View Full Version : Stupid questions but...

shake this
01-02-2012, 01:01 AM
Its been forever since I've built a ported box without the use of a box building program. Using a mac now and can't seem to find any good free one on the net. So my question is, can you change the parameters of a box and port design without affecting sound quality as long as every thing equals to the manufactures specks?

For example: if the manufacture calls for an outside dimension of 13.5" x 13.5" x 24" for a total of 2.48ft3 can I build one 14.75 x 14.75 x 20 for a total of 2.51ft3? I'm pretty confident this shouldn't affect the dynamics of the sub because I'm staying within the parameters. My questions is more with port design.

I'm wanting a rectangle port and the specs call for a 12" x 1.25" (15in2 area) by 22" in length (330in3 total). Would a port of 13.25" x 2" x 12.5" (331.25in3) cause any ill affects to the sound? Again, I'm going off the fact that I'm staying within the specs of the manufacture but I didn't know if changing the port length would cause a change in the tuning.

Sorry if this has been discussed before but it's 12:00am and I'm dead to the world as it is.

Thanks in advance for the help.

01-02-2012, 01:35 AM
changing port area and length will throw the tuning off but changing the shape will not be it the same volume. try Precision Sound Products (http://www.psp-inc.com) they have an online calculator for aeroports and the 12v.com has a host of calculators.

shake this
01-02-2012, 10:24 AM
So the length is based off the port area not total volume correct? My examples have the same volume but the area is different. The port calculator is showing a length of 39.5" for a port measuring 13.25 x 2. That just seems long to me but then again, it's been almost 15 years. LOL

Moble Enclosurs
01-02-2012, 05:00 PM
Yes, length can be based off of that aspect of area, not volume. VERY important to understand that. BUT also, can be based off of other factors that are just as important. For instance, without going into detail, if you make a port longer than it needs to be(which is not based off of a simple calculation), then you can get cancellation, and dips in the response rather than resonances that peak. This can affect everything with the response, and you may not notice it in the response graph until it is accounted for. There are a lot of things that are missed when looking at just a frequency graph. Just because the graph says it can hit [email protected], does not mean it will at the specified power given. You have to consider excursion, phase, and linearity as well as efficiency. So, tuning a port, or even constructing one in the first place is not as simple as it seems, and those who design them that way, may be satisfied, but they are missing out on other things that can be improved in the design that will turn it from an ok design that is great to listen to, to something that makes you pay attention to the notes and appreciate them.
So, this is said just to open your mind up to what can really be done with a design instead of simply saying, length is equal to the area for tuning. It can and should be more accurate than that. So, if you want to learn how to do them right, do some research or contact someone who knows fully how they work and when they work.
In your particular scenario, again, it may be acceptable. It may work out. But you may be able to hear dips in the response as well as peaks that will make it less musical if you're only concentrated on length and area being changes. So, yes, it can cause a lot of changes in the sound. You have to know at that point what it does to correct it. And there is not general rule for this, as the quarterwave theory is not always a good rule of thumb to use either. I hope this helps a bit in understanding that changes will happen and can be very important to notice before construction is done.

shake this
01-03-2012, 08:46 AM
^ Thank you for taking the time to point out some other factors that you can't see just from punching in numbers to a calculator

Moble Enclosurs
01-03-2012, 03:24 PM
Anytime :D

shake this
01-07-2012, 09:37 PM
Got the first box built tonight. We will see how it sounds in the next couple of days. Nothing fancy but it's going in a bus and won't be seen by the passengers.


01-07-2012, 10:02 PM
Looks great for a first time build. The roundovers give it a professional look.

shake this
01-07-2012, 10:24 PM
Thank you very much, I was vey happy how well it turned out. I'll be honest , I was nervous using the roundover for the 1st time. I just knew I was going to screw something up but it's pretty idiot proof