Re: Stair Cardioid Subwoofer Array
1. Langston's 2005 tests were done with the rear EAW BH760 lifted above the front sub, what Sebastian refers to as a "stair" configuration. The result of any different configuration will be different.
As I recall, his tests were done shortly after this thread hit:
subs and deploying them 'in the round'
In this post:
subs and deploying them 'in the round'
He mentions:
"Bonus: (bottom 2 BH760's only, notice the 6dB front to back peak output differential and the 10dB spread around 75Hz. This is not a cardioid arrangement, just an advantage of horn subs.)"
Four years ago I did some testing to determine the difference in directivity between three different subs types:
http://www.diyaudio.com/forums/subwoofers/184982-tapped-horn-directivity.htm
The proximity to local surrounding objects had a rather large influence on the test results, but applied to all the cabinets tested.
The bass reflex tested was basically omnidirectional within about 1 dB to 60 Hz, then drops about 3 dB at 125 rearward, and around 7 dB at 160 Hz. The front loaded horn was basically omnidirectional within about 3 dB to 60 Hz, then drops about 7 dB at 125, and above. The tapped horn was basically omnidirectional within about 2 dB to 60 Hz, then drops about 12 dB at 125, and around 9 dB at 160 Hz.
The tapped horn with a mouth extender showed the advantage of a large frontal area, it has some directivity all the way down to below 30 Hz. At 60 Hz, it has around 7 dB difference, and 125 Hz, a bit over 14 dB. A huge directionality increase from a sheet of plywood.
2. Horn subs do have more directivity in the upper range than bass reflex subs, so will show more difference in response when that upper directivity reflects off another box placed in front of it. The lower frequencies, being more omni, only "see" the front box obstruction as a small percentage of the hemisphere (if on the ground plane) they radiate in to.
3. Most of the low frequency sound waves from the rearward box do not actually "pass through an additional horn path", but yes, upper bass frequencies are compromised in the time domain due to the different path lengths around a box placed in front.
4. Yes.
5. More or less, depending on frequency and location ;^).
Art
