a Round-Over Router Bit, and just hit the inside edges on the internal and external exits for the port. It helps reduce friction of the air movement and reduces possibility for port noise.

Also, if you let me know what woofers, and how much power you plan to run to each, I can get you the Airflow rate and cone excursion estimates.

 

[KC90]

Awesome thanks Pandora. The subs for now are Alpine Type X 12s. My amp is a T2500 with a birthsheet of just under 3200RMS at 14.4 ( my voltage is usually 13.8-14)

 

[PandorasCustoms]

Okay, well I got to crunching some numbers and graphing the data, and what do you plan on pushing these woofers too?

I know you say that the AMP is 3200 RMS, but how much of that are you going to be running? The T/S parameters show these at 500 watts per Voice Coil (1000 watts per speaker), so, you are already going to have to turn this down a bit.

I figured at 2000 total watts, and began the graphing. Cone excursion is an easy fix, and can be rectified with a simple addition of the Sub-Sonic Filter (A 19mm Xmaxx is easy to work with), but when it comes down to the actual box vs port size (Rear Port Air Velocity), I am running into problems. I am showing that with an internal volume of 2.04 Cu' and 1000 watts, you will need the ports to be around 8" x 6" in order to compensate. This would bring down the Air Velocity to 58 ft/s which is generally inaudible. But, the major problem with this, is that you will be unable to recalculate the port length to accommodate this because it will too dramatically change the internal volume (After a certain length, the tuning frequency starts going back up to due to volume loss.)

I am going to run some ideas through my head and see what I can think of (This is something that I have calculated while on a break at work and haven't had time yet to sit down and really number crunch), but get back to me if anything seems to pop-up for you.

 

[KC90]

I have my gain turned right down. Not sure how much wattage is going through where my gain is set but the Xs can take it pretty good. So yea probably around the 2000 mark.

8x6 is a bit big, How about putting the port up on top? My box is 18" high (16.5" internal)

 

[KC90]

Nevermind had a mind block... I can make the box itself bigger? give it more depth to add volume to compensate for the port displacement..


Edit... to hit 35hz with 8x6 port would need to be loooong in length... damn :/ tricky this is...

 

[PandorasCustoms]

Well, it is a little more detailed than that. It isn't just a port size that matters, the Rear Port Velocity is combination of a few things: Woofer Size, Cone Excursion, Volume of the Enclosure, Volume of the Port, and Port Dimensions.

So, as you change everything around, the numbers keep moving around. Each number adversely effects the other except for the Woofer Size.
But, I will run some numbers tomorrow and see what I can come with regarding a different internal volume amount (pre and post port displacement)

 

[KC90]

Yea I did some research and finally realized its a damn vicious circle... Might just have to go back to slot.. Thanks for helping me with this, let me know what you find. Till then I'll keep researching lol.... The velocity actually got my interest now..

 

[PandorasCustoms]

Okay, so, I looked up "rule of thumb" number again just to make sure, and from what I am getting, 55 ft/s is the max you would want to have regarding air velocity in the port.

So, from a new calculation, you would need the following dimensions per chamber:

• Port Opening: 7" x 7"
• Port Length: 37.5"
• Gross Internal Volume: 3.95 Cu' (6480 Cu")
• Port Displacement: 1.30 Cu' (3363.50 Cu")
• Net Internal Volume: 2.45 Cu' (4227.66 Cu")
• Rear Port Air Velocity: 65 ft/s

I know the 65 ft/s is higher than the actual estimated value that we want to see, but this number will only be generated during test tones, and situations where you are pushing full power to the beast.

Really, from what I can tell, the main thing that is pushing the velocity number so high is the amount of power you want to push with these.

 

[PandorasCustoms]

In addition, this number is generated with a 25hz Sub-sonic filter in place, to avoid over excursion of the voice coil below tuning frequency.

 

[KC90]

The only time Ill be test toning is when the next bass race comes to town, just to actually see what my system can do on termlab. The other 364 days of the year are just daily bumpage back and forth from school/work.

By the looks of it I'll have to really make this a big box @.@. I can do slot again - Have them in the middle | _| | |_ | .. Hmm... Back to the drawing board.

Edit... 37.5" length... I could make the box deep enough for that... Wouldnt need to do slot.. Im trying to picture in my head the enclusore and where it sits in the eX... Another rule is to allow at least 2" between the port and back wall right? This could be doable and look good too.. I'll take some more measurements of my cargo area.

 

[KC90]

Ok I got a quick rough measurement of around 40"... Give or take the angle of the back seat. Looking tho, gave me an idea to where I can still utilize the wheel wells...

Now the well goes out about 5" (Ill probably make the port 5.25-.50 wide) so I could make the port about 9" high give or take an inch or 2. Using the "L" port I could wrap the remainder of the port length.This could work right Pandora?

 

[PandorasCustoms]

Hey, one thing you don't want to forget, you can bend the ports even if you are not doing slots. The ports on my enclosure are like a labyrinth (I have about five 45 degree turns in each port). Just as long as you maintain the port size throughout and calculate the angles correctly. It can work really well. I saved a lot of length by doing it.

But, as far as the ports over the wheel well idea...
Here is a box I designed for 2kv8...

I can get some ideas running on how to make one like this work out for you...

 

[PandorasCustoms]

If you are willing to give me a day or so, I can come up with a design for you and try to incorporate a port setup that should work for you.

Just let me know the MAX dimensions you want the box to take up, and I can try and work in mock-ups in Auto-CAD.