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midnightE39

Not sure why there's cancellation.

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So i've got an Fi SSD15 in a 3 cube box @ 37hz.

 

sounds really awesome and clean on the lows, up to about 55hz. there seems to be a massive hole in the bass response between 60-70hz. I have the LPF at around 110hz because despite what i hear most people cross their subs at, mine just gets louder and louder and plays clean up to that spot. there's no apparent cancellation when i open the trunk, the woofer seems to play all the way from 30-100hz effortlessly and with a fairly transient response.

 

the thing is that its in a sub UP port back configuration, and there only about 3-4 inches of clearance between the subwoofer cone and the roof of the trunk. I had tried moving the sub box all the way to the back (near taillights) of the trunk and i noticed that it solved a lot of the cancellation issues. at the cost of low end extension and overall SPL went down greatly. 

 

I'm thinking i need a new box, with the port and subwoofer on the same plane. but my trunk doesn't offer me enough vertical space to mount the 15 without a slant on its face. 2001 bmw 525i. 

 

I would have put this in Fabrication forum but I wasnt sure the problem is entirely related to the box itself, but i think it may be. i tested this with tone sweeps from youtube played through AUX on my smartphone. i've played with my phase knob and no matter where i set it, it doesnt seem to change anything. 

 

So my question is: is sub up port back in a trunk typically not a good setup? it seems like the sound waves from the port are hitting the ones on the woofer cone at just the right timing to cancel out this one frequency zone.

 

thinking about building it port back sub back with the face at a 45 degree angle and maybe an aero port on the side? or possibly through the ski hole of the car? im almost certain its just cancellation.

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I'm not sure why you'd think there wouldn't be. There are cancellations and distortions caused by surface effects, reflections, echoes and so much more in each and every sound we hear in our lives. For the most part they go unnoticed and uncared about because they're not affecting what we are trying to do or listen to at the time. For the average person the only time it becomes an issue is when we are listening to music. If you think you're trying to tackle a tough problem with a cancellation in your bass imagine what it would take to truly tackle those issues in your highs where almost all the frequencies you hear are produced and are much much more affected by those problems.

I think you've found your issue. There seems to indeed be a problem with the bass as it's reproduced in your trunk and how it sounds when it gets through to the cabin and your ears. Is sealing the sub and port to the cabin of the car an option? It would eliminate the acoustic affects that the trunk itself is directly having on it. If that's not an option then would you consider spending the time and money to upgrade your front stage to try some dedicated mid bass drivers that could pick up and deliver those frequencies much better authority so the sub doesn't have to do it?

Fighting acoustic anomalies is not an easy task. It takes time, trial and error, and many times you still have to make a compromise with more negatives than positives, obviously just not with as many negatives as there were before. On another note this was a very well thought out, well informed, and well posed query. You shouldn't have any problems getting more responses and a solution figured out on this one.

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Sealing the sub and port into the cabin would be an option depending on what it would entail. My seats do not fold down, there is ski hole behind the arm rest, and I was considering a new box with a partially external port extending through the ski hole slightly. Totally separating the 2 waves, would that likely be a solution? I'd mount inverse for wiring reasons, which would look cool too. What would I have to do to seal up the port to to the ski hole?

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What about just adding an 8 inch midbass driver facing right into the ski hole playing 60 - 350 Hz, on a mono amp ? Or 2 channel in tri mode with the 2 in the front doors on it?

Edited by midnightE39

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i would try opening up the rear deck, remove the rear speakers.

 

if you're interested in a new enclosure idea this would be a good application of a bandpass enclosure (the vent firing solely thru the ski hole). however you may not have enough room in the trunk. 

 

edit: additionally you can try a simple sealed enclosure and seal it to the ski hole in the rear seat.

Edited by lithium

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What about just adding an 8 inch midbass driver facing right into the ski hole playing 60 - 350 Hz, on a mono amp ? Or 2 channel in tri mode with the 2 in the front doors on it?

 

he's suggesting upgrading the front stage. which would require a 2 way or 3 way set up with large midbass speaker which could extend down to ~60 hz and cover the gap in frequency response. i dont think your ready to throw more money at the problem. its more likely you can alleviate the problem with some install changes.

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Fi SSD 15 standard options has a qts of .41 which IIRC isn't good for a sealed enclosure. I'm going to have a guy who advertises custom box builds on craiglist locally build me a new enclosure just under 4 cubes, port and sub back at an angle so the 15 will fit vertically (well, diagonally). He told me if i don't hear a big improvement or am otherwise unsatisfied he'll only charge me for the wood.

 

just hoping port and sub back fixes the cancellation issue.

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