i have bought a focal 13 access subwoofer. i just want to know what methods are there to get the cleanest and tightest bass reproductions. i have plans to sound deaden the entire boot. obviously the enclosure size makes a difference, my enclosure is roughly 40 litres. is this too big? should i be looking at a smaller enclosure to improve bass quality? if there are any other tips or techniques to improve the bass please mention them as well.

what sort of car you driving???

Design you box to give you the flattest frequency response curve possible, which will most likely mean porting it.

i'm driving a kia spectra hatchback

A port will certainly NOT offer the smoothest frequency response, as the port is designed to accentuate a band of frequencies.

A large sealed box that achieves a system Q of around .707 is considered ideal for smooth response if that is truly what you are after, though some modelling with a software program will tell you what the ideal sealed size is. 40 litres certainly sounds large enough though.

Also, playing around with the way the sub faces in the car will alter the frequency response and output significantly, so play around with this. Playing around with the low pass filter point and slope will also alter the sound - possibly to your liking? Try a steeper slope of 24dB per octave on a sealed system, and a lowish cut off of 70Hz or so - though this depends on the strength of the midbass output as to whether or not it makes an improvement.

That's not entirely accurate, given the massive boost to frequencies below 60Hz (ie transfer function) a ported box matched to the vehicle's acoustics (steep roll-off below 50Hz) will deliver a much flatter response curve (in car) than a typical sealed box.

Most sealed boxes generate too much output from 40-70Hz, resulting in "thick" or "boomy" bass.

Loud?

Really?

I disagree based on my own experience. If you measure transfer function you'll see that in most cars the low bass emphasis gradually increases as frequency decreases in roughly the same rate as the roll off on a sealed system. But still, measuring transfer function is a damn tricky game, as woofer orientation and bass loading play havoc with linear response.

My own experiences of building and installing literally hundreds of woofers in my reviews and work over the past ten years has given me this opinion. Backed up by measurements.

Adding a port - even one tuned at 30Hz, will achieve a less linear response in most cases than a well designed sealed system. This is especially evident in ported systems tuned higher, as just half an octave below tuning the port is 180-degress out of phase of the woofer and causes all kinds of problems with linear response.

There are, of course, some ported designs that can achieve very linear response, but we're talking in general here, and my experience with many ported and sealed systems has meant that I have formed my own opinion.

As, I assume, have you Loud?

It really depends on the subwoofer used, as well as the box location etc But more often than not, it is true that a sealed box may be more ideal.

There are several things you can do -

Adjust the position/angle of the box. You may find that aiming the sub in a different direction may sound better.

Adjust the lowpass filter frequency of your sub amp, as well as the highpass filter frequency of your front speakers (and rear fill if applicable). A front stage with good midbass response is important.

Increasing/reducing the size of the enclosure, but I should point out that you need a significant change in volume to produce a significant change in sound. For someone to give a recommendation, we would need to know the T/S specs..