[slosjo]

I hope this thread can become a general discussion about infinite baffle subwoofer systems.  I've been doing a lot of reading on the subject lately, on this website and others.  I would like to initiate another discussion specifically centered around GR Research woofers and servo amps in a home theater setting.  What I'd really like to get out of this discussion are the following major points, putting cost aside for the time being:
 
-What are the differences between a well done infinite baffle subwoofer system, and a well done ported or sealed array of subwoofers, in terms of sound, feel, etc?  I've read about lack of box coloration, less punch, more open, etc.  I'm hoping that someone who has heard both can put together a combination of adjectives that will allow me to grasp the concept.
 
-Is servo control as important of a feature in an IB system as it is in a sealed (or ported) system?
 
-How important is displacement when designing an IB system?  Some of these guys are installing (4) or ( 8 ) 18" FI subwoofers with thousands of watts of power.  While I'd sure like to hear one of these systems, I'd also like to know how much is really necessary.  A better question might be how much more displacement is required when compared to the aforementioned "well done" sealed subwoofer system?  If I can achieve satisfactory results with (2) 12" servo subs in boxes, do I need (4) 12" subs in an IB configuration to achieve satisfactory results? (I understand that "satisfactory" is a very subjective term, but I hope you understand my point)
 
-Do IB systems with servo control require less power than those without servo control (given a room with x number of square feet)?
 
 
I'm sure I'll have more as the discussion continues.  Thanks for any input.
 
Chris

[rythmik]

I hope this thread can become a general discussion about infinite baffle subwoofer systems.  I've been doing a lot of reading on the subject lately, on this website and others.  I would like to initiate another discussion specifically centered around GR Research woofers and servo amps in a home theater setting.  What I'd really like to get out of this discussion are the following major points, putting cost aside for the time being:
 
-What are the differences between a well done infinite baffle subwoofer system, and a well done ported or sealed array of subwoofers, in terms of sound, feel, etc?  I've read about lack of box coloration, less punch, more open, etc.  I'm hoping that someone who has heard both can put together a combination of adjectives that will allow me to grasp the concept.
 
-Is servo control as important of a feature in an IB system as it is in a sealed (or ported) system?
 
-How important is displacement when designing an IB system?  Some of these guys are installing (4) or ( 8 ) 18" FI subwoofers with thousands of watts of power.  While I'd sure like to hear one of these systems, I'd also like to know how much is really necessary.  A better question might be how much more displacement is required when compared to the aforementioned "well done" sealed subwoofer system?  If I can achieve satisfactory results with (2) 12" servo subs in boxes, do I need (4) 12" subs in an IB configuration to achieve satisfactory results? (I understand that "satisfactory" is a very subjective term, but I hope you understand my point)
 
-Do IB systems with servo control require less power than those without servo control (given a room with x number of square feet)?
 
 
I'm sure I'll have more as the discussion continues.  Thanks for any input.
 
Chris

Just for the record, I am not a big fan of IB as I can see several shortcomings of IB speakers:
1) You cannot figure out in advance the best location of the sub.  It is not like other "boxed" subs you can just move it from one place to another until you find the best bass. 
2)   Speaker drivers fire the sound on both sides. Where does the sound from the back go? In boxed subs, the backwave is absorbed by the damping of the drivers plus the damping material, or even by re-radiation is short amount of time because the dimension of the box is small. And yet we can still increase damping of driver and minimize the re-radiation using servo servo. On the other hand, the back cavity of IB speakers is huge. Where does that sound energy go? The sound wave travel a long time in the cavity.   
3) I don't like the idea of mounting subs on stuts. Try pound the interior walls of any house and then pound the wall of any boxed subs. There is no comparison.  Any energy source fires directly on the wall structure will have more sound coloration or sound localization.  We tend to think if I have a 20hz signal, then my wall can only resonate at 20hz. In reality, wall vibration is a nonlinear mode when the amplitude gets large enough. Meaning the source may be pure, but the energy resonating on the walls will contain harmonics.  Jim Salk once brought a 12 sealed servo sub to an audio get together in which the host actually had an huge 18" IB sub.  Among all other things, he mentioned several people comment the servo made the dialogue in movies more intelligible.  That means there are energy leaked from IB subs into upper bass to make the vocal sound blurry.  I really speculate that has to do with the implementation of IB. 



 

[Tyson]

I've heard IB subs several times (including the infamous 12 Shiva's dancing), and they were all unimpressive. 

[ebag4]

I have 4 AE IB 15's in an IB driven by 2400 watts in my HT, I love it for movies but my preference is the bass section of my V1s for music.  The servos are more articulate but the output of the IB is perfect for movies.

[rythmik]

I have 4 AE IB 15's in an IB driven by 2400 watts in my HT, I love it for movies but my preference is the bass section of my V1s for music.  The servos are more articulate but the output of the IB is perfect for movies.

I agree. There is no doubt that IB has upper hand in SPL department, which is good for special effect. 

But for me, movie watching is more than just special effects.  It constantly switches scenes in the movies. The sound effect should reflect that and a good articulate sound system can let us notice that subtley (outdoor scenses vs indoor scenes, or even just different camera angle or camera distance).  Another commonly heard comment is the system A makes you feel the sound is around you (everywhere) vs system B has the sound stage all behind the screen. For me, that is also an important factor in movie watching. I'd like to hear the realism even without special effects.

[slosjo]

Just for the record, I am not a big fan of IB as I can see several shortcomings of IB speakers:
1) You cannot figure out in advance the best location of the sub.  It is not like other "boxed" subs you can just move it from one place to another until you find the best bass. 
2)   Speaker drivers fire the sound on both sides. Where does the sound from the back go? In boxed subs, the backwave is absorbed by the damping of the drivers plus the damping material, or even by re-radiation is short amount of time because the dimension of the box is small. And yet we can still increase damping of driver and minimize the re-radiation using servo servo. On the other hand, the back cavity of IB speakers is huge. Where does that sound energy go? The sound wave travel a long time in the cavity.   
3) I don't like the idea of mounting subs on stuts. Try pound the interior walls of any house and then pound the wall of any boxed subs. There is no comparison.  Any energy source fires directly on the wall structure will have more sound coloration or sound localization.  We tend to think if I have a 20hz signal, then my wall can only resonate at 20hz. In reality, wall vibration is a nonlinear mode when the amplitude gets large enough. Meaning the source may be pure, but the energy resonating on the walls will contain harmonics.  Jim Salk once brought a 12 sealed servo sub to an audio get together in which the host actually had an huge 18" IB sub.  Among all other things, he mentioned several people comment the servo made the dialogue in movies more intelligible.  That means there are energy leaked from IB subs into upper bass to make the vocal sound blurry.  I really speculate that has to do with the implementation of IB. 

1. Certainly a good point to consider.

2. With a boxed sub, these back waves cause distortion as they reflect back and hit the speaker cone.  My understanding is that servo control minimizes that issue, allowing the speaker to be more accurate.  Would it be safe to assume that the same woofer in an infinite baffle arrangement would not have to contend with those back waves, and could be even more accurate?  Is this not one of the virtues of open baffle subwoofers?

3. I understand your concern with this point.  It seems to me though that there are many ways to avoid this issue.  Installing the drivers in a manifold would be one way.  I agree that it would be almost impossible to avoid shaking the wall apart if you install the woofers in a line array attached to the studs.  I looked at some photos of one horizontal line array where the guy anchored the enclosure to the concrete floor.  It seems like that might be a good solution.

I would love for someone to explain to me why open baffle subwoofers are so great.  I've read many threads about them here, yet I still don't really understand.  It seems like some of the reasons might also apply to IB systems.
 

[lokie]

Thanks for the responses. This is the first time I have ever heard anything negative about IB subs.

I have a room that has  crawl space both beneath and above the room. Number one concern is 2 channel.

It's our living room, so the appeal of less boxes is a big plus. My plan is (was) to place a multitude of IB's in a  Geddes style arrangement.

[Danny Richie]

2. With a boxed sub, these back waves cause distortion as they reflect back and hit the speaker cone.  My understanding is that servo control minimizes that issue, allowing the speaker to be more accurate.  Would it be safe to assume that the same woofer in an infinite baffle arrangement would not have to contend with those back waves, and could be even more accurate?  Is this not one of the virtues of open baffle subwoofers?

In a boxed design the box is not large enough to allow a sound wave to propagate within the box. The sub simply doesn't play up high enough in range where wavelengths are shorter and the box dimensions are just too small for the longer ones that it plays. What it does have to deal with is pressure changes and the delay of the pressure changes due to compressing air.

In an IB sub the rear space can be quite large allowing long wavelengths to propagate in the space and return to the cone. So often times there can still be some issues.

I would love for someone to explain to me why open baffle subwoofers are so great.  I've read many threads about them here, yet I still don't really understand.  It seems like some of the reasons might also apply to IB systems.

Open baffle woofers load the room differently and in a way that minimizes room boom.

[slosjo]

Danny, according to your website, the SW-12-16FR woofer is designed for IB and OB applications.  Have you ever constructed / heard an IB servo arrangement?  I'm interested in this because I'm going to be constructing a home theater in the future; and not a Best Buy home theater.  There's a lot of info on the web about IB, and a lot of folks saying that the LFE associated with a well done IB system is the Pièce de résistance.  I'm simply trying to understand what makes it different, and why it's superior (in the minds of some...perhaps I should ask them).

As far as I can tell, the systems that really perform all have one thing in common: displacement.  Lots of large woofers in line arrays or manifold arrangements.  The popular driver seems to be the FiCar IB 18" driver.  Now I would have to assume that if you achieve enough displacement with a quantity of 12" servo controlled woofers large enough for the ft^2 involved, it would be that much better. 

In an IB sub the rear space can be quite large allowing long wavelengths to propagate in the space and return to the cone. So often times there can still be some issues.

 

I'm assuming that the servo control would be able to mitigate the effects of this, correct?

Ultimately, I want to build an over-the-top home theater.  In my opinion, the ability to reproduce LFE with authority and accuracy is the cornerstone.  I'll be building some arrangement of GR speakers to round out the system.  So do I pursue some sort of IB subwoofer arrangement, or do I build several GR/Rythmik sealed or ported subs?  Or perhaps OB servo controlled?  I'm really up in the air at this point, and any info that folks could provide to push me one way or the other would be much appreciated.

[Danny Richie]

Danny, according to your website, the SW-12-16FR woofer is designed for IB and OB applications.  Have you ever constructed / heard an IB servo arrangement?

I don't run a dedicated home theater system, but I have a lot of customers using our FR woofer in that application. It is ideal for it.

As far as I can tell, the systems that really perform all have one thing in common: displacement.

Not necessarily. Displacement is needed to sweep the volume needed to hit high SPL at low frequency ranges, but that really has nothing to do with quality or performance.

Lots of large woofers in line arrays or manifold arrangements.  The popular driver seems to be the FiCar IB 18" driver.

That's a good woofer for high SPL in a lower range. It is not good for sound quality. Check the moving mass. It is very heavy and will have a lot of stored energy. And it only has its suspension to control it and return it to rest. It will have a lot of overshot and a long decay rate that will muddy the bass.

Now I would have to assume that if you achieve enough displacement with a quantity of 12" servo controlled woofers large enough for the ft^2 involved, it would be that much better. 

The servo woofer is much lighter to begin with. It has less than half of the stored energy issue to deal with before even adding servo control. With servo control the stopping force controlling the woofer very significant compared to a typical woofer. There is really no comparison to a heavy un-controlled woofer.

The servo woofers will also play lower as the servo system maintains a linear response that is flat to 20Hz and -3db down in the teens.

If you need more SPL simply add more woofers. 

I'm assuming that the servo control would be able to mitigate the effects of this, correct?

That is correct.