dallasjustice
Major Contributor
Assume a rectangular room with two dominant axial length modes. The modes of interest are the 1st order axial length mode (1,0,0) and the 2nd order axial length mode (2,0,0). In most medium to large listening rooms with a rectangular shape, these modes are very unlikely to be treatable with room treatments. Inverse EQ filters aren't a perfect solution either.
One way to eliminate these modes would be a two sub array I've discussed before here called the "source/sink" method. This works very well but can be a little complicated to setup. The benefit for the source/sink method is that it mostly eliminates the above mentioned problem modes. The downside is that low frequency time alignment is less than perfect. IMO, it's not audible and the benefits greatly outweigh the negatives.
The proposed cascaded method for eliminating these modes would require the subwoofer to be placed in the so called null position for each respective mode. For example, if a subwoofer were placed at the midway point between the front and back walls, and played low frequency logsweep, the 1st order axial mode would NOT be excited. However, the 2nd order axial mode would be excited by this midwall subwoofer, which is very undesirable.
A second subwoofer could then be placed at the null position for the 2nd order length axial (2,0,0). In this position, there would be no (2,0,0) excitation but the 1st order mode would be excited, which also isn't desirable.
Normally, subwoofers are low passed with a crossover point around 80hz. What if there were a cascaded series of subs each of which operate only within the frequency range which does not excite the unwanted mode? Using the example above, the midwall sub would be low passed slightly below the 2nd order axial (so it doesn't excite the 2,0,0) and crossed over to the second sub which is low passed up to the normal crossover frequency (say 80hz). IOW, there could be a series of subs each working only within the frequency most optimal to each sub's physical location in the listening room. I've thought about doing this before, but I always thought the crossovers might be a little too complex.
It looks like the newest version of audiolense may be designed to build more complex subwoofer crossovers to include a cascaded subwoofer array.
Here's an email I just received from Bernt concerning the new audiolense 5.0.
One way to eliminate these modes would be a two sub array I've discussed before here called the "source/sink" method. This works very well but can be a little complicated to setup. The benefit for the source/sink method is that it mostly eliminates the above mentioned problem modes. The downside is that low frequency time alignment is less than perfect. IMO, it's not audible and the benefits greatly outweigh the negatives.
The proposed cascaded method for eliminating these modes would require the subwoofer to be placed in the so called null position for each respective mode. For example, if a subwoofer were placed at the midway point between the front and back walls, and played low frequency logsweep, the 1st order axial mode would NOT be excited. However, the 2nd order axial mode would be excited by this midwall subwoofer, which is very undesirable.
A second subwoofer could then be placed at the null position for the 2nd order length axial (2,0,0). In this position, there would be no (2,0,0) excitation but the 1st order mode would be excited, which also isn't desirable.
Normally, subwoofers are low passed with a crossover point around 80hz. What if there were a cascaded series of subs each of which operate only within the frequency range which does not excite the unwanted mode? Using the example above, the midwall sub would be low passed slightly below the 2nd order axial (so it doesn't excite the 2,0,0) and crossed over to the second sub which is low passed up to the normal crossover frequency (say 80hz). IOW, there could be a series of subs each working only within the frequency most optimal to each sub's physical location in the listening room. I've thought about doing this before, but I always thought the crossovers might be a little too complex.
It looks like the newest version of audiolense may be designed to build more complex subwoofer crossovers to include a cascaded subwoofer array.
Here's an email I just received from Bernt concerning the new audiolense 5.0.
