Cab placement affecting sound

[BassAdder60]

I have a MarkBass MB58R 102 cab that is rear ported 

 

at rehearsals the hall is large often meaning my cab is several metres away from a back or side wall 

 

If the same cab was placed near a rear wall say 12” away would this increase the low bass tone IE make it sound deeper ? 

[BigRedX]

It's got little to do with the porting and everything to do with the position of the cab and you within the room. You don't need to move the cab, you'll get a different sound simply by standing in a different location in the hall.

[Downunderwonder]

The low end can definitely change with cab position. Put it 4' from the wall and your lows will be much diminished by the reflected bass coming back out of synch.

39 minutes ago, BassAdder60 said:

if the same cab was placed near a rear wall say 12” away would this increase the low bass tone IE make it sound deeper ? 

True. 12" is close enough that the reflection adds to the cab.

[itu]

Cabinet: 

on the floor +6 dB (one plane) 

against the wall +12 dB (two planes)

in the corner +18 dB (three planes) 

 

Numbers fixed, thanks to @Bill Fitzmaurice. 

 

Room dimensions usually amplify certain frequencies, see: standing waves. Depending on the placement of the cab, and materials some frequencies may be attenuated, too. Use an RTA to analyze the space and the response. 

Edited 57 minutes ago by itu

[BigRedX]

14 minutes ago, itu said:

Room dimensions usually amplify certain frequencies, see: standing waves. Depending on the placement of the cab, and materials some frequencies may be attenuated, too. Use an RTA to analyze the space and the response. 

 

Also depends on the position of the listener or measuring point, hence my original post.

[Bill Fitzmaurice]

3 hours ago, itu said:

Cabinet: 

on the floor +3 dB (one plane) 

against the wall +6 dB (two planes)

in the corner +9 dB (three planes) 

Compared to free-space, which is outdoors and elevated by at least a wavelength, on the ground is half-space, closer than 1/4 wavelength to a wall is quarter-space, closer than 1/4 wavelength to a corner is eighth-space. Each space reduction adds 6dB. This mainly applies to the lows, where speaker output is 360 degrees. 1/4 wavelength at 120 Hz is about 70cm, so ideally that's the furthest out you want the cab baffle from the wall. 

Quote

Also depends on the position of the listener or measuring point, hence my original post.

True. Where either the cab or you relative to each other or a boundary results in a 1/2 wavelength differential between the original source and a reflection there's a cancellation notch. Said boundaries include the floor and ceiling, so often the worst listening position is on the stage, where you can be getting multiple low frequency cancellations from walls, floor and ceiling. Further back in the room where the distance relationships are much longer the lows can be considerably louder than on the stage. This phenomenon was responsible for the myth of wave propagation, the notion that one must be a given distance from the source for a sound wave to fully develop and thus be fully heard. It's easily disproved by listening to the same speaker outdoors, where there are no boundaries that can cause cancellations.