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Discussion Starter #1 (Edited)
Things fell into place and I was able to complete sub #2 yesterday. Figured I may as well show it off along with the rest of my theater system :bigsmile: The driver is an Avalanche 18, tube is 28" diameter, endcaps are 30" diameter, baseplate is 36" diameter, legs are 8" long, net volume is ~650 liters, and tuning is ~13hz.
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Discussion Starter #2
For scale, the tv is 42" and main speakers are 41" tall. The subs may seem big, but the room would be pretty barren looking without them, and with them being all black, they really do start to disappear after you see them for a few hours. My next planned upgrade is to get a tv in the ~60" range, but I'll probably wait until I end up moving to a new place for that, which will probably be within a year.

Haven't fired sub #2 up yet, I'd like to let some of the caulk dry longer and I'll need to put a resistor in line of the fan on my second amp. I'm not really expecting any eye opening difference though, as the first one never came close to sweating at my normal listening levels of -10 to -15 and my amp never onve clipped.
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Discussion Starter #3
The subs are as much of a conversation piece as they are a performance element of my home theater system. Call this an arrogant statement, but I really noticed a surge in DIY subwoofer activity after I posted about my first sub three years ago. I notice something similar even with friends or coworkers when they see and experience my subs and I explain to them the realtive ease and low cost of building one. They may not opt for the same scale of sub, but they change their mind from wanting to purchase a sub or not even thinking they needed a subwoofer in the first place to wanting to build their own. Performance per dollar, it is by far the way to go. I built both of these for $1500 - one would be hard pressed to get something equivalent commercial or even DIY nowadays, as I managed to get a great deal on the Avalanches when they were on closeout. The tube enclosure, fabric sock finishing, and pro amps also played heavily into the savings.

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Awesome!

I know what you mean about not expecting a big difference. I keep thinking I want more bass, but then reason kicks in and tell me I'm nowhere near using the potential of my current subs, and more would be 'wasted'. Still, 4 gotta be better than 2, right? :p

They look very well built, and absolutely dwarf the front system! :D
 

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Discussion Starter #6
Lol, yeah, all the other equipment looks tiny in the first picture of the front of the room - I don't know if it was the angle or what. In the second picture, you get a better sense of what it really seems like.

Still, 4 gotta be better than 2, right?
Yes, but it only counts if the difference is audible :spend:

A few good initial tests that come to mind to test if I was getting any compression with the single sub vs two are the car explosion from The Matador, the ground breaking scene from WOTW, and there was something from Monsters Inc that was pretty dynamic and powerful.....I forget which scene exactly, I haven't watched it in some time.
 

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Discussion Starter #8
Thanks Sonnie. It's a pretty potent system due to the close proximity of my listening position to the speakers and subs, keeping sensitivity very high and distortion low (relatively speaking). The tower surrounds and mini tower rears also help in that regard.

Those carpet covered, sandwiched sheets of OSB on the left wall were initially supposed to be a soundproof wall I was going to use to block off this room from others to really let loose, but I found I could listen as loud as I want without bothering my townhouse neighbor, so I left them there to possibly act as a resonant bass trap.
 

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Those carpet covered, sandwiched sheets of OSB on the left wall were initially supposed to be a soundproof wall I was going to use to block off this room from others to really let loose, but I found I could listen as loud as I want without bothering my townhouse neighbor, so I left them there to possibly act as a resonant bass trap.
...But what are those square pillow looking things? Are they bought or DIY?
 

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Discussion Starter #10
DIY broadband absorption pannels. 8" thick fiberglass insulation over 1/8" hardboard, wrapped in two layers of rigid polyester fabric. My room has a lot of bare wall space, so I figured some absorption pannels could only help.
 

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Hello Mr. Callas,
Nice missile silos! :dumbcrazy::bigsmile:

I am salivating at the moment , waiting for when my IXL.18 from Mark turns up!
Cant wait.....


Sure does look like a small t.v!!! Certainly puts things in perspective.

all the best
Andrew
 

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Discussion Starter #13
After several hours of monotonous measuring, adjusting, and measuring again, I finally ended up in pretty decent shape. Measuring just the response of my first sub (right) where it was at, a few feet in front the front right corner, things looked good. Measuring the response of the second sub (left) where it was at, a few more feet in from the front left corner, things looked good except for a very large dip from 50-60hz. Combined, the FR looked pretty awful. I knew right then I was in for a long day :doh:

I started moving the subs a foot at a time in any which direction, front, back, left, right, diagonally, etc. I tried all types of asymetric placements - looking back I tried most everything but putting both subs next to each other. The opposite corner thing wasn't an option because the right back side is the door to the house and the left back side opens to a hallway to the rest of the place.

I got to the point where I was able to get very respectable looking FRs from each sub by themselves, but then with both on at the same time, things would go downhill. At that point, even though it is typically not recommended for a good FR, I put each sub directly in a front corner. First thing I noticed was that I gained quite a bit more sensitivity when compared to having the subs just a couple feet from the corners - I wouldn't have expected to have gained the amount of boundary gain I did as compared to only having the subs away from the corners a few feet. Each sub measured by itself looked pretty brutal, but combined, the low end was quite smooth. There was a narrow but deep null ~55hz, less intense than the one from just the left sub when it was moved in a bit, and the 80-100hz looked terrible, likely a phase problem I thought, as I upped the crossover to 80hz since having the second sub. I fixed the problem at 55hz by moving my seating position up about 6", and then I painstakingly took sweeps while adjusting the receiver subwoofer distance 6" at a time. I didn't get anything decent until 23' :explode:

Things look pretty good combined considering I'm not using any EQ. There is still a null around the crossover that I don't care for, but it will have to do for now. I prefer staying natural without any EQ, so on a rainy day I will tweak things a bit more (probably receiver L & R speaker distances) to flatten out the null some - I'm sure it can be fixed without EQ. After recalibrating my system from moving the seat foward 6", I am seeing a 5db sensitivity gain from the second sub.

Using music, things sound great as ever - no pros or cons as compared to one sub. Dialing in the sub level by ear, I found I preferred 3db hot, same as always. It would be pretty difficult to highligt the headroom advantage with music, so tomorrow I will try some favorite movie scenes as well as hit either Spiderman 3, Superman, or Transformers HD DVD, all of which have been waiting patiently on my rack for me to finish sub #2 before watching them. Yeah, I still haven't seen Transformers yet :innocent: Based on some Spectrum testing, Superman looks to be a celebration of bass.

dual sub august 2008.jpg
 

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Looks good Steve. I've got the same kind of issues in the 70-120hz area with a couple of big nulls making the response look like a saw blade. I don't really like to use EQ either if I can help it. Especially not with nulls like that or other narrow band stuff.
 

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Discussion Starter #15
Well I realized after the fact that only one speaker was being used with the sub in the sweeps, so for all I know the real FR around crossover could be much better or much worse. I'll have to test again next weekend with either both speakers or all seven running at the same time, not just one.
 

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:hissyfit: You have 2? I am still trying to get around to getting my one together. I need to get to work. I can only imagine what it's like to be in that room. :R Sweet!!!!
 

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I have a slight notion of what it's like.... I just watched 'Serenity' at -10 from reference, and was seriously afraid for the structural integrity of my house. Seriously. So how people can do stuff like that at reference and still have a roof over their heads is beyond me. And I have puny little 15" drivers! :hsd:
 

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Discussion Starter #19
Nah, but a 57-62" screen would be a nice improvement. I've been in a handful of HTs with projectors, from LCDs to DLPs to even a couple CRTs, and they just don't have the punch and 3d of a good flat pannel.


I just watched 'Serenity' at -10 from reference, and was seriously afraid for the structural integrity of my house. Seriously. So how people can do stuff like that at reference and still have a roof over their heads is beyond me. And I have puny little 15" drivers!
I can't watch at reference, it's just too loud. I watch at -10 to -15, and that is spirited enough for me.
 
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