Originally Posted by craig john
You are focusing on something that is simply not important. It's the combined frequency response of the two subwoofers that is important. If you need to set them up so one is 6 ft. away and the other is 12 ft. away, because those positions provide the best frequency response, that would be far better than 2 subs with equidistant drivers.
In your scenario, with the offset drivers, you also have offset ports. There is no way to get symmetrical positioning of both the drivers and the ports. They both contribute to the output, but in different frequency ranges. How would you plan to optimize that aspect? Answer: You can't, so stop worrying about it.
Get yourself some measurement gear if you really want to be OCD about setting them up.
def going to take some measurements when i decide on my subs and get them in my house.
I was just going to start at 1/4 room width and 3/4 room width distances looking at audioholics multiple subwoofer setup and calibration guide as they suggest.
They are very clear that multiple subwoofers should be as symetrically placed as possible in a rectagular room. In regards to where to place the subs in the 1/4 room width and 3/4 room width it states
Note: The distance from the walls to the subs should be measured at the acoustical center for each sub which is usually near the dustcap of the drivers.
So since the pb12-nsd woofer is offcenter, is the accoustical center the center of the sub, or the center of the woofer?
The article goes on to say
The goal is to time align the subs to the room which is NOT necessarily the distance to the listening position. In order for more than one sub to get "traction" against the same room mode they must be symmetrically placed to the mode.
"Editorial Note about Subwoofer Placement & Combined SPL Output
Placing your subwoofers as symmetrically as possible with respect to the listening area can be useful especially if one favors a particular listening seat but we should attempt to make the bass good for all seats"
Figure 1c. 1/4 W Placement
Although this isn't spelled out in the CEA recommendation, Dr. Toole references it in his book as a good solution for two subwoofers but suggests additional subwoofers may be needed. In my experience I've had excellent results placing two subs against the front wall at locations of 1/4 the room width. I've had even better results placing two additional subs in a similar manner against the back wall. This configuration can achieve nearly as good frequency response performance as the 4 Corner placement with nearly as much bass gain as well.
see diagram 1a
Obviously taking measurements are important but getting these things symetrically placed to cancel each others nulls and peaks from room modes is obviously important. its the point of running dual subs, I thought. And if the driver is off center i'm not sure we can satisfy this statement from the article: "In order for more than one sub to get "traction" against the same room mode they must be symmetrically placed to the mode."
i might need to look at another subwoofer that has the drivers and port centered in the box. i know the pb12-plus does, but would 2 pb12-plus subs be overkill in a 13x18x8 room?
My goal is to achieve lfe bass peaks from blurays in that room of 109db in the 20hz to 80hz range.