Sub box capacity

I have a feeling my sub box is to small for the new speaker I have.

I brought and installed a new B&W FST Kevlar unit to install into my 5.1 Home cinema set-up. The sub box, which is active and contains all the relevant power supply, amp and components is about 350mm deep, 300mm high, but only 130mm wide.
The trouble is, the driver is installed on the left side (no other way), so the distance from the rear of the driver and the other side of the box behind it is probably only about 4cm.

The box is ported by a 3 inch hole at the front of the box, but I believe the air flow behind the driver is being restricted due to lack of space. I reckon, due to the short distance, the air pushed out of the back of the driver is rebounding and being pushed right back on the driver, causing it to flex and vibrate incorrectly. What do you guys reckon?

Time for a bigger box..........?

??? Above ???

Anyway, anyone who can confirm this for me will be much appreciated. It is an Eltax system connected via some synth boards and then too the Apple Mac (seeing as you all love names n numbers so much!!) Its a custom build so I can sample, mix and produce music through the onboard software and the Yahama mixer. I dont think any of this is so relevant to the B&W's performance so I wont spurt out any other names and brands to show off and try and make myself sound big!! (never meet a girl who gives a flying s**t whether its Denon, Bang & Oufslen or Monitor Audio anyway)

Realy, im just looking for an excuse to make a box, something ive always wanted to do!!

[alexs2]

Not entirely clear what you're after with this.....are you saying that you've bought a new drive unit and installed it in the existing sub box as a replacement for the original?

If you have,then matching one drive unit to another manufacturer's box and electronics can be difficult,given that the drive unit ideally should be matched to the cabinet for best performance.

You will also find that giving some of the forum members a slightly clearer idea of what the associated equipment is,enables them to give more than a vague overview of what might help.....I don't think that many of us are interested in "sounding big" as you put it,but we do have an interest in trying to be as helpful as possible.....by all means make a box,but find out enough about the drive unit,and the cabinet size required,plus the amplifier power requirements,impedance,and crossover frequencies first.

Wilmslow Audio can be a very helpful source of information,but they also will want to know more!

[GaryG]

Do you have the Thiele/Small parameters for your new driver?