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Discussion Starter #1
hi guys
i'm just starting an attic projector theater build and from what i'm reading about ib set ups it seems to be what i'm after. when my trouble lies is the use of feedback unit.
can someone explain the use of this unit as in what it does verses not using it for anyone like me new to this type of bass set up?

thanks
gordie
 

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Re: infinite baffle how to

The BFD is nothing more than a very versatile parametric EQ, and could (and should!) be used for any type of sub...
 

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Discussion Starter #3
Re: infinite baffle how to

ok thanks
but where does the response down to single digits come from when say a given sub has a fs of 20 hz?
from what i've read , people who have tested ib setups say bass extension down to 8 hz is possible.what is going on with an ib that can't be had from other box types?
please keep in mind while i'm not new to diy speaker building i am to ib designs.
thanks
gordie
 

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Re: infinite baffle how to

ok thanks
but where does the response down to single digits come from when say a given sub has a fs of 20 hz?
from what i've read , people who have tested ib setups say bass extension down to 8 hz is possible.what is going on with an ib that can't be had from other box types?
please keep in mind while i'm not new to diy speaker building i am to ib designs.
thanks
gordie
Nothing is going on with IB that cannot be had with a properly ported design. You can tune a ported sub to 8-10Hz if you wanted and it will more than likely have more output in that range than an IB will have. However, there is so very little that you can watch on DVD that has any usable output at 8Hz, designing a sub for that frequency range is really not very frugal.

I don't think frequency response extension is generally the determining factor on whether to go IB or not. Probably the major reason to go IB would be lack of room for a box type sub in your room. Another reason for IB's is the "cool factor"... or at least those were my reasons for almost building one.

If you've got the money and like playing around with multiple drivers in an array or manifold type design, have the available attic space, crawl space, or adjacent room space, then it might just be what you are looking for. However, I would suggest some test measurements to make sure your potential locations will have sufficient response.

I was going to build an IB at one time... chickened out because it got too complicated, more so because of the "work" space limitations in my attic.
 

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Re: infinite baffle how to

There is a IB specific websight that has a really great FAQ section "Cult of the infinitly Baffled"

I hope you have a great time with your HT build, The Shack has been very helpfull for my HT build unfortunatly I haven't been able to work on it for several months, but that doesn't keep me from researching out my thoughts. My IB array is framed up and thats about it.

Rick.
 

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Re: infinite baffle how to

Owners of IB systems really seem to like how they sound. The theory is that the lack of a box means there is no pressure acting on the back of the driver and it is allowed to move as freely as possible resulting in better sound, tighter bass etc... Personally, you waste a lot of low end output by not using that back pressure through a port. Drivers with a low fs are a must as it is difficult to eq below 20hz. Room gain plays a huge role in bumping up low end response.
 

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Re: infinite baffle how to

Owners of IB systems really seem to like how they sound. The theory is that the lack of a box means there is no pressure acting on the back of the driver and it is allowed to move as freely as possible resulting in better sound, tighter bass etc... Personally, you waste a lot of low end output by not using that back pressure through a port. Drivers with a low fs are a must as it is difficult to eq below 20hz. Room gain plays a huge role in bumping up low end response.
thanks very much
i'm a huge fan of transmission line type of output. any speakers or sub i build in a tl alinement has beautiful smooth unlimited cut off bottom end. the only downside is hugh hugh boxes.
i'm using now 2 adire 15" tempest subs each in 11 cu ft 20" sono tube ported with a 5" x 38" port tuned to 11 hz. while the output is intense alright, its nothing like a tl. so when i read all other users comments on there use of ib they all say the same. all claim that the bottom end doesn't exist.it's so realistic and life like that some report confussion with real thing.one guy writes that he was awakened one night with what he thought was a tornado. his son and friends where watching twister. now no ported or sealed sub in any amount can do that. why is ib all claimed as the end all be all?
what are the thoughts on the manifold mounting ? why doesn't the cones facing each other cancel each other out?

thanks
 

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Elite Shackster
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Re: infinite baffle how to

I've never heard an IB and would love to but I have a theory on why they are considered the be all end all. Almost every IB build I have seen uses many more drivers than most would put in a sealed or ported box in their living room. They put in a lot more effort and get above average results and rave about it (deservingly so). Physics dictate that ported enclosures will give you more output all things remaining the same, and if properly design should be of negligible distortion and you won't have to cut any holes in the wall. Also an IB not properly decoupled can literally move the wall as it plays and sound from the back of the driver radiates throughout the home as the poster you quoted probably knows from his description.

If you can tolerate a large enclosure in the room and max output is your goal IB isn't the solution. But it is a very good subwoofer system :bigsmile:
 

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Re: infinite baffle how to

what are the thoughts on the manifold mounting ? why doesn't the cones facing each other cancel each other out?
Because they're wired so the cones move towards each other, forcing the air out the mouth of the manifold. Picture a 4th order bandpass with 2 drivers, without the port. (Overly simplified, yes)

Personally, you waste a lot of low end output by not using that back pressure through a port. Drivers with a low fs are a must as it is difficult to eq below 20hz.
You're right - the back wave is "lost" with the IB, since it's not being directed into the listening area, the same as with a sealed enclosure. That's why multiple drivers are typically employed.

The nice part is since material costs are very little, it typically won't break the budget to buy a few more subs.. ;)
 

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Elite Shackster
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Re: infinite baffle how to

Because they're wired so the cones move towards each other, forcing the air out the mouth of the manifold. Picture a 4th order bandpass with 2 drivers, without the port. (Overly simplified, yes)
The shape of the manifold doesn't affect the sound unless it's really long or oddly shaped. Having the drivers opposed to one another is supposed to cancel out vibration.
 

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Re: infinite baffle how to

A few other things to strive for with a manifold are...

1. The area of the opening of the manifold to the room should be no less than the cumulative Sd of the drivers used (if you use two 18" drivers with 1210 cm^2 Sd, then the opening should be no less than 2420 cm^2).

2. Each pair of drivers should be parallel to each other and firing towards each other. You could have have a longer skinner manifold with two drivers on each of the longer sides and none on the shorter side or a square manifold with one driver on each of the four sides. Either way is fine. The thing you want to be careful of is you want all of the drivers equidistant from the opening so they are all in phase with each other. The other practical thing is if you have a rectangular opening and two driver on each of the long sides, I'd brace it in the middle to keep it from flexing. Typically the choice to go square or rectangular is dictated by the internal structure of the house (distance between the studs, proximity of walls, ceiling, roof, pipes, etc.).
 

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Discussion Starter #13
Re: infinite baffle how to

A few other things to strive for with a manifold are...

1. The area of the opening of the manifold to the room should be no less than the cumulative Sd of the drivers used (if you use two 18" drivers with 1210 cm^2 Sd, then the opening should be no less than 2420 cm^2).

2. Each pair of drivers should be parallel to each other and firing towards each other. You could have have a longer skinner manifold with two drivers on each of the longer sides and none on the shorter side or a square manifold with one driver on each of the four sides. Either way is fine. The thing you want to be careful of is you want all of the drivers equidistant from the opening so they are all in phase with each other. The other practical thing is if you have a rectangular opening and two driver on each of the long sides, I'd brace it in the middle to keep it from flexing. Typically the choice to go square or rectangular is dictated by the internal structure of the house (distance between the studs, proximity of walls, ceiling, roof, pipes, etc.).
well
now thats what i'm talking about.because i'm new to ib i don't know the facts.the manifold opening is that important wow! you're the first to shed light on this.i couldn't understand why people built ib manifolds and not mounted the ib subs in the wall pointing into the room. so the maniflod must be acting somewhat like a port right? is it the manifold that makes the output so low?
thank you for your thoughts
gordie
 

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Re: infinite baffle how to

1. The area of the opening of the manifold to the room should be no less than the cumulative Sd of the drivers used (if you use two 18" drivers with 1210 cm^2 Sd, then the opening should be no less than 2420 cm^2).
I think that should be the Vd of the sub (the volume of air displaced by the cone) not the Sd (surface area of the cone).

from post #10:

Air movement generated by the driver shouldn't encounter any reduction in the CSA through which it has to flow

http://www.hometheatershack.com/forums/diy-subwoofers-sealed-ported/6171-sonosub-baseplate-distance-sub.html

Although this was originally posted for sonotube base plates, it would apply equally to an IB manifold.
 

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Re: infinite baffle how to

I'll have to look into that. My presumption is the driver acts like a piston, and since the frequencies being recreated are so low, diffraction from the edge of the maniforld (and thus off axis response) isn't affected. If the opening of the manifold is less than the Sd, then the manifold acts like a bandpass filter thus altering the frequency response and requiring additional EQ.

As for the purpose of a manifold vs an array, the manifold has the woofers firing directly towards each other, thus the mechanical forces involved with their movement offset each other and greatly reduce the stress on the wall/floor/ceiling. The sides are also much smaller and properly braced. An array doesn't have that, thus it is very easy for the wall to flex/move when drivers move, which can have a dramaticly negative effect on response. Think of the amount of bracing a boxed subwoofer has. Then imagine two or four 18" drivers along one side of the box and not putting any internal bracing in it. Having a manifold also decreases the cutout into the room and allows the drivers to be vertically aligned if attached to the ceiling or floor (which prolongs the driver's length of life). There are a few drawbacks to using a manifold... they are more work to build and make the drivers more difficult for visitors to see (having two or four 18" drivers facing you is pretty dramatic!).

Hope this helps :D
 

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Re: infinite baffle how to

It is Vd. My bad. Nobody has their manifold openings as large as the combined Vd, but this does hilight the importance of only having your manifold one driver deep. Another thought, Vd is volume displaced whereas Sd is cone area. Since I'm talking about the size of the opening (measured as area), I still think Sd is more applicable. Practically speaking, If you make the opening of the manifold as large as you reasonably can (say at least as big as the combined Sd, if not 50% larger), then you'll be in good shape.
 

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Discussion Starter #17
Re: infinite baffle how to

I'll have to look into that. My presumption is the driver acts like a piston, and since the frequencies being recreated are so low, diffraction from the edge of the maniforld (and thus off axis response) isn't affected. If the opening of the manifold is less than the Sd, then the manifold acts like a bandpass filter thus altering the frequency response and requiring additional EQ.

As for the purpose of a manifold vs an array, the manifold has the woofers firing directly towards each other, thus the mechanical forces involved with their movement offset each other and greatly reduce the stress on the wall/floor/ceiling. The sides are also much smaller and properly braced. An array doesn't have that, thus it is very easy for the wall to flex/move when drivers move, which can have a dramaticly negative effect on response. Think of the amount of bracing a boxed subwoofer has. Then imagine two or four 18" drivers along one side of the box and not putting any internal bracing in it. Having a manifold also decreases the cutout into the room and allows the drivers to be vertically aligned if attached to the ceiling or floor (which prolongs the driver's length of life). There are a few drawbacks to using a manifold... they are more work to build and make the drivers more difficult for visitors to see (having two or four 18" drivers facing you is pretty dramatic!).

Hope this helps :D
thanks jagman
it all helps. i'm mostly interested in how is it possible for 4 18" subs with an fs of 26hz have clean ouput down to 6, 8 or 10 hz? the people that claim this even show graphs with clean usable output to below 10 hz.
so what i need to understand is the relationship between room , manifold and the feedback pro unit that make useable output to single numbers. also it would be nice to know before spending the 3 or 4 grand for a ib system.

thanks
gordie
 

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Re: infinite baffle how to

so what i need to understand is the relationship between room , manifold and the feedback pro unit that make useable output to single numbers. also it would be nice to know before spending the 3 or 4 grand for a ib system.
3-4 grand? :unbelievable: half that... TOPS. and that's for one kick- setup. (4 18's, EP2500, BFD, mic, cabling, wood, etc..)

The BFD is just an EQ, and can be applied to any kind of setup. What makes the IB work is the lack of air spring pushing on multiple, large woofers.

Did you go over to the Cult of the IB site? There's plenty of builds and a FAQ that should answer most of your questions..
 

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Discussion Starter #19
Re: infinite baffle how to

3-4 grand? :unbelievable: half that... TOPS. and that's for one kick- setup. (4 18's, EP2500, BFD, mic, cabling, wood, etc..)

The BFD is just an EQ, and can be applied to any kind of setup. What makes the IB work is the lack of air spring pushing on multiple, large woofers.

Did you go over to the Cult of the IB site? There's plenty of builds and a FAQ that should answer most of your questions..
well remember i'm in canada. 4 soundsplitter 18's are 2200 alone. a crown k2 amp is 1000.
as far as cult of ib site i'm also a member there but i couldn't get the basic info needed.
they all answer me way over my head when what i need is info from the bottom up.
thanks to all here at home theater shack for giving me answers that are simple enough for all us new people to ib setups.

thanks
gordie
 

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Re: infinite baffle how to

I would read and re-read the FAQ over there. It gives a lot of the basics you are looking for. Also, an Fs of 26 is pretty high for an IB application. My 18's have an Fs of 16, which is nice, but I have to be careful not to bottom them. I would consider the Fi Car Audio IB3 18" drivers as they are inexpensive and designed specifically for IB use. With 4 two ohm drivers (so the amp sees stereo at 4Ohms each), a Behringer EP-2500 will deliver 325 watts per driver. That is enough for them just to approach but not pass excursion limits in the sub 15 Hz range when the amp is maxed out. Even though the Fs is 23 Hz, they model very nicely. The Crown amp is nice, but probably overkill. My suggestion is to model the subwoofers you prefer with WinISD. Sonnie did a nice comparison on another thread in the IB section of the Shack. The thread was titled something like "best IB drivers" and is very recent. Another thing to remember is LLT subs do boost the lower teens requiring less EQ, but doing so isn't free. There are distortion components. Sime like it. Some don't mind it. Some are bothered by it. That is a personal decision. There is no wrong answer.
 
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