Box info for SPL

[BanginJimmy]

This subject has been brought up quite a few times in the short time I have been on this forum so I figured I would write a short tutorial on what you need to do to build the best SPL box you can.

First some basic terms you will need to know.
SPL - Sound Pressure Level, this is the amound of air pressure inside a given vessel. It is measured in Decibles (dB)

Burp - a short burst of a particular tone


To start you need to know what your vehicles resonant frequency is. To do this you will need a sub in a sealed box, a disk with tones, and an SPL meter. Your vehicles resonant frequency is the frequency that your vehicle naturally resonates loudest resulting in the largest cabin gain.

To get your resonant frequency, start at 30hz and burp it. Take the number your SPL meter gives you and record it. Continue raising the frequency, and recording your results, in 5hz incriments until your SPL number goes down. Then go back to the frequency that gave you the highest number and start moving up in 1hz incriments. Go up and down until you find the frequency that give you the highest SPL. This will be your resonant frequency.

After you get your resonant frequency you will want to start modeling your sub out. For this you will want to use an enclosure design program like WinIsd, http://www.linearteam.dk/default.aspx?pageid=winisdpro. When you open WinIsd click on new project and select the sub you will be using from the list. If the sub you are using is not on that list then you will have to manually load all of the TS parameters. After you find your driver click next, select how many you will be using, click next, then using the drop down screen select vented and click next again.

Click on the tab for box. Set your tuning frequency for ~5hz below your resonant frequency. This will be a starting point for the actual box. From this point its trial and error.


Now you have to measure your available space. For example your trunk has 5cuft of available space. You are going to want a large port so start by entering 3.75cuft into the program as your box volume. this will give you a length for your port. Now that you know the length you can get the volume of the port. Volume is length x width x height/1728. That will take your measurement in inches and convert it to cuft. After you find the largest box you can get and still have a port enter that. in your box requirements.

Now go back and model everything up and make sure your box peaks at or near your resonant frequency. If it doesnt, then go back and adjust your box and tuning frequency until it does match or is within 1 or 2 hz.

I know this is VERY general and for those of you that are more advanced and have access to better programs there are better ways to go about this. This should help those of you that are new to car audio and SPL get started. As you learn more and have access to better programs alot of what is mentioned here will be obsolete. I use us Bass Box Pro 6 for 99% of my work and am very inexperienced with WinIsd so If any of you that are more familiar with it want to chime in with better ways of using it please do.

I know there will be alot more questions asked about this, so post up and I will do my best to get you an answer.

[rollininstyle2004]

Nice little writeup

[v3rd1g0]

i agree nice

[97_luder]

thanks