Pretty good. Wish I had some of his equipment. Yeah I was told a good while ago that theoretically ya get a 3db boost for every in phase reflection achieved which is why rear firing subs in SUV's and trunks are louder. Its also why corner loading works well in the home and downfiring subs are popular.
In order for there to be ANY cancellation from a "pair" of soundwaves they've gotta be more than 90 degrees out of phase. Thats the same thing as saying that one sound wave meets up with another after traveling more than 1/4 of its wavelength.
For example the 60 Hz wave that was described has a wavelength of (speed of sound)/f or 343/60 = 5.72 m = 18.76 ft. So in order to at least get some cancellation one wave has got to be at least 4.7 ft ahead(or behind) the other. You theoretically get total cancellation when these two guys are 180 degrees out of phase, 1/2 a wavelength apart, or with 60 Hz, 9.4 ft ahead/behind one another.
What seems to be a cool thing about this is that since lower frequencies with longer wavelengths are less prone to cancellation(unless you're backfiring 8 15's in a Greyhound bus or somethin) you should be able to actually "tune" your backfiring box a bit by adjusting the distance from the surface its firing into.
For example If you want all the bass you can get do like the guy said and get that box "close" to the rear "wall". Or say ya built a box that ended up being peaky at 60 Hz in your car. Firing that box 4.7 ft.(one half of half a wavelength: remember the wave has to travel that gap twice) away might cut out a good deal of that 60 Hz boom that was buggin ya before.
I dunno, thats my theoretical take anyways. Let Jonathan or Glass bring it into real world perspective. Was a pretty neat lil article. Hope I got it right.
Of course as was mentioned this was the normally incident(perpendicular to the wall) stuff and doesn't include the waves goin off at weird angles from the subs. Those are the ones that can really get out of phase which explains why he got more output with the trunk open.
i have done this test on my cousins explorer, if you fire it backwords it gives you an spl gain, if its angled it gives an excellent sql, and fireing it up seemed to give the best sq, for me anyway, but all vehicals are different so i think its kind of baised
Lol, Sean you do know I'm pretty much wingin it in these posts. I have very little practical experience in these things and I've been out of school for over 10 years so I'm constantly havin to dig out text books and "relearn" a lot of this stuff.
Man, I was high on the acoustics when I was trying the the Ocean Engineering thing. Sonar transducers are just high output piezoelectric super tweeters on steroids.
Sure wish I had gotten that degree.
Hey, you haven't bid on any Xtant amps at Ebay have you. There's a "sean" who bid on one I got my eye on. No use jackin the price up if its you.
hey guys, sorry to say but all those ways are right and wrong. ALL cars and suvs are different, a ford explorer, yes fires back w/ports back,(facing down sounds clean but not as loud), but how about a crx? any of you guys have an idea on how to make those loud, mine does 162.1 on a termlab mic right now, guess how my box is, btw, i have 4 dd 9512 and 4 mmats amps
lol no fishy i havent bid on any xtant amps got three mtx amps right now is nuff for me....by the way i can tell you had some kind of keen technical mind by the way you talked in this and other posts ive seen you post in
hey zac for the record on thing you forgot to realize the post is about sound wave cancellation so your right each vehicle can be different but you also fail to realize knowledge is power and what i share isnt just for me its for the benefit of those on this message board as well (speaking to your cut paste comment)