Plans for BIG 2x Ascendant Avalanche 15 subwoofer/TV stand - diyAudio
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Old 29th October 2006, 07:15 AM   #1
BHTX is offline BHTX  United States
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Default Plans for BIG 2x Ascendant Avalanche 15 subwoofer/TV stand

Hello DIYers,

I really need some help here...coming up with plans for a large subwoofer enclosure that I would like to build (or have built for me...somehow). This enclosure would also serve as a TV stand for my 67" Samsung DLP 1080p HDTV. I'm tired of seeing these two Ascendant Audio Avalanche 15's sitting around here, not being put to good use with my Eminent Tech LFT8a's. For the last couple of months or so, I've had one of them in a smallish 2 cubic foot sealed prefab box, sitting underneath the right side of my TV, powered by a Dayton HPSA 1000 amplifier. Needless to say, I think I could do a bit better. And...my TV is in desperate need of a better stand. I'm still using the stand that came with the 27" Sony Trinitron from 1989 that this Samsung replaced. The plastic part on the bottom of the TV that sticks out is just big enough to barely cover the old tv stand. But it looks silly, and the stand feels like it's about to bust loose and fall over!

Just from messing around with WinISD (it's all I really know how to use), I've come up with 6.5 or 6.6 ft^3 @ 19Hz for EACH woofer. This of course, would come out to around 13 cubic feet for both woofers, although I would like to have them in separate enclosures and run them in stereo. The ports would be firing out both sides of the enclosure, probably as far back as I could get them (closer to the wall), aiming towards the corners of the room (rectangular)...

I would like to verify that the t/s parameters that I'm using are correct, as it's been a while, and I can't remember how I got them:

Qts: 0.30
Qms: 3.50
Qes: 0.33
Vas: 300.6 L
Fs: 15.70 Hz
Re: 3.20 ohm
Le: 2.40
Xmax: 27mm
Z: 4 ohms
SPL: 87.00 dB
Pe: 800 W
BL: ????
dia: 15 in
Sd: 7.490 m^2

Anyway, my problem is...besides the fact that I've never built an enclosure and have NO experience whatsoever with working with wood (therefore no tools or supplies, etc)... I need help coming up with the EXACT dimensions. After measuring how much space I have to work with for both subs and writing it down, then converting it to feet to convert to cubic feet, then dividing that in half for each enclosure...I've come to realize just how accurate everything has to be, as just rounding things up to the nearest hundredth or thousandth can end up getting things out of whack when dealing with an enclosure of this size. And port lengths to one hundredth of an inch?? How the hell am I supposed to go about this?? I know it's not going to be 100% accurate, but I just want it to be as close as possible.

Also, I'll most likely end up buying the 3/4" MDF from Lowes or Home Depot for just over $20 for a 4'x8' sheet, and handing it over to some one else for them to cut....that someone else not knowing anything about audio. With that said, I also need to know the best way for the MDF to be cut, in regards to gluing the pieces together.

Getting on with it. In order for the enclosure to function as a TV stand, it needs to be ROUGHLY the following dimensions:

62.5w x 20d x 18h (inches) ...Give or a take a few inches on the height and depth as needed.

Correct me if I'm wrong, but this leaves me 13-14 cubic feet externally to deal with, which is just about right for the 6.5 ft^3 per sub enclosure that I'm interested in building.

According to WinISD, it'll take a good 3-4 ports per sub to get a really low vent mach. At 6.5^3 at 19Hz, 3 vents at 3" diameter at 21.32" length = 0.05. 4 vents at 3" diameter at 29.16" length = 0.03...so I figure that's about as low as I can go and that's really pushing it.

I had considered utilizing a passive radiator, but after looking into it, I just assumed that it'd be even more complicated...not quite ready for something like that yet. I obviously have a fair understanding of how simple sealed and vented enclosures work, but I've just never built one, and I'd really like to build something nice now to use these two woofers, as well as a new TV stand for this big behemoth I sit and stare at every day.

And incase anyone wants to mention it...I'm already well aware of the large "sonosub" designs that have been floating around the net (AVS Forum, etc), some of them also referred to with some made-up acronym that I can't remember off the top of my head at the moment. I came across them several weeks ago and was pretty attracted to them, but came to the conclusion that it was just a little too big for my tastes. I believe the Avalanche 15 requires a significantly larger enclosure than a Sound Splinter RL-p, which I saw several people using with that design. It was similar to an EBS, except even much larger, and was supposed to complement room gain. Seemed great, but too large, especially for two of them! On the other hand, I can do it this other way...and have my cake and eat it too.

Anyhoo, I'll see if I can attach a screenshot with WinISD to show you guys what I'm looking at...

Thanks in advance!!
Brandin
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File Type: jpg ava15-65ft-19hz.jpg (74.2 KB, 183 views)
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Old 29th October 2006, 12:45 PM   #2
Paul W is offline Paul W  United States
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One thing you may want to seriously think about is how to isolate the electronics in that very expensive monitor from vibration. Wall mount, or a stand over the sub isolating the monitor?

Big boxes will vibrate like a drumhead (and sound terrible) unless they are incredibly well braced. Make sure to deduct the volume of the bracing, port, etc from box volume. .01" tolerance? Volume is not THAT critical. If anything, build the box oversize...you can work with the tuning...or toss some old books in the box. Too small is much tougher to deal with.

If you have a spot for it, consider IB and get rid of the box entirely.
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Old 29th October 2006, 09:43 PM   #3
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What you're refering to is the LLT (Large Low Tune).

Looking at your FR graph, would you want to go slightly larger to say 7-7.5ft^3 tuned to 17-18hz? I've not plugged that sub into WinISD, but I'm betting you can go slightly larger and slightly lower to help increase that bottom end. With 27mm of xmax (one way?) you should have enough excursion to play with.

Another thing, you can go with bigger dia. and longer ports by putting a 90 elbow on the pipe. Having 4, 3" pipes could cause audible chuffing due to the high surface area to total port volume. Ideally you want as little surface area (at the mouth of the port) for the air to touch as possible.

As already mentioned you will want some way of isolating the TV from the sub enclosures, though I can't think of anything effective off the top of my head that looks classy.
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Old 30th October 2006, 07:40 AM   #4
BHTX is offline BHTX  United States
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Ah yes...isolating the TV was something I had thought about before, but seemed to have completely forgotten temporarily. I guess I must have assumed it'd probably be ok, and forced the problem out of my head (not a smart move). I'm stumped on that one, too. There's only 2 or 3 possible solutions that I've come up with, and none of them seem very attractive. I guess I'll have to come up with something though.

6.5 cubic feet before displacement is REALLY pushing it, as the height that my monitor currently sits would be raised about 4", and the depth would be over 20"...probably around 22" or more. My TV really only needs less than 17" of depth, but I figured it'd be ok to add a few. It's currently sitting about 3-4" from the back wall anyway. Still, I tried 7.3 ft^3 @ 18Hz, and it's just not doable. And it seemed like any slight gains resulting from the increase in size would only be under 22Hz with a 1-2dB increase below 20Hz, after it's way under the -3dB point. I'd still like to do it, but I just don't think it's possible.

I'll definitely be bracing this enclosure quite a bit, although it has to be something relatively simple. I've come across a few jpeg's of other people's projects, and seen a couple of things I might be interested in trying. My main concern is how much bracing I'll be able to do before screwing myself over with the enclosure volume.

After spending a little more time browsing the net to see what's available as far as ports go, the flared ports definitely look attractive. Any downside to using these? For the 6.5 ft^3 @ 19Hz box (x2), WinISD shows a vent mach of 0.10 for 1 6" port. I'm very interested in the 6" flared port stuff from PSP:
http://www.psp-inc.com/psp-inc.com/p...on%20ports.htm

I'm assuming the flares change the required length of the ports just a tiny bit??...

WinISD shows 27.44" for 1 6" port.
PSP's Port Length Calculator says:
Straight Length Port required 28.08
Flare Length Port required 29.08

With less than 1.5" left behind the inner flare opening, I'm afraid I might have to extend the enclosure just a bit wider than the TV? I haven't seen any 90 elbows for 6" tubes. The hardware store might have something available, but I'm just not so sure about the 90 bending thing. *scratches head* Hrmmmm....maybe this isn't such a good idea afterall? I don't know. I'm still thinking though. *sighs*

Thanks for the help so far. I'm still very interested in doing this...but I think the size of the project just makes me a little frustrated, lol. I get discouraged easily. Ah well... I'll be checking this thread again and again throughout the day tomorrow...

Oh yeah, almost forgot. That's an REALLY nice IB setup you have there, Paul W. I'll bet it sounds awesome. Unfortunately, no space for an IB right now, or I might consider it.

Brandin
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Old 30th October 2006, 09:30 AM   #5
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You can do port flares yourself with a router, or with body filler.
http://www.users.bigpond.com/bcolliso/flares-35mm.htm

Flaring the port does increase the length it needs to be overall, but you can also extend the port outside the box a little bit if you get creative. For example.
http://www.klone-audio.com/
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Old 30th October 2006, 12:42 PM   #6
Paul W is offline Paul W  United States
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Flared ports reduce turbulence, so they are recommended. As I recall, each flare end reduces the effective length of the port by about 1/2 the flare radius.

Minimum end clearance would be "virtual cylinder" able to pass at least the outside area of the flare...more can only help reduce turbulence.

Building one large box with 2x the volume would provide room to extend ports deep across the back of the box, slightly offset from each other. Try to locate a supplier of 6" ports (or DIY) that allow length adjustment after the box is built.

If you are running out of room for the box, or it ends up boomy in your room, seal the enclosure and use EQ to adjust low end response to match the room. You'll very likely need EQ for the room no matter which way you go.

Have fun...and don't forget to protect that TV
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