Half space? help

[marsonpee]

Hello

tonight I had one of my usual gigs in a hall that had a varnished brick floor. What I noticed is that I hardly got any bass from the subwoofer compared to when I do gigs in venues with wooden floors. What I wanted to know is why this is happening? I have a rough understanding that the sub couples with the floor to gain 3dB of spl but why do wooden floors sound louder?.

One thought I came up with is that they resonate and the bass is transmitted through the floor by vibrating the boards? My other thought was that I remember reading an article about subwoofers under stages and how half spcae coupling there was destructive, in the same article I remember it saying something like that the underside of the floor acts like another subwoofer (which im most probably confusing with normal half space coupling)

[Simon Lewis]

Half space loading simply means that there is an increase in acoustic output as the source is radiating into a hemisphere, instead of a full sphere. Depending upon the cabinet and the crossover frequency, we can generally assume that the bass will be omnidirectional, but this isn't completely true.

 

The issue of the wood/brick floor is probably as you surmised - it could be that the wooden floor is resonating, although this wouldn't necessarily add coherently to the bin's output.

 

There could have been other factors such as room modes, loudspeaker placement etc.

[marsonpee]

Cheers, that's cleared a few things up for me.