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Discussion Starter · #1 · (Edited)
Discussed the project beforehand here:
http://www.hometheatershack.com/for...23415-avalanche-15-7-cubes-advice-needed.html

The plans: 7 cubes, two 4" ports, 19hz


It was not fun working outside below freezing! MDF dust literally froze to the ground and had to take a shovel to it to get it off. Moving the subs in and out repeatedly was not fun either.





Here's a look at the insides. Assembled using wood glue + pocket screws. PL premium on the last layer. 4" mineral wool behind the driver covered with batting to prevent fibers from flying out the port. 1.5" rigid fiberglass everywhere else. This stuff was nice in that it had a black surface that can be left exposed. The insulation took up quite a bit of volume so I'm curious where the final tune will net out, still have to measure that.





The finished product, and yes, I know they are ugly. But they are going behind my screen wall never to be seen again.



So far, I've only listened to them near field with music and they sound great. Nice, tight, punchy with accurate tonality. I can hear notes, not just boom. I hope they play just as nice behind the screen wall.



Next up, fire up REW, play around with final positioning, bass traps, and eq.
 

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Nice! I am beginning a VERY similar project with the exact size for 2 enclosures under my screen. Why did you choose 2 ports? Where did you find the precision ports? How will you power/cross them?
 

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Discussion Starter · #3 ·
Thanks.

When I was modeling it, two 4"-ports had lower vent mach than one 6"-port. Dual 6" ports would have been as long as my entire enclosure. Also, I remember reading that Chad K. had recommended 2 4" ports for my driver. I got the precision port kit from parts express and the port extenders from thriller audio. The only issue I had with the ports were that the drywall screws I used don't sit flush with the flare so it's a bit ugly... but my entire enclosure is ugly so... But the ports were well worth the money with easy assembly to boot.
 

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Discussion Starter · #4 ·
forgot to add... I'll probably cross over at 80hz and each driver will get 500 watts (using 2 channels of a samson s1000).
 

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Discussion Starter · #6 · (Edited)
I did some quick and dirty measurements to get a ROUGH idea for sub positioning and room response before installing behind my screen wall. I played with corner loading vs. having the drivers at 1/4 & 3/4 room width with ports corner loaded. There really wasn't much of a difference except at seat 1 when the ports were corner loaded... got a big spike at 12.5hz. The 1/4, 3/4 position with ports at the corners seemed to provide slightly more even response across different seating areas.



Used a sound meter (w/ correction values), test tones, plotted my results in excel and I got pretty decent results. I don't know how accurate my readings are but I'm happy so far. Pretty good output with my volume set at a measly -30... not even close to "reference". And it looks like I'll be able to EQ this thing flat... no horrible notches/nulls.



I'll fire up REW in a few days to get a better idea at what's really going on after the bass traps are setup and fine tune the EQ. Pretty excited at this point but haven't listened to any movies yet... just test tones and some bassy music. But still nervous that the higher resolution measurements will reveal problems in my room.

Regarding tune... I couldn't get an exact idea but it's somewhere between 17.5 and 19 so it looks like the fiberglass damping didn't change the expected tuning at all.

I'm still torn on how I should position these things... ports facing each other or the corners... any ideas to help me decide?
 

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Discussion Starter · #7 · (Edited)
Got them behind the screen wall.



After bass traps



I dialed in the subs with REW (sorry... too lazy to post graphs). Initially there were 2 peaks but got those dialed down and it's reasonably flat. I measured it down to 7hz and the subs keep climbing in DB's the lower it went I never saw the response drop. But something strange happens when I engage my Rane PE17. with the low cut filter at the lowest setting 10hz... the frequency response starts rolling off before that but then spikes back up a few hertz lower (wish I captured the graphs). It's as if the low pass works within a specific range but then allows lower frequency to continue passing through. Very strange and I could not figure it out. I also have huge decay times (still going strong at 600ms) across the entire band and don't know what I can do to reduce them.

Subjectively... these subs are blowing me away... literally. You can't even being to compare the output of these subs vs. my non-corner loaded IB. I was showing the shotgun scene in the beginning of Ratatouille to a buddy and he literally jumped off the sofa and watched the rest from the back of the room. Granted me and my 2 year old were closer in having a fun time but he was not expecting it at all and was visibly shocked. :D
 

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Now don't become bass snobbish on us now.:R

Very nice project and a great workout. MDF is so heavy though seriously.
 

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I measured it down to 7hz and the subs keep climbing in DB's the lower it went I never saw the response drop. But something strange happens when I engage my Rane PE17. with the low cut filter at the lowest setting 10hz... the frequency response starts rolling off before that but then spikes back up a few hertz lower (wish I captured the graphs). It's as if the low pass works within a specific range but then allows lower frequency to continue passing through
It's probably your correction values or mic - I wouldn't trust anything below 10hz without using a professional grade calibrated mic.

Subjectively... these subs are blowing me away... literally. You can't even being to compare the output of these subs vs. my non-corner loaded IB. I was showing the shotgun scene in the beginning of Ratatouille to a buddy and he literally jumped off the sofa and watched the rest from the back of the room. Granted me and my 2 year old were closer in having a fun time but he was not expecting it at all and was visibly shocked.
Excellent. I don't know what orientation your IB drivers were mounted in, but you're gaining at least 3db extra sensitivity and headroom per driver with the corner loading as well as up to 9db in the low end from the porting. It's almost unfortunate that an IB is so easy to make, as people then won't know what they're missing with a large ported sub.
 

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Discussion Starter · #11 ·
Got off my lazy **** and posting some measurements.

Before and after measurement. The lighter green (on top) is after EQ.




And here's my waterfall... like I said... huge decay times

 

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Is that sub only because that is what I get when I did my sub only. When I do the sub and speakers together it makes a big difference.

What insulation did you line the sub with.


cheers

Graham
 

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Discussion Starter · #13 · (Edited)
It's sub + mains. I don't know if I did something wrong... I'm no REW expert by any means. But to my ears... the bass sounds terrific. Not boomy, muddled, or undefined at all. Though I'm sure a golden ear could walk into my room and tell me it sounds horrible.

Insulation is CertainTeed CertaPro AcoustaBoard, Type 300, 1.5inch thick, 3lbs/ft3 density. It's pretty close to the popular OC703 but has a black film to allow for direct exposure. Very easy to work with, just took a hacksaw blade and easily cut through it. Behind the driver is just some 4" mineral wool I got a while back... not sure on the density.. I want to say 6 or 8lbs/ft3? Not sure though.
 

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Discussion Starter · #14 ·
Very nice project and a great workout. MDF is so heavy though seriously.
No kidding... you should have watched me trying to put them in place... it was like that Friends episode where Ross was repeatedly yelling "pivot" trying to get a couch up the stairs.
 

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Discussion Starter · #17 ·
Thanks.

I'm using an 80hz crossover and you're right, it does roll off hard and it definitely wasn't intentional. When I did a broader frequency sweep, the levels above the cross over point do not roll off further than what's on the graphs and maintain this level throughout the rest of the main speaker band. So I'm guessing this is some type of unintended house curve? I was actually happy that the sub starts to get louder than the mains after 70hz. Do you think it needs to be addressed?
 

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Discussion Starter · #19 ·
Did you just say too much bass????? :nono: :D

I'll post back when I retake measurements. I didn't save the full range frequency sweep files.
 
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