Box design help - Car Audio Classifieds!
Car Audio Classifieds!  

Go Back   Car Audio Classifieds! > Enclosures, Fabrication & Sound Deadening > Enclosure Discussion & Design Construction Help

Enclosure Discussion & Design Construction Help Have questions about enclosure design neeed some help thoughout your build, ask here.


Notices

Reply
 
LinkBack Thread Tools Display Modes
  #1  
Old 10-20-2008, 08:05 AM
mytyeerinpie's Avatar
Elite Master Member
 
Activity Longevity
0/20 20/20
Today Posts
0/11 sssss6375
Location: Rapid Shitty, SD
Age: 36
Thanks: 34
Thanked 9 Times in 8 Posts
iTrader: (5)
Feedback Score: 5 reviews
Default Box design help

Yeah I stole this from someone...thanks Used2Know) but I have used it a few times and I thought it would be useful here. I will add more as I find them. Kind of a compilation of many threads from other sites.
Also free google sketchup download is great for drawing up designs, boxbuilder pro6(not free), winISD once you figure out how to use it.
  1. figure out your workable cubes (space you have to fit your enclosure, the max dimensions minus 1.5 inches from external measurements (hxwxd), giving you your gross internal volume assuming you are using 3/4 mdf)
  2. choose an alignment given your speakers parameters or use an accepted real world tested enclosure size and tuning that will fit via your workable cubes
  3. use the first port length formula to figure the first unadjusted port length
  4. calculate port(s) displacement and any other internal displacements i.e. speaker(s) or any bracing and then subtract that from gross volume
  5. use the other port length formula to figure out tuning
  6. adjust length, thusly affecting your volume obviously, until you are satisfied with end result
You most likely will need to only recalculate twice or sometimes trice.



Formulas


Cubic Feet
  • height * width * depth / 1728 = Ft3
Port Displacement
  • (outside diameter/2)^2 * 3.14 *(length of port inside said enclosure)= in^3
  • then obviously convert that to ft^3
  • don’t worry about the internal flanges of an aero as they are minuscule in the whole scheme of things

Multiple Port Diameters
  • SQRT(A^2 + B^2) = total combined diameter
Slot Port Displacement
  • calculate the internal volume inside the port as well as the volume of the wood making the vent wall(s) for the port and then subtract that from the internal volume of the enclosure
  • length * width * height / 1728 = Ft3

Slot Length to Width Ratio
  • length/width = ratio
  • keep it under 9:1
Speaker Displacement
  • most manufacturers include this in their parameter specs, but if not use this following formula, not 100% accurate but works none the less
  • 4 * 0.33 * 3.14 * (depth from back of basket to rear of magnet)^3 * 0.5 * 0.6
Port Area
  • shoot for 5% of speed of sound (</ 17 m/s) and you wont have any problems
  • 12-16 square inches of port area per cubic foot of volume is the generally accepted guideline
  • area of a circle is pi*r^2
  • area of a rectangle is h*w

    or
  • dV > 39.37*(Fb*Vd)^0.5
  • dV is minimum useable port diameter
  • Fb is enclosures tuning frequency
  • Vd is the volume displaced by the speaker at its full excursion (peak-to-peak)
  • convert min useable diameter to square inches if going slotted
Port Length

  • Lv = Av*1.84*10^8/[Vb*1728*(Fb/0.159)^2]-0.823* SQRT (Av)
  • Fb = 0.159*SQRT[(Av*(1.84*10^8)]/(Vb*1728*[Lv+(.823*SQRT(Av))])
  • Vb is true net volume (all displacements taken into account)
  • Fb is the enclosures resonant frequency (tuning)
  • Av is the cross-sectional area of the port (port area)
    1. (area of a circle is pi*r^2)
    2. (area of a rectangle is h*w)
  • Lv is the length of the port
SQRT=square root

From devil driver(ROE):
The most common materials used for an enclosure are as follows:
1. MDF
2. particle board
3. marine grade, void free plywood

MDF in 1/2", 3/4", and 1" sizes is perhaps the most common choice as it is a great price/performance material. Particle board is not a quality material to use for buildling enclosures, as it will swell and flake if it gets wet and will buckle even at modest pressure levels. Of the three I have mentioned, it is the one I recommend the least. Lastly, we have the plywood category: please note that I am not referring to your average plywood. The usual, inexpensive plywood you will find in large quantities at a hardware or renovation center will be only minimally better than particle board. Plywood is typically anywhere from 3-7 ply (3-7 layers), and can perform rather poorly at high pressure levels, requiring you to double or even triple the thickness of your material. On the other hand, a typical 13 ply baltic birch or apple ply wood will give very favourable results. Of the three materials I listed above, I would only recommend options 1 or 3.

The goal of any enclosure is to keep "enclosure talk" from occurring. Enclosure Talk refers to the flexing of the enclosure's panels to introduce unwanted distortion or frequencies at an audible level. There are two approaches to preventing this:
1. Making the enclosure stiff enough that any resonance will be higher than the frequencies played by the speaker/enclosure
2. Making the enclosure heavy enough that any resonance will be lower than the frequencies played by the speaker/enclosure

MDF is typically better at adding mass, which will lower resonance. Void free plywood is typically stiffer and will raise the point of resonance. It is also very easy to add stiffness by using simple braces inside the enclosure. Speaking in generalities, it is easier to stiffen the enclosure to raise resonance than it is to add mass to lower resonance. Marine-grade Plywood will be lighter and will not be damaged by contact with water, whereas MDF will be heavier and can be damaged by water. So it certainly seems that certain types of Plywood will create a more favourable result than MDF; but this is without considering price. Void free, marine grade plywoods can cost upwards of $50 a sheet, whereas MDF is usually $15-$25 a sheet. As you can see, the difference in price is very noticeable.

So the question you need to ask yourself is: am I on a tight budget? If not, it will likely be worthwhile to purchase some quality plywood. If so, than MDF will work well for you. Keep in mind that any speaker with large levels of output will require thicker sized sheets, but 3/4" is the most commonly used size.




From ndsrctbl(ROE):


I have come to realize lately that a lot of people dont know how how to find the net volume of an enclosure in cubic feet. i thought this might help some people that are having a hard time.

I am using the example that Aroc gave me.

So now we have
14.5H X 32.5W X 12.5D=5890.625 cubic inches
5890.625 divided by 1728 = 3.4 cubic feet


now you take all the dimensions you have and minus 1.5"(if your using 3/4" MDF on each side of the enclosure)

so are new dimensions are:
13"x31"x11"=4433
divided by 1728=2.565 cubic feet.
now, if you were going to add a port to this, i would shoot for 32" of port area(width of the port x the height). a good rule of thumb is to have 12-16" of port area per cubic foot(this box will have a little more but its just an example).

to achieve this, you will have a slot port that is 2.5" wide and 13" tall(13" is the internal height of your box) this gives you 32.5", pretty close eh?

now lets just say the port is 25" long. to find out how much space this port takes up, you take the port width and add the thickness of your wood to it(that is the outside of the port). so now we have 3.25". times that by the height(13") and then by the depth(25"). lets put it into a formula.

3.25x 13 x 25=1056.25
divided by 1728=.611 cubic feet.

subtract this number by the internal volume of your box

2.565-.611=1.953 cubic feet internally.

now you have to subtract sub displacement. lets say we have a pretty beefy 10" woofer(hdc3 10" for example) and it has a displacement of oh maybe .2 cubes?

1.953-.2=1.753 cubic feet after all displacements.

i hope this helps you guys out. this box went from 3.4 to 1.753 cubes pretty quick didnt it? with some braces this example box would work great for a decently sized woofer like a hdc310. dont forget to subtract the displacement from braces if you using them.



oh and i thought i would add how to find the displacement of round ports:

use this formula, Pi x R^2 x D/1728 (3.14 x Radius x Radius x Depth of Port/1728)

i will use a 6" port that is 25" long as my example

3.14 x 3 x 3=28.26"

28.26" x 25"=706.5

706.5/1728= .408 Cubic Feet

just as you did with the slot port, minus this from the internal volume


edit I put this in the box section, I didn't realize something similiar was in the tutorial section
__________________

To view links or images in signatures your post count must be 0 or greater. You currently have 0 posts.


Posted to Monty

Quote:
as it is you would have been better off with a 50cc hot pink moped with slutty on the plate
To view links or images in signatures your post count must be 0 or greater. You currently have 0 posts.
Quote:
im sry bro but actions like this bring down you and the whole site....this is a place to help and or learn car audio along with selling used car audio equipment.....posting to get a rise out of ppl is not only childish it hurts caco on the whole.....
To view links or images in signatures your post count must be 0 or greater. You currently have 0 posts.

Last edited by mytyeerinpie; 10-20-2008 at 08:14 AM.
Reply With Quote Quick reply to this message
Sponsored Links
Advertisement
 
  #2  
Old 10-20-2008, 08:10 AM
mytyeerinpie's Avatar
Elite Master Member
 
Activity Longevity
0/20 20/20
Today Posts
0/11 sssss6375
Location: Rapid Shitty, SD
Age: 36
Thanks: 34
Thanked 9 Times in 8 Posts
iTrader: (5)
Feedback Score: 5 reviews
Default

From M5 (SSA)
So you designed and built a box and think you know what it is tuned to, but there are a lot of reasons to verify that you are right. Some of these are:
1) To make sure you understand the math behind designing the box
2) To check up on the person that did the design for you
3) To check on your building skills
4) To verify where you are so that when you redesign to deal with an acoustic difficulty that you found you are able to.
Whatever the reason, there is a simple way to do this.

You will need the following equipment:
1) Your system installed in your vehicle.
2) A CD with a variety of low frequency tones on it, I’d use 1 or 2Hz spacing from somewhere below where you think it is tuned to somewhere above.
3) The DMM you used to set your gains (an Oscope or other voltage measuring device is also fine).
4) A resistor. Generically speaking almost any resistor will be fine, but I would highly recommend using one that will dissipate a lot of power (100w is logical) and is at least double the DCR of your coils. As a good starting point a 20ohm resistor would be fine. For example you could use this one from Mouser which is nearly noob proof for the reasons I just stated:
http://www.mouser.com/search/ProductDetail...71-HL100-06Z-20

Once you have assembled your gear, the testing is pretty easy. Here are the steps:
1) Wire your resistor in series with your driver. For example, take the + output from your amplifier and run it to the resistor, connect the other end of the resistor to the + input on your sub. Leave the – output of your amp connected to the – input on your sub. Your resistor is now functioning as a voltage divider and will let us measure a manageable voltage range on the DMM.
2) Connect your DMM across the resistor. One lead on each side of the resistor.
3) Play your first tone on your CD. Since you know the approximate tuning value of your box, start slightly lower and work your way up. NOTE: Please do not play your system loud through the resistor as it is completely unnecessary. A very moderate to low level is just fine. I will repeat: a moderate level is fine do not do this with your system wanging.
4) Record the voltage readings on your DMM for each frequency. You will end up with a table of values like I list here (note for a ported enclosure the lowest voltage value will be at the port tuning frequency):
1.4V at 28Hz
1.5V at 29Hz
1.4V at 30Hz
1.3V at 31Hz
1.2V at 32Hz
.9V at 33Hz
1.1V at 34Hz
1.1V at 35Hz
1.3V at 36Hz
In this case the ported box is tuned to 33Hz. (You do not need to use 1Hz spacing, but can use whatever you determine is accurate enough.)

For those of you with access to an arbitrary function generator and data acquisition system the process is even easier. Since I do, I set up a 0.25Hz frequency sweep from 20hz to 60hz and record the voltage across the resistor at all frequencies. This makes the whole measurement time a couple of seconds and gives a very accurate measurement for the tuning frequency of your box. The analyzer will create a table like I made by hand above and all you have to do is look for the lowest voltage.

You can do this for a Sealed box as well. When looking to find the Fb of a sealed enclosure, you can do exactly the same test only now look for the peak voltage instead of the lowest reading. In the case above if the box were sealed it would be tuned to 29Hz.
__________________

To view links or images in signatures your post count must be 0 or greater. You currently have 0 posts.


Posted to Monty

Quote:
as it is you would have been better off with a 50cc hot pink moped with slutty on the plate
To view links or images in signatures your post count must be 0 or greater. You currently have 0 posts.
Quote:
im sry bro but actions like this bring down you and the whole site....this is a place to help and or learn car audio along with selling used car audio equipment.....posting to get a rise out of ppl is not only childish it hurts caco on the whole.....
To view links or images in signatures your post count must be 0 or greater. You currently have 0 posts.
Reply With Quote Quick reply to this message
Sponsored Links
Advertisement
 
Reply

Bookmarks

Quick Reply
Message:
Options

Register Now

In order to be able to post messages on the Car Audio Classifieds! forums, you must first register.
Please enter your desired user name, your email address and other required details in the form below.
User Name:
Password
Please enter a password for your user account. Note that passwords are case-sensitive.
Password:
Confirm Password:
Email Address
Please enter a valid email address for yourself.
Email Address:
Location
Where you live
Level of Car Audio Knowledge
What's your level of car audio?

Log-in



Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
 
Thread Tools
Display Modes

Posting Rules
You may post new threads
You may post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On


Similar Threads
Thread Thread Starter Forum Replies Last Post
What You Think of this Design.. s Beatz General Car Audio Discussion & Questions 16 11-22-2008 05:01 PM
If you were to design a sub madmat General Car Audio Discussion & Questions 12 11-16-2008 07:45 AM
Can Someone design this for me. worstenemy453 Box Requests 7 11-12-2008 06:31 PM
Box design tater Enclosure Discussion & Design Construction Help 4 10-18-2008 12:47 AM
box design for 15'' L7 ba11in Enclosure Discussion & Design Construction Help 4 09-24-2008 03:01 PM

» Amps
A/d/s/
Advent
Alphasonik
Alpine
American Bass
ARC Audio
Atomic
Audio Art
Audio Gods
Audiobahn
Audiocontrol
Audiopipe
Audison
Aura
Autotek
Avionixx
Bazooka
Beyma
Blaupunkt
Boss
Boston Acoustics
Bravox
Cadence
Cascade (CAE)
CDT Audio
Cerwin Vega
Clarion
Clif Designs
Concept
Coustic
Critical Mass
Crossfire
Crunch
DB Drive
DC Audio
DC Power
DEI
Denon
Diabolo
Diamond
Digital Designs
Directed
DLS
Dual
DYnamat
Dynaudio
Earthquake
Eclipse
Elemental Designs
ESX
Eton
Farenheit
Fi Car Audio
Fix My Speaker
Focal
Fusion
Genesis
Ground Zero
Hafler
Helix
Hertz
Hifonics
Hushmat
Image Dynamics
Infinity
Interfire
JBL
Jensen
JL Audio
JVC
Kenwood
Kicker
Knu Konceptz
Kole Audio
Kove Audio
Lanzar
Lightning Audio
Linear Power
MA Audio
Magnat
Marantz
Massive Audio
MB Quart
McIntosh
Memphis
Metra
MMATS
Mobile Authority
Morel
MTX
Nakamichi
Niche Audio
O2 Audio
Ohio Generator
Optima
Orion
Oxygen Audio
OZ Audio
PG Audio
Phase Linear
Phoenix Gold
Pioneer
Polk
Power Acoustik
Powerbass
Powermaster
Precision Power
Profile
Pyle
Pyramid
RadioShack
Rainbow
Rampage
RE AUdio
Rockford Fosgate
Scanspeak
Scosche
Seas
Sony
soundstream
Sparkomatic
SPL Dynamics
Stinger
Sundown Audio
Swiss Audio
Targa
TC Sounds
TREO Engineering
TRU
Tsunami
Ultimate
US Acoustics
US Amps
Velodyne
Vifa
Viper
Visonik
Xtant
Zapco
Zed Audio
Powered by vBadvanced CMPS v3.2.3
Links
Amp Guts
amplifier, amp guts, ampguts, car audio classifieds, speakers and subs for sale with listings of 12 volt sound systems. Security systems for sale for aftermarket car audio equipment with amplifier and amps for sale
Car Audio Forum
car audio forum, moble audio, car stereo, wholesale car audio, 12 volt, with, amplifier, amp, subwoofer, sound quality, buy car audio, and sell automotive stereo systems for cars
Car Audio Sound Quality Forum
Sound QUality science based car audio forum, amplifier, subs and speaker design, fabrication help, sound systems forum, aftermarket car audio website for sound quality.
Car Stereo Forum
DIYMA car audio stereo forum for 12 volt car audio subwoofer and amplifier systems that have sound quality with wholesale car audio products.


All times are GMT -5. The time now is 01:02 PM.


Powered by vBulletin
Copyright ©2000 - 2019, Jelsoft Enterprises Ltd.
SEO by vBSEO 3.6.0
vBulletin Security provided by vBSecurity v2.2.2 (Pro) - vBulletin Mods & Addons Copyright © 2019 DragonByte Technologies Ltd.