So ive currently have got an Fi SSD15 in a 3 cube box, ported tuned around 31 hz. it murders the lows, and theres no port noise that i can tell despite it having only about 11 sq inches per cubic foot of box volume.

 

the problem is, there seems to be cancellation in the 50-65hz range. it hits great below that and even gets louder over 65hz until it starts rolling off around 85hz.

 

this is in the trunk of a 2001 BMW 525i. i have the sub fired up with the port back. im very frustrated with this lack of a crucial sub bass octave. i'm about to build a new box, in the neighborhood of 4 cubes with a port tuned around 35 hz, with at least 14 sq inches per cubic foot of internal volume. should this fix my problem? i'd really appreciate some guidance here. it isnt my car's fault, because i used to have 2 kicker CVR 12s tuned @ 40hz that hit this range of bass just great. when it comes to box size, is bigger always better as long as the port ratio remains proper? could it be because my sub is fired straight up? with only aobut 4-5 inches between it and the trunk roof? help me understand what to do to get my 55-65hz range back please. i waited a month for my Fi subwoofer and ive been very pleased with it otherwise except for this one thing.

 

thanks in advance.

There is no relation between box volume and port area.  At all.

 

There could be a few reasons for your lack of 55-65Hz range.  But first off, have you swept with test tones to be sure you actually have a dip in output in that range or are you taking a guess?

 

One of the most common reasons for this response is an exxagerated low end.  This normally happens when an alignment thta is relatively flat (like yours) anechoically is placed in a car with a ton of cabin gain down low.  It is like you have just added 10db+ on your last few octaves, and then you don't get so much boost right above that.  It pretty much makes it sound like you have a big hole in your response, and in reality you do.  The easiest solution for this is picking an alignment that isn't flat, but instead is rolled off more on th elow end with a higher ripple in response up higher, no doubt that is how your setput with the Kickers was working.  This is why many people find they like the sound off a seale dbox because it is "punchy" hits th ehigher notes better.  But in reality, they just have an alignment that peaks in mor eof the range they want, it has little to do with the box actually being sealed.  By the way, you can make a ported box peak wherever you want by manipulating tuning and box volume (notice port area isn't mentioned, because it doesn't play into anything here) but you always have to give something to get something.  So if you make a box that has a peak up high, you will loose low end and possibly have some other undesirable after effects...

 

The other common problem (well not so common) is actuall cancellation due to the sound waves arriving at the listener at slightly different times and cancelling each other out.  The only way to fix this is to move the enclosure, or change orientation.  Sometimes this problem is very tough to overcome with drastic system changes.  This i sone of the biggest reasons some cars are so much louder than others (inside) with identical equipment...

 

Hope this helps...