[RNRGAGNE]

Hi Guys,
I'm being forced to move my HT to a room where I won't be able to use my (4ohm) AE IB15's in an IB. (They're the older ones with the big chrome phase plugs). I have them in a twin IB line array, with a pair on each side running as L/R subs, and EQ'd with Audyssey Pro.
I'm considering possibly doing an open baffle with them and would like some advice.
WARNING; I'm not all that knowledgable on this subject and did an IB because it was super simple, I just had to make sure the room they backed into was big enough, and Audyssey did the rest lol!
Here's what I'm thinking;
I have a 100" diagonal screen that'll be in about a 12' to 13' foot wide room. I was thinking I could frame the screen with a pair of twin IB 15's in a floor to ceiling baffle with a false wall made of speaker cloth between the baffles and screen wall.

Sort of like this; __/"""""""\__

I listen to a lot of live concert music at close to concert levels and accuracy is my prime desire, but going low for movie effects is also a requirement. So my questions are first, is this practical? How wide and how far out from the wall would the baffles have to be? Since you won't see behind the baffles could I, or should I, put some absorbtion materials in there? Will they have enough output to run as L/R subs? And lastley, how much power would I need for them?

Thanks in advance.

[RNRGAGNE]

Oh, and I suppose I could do wings or suspend the baffle in a frame if the floor to ceiling idea isn't a good one. (I don't really understand how the back waves affect things with an OB design.)

[JohnR]

I listen to a lot of live concert music at close to concert levels and accuracy is my prime desire, but going low for movie effects is also a requirement.

OB may not the best choice then. At the least, you'd want to build a prototype before spending a lot of time/money on it. If you're able to make a baffle from floor to ceiling though, you've probably got room for a big enough sealed box - I'd suggest figuring how big a box that would create, and then model the drivers (using e.g Unibox) in that size box to see how much eq you'd need to flatten out the response.

[ebag4]

Those are the same drivers I use in IB in my HT, excellent bass!  You might PM gitarretyp
here on AC.  If I remember correctly he used these (possibly a later generation) in an OB alignment for a while before moving to a pair of GedLee speakers.

Best,
Ed

[mcgsxr]

OB bass is intoxicating (to me) for texture and accuracy, but overall output suffers vs sealed or ported or IB etc.

With 4 OB drivers, you will essentially "see" about the output of 1 sealed.

Sounds like you could build large sealed floorstanding boxes, and that would drive the HT experience very convincingly I suspect!

[RNRGAGNE]

Thanks guys,

I'm realizing it might not be practical for my application. I got some advice from ThomasW on another forum (I think you guys know him here from some surfing I've done) suggesting I'd be risking frying the IB15's in a large box application. Others did say the IB15's modeled extremely well in large boxes which is tough hear and not do lol!

Looks like my budget is going to take a hit - and I might go back to some Rythmik sealed servos which were probably the second best bass I've heard next to the IB.

[scorpion]

Have a look at my Blindstone effort: http://www.audiocircle.com/index.php?topic=88075.20 . I replaced 2 Eminence Alpha15s with one IB15 per side.
Results are excellent. I suppose that IB15 specs are the same for those earlier units. I see no reason why an OB wouldn't be successful. Just let Audyssey do the same job with the OB-setup. You will have to EQ in the low bass but X-max for the unit is so high that 2 per side will be more than enough. Do you have specs for your units, I have supposed that X-max is like 18 mm as for the newer IB15s, now at least temporarily unavailable.
And the bass quality will be the same if baffles are made rigid and resonancefree, size I think is not so critical.

/Erling

[gitarretyp]

I used a pair of the IB15 (newer version) per side in an OB configuration and thought they worked very well. In an OB, even with lots of EQ applied, I wouldn't expect much from them below 20 Hz--at least compared to using them in an IB. My advice would be to throw a baffle together (cheap plywood is fine for a test baffle) and see what you think of them in this application. I ran them with ~350 W per driver, and that was plenty to utilize the full output capabilities on an OB. As for baffle size and placement, as wide as possible and at least 3' from the rear wall is best. Also, keep in mind the large xmax and mms of these drivers when building the baffle--heavy and well braced.

[RNRGAGNE]

Thanks for the replies guys. A couple of question/concerns if I may..

I think three feet from the front wall will be pushing it, how important is that factor, and what are the effect of being closer?
What kind of SPL should I expect?
Are wings a way to increase baffle size without getting wider into the room?
gitarretyp; You said you ran 350w per driver, does that mean I'd need 700w for each side?
They're 4ohm speakers, and I have several ICE amp channels at my disposal with either 1000w, 500w, 250w @ 4ohms, which double into 2ohms...
The room is going to be at best 12' to 12.5' feet wide by 18' long, my screen is about 7.5' wide leaving only about 2' to 2.5' feet on each side. But the kicker is that my mains would have to go in front of the baffles, they're Paradigm S8's and while having a narrow front profile they're about 2' deep if not a tad more.
The more I think about this set up the more I like the concept. What I like the most about my IB is how I never loose the "tonality" of bass instruments even at near concert levels. I'm assuming an OB set up would be similar. Using my IB15's & possibly just adding an LFE only sub might be a slick dual purpose set up...

[ebag4]

Why not put the OB subs in a low baffle under the screen and between the speakers similar to what I have done with my IB (see pic, of course your baffle would be pulled away fom the wall)?  I assume your mains have the ability to reach down to 80 Hz, that would allow you to run the subs in mono or you could still use 2 per channel.  If you use a center channel you could possibly use the sub baffle as a stand.





Best,
Ed

[RNRGAGNE]

I've pretty much resigned myself to having an audio rack as a center channel stand for this room otherwise it might be a good idea. Still, I'll give that some thought. I wonder about the back wave vibrating the screen in that configuration.

I like your set-up though.. reminds me of the one I have to dismantle  ;

[jk@home]

I have 4 newer AE IB15s that I had entertained the though of using for OB, have a thread here about the subject. Ended up going the normal IB route, due to concerns of too much "real estate" being taken up in my smallish room (see "johnvb's project" on the Cult site).

But of all the designs I looked at, IMHO, I though the H frame made the most sense, better performance and sturdier than a flat baffle, but not too complicated to build, such as a W frame.

[mcgsxr]

Perhaps more creative types can envision a model where you can leverage the IB15's in OB, but give the constraint of having about 1 foot of depth, and placing the subs behind the mains, I think exploring sealed subs is your best option, with IB being out.

You don't need to build enormous sealed boxes, you can just stack the 15's in a 1 foot deep box, and build the boxes to whatever other dimensions will optimize the internal air space for the IB15's.

EQ will likely be your friend, and sealed subs are typically quite good for tonality, and controlling excursion etc to minimize damage (not that those boss subs will need that!).

[RNRGAGNE]

Thanks for the suggestion. That was my initial idea for using these drivers, basically build them into towers flanking the screen, but as I mentioned above, I was told I could fry them in that application by ThomasW who seems to know what he's talking about.
Now, if it's only a "possibility" or if there's something I can do to mitigate the risk I'd like to know.
I do know they modeled extremely well in a large box, and that's  enticing.

For EQ I'll be using Audyssey Pro, and by mid winter I'll be upgraded to the XT32 Pro platform which has significantly improved bass EQ capabilities.


Oh, and I'm not ruling out the OB idea just yet either, if I can get some answers to the questions I posted above it'll go a long way to helping me decide a course of action.

[JohnR]

I suspect that "frying them" would be if you overused bass boost to get them back up to flat at high levels and low frequencies. Again, you would have to figure out what size box you are likely to have and model them to see how they behaved in that size box.

[RNRGAGNE]

Correct me if I'm wrong, but running a pair, would increase the SPL and reduce the workload as well wouldn't it?

[JohnR]

Basically - but at low frequencies you will have a steeper rolloff because each driver has in effect half the volume. You'd really need to model it to see what the tradeoffs would be...

[RNRGAGNE]

Here's what someone modeled for me on another forum;




He said;

Well, say you have 16x16 interior space, 8 ft tall. That would give you approximately 400L of internal volume. I'll assume 2 drivers per side.

Throwing that into Winisd (which is conveniently open and already has the IB15 file loaded ) I get a HF max of 115dB if two drivers are installed, excursion limited down low, with a peak at 35Hz of 120dB for the ported, 117dB for the sealed. Overall the system are 3dB down at 20-21 Hz. See the attached file. Going ported vs sealed seems to give you and extra dB or two, but more importantly uses a LOT less excursion between 12 and 24 Hz--that translates to EQ wiggle room .


Now this was offered up before the advice of not using these drivers for that application period.  As a neophyte, this is all very confusing.
I have the materials & amps to build the towers or OB's without spending any more money, and I might be able to afford to build or buy a third sub for LFE movie effects and still come out ahead of buying or building a pair of subs. So in theory these units could only be for music where playing into the 20's isn't really that big a deal. My pre-amp can handle routing to three subs, and i can run an L/R/LFE set-up easy enough.

[JohnR]

You'll be able to get them into the 20's in OB, the thing is that music won't require the same level of output as HT will.

[JohnR]

PS the picture is not visible, it might be for someone already logged into avsforum but otherwise not.