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Discussion in 'Home Theater Projects' started by Geoff L, Dec 17, 2004.
Fitzmaurice has an agenda, and that is to sell plans to his designs.... nuff said.
Hey Thomas - Don't think Bill was really downing the driver, I just used it as an example, since I hear this about high excursion drivers all the time. I have seen it brought up more than once in discussions of the extremis 6".
I have actually bought a couple of sets of Bill's plans for some PA setups. They are actually pretty awesome considering the price to build and their application. I don't think he is trying to get rich on $10 a pop for plans. I posted the driver pic there as OT, as there seems to be a few real bassheads over on his forum. He did say "But it is interesting.", which I would consider a compliment from him. . .
Once again it has been a busy week and I haven't had a chance yet to reply. Her are some answers to your questions:
There are some enclosure recommendations up on the website for the Avalanche 18 along with the other drivers. For your preferences I would recommend the 20 cubic foot enclosure tuned to 13 Hz. Going with a 700 Liter/25 ft^3 enclosure tuned to 10 Hz will only get you more output once you drop below 11 Hz. From 11 Hz on up the 20 cubic foot alignment will have a definite advantage in output. Trust me when I say that in that enclosure it wil go LOOOOWWWWW.
I appreciate both your and Rob's input on this. I agree that there definitely would be people who would love this type of driver even it it cost a lot more. However, there aren't as many people as you think who want such a driver. There are also several realities that go with it.
I had some initial prototypes of a very high excursion subwoofer design of ours to compare to the Avalanche 18 and Avalanche 15. I am telling you that a pair of Avalanche 15's or a single Avalanche 18 in a sealed enclosure will be louder than you expect.
There are also certain reailites that go along with this type of higher excursion subwoofer. There is an inertia issue as well as an enclosure issue. You should see what happens to a 2 to 3 cubic foot enclosure when a driver starts trying to move 90 mm peak-to-peak. Honestly, it gets ridiculous. The enclosure needs to be at least 2+ inches thick to deal with that kind of onslaught of internal pressure. You end up with a 300 to 400 pound enclosure in your living room.
Then you need to buy an amplifier that can actually get it to move that far. Even an inexpensive 2000 to 4000 watt amplifier isn't that cheap. Beyond this, your outlet usually becomes the limiting factor. Unless you have a large dedicated breaker just for your subwoofer, you may not be getting that much power. I have a friend who ran his Crown K2 from his 220 Volt air conditioning outlet becuase when running it off the standard outlet it used to dim the lights on several floors of his old apartment building.
I will further state that from the get-go, the biggest priority with this company was actually to design and offer this super high excursion subwoofer. I have been thinking about such a subwoofer design for years. At one point, the Avalanche 18 was finished with the current revised suspension. I threw it into a 5 cubic foot sealed enclosure with 750 watts and suddenly I didn't care about that other driver anymore. As mentioned above, I also took a pair of Avalanche 15's and threw them into a 4 cubic foot enclosure with 1500 watts and it was even louder. It was so loud that I began wondering what the higher excursion subwoofer was going to offer over the Avalanche subwoofers. I just decided to put off the development for awhile.
If people are knocking down our door to have it made, than I can certainly re-consider the idea of producing it. For now, I think that the Avalanche subwoofers have the ability satisfy the output cravings of most bass lovers out there. Hopefuly this gives you a little more perspective into why the ultra high excursion driver is on the back burner.
Your question is excellent and you hit the nail on the head. Having two different voice coils allows a larger range of Qts. There will be a wiring tutorial up by tomorrow morning explaining how to wire the Atlas subwoofers for an infiite baffle or dipole arrangement. You can power the smaller voice cols in this setup in series and get higher Qts figures than when powering the larger voice coil.
Having the smaller voice coil also allows you to run a pair of drivers in series and still arrive at a 4 ohm load instead of a 2 or 8 ohm load. This often makes your amplifier options much simpler.
You can also power both voice coils in series and get a 6 ohm load. This gives you a Qts .02 higher than the lowest Qts rating when using just the 4 ohm voice coil. It also gives you the strongest motor configuration and the BL is higher.
Saw that, cool. What type of porting are you recommending for the reflex designs? I've been toying with multiples of the ubiquitous 4" Precision Port, but do you have something rather more clever in mind? I've been thinking of something around 14ft^3/16Hz using three of the aforementioned ports.
After reading up on Sonotubes and seeing different designs and different theories (Harmon white paper) I am thinking that I am best suited to Build a pair of Atlas 15's in your ported alignment as was posted on your site.
I'm still not sharp enough to figure out what to enter into WinIsd for BL and SPL. :b
I need to figure out how long of a 4inch port to use for the 16hz tuning.
I'll probably try a 22" diameter Sonotube cut to a 50" length for a total of 311.462 liters which is almost exactly 11 cubic feet.
I'll order when budget permits. Christmas was not kind to the checking account.
I may start with 1 and then do another later.
Hmm, I don't use WINISD, but what I posted here http://www.hometheaterforum.com/htfo...92#post2505992 will work for a sim, so pick whichever the program prefers.
WRT BL, it can be calc'd for a 'close enough' sim:
Cms = Vas/(Sd^2*rho*c^2)
Vas needs to be in m^3, so multiply liters by 0.001
Sd needs to be in m^2, so multiply cm^2 by 0.0001
rho = density of air in kg/m^3, or ~1.20997 at a typical room temperature
c = speed of sound in meters, or ~344.424 at typical room temperature
Mms = 1/[(2*pi*Fs)^2*Cms]
BL = [(2*Pi*Fs*Re*Mms)/Qes]^0.5
But Mms is given as 269g, so we can skip the other formulas in this case, though it needs to be converted into kg, or 0.269:
BL = [(2*Pi*15.7*3.2*0.269)/0.334]^0.5 = ~15.945, or a bit lower than the calc'd ~16.13.
Too much to resist. I've got a pair of Atlas 15's on the way to use in IB with a large closet (which has served this purpose before) adjoining my room receiving the backwave. I'll be cutting it close at 5 x Vas for the pair. I'll run their 2-ohm coils in series and go for a Qts of ~.7 (I'll play with is a bit). I've got an old PE #300-800 150w plate amp with no boost/rumble filter that should do nicely. The Avalanche 18 is mas macho, but the Atlas drivers are just too appealing in their ability to provide almost any Qts at useable impedance. Here's what Unibox predicts:
With such (presumably XBL-clean) output available with so little power applied, I think I'm in for a treat. Chad, as you might expect, was a pleasure to deal with and has been over-the-top helpful.
Also,with Chad's permission, here are some pics of the upcoming Avalanche 12:
No specs yet. Beautiful, no?
Indeed, very beautiful. I love the motors on the Avalanche series. ETA on the specs?
I finally made it out to Ascendant's to see Chad Tuesday night. I caught a glimpse of the nicely proportioned beauty you posted the image of. I also got to very casually give a listen and observation of the Avalanche 15 & 18 in action (Sealed boxes).
Basically I confirmed what I suspected and hoped. The important factor wasn't so much what I heard, but rather what I didn't. The Avalanche driver behaved very nicely and sailed right through Planet Drum (1st track I think) where some of the low sweeps and pulses will often modulate other bass being reproduced. While hardly a measurement, it was at least a subjective reality check which has left me disappointed with lesser subs. While I'm certainly a bit more greedy with headroom and EQ than most, I would advise those who like very high levels to try and design in a bit more output than you think you might want or need. Without the upper bass character change you don't get the sense of reaching the limits. In other words, it may sound great at louder levels than you currently listening at.
I am still very suprised at how soft (in compliance) the surround and suspension are. I have a single Atlas 15 I'm putting in a modest attic-IB for a sun-room system at my parents place. After that I think I may use the bigger brother in a few custom projects I'm working on where I can't fit our ContraBass. Four sealed Avalanche 15s should do the job.
No ETA as of yet...I'll keep pestering him, though.
My 4 will be here on Saturday (and the 18" for the car)!!!
Here is a review I did of the bigger 15's for those who are interested.