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 Post subject: Home theater
PostPosted: Mon Sep 11, 2006 12:44 am 
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King of Pompous
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Not car audio but figured a lot of you guys may like to have sound at home too. What lies before you is an infinite baffle system for the home. Essentialy you are using another part of the house (in my case the crawlspace under the house) as a subwoofer enclosure. Basements, attics, crawlspaces, and spare rooms are all candidates. You need a very large space that can be sealed off from your main room. Why do this?

Better sound quality...arguably the best...because you are letting the speaker be completely uncoloured by an enclosure. You are also gaining a lot of efficiency because the sub will need far less power from an amplifier to make it reach full excursion. Power compression is gone and your efficiency is through the roof. There is absolutely no decay...when the bass stops the sub stops..no weird resonances that you can get from an enclosed system.

No big enclosures around the house. Before I did this I had a pair of 7 cube enclosures that were...err...part of the decore. They were huge and ugly. With the IB in place you would have to look down the register to see that they are subs and not part of the heating system.

There is not an enclosed speaker system on the planet that will match the low frequency extension that an IB system can do. I can drop as low as 5Hz on mine and you feel things shaking and the subs aren't straining. You won't get a ported enclosure to do it...or a bandpass...or a horn...or a etc. etc.

So what sux about it?

The enclosure is physicaly attached to your foundation one way or another. You will get vibrations everywhere in the house. I have loosened floor boards that need some tightening and I have found every loose panel in the house.

Getting your wife in on the game of cutting a hole in the floor/wall to load a manifold of subwoofers can be a challenge. Turns out that Denice likes the fact that she now has an extra place for a chair or two now that the sub enclosures are gone though.

You generaly need more subs than a typical system...but not always. I had two 15's before in enclosures and the same ones now fire into the crawl space. I have more output than when I started because of better room placement. My subs sit directly under the TV....the bass never seems to come from a different spot than the screen. I also ran out of bass around 25Hz in the enclosures...now I have all kinds of output to 5Hz. IB systems typicaly need some EQ'ing to get them right though.

My only plans to the system are a "proper" amp and I will likely move to either a pair or quartet of 18's. Reason is not entirely output related either. I want to flatten my bass to 10Hz. Anything over 20Hz is a thrill ride in my home. There is lots below that but there could be more too :P.

On to some pics:

This is how they look in the floor. Simple enclosure made from 3/4" plywood braced on the outside with 2x4's. 15's are facing each other to help cancel out some vibrations through the foundation.

Image

This is what it looks like from the outside. Yes the floor looks like shit...but heaps better than the people who had is painted rusty red :blaaah:. When the floor is redone it will actualy get a 3/4" layer of plywood to stiffen it up.

Image

So...on to the meat....Heres a clip from War of the Worlds. Its when the tripods first start vaporizing everybody. Its a little long and I had to have my finger over the MIC of the camera so that it didn't distort to hell (reference volume is a tad over 100db) and sound like complete shit. The carpet was thrown over the hole a bit to give you an idea of how much output I'm getting from a 75Wx2 receiver...yes....75Wx2. the last couple of "blips" was when it was walking away. You don't see it well but the carpet is jumping about 2" on the "normal" stuff and the big jumps are about 3".

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 Post subject:
PostPosted: Mon Sep 11, 2006 7:39 am 
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Just a few Q's
Since they are facing each other, do you have one wired out of phase?
Did you have alot of trouble sealing the room, or do you find that you have phantom farting noises :-P ?
With that amp, how can you control those large drivers, and still keep up and couple with the small main speakers?
Where do you cross them over?

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PostPosted: Mon Sep 11, 2006 11:00 am 
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IIIRC I wired them out of phase. They've been down there for almost a year now :P.

Sealing the room wasn't really an issue. The subs fire under the house into a 1000^+ enclosure :P.

Controling the drivers with a small amp is easy because you aren't restricting cone movement with an enclosure. Your essentialy running the sub in freeair so getting it to full excursion is easy becasue you are only limited by the suspension of the subs. As you can imagine attack is phenomenal because there is no air suspension from an enclosure. When you set it up this way your subwoofer sensitivity matches that of the speaker you are using. In my case the subs were something like 92db @ so 95db per pair. When you mount a speaker in an enclosure you mess with the sensitivity ratings a bit...with IB it is unaffected. If you can believe this the subs aren't anywhere near full X-max either. They are my old 15's from the black Swift.

Subs are crossed over at 80Hz to my mains. Fronts consist of Athena ASF2.2's and rears are ASF1's. I'm currently building a center channel with matching drivers from my other set of 1.1's. Center channel I have now (Athena as well) works great but the mains will outrun them in output should I ever go to a bigger house. All processing is done through a Marantz SR8500THX receiver. Sub amp is a cheapo Technics 75x2 from about 6 years ago EQ'ed with a vintage Audio Control unit. Eventualy it will be replaced with a Behringer amp.

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PostPosted: Fri Sep 29, 2006 12:16 am 
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nice, m. :D

i have done several infinite baffle subwoofers by installing baffle boards in fireplaces. one time a friend and i argued over whether or not it was really a modified transmission line or IB system.

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PostPosted: Fri Sep 29, 2006 12:21 am 
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It would still be IB because the rear wave wouldn't interact with the front :P. Yup they are nothing short of amazing when implemented properly. As soon as Mach5 has 18's in stock again I'll be replacing the 15's with a pair of them. Also getting a prototype 20" sub to "experiment" with. Won't work for an IB setup but likely a killer PA sub...or a really big tube for mo beta bass in the garage.

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PostPosted: Fri Sep 29, 2006 1:50 am 
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you are all insane........completly, utterly, unquestionalbly coo coo.......and thats why i love you guys.......keep up the good work. :yeahyeah :D :D :D :D :D :D :D :D

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PostPosted: Sat Nov 11, 2006 1:59 am 
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This is the latest sub...next to a 12" DEI


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