**For JohninCR**
I ripped this off the DIY-Systems site under the bass horn link:

Additional info to take into account

Until now only a small part is explained, there is more to it! Now we mainly know how to calculate the actual horn it is useful to know how two horns beside each other have influence on the response, and how the driver cabinet (the back chamber) has influence on the speakers parameters when adapted to the horn.

When the mouth area Am of two horns are placed beside each other then the result will be a better performance in the lowest bass because the area is now doubled. The next formula can be used to see if we can lower the frequency Fg by the enlargement of Am.

Mind in the calculation where you want to place the horn, by placement in the corner the surface Amt must be multiplied by 8 !

Basic formula for calculating the lowest frequency radiated by the horn...

An advantage is that the new horn can be calculated as being shorter. Because we work in stereo the efficiency is 6dB higher (two speakers instead of one) and the power capabilities (mechanical and electrical) improves.

What has changed is the larger (total) throat area Ah. In reverse you could say its the smaller (half) mouth area Am. The bigger the throath- or the smaller the mouth area the shorter the hornlength.

Suppose a Fg of 30Hz is wanted, according to the next formula the mouth area Am (m²) will be:

Calculating the horn mouth area...

Placed in a corner the result will be 1.32 m². When two horns with their mouth close to eachother are used, the result can be divided by 2 (0.658 m²). By calculating the contour (flair) of the horn it becomes clear that for the same Fg a shorter horn is sufficient. Of course it is possible to use more than one speaker in a horn, Ah is then multiplied by the amount of speakers.

The advantage of more speakers is that the power (mechanical and electrical) improves, the throath can be enlarged (shorter horn) and, not less importent, the speaker selection is less critical.

It is found here:

http://www.diy-systems.com/
Bass horn design section

Hope this helps

Mark