[thomasjefferson]

Alrighty then, testing an image post?  This is a cutaway view of the OB sub described in the last post.  Also of interest: a few virtual views of this sub and some other speakers (designed but not built).  Note that in the bottom image the sub is horizontal, which would be coffee table orientation without the junk on top.  Cables would be a problem!

[HAL]

The top picture shows the four drivers setup so that the null in the OB response is pointing at the listener. 

I thought the drivers had to point at the listener in OB operation 

[Danny Richie]

The top picture shows the four drivers setup so that the null in the OB response is pointing at the listener. 

In the top picture the side panel has been removed. The listener would then be to the left or to the right as per the drawing. As per the other pics it is oriented correctly for listener position.

I thought the drivers had to point at the listener in OB operation

Yep, it does.

[thomasjefferson]

The null is beside the cabinet, midway between the front opening and the back.  At sub-bass frequencies it doesn’t matter that much whether the driver cone moves toward you or toward the ceiling/floor.  The sound output is shaped by the sides of the cabinet, i.e. the light colored wood panels in these images.

In the middle image, you see the shadow cast from the left speaker onto the left side of the tower sub?  That’s where the null is.  I’ve tried listening to the null by putting my head right there, and it does sound muted. 

If I hold my forehead right at the middle of the light colored sidewall, the sound changes when I rotate my head so my ears change from on-axis with the null (muted) and perpendicular to the null (not muted).  Even at the null there’s sound that arrives from room reflections.

=TJ

[HAL]

I guess what I was thinking is the driver null is (i.e. the basket mounting ring) pointing at the listener. 

Just so I understand the drawing, is there a back panel on the subwoofer cabinet?  It looks like it has one in the rendering.  With the back panel on, the woofers would look to be in an isobarik style of setup. 

Understand that low frequencies radiate in all directions.  With the sides on, the pressure wave would come out the front, but with a back panel on, it would only come out the front.   

[Danny Richie]

Nope it is open on the front and the back.

The null is a mid way point down the center of the side panel.

It is just like a W frame design but with the woofers laid over a little further.

[HAL]

Danny,
Ok, now I understand!