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-   -   IB array (https://www.avsforum.com/forum/155-diy-speakers-subs/2885593-ib-array.html)

Gorilla Killa 07-02-2017 12:51 PM

IB array
 
Im not sure how to model this in Horn Response. Does it matter if using an IB line array how the box is built. If I had 4 18's in a 80 x 24x x40d, drivers mounted on the 80x24 front baffle, the rear open to another room. Im trying to determine if the enclosure is considered big enough to not cause any issues. The depth of the box at 40" gets it to the wall behind the screen.

diy speaker guy 07-02-2017 01:31 PM

I can sim it but I need an accurate drawing or description. I have no idea what you have in mind. You're talking about a box and then saying it's open to another room, if you want an accurate sim I need to know exactly what the dimensions and openings are.

Absolutely it matters how it's built. If you have a long line (like a floor to ceiling transmission line) you will have terrible resonances all through the passband. You could end up with something terrible like the 12 Dancing Shivas or even worse the Basszilla or whatever it's called.

Gorilla Killa 07-02-2017 02:09 PM

I may have this on the floor but for the sim not sure it matters. It will be 80x24x40. Poor choice on the use of then word enclosure as it will be open in the rear same as front baffle 80x24, only impedance on air flow will be a grill with speaker cloth. Its 40" from the bottom of my screen to the wall in the rear where it will be open into the adjacent room. The pic below is a good example, not a traditional IB manifold firing out of a mouth


http://images.static-bluray.com/htga...42686_full.jpg

Bill Fitzmaurice 07-02-2017 02:52 PM

If the open back is firing into another room you'd just model it as a sealed direct radiator enclosure with the rear chamber volume being that of the other room. You'll find there comes a point where additional rear chamber volume doesn't make much difference.

diy speaker guy 07-02-2017 05:20 PM

Quote:

Originally Posted by Bill Fitzmaurice (Post 54015777)
If the open back is firing into another room you'd just model it as a sealed direct radiator enclosure with the rear chamber volume being that of the other room. You'll find there comes a point where additional rear chamber volume doesn't make much difference.

Wow, that is shockingly bad advice.

OP, I'll show you just how shockingly bad the results can be if you follow this advice.

If you sim it as a simple sealed box you will get a nice flat(ish) frequency response with no resonances.

BUT if you put it into a U baffle 40 inches deep you get a big notch at 55 hz in the theater room and a massive whopping 10 db spike at 60 hz in the adjacent room that you are using for the IB space.

If you consider the fact that there's a 15 db difference in the response around 55 - 60 hz, that means that even if your dividing wall is concrete you will very likely hear this frequency range playing LOUDLY in the other room. You might even hear room rattles from the adjacent room too, since it's playing 15 db hotter than the theater room.

Do you know what a U baffle is? It's a very short transmission line. And a 40 inch long transmission line with a frontal face area of around 12400 sq cm is going to give you that terrible dip/peak in the theater/adjacent room.

If at all possible, DO NOT use a 40 inch deep U baffle. It's terrible design. Here's the sim that shows the proof.

Dark black trace is what you will measure in the theater room, light grey trace is what you will measure in the back room. From 20 - 90 hz it's going to be WAY louder in the back room than in the theater room and eq can't fix that.

(In addition there may also be resonances in the height dimension too, since the height is 80 inches, but Hornresp can only sim the depth dimension, not the height dimension.)

Almost forgot to mention, I don't know what drivers you have so I used 4x HT 18, not that the drivers make any difference at all wrt the massive resonance problem a 40 inch deep U baffle will cause.

http://i67.tinypic.com/10z3bxv.png

RickJames 07-02-2017 07:05 PM

Quote:

Originally Posted by diy speaker guy (Post 54017825)
Wow, that is shockingly bad advice.

Did you not read where he says the rear open to another room
?
Your model is AFU, BTW. S1, S2 and L12 should all be zero, the volume of the room that the rear opening on the box fires into is entered into Vrc. What you did would be appropriate if it was an open baffle, but by his description it isn't, it's an infinite baffle, just as implied where he calls it an IB.

diy speaker guy 07-02-2017 08:57 PM

Quote:

Originally Posted by RickJames (Post 54019409)
Did you not read where he says the rear open to another room
?
Your model is AFU, BTW. S1, S2 and L12 should all be zero, the volume of the room that the rear opening on the box fires into is entered into Vrc. What you did would be appropriate if it was an open baffle, but by his description it isn't, it's an infinite baffle, just as implied where he calls it an IB.

You're funny. What you are describing is a sim that doesn't take the 40 inch manifold into account at all which is why I said Bill's advice was shockingly bad in the first place.

Assuming both rooms (the theater room and the adjacent room) are close enough to infinite (compared to combined driver Vas) my sim is just fine. The driver side fires into the theater room and the back side fires into the adjacent room and the response you see in my sim is exactly what you will measure in each room. Guaranteed.

I was able to sim the 12 Dancing Shivas project just fine. It's 12 drivers in a very long manifold. My sim matched the measured response almost perfectly - both the measurements from the listening room AND the back room. The only reason I even bothered to sim that garbage was because somebody told me it couldn't be done.

Since you don't seem to understand Hornresp at all I'll break it down for you. The drivers are in a U baffle in between two rooms of assumed "infinite" size. Therefore the volume of the rooms doesn't need to be input into the sims at all. All you need to do is sim the U baffle by itself and the driver side output is what you will measure in the theater room and the U baffle back is what you will measure in the back room. This is really simple and pretty basic.

I know what I'm doing and my sim is just fine.

diy speaker guy 07-02-2017 09:01 PM

BTW, it's also pretty funny that Bill won't directly address me but you seem to hop right in every time I correct him. You've been a member since 2006, have only 175 posts and you only post about Bill's products or in threads where Bill has been corrected on technical details. Something fishy about that, no? Or maybe not considering that Bill has been banned from other forums for sockpuppeting.

diy speaker guy 07-02-2017 09:27 PM

Quote:

Originally Posted by RickJames (Post 54019409)
What you did would be appropriate if it was an open baffle, but by his description it isn't, it's an infinite baffle, just as implied where he calls it an IB.

To address this point in particular, if I had simulated it as open baffle the response would look like this. No bottom end at all due to OB cancellation. This should be pretty obvious.

http://i65.tinypic.com/2u3uv5k.png

Gorilla Killa 07-03-2017 03:42 PM

Thanks for doing that @diy speaker guy , i almost just ran with it and im glad I didnt. I was trying not to close off a closet, looks inevitable at this point. Thanks for showing how you did the sim, thats definitely not how I would have gone about it.

diy speaker guy 07-03-2017 04:24 PM

No problem and if you want to talk about details we can. By the way, what is the volume of the rooms? Both the theater room and the back room.

The easiest way to do this is either eliminate the U baffle completely and put them flush on the wall or at least decrease the depth of the U baffle to push the resonances higher in frequency and out of the passband.

Or you could go with a more traditional manifold as long as it's as shallow as possible.

Gorilla Killa 07-03-2017 06:18 PM

Theater room is 2300 cft, adjacent room is over 3000 cft open to stairwell. If i do the traditional manifold it will stick out into the back room quite a bit, which is where we hang more often than not if not watching a movie.

I have a manifold in a closet in the theater room which is firing into the back room. It was used as an IB for the back room until the theater was moved along. Since its in the closet in the theater room its not usable due to the heavy resonance and decay as you would imagine.

The depth was so I could get the drivers completely out of the closet. Ill pull my screen down tomorrow and see whats doable, not sure if the depth is a no go that anything but flush with the baffle and sealing up the closet and using that. The closet is about 280cft

LTD02 07-03-2017 07:00 PM

the key here for folks trying to follow along is the infinite baffle can be simulated as diy speaker guy has done IF:


each side of the system is viewed independently. usually we view the output of both sides of the system combined (i.e. the total horn response).


in this case, to see the response in the room with the drivers, go to Tools > Output > Direct Radiator


to see the response in the room with the manifold section, select Tools > Output > Horn

Bill Fitzmaurice 07-03-2017 07:02 PM

Quote:

Originally Posted by Gorilla Killa (Post 54038745)
Theater room is 2300 cft, adjacent room is over 3000 cft open to stairwell. If i do the traditional manifold it will stick out into the back room quite a bit.

Why do a manifold at all? Wall mount them. If you don't want them sticking out into the rear room do a manifold just deep enough to prevent that.

diy speaker guy 07-03-2017 08:11 PM

Quote:

Originally Posted by LTD02 (Post 54039377)
the key here for folks trying to follow along is the infinite baffle can be simulated as diy speaker guy has done IF:


each side of the system is viewed independently. usually we view the output of both sides of the system combined (i.e. the total horn response).


in this case, to see the response in the room with the drivers, go to Tools > Output > Direct Radiator


to see the response in the room with the manifold section, select Tools > Output > Horn

Yeah, that's a more clear and concise description than I provided. The only thing I would add to this is that for the sim to be valid if done this way the rooms (both of them) have to be way, way, WAY larger than the driver's combined Vas. I think this is definitely the case in OP's proposed project. If not you have to simulate it both ways (in this method and also as a simple sealed box) and mentally note the resonance issue and the bass rolloff issue (qtc) separately and mentally combine them to see how it's going to act.

diy speaker guy 07-03-2017 08:12 PM

Quote:

Originally Posted by Gorilla Killa (Post 54038745)
Theater room is 2300 cft, adjacent room is over 3000 cft open to stairwell. If i do the traditional manifold it will stick out into the back room quite a bit, which is where we hang more often than not if not watching a movie.

I have a manifold in a closet in the theater room which is firing into the back room. It was used as an IB for the back room until the theater was moved along. Since its in the closet in the theater room its not usable due to the heavy resonance and decay as you would imagine.

The depth was so I could get the drivers completely out of the closet. Ill pull my screen down tomorrow and see whats doable, not sure if the depth is a no go that anything but flush with the baffle and sealing up the closet and using that. The closet is about 280cft

A picture would help me picture it better. I'm not sure why you can't mount them directly on the wall. Unless you ARE mounting them on the wall and using the U baffle to fire right through the closet (without interacting with the closet) and into the next room. In which case I'd probably pick a different spot to put the drivers. If there is a specific NEED to put them in a 40 inch tunnel I'd do H baffle, not U baffle. That will push the resonances up way higher in frequency even if you still use a 40 inch depth. I can sim that scenario too.

280 cu ft is not much for IB for four 18s so it is good that you won't be using the closet.

Can I get the t/s of the drivers you are using?

Gorilla Killa 07-04-2017 05:23 AM

1 Attachment(s)
The plan was to enclose closet with a false wall and put treatments on it,but in a way it could be removed easily.

revc 2 ohms

fs 18hz

qts .65

qes .77

qms 4.4

le .93 mH

vas 9.4 ft^3

sens 85.5 db 1w1m

spl 91.1 db @ 2.83 vrms

Bl 13 Tm

xmax 25mm

xmech 100mm p-p

Torkild 07-04-2017 07:03 AM

Quote:

Originally Posted by Bill Fitzmaurice (Post 54039417)
Why do a manifold at all? Wall mount them. If you don't want them sticking out into the rear room do a manifold just deep enough to prevent that.

No, please don't flat wall them.
Do no put that mechanical energy into the wall.
For ones own sake keep them as dual opposed, and make manifold as swallow and wide as possible.

diy speaker guy 07-04-2017 07:11 AM

Quote:

Originally Posted by Torkild (Post 54045385)
No, please don't flat wall them.
Do no put that mechanical energy into the wall.

If you place them flat on the wall it will be necessary to completely decouple them from the wall. This is actually pretty easy if it's a horizontal array, quite a bit trickier for a vertical array. Otherwise as this quote mentions you will have massive issues with wall shaking and rattling noises.

Quote:

For ones own sake keep them as dual opposed, and make manifold as swallow and wide as possible.
This is always good advice and you should strongly consider it, OP.

I'll check your t/s later today, I have no time now.

Samps 07-04-2017 08:29 AM

Does push/pull work for a flat wall IB?

LTD02 07-04-2017 07:13 PM

Quote:

Originally Posted by Samps (Post 54047185)
Does push/pull work for a flat wall IB?


that's actually a pretty good question because if the drivers tend to be coupled via the air in the box (or manifold) and that effect is removed with a flat wall i.b., what remains to couple the drivers? to the extent that the wavelength is long relative to the drivers, the air pressure will be rising between them coupling them together in some sense, but how far up in frequency and what percentage of coupling you get, i don't know. does each driver pressurize the air in front of the other or do the drivers behave as though there is barrier in between. based on the way bass horns sum in free air, my guess is the latter, which would mean little push-pull type coupling.

MKtheater 07-04-2017 08:29 PM

The point of IB is to have no box. I would just wall mount them and brace where possible if needed. Just make sure the locations are good for response.

jeno 07-05-2017 02:20 AM

Quote:

Originally Posted by diy speaker guy (Post 54045537)
If you place them flat on the wall it will be necessary to completely decouple them from the wall. This is actually pretty easy if it's a horizontal array, quite a bit trickier for a vertical array.

How would you do that? I might build a IB in the future, if flatmounted I would really like to have some ideas on how to decouple.

diy speaker guy 07-05-2017 04:49 AM

Cut a hole in the wall just a tiny bit bigger than your driver mounting baffle. Whether you cut out the wall studs as well or just work around them is up to you but the baffle cannot touch the studs or any part of the wall. Bolt your driver mounting baffle in place attached to the floor and as well braced as possible, again with none of this touching the wall. Then fill in the crack between the baffle and the wall with silicone, foam weatherstripping or whatever else you want. If you do a good job you can paint right over it and it will appear to be part of the wall even though it's decoupled physically. Clearly it has to be VERY well braced for this to work or it will vibrate back and forth. And it can't touch the wall anywhere aside from the silcone/weatherstripping fill.

Since it's going to be bolted to the floor and braced to the floor and the floor is attached to the wall there will be some transfer of energy into the wall still through the floor but not nearly as much as if they were mounted directly on the wall.

Alternatively if you don't want it coupled to either the floor or the wall just build a shallow U baffle to place in the hole in the wall. Then the transfer of energy will be almost zero to the floor and wall from physical shaking but the whole U baffle will probably walk around unless it's very very heavy, like built of concrete.

jeno 07-05-2017 06:10 AM

Thanks, bolting to the floor could work. For vertical arrays a decoupled u-baffle or something similar might cause trouble if it moves too much. I guess you could lose some output. Maybe a really, REALLY rigid wall wall would be just as easy and more predictible. Or just stick to the good old manifold...

Thomas-W 07-05-2017 06:43 AM

Attempts to 'isolate' a baffle by suspending it in a membrane (silicone) will be counter productive. Reason being that any reactive motion in the membrane (aka flex) will result in decreased the output from the drivers.

The best solution for those needing to use flat baffles is to make a very stiff baffle board securely attached to a braced wall.

Manifolds are the best solution for most installations.

diy speaker guy 07-05-2017 07:23 AM

Quote:

Originally Posted by Thomas-W (Post 54062753)
Attempts to 'isolate' a baffle by suspending it in a membrane (silicone) will be counter productive. Reason being that any reactive motion in the membrane (aka flex) will result in decreased the output from the drivers.

That's why I said to decouple it by not touching the wall and bolting it to the floor. Floors are usually much stronger than walls. Or use a VERY heavy flat or U baffle not touching the wall. The silicone is just there to close the gap, it doesn't do anything else. Nothing is being suspended in a membrane. You just need something flexible to close the gap between the mounting baffle and the wall that the baffle is not touching at all.

Quote:

The best solution for those needing to use flat baffles is to make a very stiff baffle board securely attached to a braced wall.
No it's not, unless the wall is made of thick concrete.

Note that in OP's case, he's using four 18s, each with about 560 grams Mmd. That's a total of over 2 kg of moving mass. I don't care how well you brace it, it's going to shake the entire house, not just the wall it's attacked to. If it's bolted to the floor though, it won't be as bad because floors are generally MUCH stronger than walls.

Quote:

Manifolds are the best solution for most installations.
Manifolds do solve a lot of problems by their very nature. They are often a good choice AS LONG AS THEY ARE SHALLOW to prevent resonances inside the passband.

gangrew 07-05-2017 09:52 AM

Member rms8 did a similar install where he bolted the manifolds to the floor, and decoupled from the walls. Post #11 of his build thread has some explanation of how he did it.

https://www.avsforum.com/forum/19-ded...-finished.html

RickJames 07-05-2017 11:24 AM

Quote:

Originally Posted by diy speaker guy (Post 54020905)
BTW, it's also pretty funny that Bill won't directly address me but you seem to hop right in every time I correct him. You've been a member since 2006, have only 175 posts and you only post about Bill's products or in threads where Bill has been corrected on technical details. Something fishy about that, no? Or maybe not considering that Bill has been banned from other forums for sockpuppeting.

You know perfectly well that Bill put you on his ignore list years ago, because you couldn't carry on a civil conversation that wasn't dominated by personal insults. For instance this.

Quote:

Wow, that is shockingly bad advice.
I'm a BFM fanboy and proud of it. You're not on my ignore list, you're on my watch list, and when you insult BFM I will respond. And the idea that you, who has no body of work to be found, could ever correct someone with Bill's resume is ridiculous. DIY speaker guy? Really? Chutzpah in the extreme.

Apologies to the OP and all others with this thread derail, but some things can't be left ignored.

diy speaker guy 07-05-2017 11:34 AM

Quote:

Originally Posted by RickJames (Post 54068457)
You know perfectly well that Bill put you on his ignore list years ago, because you couldn't carry on a civil conversation that wasn't dominated by personal insults. For instance this.
"Wow, that is shockingly bad advice."

How on earth is that a personal insult? It IS shockingly bad advice and I showed why very clearly. With pictures. That you didn't understand.

Quote:

I'm a BFM fanboy and proud of it. You're not on my ignore list, you're on my watch list, and when you insult BFM I will respond. And the idea that you, who has no body of work to be found, could ever correct someone with Bill's resume is ridiculous. DIY speaker guy? Really? Chutzpah in the extreme.

Apologies to the OP and all others with this thread derail, but some things can't be left ignored.
I am flat out saying that "you" are not a real person. Your account is Bill's sockpuppet account. The only reason neither "you" nor Bill has reported this allegation to the moderators like he usually does is because "you" and Bill don't want the moderators to look into it. I'm sure Bill is using a VPN to mask his IP when he posts as "RickJames" since he's been banned from other forums for the same behavior.

I do have a body of work to be found - at least as large as Bill's. And I've been correcting his mistakes for years. The reason he won't respond to me anymore (using his own name) is that the mistakes he makes are not defendable.

Resumes mean nothing to me. I've met people with no resume that are masters in their craft and people with long resumes that had no idea what they were doing.

The fact that you didn't understand my Hornresp sim clearly shows that you are not qualified to judge me. "You" can tell your friend Bill I said so.

It is kind of flattering that you think I'm dangerous enough to be on your "watch list" though. I like stalkers.


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