WS6T3RROR

i've built a lot of boxes and systems sometimes experimenting, but this time i'm going to build it exactly to recommended specs. That raised a few questions for me. when i figure the internal volume of the box i subtract the port volume right? i know you're supposed to subtract speaker displacement but am unsure about port vol. my speakers are rockford 8" he's and the port specs are 2.5" x 11.25" but do they mean internal diameter or do they mean external diameter.

and for people who really have a lot of experience whats the best face of the box to mount the port on? the illustrations in my install manual show it in the side on smaller subs and in the face with the sub on anything over 10"

Also i plan on putting the box on the shelf under the back glass but which way to you suggest pointing them when i had systems in it before the sub was always pointed at the glass which really seemed to enhance the sound it produced since i guess the sound waves were splitting and multiplying against the glass.

any other input you guys have is welcomed. btw the amp is a an old 400.4 rockford the birthsheet says it peakes at 616 watts @ 2ohms which is always how i hook it up.

i had a ported box and an hx2 before but the box wasnt really made properly in any way shape or form. the plan is to do it right this time. it sounded good but i didnt think it was doing all that it could especially with the bad box and the less than spectacular power i was feeding it.

thanks in advance

megabass

Usually, ports are located on the same face as the subs are mounted. Not always, but usually.

For port volume, you should use the external diameter. Although port walls are pretty thin. Just use the formula pi*R(squared)*H to get the volume for each port. Simple 7th grade geometry. HTH

WS6T3RROR

yeah i know how to figure up port volume (mech engineering/ math major) but what i meant was that when they recommend a port volume in general are they suggesting that as outside diameter or an inside diameter. in the past i've used pvc as a port and all of it i've dealt with has been 2.5 or 3" inside diameter and about a half inch larger outside diameter. i guess i may go with some sort of prefab port this time i need something 2.5" x11.25 i'm open to suggestions.

and if the port is shown in an example in the install manual would you take that as the way its to be done. the other thing is if its not mounted on the same face as the speaker what effect does it have on sound or spl if any?

thanks
jdavis

megabass

The location may or may not affect spl. It just depends. Suppose in your box (behind the seats) you have the subs facing the rear and you have the choice of putting the ports in the top (up) or on the same face as the subs (rear). The latter will likely give you better spl--simply because of the reflection of the sound waves.

You should still calculate the outside diameter of the ports. Think about it--the port material is still "taking up space"--isn't it? Just stretch a tape across your port and get the actual diameter. Sometimes, those standard size ports like 3" and 4" are not true sizes. Sometimes, they're a hair smaller. And many of them are tapered a little so the fit snug as you seat them.

2.5 is kind of an odd size. You may have to settle with a 3" port. look around at www.partsexpress.com and see what they have. What I do is use a nice prefab port and if I need it longer, I just extend it with a piece of pvc or cardboard tubing of the same diameter. And if your port length is longer than the inside of your box, I have a trick to that too, but it's a trade secret