Manifold question

[ginmtb]

Great site! I'm doing an IB under the sub floor and have these arch bases to shoot the manifold out through. Check out my site:

mikesremodelpage.blogspot.com/2006/09/let-cutting-begin.html

On the left hand side of the arch base, is just more of the box - should I wall this off so the sound goes straight out the main opening? Does it matter? I'm going to mount my EP1500 and FDP in the left opening, so part of that hole in the sheetrock will be partially obstructed. Any concerns with that?

Guess I probably should've asked these questions before I cut and bought all the stuff. But I really didn't have any other options anyhow, so hopefully this will work (and work well).

Thanks for your input!

Mike

[ginmtb]

FYI - each opening in the subfloor is about 13"x14.5". The openings in the arch base are 12"x17" and 12"x15 approximately.

I'll be using two MJ-18's. My room is huge, so hopefully that will be enough - this is no THX certified HT. My ported 15" Shiva seems to provide enough bass for the room.

The manifold will be rectangular, approximately 22"x32"x22".

Thanks!

Mike

[ThomasW]

Guess I probably should've asked these questions before I cut and bought all the stuff. But I really didn't have any other options anyhow, so hopefully this will work (and work well).

Yes that would have been a good idea........

I don't think you're going to get enough output from just a pair of the Mach 5 18"s, they simply don't move enough air.

BTW, it would be handy to know the size of the room, and distance from the arch to the listening position. That's what determines how many drivers (how much displacement you'll need).

You'll need to close off the left and right sides of the cutout so the sound is only coming the area defined by the actual cutout. In addition I'd fabricate a piece of OSB or plywood that creates a 45 degree angle 'wave-guide' from the bottom back of the opening to the front top of the opening below the upper horizontal stud. The idea is to not have a bunch of areas where the sound can get trapped with no way to exit.

[ginmtb]

The room is a big living room - 20'x25' with vaulted ceilings. It is also open to the dining room, family room, kitchen, and upstairs - a lot of area. The listening position is about 12'-14' away from the arch base however. The IB is located approximately inline with the front right speaker, and about 2' away from the front/screen.

Sounds like I may need to add a couple more? Not sure I can pull that off based on the configuration of my subfloor (some concrete might be in the way to add speakers to all four sides of the manifold. Are you saying that 2-18" Mach 5's in an IB won't create as much bass as a single 15" Shiva in a ported enclosure? I know y'all say the bass is different based on what I've read here. But I've never heard an IB setup so I have nothing to compare it with.

Doh!

Mike

[ginmtb]

admin said:

You'll need to close off the left and right sides of the cutout so the sound is only coming the area defined by the actual cutout. In addition I'd fabricate a piece of OSB or plywood that creates a 45 degree angle 'wave-guide' from the bottom back of the opening to the front top of the opening below the upper horizontal stud. The idea is to not have a bunch of areas where the sound can get trapped with no way to exit.

Hmm... the wave guide might be problematic since I had planned on mounting my amp and eq in the left opening - which will reduce the opening size by about 1/3. I can close the sides off though. In looking through the gallery, I've seen a couple of setups that hide the exit of the IB in an entertainment center and there isn't a wave guide. I'll see what I can do.

Thanks!

Mike

[ginmtb]

Guess I'll build the manifold to accept four 18's and start out with two - will be easier to sneak past the wife that way too... Seems easy enough to build the fill plate. Now that's assuming I can put the four there. If not, it sounds like I might be hosed.

If I can't do the four 18's, would four 15's work better than the two 18's? I might be able to squeeze them in along the longest dimension. I don't have a ton of room in the budget - I was considering the PE IB subs initially until I saw the review on the Mach5's here.

So tell me this - assuming I don't want 100db+ in my HT, am I going to need more than two 18's? I know the site says to err on the conservative side and go with more woofers, but not sure that can happen.

Oh and I just thought of another option for locating my amp and eq - I have a closet nearby that could be used to house them. Now I figure this out after running electrical to the arch base... another doh moment! So maybe I can run the "wave guide".

So much for being a lurker and trying to figure this out on my own.

Mike

[ryans]

"Are you saying that 2-18" Mach 5's in an IB won't create as much bass as a single 15" Shiva in a ported enclosure? "

I don't speak for Thomas, but I'd say 2 Mach 5's in a sealed or IB app should be able to equal a vented Shiva in the low bass and have a significant advantage above 50Hz or so.

This sounds like one of the rare cases (like my own) where the goal was not to significantly surpass the output you're already getting. The norm around here is more like the guy who wants more output than his twin-woofer SVS gets him. So you can see why there's a strong tendency to recommend aggressive systems.

"So tell me this - assuming I don't want 100db+ in my HT, am I going to need more than two 18's?"

Impossible to say for sure. But I think 2 will get you at least 100dB down to 20Hz ... or lower. WinISD pro says that with 300 watts you get 106dB at 20Hz at 1 meter. You're sitting farther than 1 meter, but even in large rooms, boundary gain can be significant.

Remember than one of the benefits of overkill is that the woofers are never asked for max excursion - they stay within their most linear operating region. So definitely build in the ability to house 4 woofers.

[ThomasW]

ginmtb said:

Hmm... the wave guide might be problematic since I had planned on mounting my amp and eq in the left opening - which will reduce the opening size by about 1/3. I can close the sides off though. In looking through the gallery, I've seen a couple of setups that hide the exit of the IB in an entertainment center and there isn't a wave guide. I'll see what I can do.

What's to the left of the left hand opening? Can you put the equipment in there and use the 2 current openings for the IB?

The room is big. Even if you can't buy the additional 18"s now, you need to plan for adding them in the future.

[ginmtb]

Thanks for the reply. While I would LOVE to have a THX type theater, that's not going to happen. Budget considerations, WAF (Wife Approval Factor), etc. will prevent me from doing that. But I would like to have something that performs well, and I will build the manifold to accept four woofers assuming I can do that. I do like the idea of not pushing the woofers too hard.

Of course, I purchased the EP1500 with the thought of just two 18's in mind, but I suppose I could run them in mono bridged mode to get more power to the woofers. Shoulda just bought the 2500 for not much more money. Oh well, at least I came up with a better location to put the amp and BFD.

[ginmtb]

admin said:

What's to the left of the left hand opening? Can you put the equipment in there and use the 2 current openings for the IB?

The room is big. Even if you can't buy the additional 18"s now, you need to plan for adding them in the future.

There is nothing to the left of the left opening. But I didn't want to cut anymore holes in that base and if I close off that side I won't be able to get to it.

I will put the amp/eq in the closet noted in my diagram:

photos1.blogger.com/blogger/2858/1930/1600/home_theater_layout_version2.jpg

Don't know why I didn't think of this before - your suggestion of the wave guide and closing off the sides though made me think of the closet - so thank you. I was going to pretty much leave my amp/eq on full time since the fabric panel would be removeable, but not something I'd like to take off everytime I used the system.

I will definitely build it to accept four woofers assuming I can fit four woofers - back under the subfloor it is.

Thanks and I will continue to take photos and utilize y'all as a great resource. No more learn by doing (the motto at my college - Cal Poly SLO).

Mike

[ThomasW]

The link doesn't work.

[ginmtb]

admin said:

The link doesn't work.

Try this one and then click on photo to enlarge:

mikesremodelpage.blogspot.com/2006/09/ht-layout.html

Sorry about that.

[ThomasW]

Placement should be fine. Did you try your Shiva in the same location?

[chrisbee]

The link worked fine for me.

I just copied and pasted it using the forum's img /img postcard symbol. (4th symbol from the left above the smilies)

[ginmtb]

admin said:

Placement should be fine. Did you try your Shiva in the same location?

I actually have not - I will do that though - that will be a good test. It obviously won't be in the exact same spot as the IB as the cabinet is basically a 2' cube and won't fit in there. Just need to move the beast (and the even heavier entertainment center that it is behind).

Thanks for the input!

Mike

[ginmtb]

Okay, so I finished my IB - and I'm totally happy! Didn't do half of the things that I discussed above. I didn't build it for four 18's, I didn't mount the amp in the closet, I didn't build the wave guide, etc. But it sounds great and I can't even imagine why I would need more (I know, you can never have too much bass). I got a little sloppy on the build since I did it all in the crawl space. Fortunately no one will see my work...

I played the THX opening and watched The Incredibles on it and my daughter kept asking why the couch was shaking.

I did have to boost it quite a bit below 30hz, and it rolls off pretty sharply below 22hz, but it is great for my needs. Turns out the Shiva I had was a 12", not a 15" (duh). So this is a tremendous boost over that.

Thanks for all your help. Definitely glad I did this.

Mike

[ThomasW]

Hi,

Good news that everything is working to your satisfaction....

The mj18"s will have that roll-off due to their higher Fs. Be careful with boost below 30Hz with only the 2 drivers, since the really low bass may sneak up and bottom them with highish output levels.

Please add yourself to the "Cult" map.... ;D

[twisterz]

This looks great. I just wonder how your remote is working, it looks like your equipment is behind you. You might look for an RF programmable remote (great WAF) that way you don't have to point it at anything and macros can make it a one touch to get everything started.
My wife loves our MX850 from Universal Remotes.

[ginmtb]

ThomasW, thanks for the advice - I tuned back the boost below 30hz and I haven't noticed an appreciable difference. The THX opening is still amazing!

As for the remotes, I have a crawl space and was able to run a wired remote system to my coffee table (via emitters). So all you see is a small box, about 3"x1"x2" that controls all the remote commands. I use the Harmony 880 and love it.

Mike

[twisterz]

Great Job

Any Pics?