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Porting and box size?

post #1 of 6
Thread Starter 
Sorry to make another thread but this is a learning experiance and maybe im just not typing the right context into google to get my answer..

When you look at drivers, when they give a sealed vs ported enclosure they all seem to have a small sealed enclosure, and a vented enclosure twice the size.. For example the 15" Ultimax im sticking in one of EricH's flat packs calls for a 3.1 cubic ft sealed enclosure and a 6.1 cubic foot vented enclosure..

I was playing around with some web program on google, types in EricH's flat pack diemesnions and stuck a 3" diameter 13" long port for a port size and It said it was tuned down to like 20HZ IIRC

but what is the reasoning behind having a bigger enclosure? if the enclosure is to small and ported does it harm the driver? or can you really just stick a 3" port in a box like that and get the output you want...

Excuse my ignorance, especially if this is something thats been answered or talked about countless times, just not finding the answer, or maybe its not in simple enough terms that I am realizing the answer is in front of me.
post #2 of 6

A single 3" port is not enough, you will get chuffing. The ultimax really wants a very large enclosure to be vented (14cu ft would be best). Once you start lowering the enclosure volume you lose a lot of the low end response.

 

Here is a graph showing different enclosure volumes, all with 500w and a highpass.

 

post #3 of 6
Smaller volumes (under 8ft3) look better when you tune very low, like 16hz or lower. That leads to crazy port lengths ofcourse.
post #4 of 6
Thread Starter 
Thanks guys, pretty much what I was looking for, maxes sense with the chuffing, dident really think of that, thats a lot of air trying to move through a tiny ass port

Curious to know how this in a sealed enclosure in my room audyssyed will compare to the RW-12D I currently have.
post #5 of 6
Quote:
Originally Posted by Shady195 View Post

but what is the reasoning behind having a bigger enclosure?
How well it works. Modeling programs default to the flattest possible response with the specs of the driver, which often will result in a smaller sealed cab than vented. It also usually results in less low frequency extension and output with sealed. You don't have to use a larger box with vented, you may change the box size and tuning to get the result you're looking for if it's other than maximally flat.
post #6 of 6
jay really hit on the key point. as the enclosure gets smaller, the port must become exponentially longer in order to provide the same tuning.

this is why you will never see a very small enclosure, with a big driver, and a very low tuning using a port.

for that purpose, passive radiators can be used.
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