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post #1 of 15 Old 02-02-2012, 09:00 AM - Thread Starter
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Hi All,

I have attached a pic of our basement blueprint.

Nothing is finalized as we will not be breaking ground until April/May (so things are still in constant flux).

I am having an extra room added to the basement under one of the garages via SpanCrete.

RED = Concrete walled room under garage#2.
BLUE = wall where 4' door will go
GREEN = proposed framed walls (rough)
YELLOW = rear concrete wall which will have a 4' opening into the rest of the basement (exact location still undecided.

My plans are to have a small recessed wet bar on the rear wall. The IB arrangement will be on the front wall at the bottom. It will be eight Fi-IB318's in a row spanning the bottom of the wall.

Hopefully from the crude lines I drew in one can see that the framed walls will not be tight against the concrete. The front wall will be framed ~ 1' from the concrete wall and the right side framed wall (opposite the "door wall") will be framed ~ 18" from the concrete wall. This space would allow me to creep back to the front wall, but behind it.

Here is my concern....
Since this is an IB setup....does the space immediately behind the drivers have to be 4-10 times VAS, or can the whole unsealed volume be 4-10 times VAS.....meaning....the air space immediately behind the drivers would barely be enough for 4 times VAS, but since the air is free to move throughout the whole basement via the 4' opening along the rear wall of the concrete....will this still work?

I hope that is clear????? :-/

I'm afraid that it will work more like a ported sub due to the 18"x10' cavity (the opening which allows me access behind front wall on right side) which leads to the 4' opening to the rest of the basement.
LL


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post #2 of 15 Old 02-02-2012, 10:07 AM
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The space behind the drivers should be at least 4x Vas (that is the minimum recommendation but more is better). I'm not understanding what you mean by the 4' cavity to the rest of the basement. I see the cavity behind the screenwall but do not see how this would open up into the rest of the basement. If you mean travel behind the wall on the right side of your plans, then no that space would not be counted. My understanding is that using small long spaces (like a chimney for instance) would act as a poorly tuned transmission line instead of an IB.

Personally I think you might be better off using 4 IB 18's at the front and then adding a couple of other subs in the rear or sides of the room to help smooth out the response. Even though that is a big room, 4 18's will fill it nicely.

One additional thing - the backwave of the IB should be completely sealed off from the listening area.
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post #3 of 15 Old 02-02-2012, 10:24 AM - Thread Starter
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Quote:
Originally Posted by stockmonkey2000 View Post

The space behind the drivers should be at least 4x Vas (that is the minimum recommendation but more is better). I'm not understanding what you mean by the 4' cavity to the rest of the basement. I see the cavity behind the screenwall but do not see how this would open up into the rest of the basement. If you mean travel behind the wall on the right side of your plans, then no that space would not be counted. My understanding is that using small long spaces (like a chimney for instance) would act as a poorly tuned transmission line instead of an IB.

Personally I think you might be better off using 4 IB 18's at the front and then adding a couple of other subs in the rear or sides of the room to help smooth out the response. Even though that is a big room, 4 18's will fill it nicely.

One additional thing - the back-wave of the IB should be completely sealed off from the listening area.


Thanks for the reply.

Yes the back-wave would be completely sealed from the HT room. Somewhere along the YELLOW line will be an opening ~ 4' wide to run conduit/plumbing/HVAC...remember the room is 100% closed due to the concrete. If you look closely you can see they have already incorporated the 4' wide opening along the YELLOW line in this iteration of the BP's. The BLUE line will also have a 4' wide break, but this would be for the entrance door into the theater where as the 4' wide opening along the YELLOW line would not enter the HT at all. It would just allow me to walk inbetween the framed wall and concrete wall on that side to gain access behind the screen (front) wall.

So you think mounting 4 IB318's in the front wall, then the other 4 in the rear wall would be better?

THANKS,
Rob


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post #4 of 15 Old 02-02-2012, 11:15 AM
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Why not just put an access hatch in the front wall to access behind the wall rather than give up all that space for the walkway. I cant imagine ever wanting to walk down that corridor anyway especially when the wall has insulation, cobwebs, dust and everything else that is going to collect back there. I'm not sure I would do another IB sub in the back of the room - I would probably run a couple of sealed high output subs to help smooth out the response. I plan to do this after my room is complete and I can take measurements and place them in the best location.

This is what I did for my access panel.

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post #5 of 15 Old 02-02-2012, 11:56 AM - Thread Starter
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Originally Posted by stockmonkey2000 View Post

Why not just put an access hatch in the front wall to access behind the wall rather than give up all that space for the walkway. I cant imagine ever wanting to walk down that corridor anyway especially when the wall has insulation, cobwebs, dust and everything else that is going to collect back there. I'm not sure I would do another IB sub in the back of the room - I would probably run a couple of sealed high output subs to help smooth out the response. I plan to do this after my room is complete and I can take measurements and place them in the best location.


Yeah, I DON'T need that walk way, but put it there in hopes of increasing the total cubic area the drivers had access to for the rear wave....but it seems like that would not be ideal.

I could simply put the screen wall on the opposite end and the rear wave would have unfettered access to the rest of the basement (2,000sqft), the only problem with this layout is that the theater entrance would now be in the front of the room. I'd rather have the door towards the back of the room for those that can't hold their blatter and must exit the room. With the door in the front, it would interrupt everyone else.......but i typically pause the movie anyway in those cases.....hmmmm


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post #6 of 15 Old 02-02-2012, 02:10 PM
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I like the layout as you have it. It looks like you have 30 feet of length? from the front wall (where it juts out) to the back. If it were me - I would widen the room a bit with the walls built a few inches from the concrete and build the IB chamber out from the front wall a few feet. That should bring you up to 6x vas or so with 8 drivers and 12x vas for 4 drivers. If you only used 4 drivers you could probably leave the front wall where it is. My Vas calculation is just based on your calculation of 4x vas - I cant really see the dimensions on your floorplan.

My room was 31 by 15. I put a 4 foot deep chamber at the screenwall end of the room for the IB subs. It is completely enclosed so I do not have to worry about sound transmission to the rest of the house. This left me with about 26 feet of length usable in the theater room.
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post #7 of 15 Old 02-02-2012, 02:13 PM - Thread Starter
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In this iteration I have swapped the screen wall. Makes more sense this way anyway due to the indent on the back wall, which would be perfect for the wet bar.

The YELLOW line depicts where the opening in the concrete will be. This would allow the IB318's to the rest of the basement.
LL


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post #8 of 15 Old 02-02-2012, 02:24 PM - Thread Starter
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Quote:
Originally Posted by stockmonkey2000 View Post

I put a 4 foot deep chamber at the screenwall end of the room for the IB subs. It is completely enclosed so I do not have to worry about sound transmission to the rest of the house. This left me with about 26 feet of length usable in the theater room.


If I left the original idea of the screen on the bottom of the drawing but brought that wall out 4' from the concrete, I would have ~ 1080 ft3, which would be perfect for 8 IB318's (30480L @ 10x VAS).

This would make my room 26-27ft long. Seems like a huge waste, BUT....this would keep the subs backwave completely isolated like yours.


## DIY Rustic ConcreteBunker HT Build w/8 x 18" IB subs & 25KW ##

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post #9 of 15 Old 02-02-2012, 02:27 PM
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Are you planning on any soundproofing? I've heard stories of people that used the basement for the backwave and could rarely use their subs because of the sound throughout the house. The backwave is as loud as the front wave and will be painful to anyone trying to use any other part of the basement.

Also the wetbar might be better outside the theater room as the fridge (if your planning one) is likely to be noisy.
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post #10 of 15 Old 02-02-2012, 02:30 PM
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Originally Posted by rms8 View Post

If I left the original idea of the screen on the bottom of the drawing but brought that wall out 4' from the concrete, I would have ~ 1080 ft3, which would be perfect for 8 IB318's (30480L @ 10x VAS).

This would make my room 26-27ft long. Seems like a huge waste, BUT....this would keep the subs backwave completely isolated like yours.

If you did not want to give up the space - go with 4 IB3's and put them in the area that juts out. That space is not very valuable because of the placement and You are likely to never use the full potential of the 8 anyway.
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post #11 of 15 Old 02-02-2012, 02:34 PM - Thread Starter
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Originally Posted by stockmonkey2000 View Post

Also the wetbar might be better outside the theater room as the fridge (if your planning one) is likely to be noisy.


I have a minifridge in my current HT and it's never been noticeable while running. That fridge is just up along the rear wall. The minfridge for the new HT would be recessed into the wetbar.

I get what you're saying regarding the backwave and the rest of the home. It will be a 2 story so the bedrooms would be quite a ways up but would still probably get some residual vibrations. If I stayed with the 2nd layout I could build a room around the subs to act as a chamber, making sure that the volume inside it would be 10x VAS.


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post #12 of 15 Old 02-02-2012, 02:43 PM
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You might not notice it in your current room, but if you do a room with full soundproofing, you might notice it. I have 2 A/C condenser lines that run through my soffit in my theater. I never noticed any sound from them until the room was enclosed with all the soundproofing. Before that the sound was drowned out by the environmental noise. Inside the room it was so quiet that the condenser lines were the only thing I could hear. It was surprising how obnoxious that sound had become in the quiet room.

The goal should be to have the noise floor in the room at 22dba or less which is the lowest level recorded on a soundtrack. Most inexpensive mini fridges are fairly noisy and even the more expensive models are likely to be louder than 22dba at times.

By the way I think my IB chamber was 8x vas and was filled with insulation which supposedly makes the chamber appear larger. Many here have done lower than 8x and still had good results. I think you could get away with less than 10x if you needed to.
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post #13 of 15 Old 02-02-2012, 02:57 PM - Thread Starter
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Originally Posted by stockmonkey2000 View Post

By the way I think my IB chamber was 8x vas and was filled with insulation which supposedly makes the chamber appear larger. Many here have done lower than 8x and still had good results. I think you could get away with less than 10x if you needed to.


At our last meeting (last night) I requested a quote for an 11' pour vs. the standard 10'. If the price is right from the concrete-sub, then I would only need to pull that wall out 3' to get 10xVAS. I should check how close to "optimum" it would be with an 11' pour and only 2' out from the wall.

Thanks for all the input!


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post #14 of 15 Old 02-02-2012, 03:24 PM
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I second what stockmonkey2000 says about total containment of your backwave.

My backwave goes into the mechanical room for HVAC/etc.
I've sealed it as much as possible, outside door w/seals to that room, etc, what a PIA, still some sound gets transmitted to other parts of the home.

If you can totally contain the backwave in isolated room, that is best.
If I had a "do-over" when building my home new, that is what I'd do.

Good luck, btw do you have a thread over at the IB cult? Start one.
http://ibsubwoofers.proboards.com/index.cgi?
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post #15 of 15 Old 02-02-2012, 04:05 PM - Thread Starter
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Good luck, btw do you have a thread over at the IB cult? Start one.
http://ibsubwoofers.proboards.com/index.cgi?


Yes, I started one over there at the same time hoping Tom would chime in


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