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Paducah Home Theater

some new copper toys, aka. RC-7ii center build thread

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Man, that looks like fun. Especially when your finished and enjoy the fruits of your labor knowing that you built it. Awesome.

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Acoustic foam and port day.  Should have skipped that last brace and put the port a little closer to the woofer. Maybe next time. Actually I say that but it's a tighter squeeze than I would like either way, those flares take up more room than I had visualized.

 

ports_zpspbcdwwos.jpg

Edited by MetropolisLakeOutfitters

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Looks great man, good job. As I see this coming to shape, I find myself looking at my 7ii and trying to figure a way to get that center 7ii. Dang you!! LOL. 

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Final assembly before a test drive.  Don't want to invest in veneer until I know it won't sound like ***.  There's a couple of spots where I need to build up with bondo or something on the edges before I do so.  I don't have a table saw and had it cut on the panel saw at Lowes.  I figure if that's the worst part of it then I got lucky.  Picked up some velvet thinking that maybe I could just wrap it in that like people do with sub boxes and carpet, thought it would kill reflections around the screen, but my wife did NOT like that idea, going with black ash veneer if it sounds ok.  

 

IMG_2961_zpsptabennv.jpg

 

IMG_2962_zpsem8ora9i.jpg

 

IMG_2963_zps6m9wcx6k.jpg

Edited by MetropolisLakeOutfitters

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Outstanding idea & build. I'm jealous. Great job. I hope the end result performs well.

 

Lloyd Dobler approved.

 

 

H2TrHwO.jpg

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Need to run audessey.  First impressions are that I gained quite a bit of panning ability for lower frequencies such as floor toms and voices of transformers.  Didn't gain much otherwise.  But yeah on floor toms, the entire front wall sounds like one source, definitely never had that before.  Also strange that if I elevate the front at an angle, it gets very dead, it is much brighter when it is flat and I'm listening off-axis with my head above the plane that it is on.  I don't understand why, maybe something to do with placement of the woofers vs. tweeters.  Definitely an issue though.  I had originally planned to elevate it behind the screen and fire it right at my head but based on what I'm hearing, that's probably not a very good idea, I just don't know why.  

Edited by MetropolisLakeOutfitters

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Well well well !! At least you're bracing them! Fingers crossed !!

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Just ran audessey. Definitely got my panning back. Switching from thx to rf-7ii's and a 64 got rid of much of that but now its back. Helicopters and drones seamlessly swirl around much better now and can sound like the source is often between two speakers which hasn't been normal. It still isnt perfect and human voices didnt improve at all but Transformer voices is a different story. Anything remotely low now sounds huge comparatively. My receiver even tried to set the center as large / full range.

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Biggest question at this point is what im losing by not flush mounting the drivers. I know there is cabinet diffraction and all but realistically what is the difference in terms of sound? I dont know. There are some slight differences in the highs, not sure what else it could be other than maybe this and the general layout. Without a cnc machine this would be a pita.

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Really cool! Did you consider putting the ports in front? And if so what was the reason to go with rear?

I thought about it but since there are no published specs on the woofers, I figured it would be safest to make a copy of the current cabinet or at least as close as possible. However, as it is right now, the ports don't really do anything at all. I did something wrong, just don't know what. In normal RF-7ii's there are what seems to be two 4" (internal diameter) flared ports that are 8" long mouth to mouth. Tried to mimic that but you can put your ear up to the ports and no bass comes out at all even though the woofer is flexing. I don't know if it is because they are spread out, or if I got my size wrong due to the flares being significantly different, or what. Guess I will have to experiment. What's confusing to me is that even if the tuning is off a little, I would think that SOMETHING should come out. Nope, only some midrange junk, that's it. There's got to be some kind of rule about ports that I'm completely ignoring but I don't know what it would be. Maybe those braces are doing funky things and making stuff cancel out, I have no idea.

Edited by MetropolisLakeOutfitters

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I wish I knew and the first thing that came to mind is the bracing. But I looked at the pics again and I just dont see how the braces could be causing any problems. I have no clue if this is even remotely close but I wonder if the braces are too high? Meaning maybe instead of flush with box maybe 1 inch lower? I wish I could help, I really want you to succeed with this DIY.

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Did you use a port calculator ?

 

No like I said I just tried to copy the existing design and volume as much as possible.  Same woofers, very similar interior volume.  

 

To be honest I don't even know how a port calculator works given the situation.  Seriously, take the dimensions of an RF-7ii minus the wall thickness and subtract a little for driver/bracing/ports, use two 4" ports, and design based on the idea that you're just about flat down to 30 hz.  Doesn't make any sense.  Even at 35 hz which may be a little high given the frequency response, you'd have to have a 5 cubic foot box not counting port/driver/bracing displacement in order to have two 8" long 4" ports.  Lower the frequency or make the box smaller and the ports just get longer, but they're not.  How does that make any sense?  I don't see how it can reach down to 30 hz without being tuned to not much above that, and the numbers don't make any sense to me if you do that.  

 

If the interior volume were about 3.5 cubic feet after displacement and it was tuned higher than I'm expecting like around 40 hz, even if I were like an inch off, you're talking about a tuning frequency difference of only 2 hz, like 40 vs. 42.  It should still produce "something".  That's what is confusing me, I literally hear zero bass.  Nothing at all comes out of the ports.  I halfway expect that the woofers may be cancelling each other out inside the box or something, I've built several ported subs in the past and have never seen anything not produce any bass out of the ports even if I screwed up a little.  

Edited by MetropolisLakeOutfitters

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As close as it was on the bass even with the ports being messed up, honestly I'll probably just try a sealed box if I try again, having actually heard it, I don't see the point in jacking around with it on a center channel.  The bass was awesome compared to an RC-64ii, was not an issue at all, ought to just seal it like I originally thought in my opinion.  If anything it was the highs and off-axis response that was an issue.  I think this design probably needs to be in a vertical orientation to sound the same, and like I said before, the baffle diffraction due to not flush mounting everything makes me wonder about stuff but may not be an issue.  

Edited by MetropolisLakeOutfitters

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Cheap plain foam that I cant find, like eggcrate material except flat and thin . This was about the same thickness but it is more dense. Not sure if that messed anything up or not.

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Need update. How do you like it? Are you opening shop to start building RC7ii Centers? Does it sound as awesome as it looks?

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