Knocked His Block Off

The Mermans do females great, but there is a suck-out at 250 Hz, with a dip below and peaks above and below the dip that affects male voices. I attribute most of this to the cabinets that are made of plywood, have little bracing, and no insulation. I can move the cabinets about the room and the suck-out (measured in the near field) persists.

I can rap on the box and see this same resonant pattern on the RTA with the mic held against the cabinet. And, the L300s don't have this suck-out, so it is not the room.

So, I am improving the boxes. The first step is to get rid of the handles. These are thin aluminum and "ring" when rapped. Contrary, to the logo, they are not JBL.

I designed block-off plates in CAD and cut them out of 5mm smoked acrylic on a laser cutter. This just fills the handle's recess.

I haven't done any testing yet, and will probably back the acrylic panels with acoustic foam when I do the insides.

http://www.audioheritage.org/photopo.../DSC_00185.JPGhttp://www.audioheritage.org/photopo.../DSC_00216.JPGhttp://www.audioheritage.org/photopo.../DSC_00252.JPGhttp://www.audioheritage.org/photopo.../DSC_00282.JPG

No real noticable difference on the RTA. (Maybe 1 dBA reduction between the suck-out and peak.)


But the increased cabinet volume, though small, would help and there is the possiblility/probability/reality that the handles produced some ringing that can heard rather than measured with an RTA. Other measurement techniques may account for ringing.