Sorry, but I have away for a while. I have tried changing the 'loading' of the Ultra-X12 driver and/or vent. The changes were definitely audible, but never sounded as 'tight' as the bass of my ancient Transtatic I (KEF B309 in a TL + KEF mid-bass in TL + ESL mid-treble , , the best overall sound of any loudspeaker I have ever owned). 'Chuffing' or other strange sounds not a problem, just the quality of the bass. I am beginning to think that realistic, really 'taut' bass can not be produced by a downward firing subwooferdue to the necessity of the driver to 'squeeze' the air out from under the sub + the vent tuning is effected by the sub-floor space.