[Sonnie]

The Official IB FAQ is authored by current and previous staff members of Home Theater Shack. We appreciate all of those who participated. If you see anything that needs correcting and/or have anything that might be good to add, please let us know.



Infinite Baffle FAQ

What is an IB (Infinite Baffle) Subwoofer System?

In very simple terms, an IB is basically an extremely large multi-driver sealed subwoofer system. In more detailed terms, an infinite baffle is a unique type of subwoofer alignment where the drivers are mounted on a sealed baffle in free air. The space behind the baffle is generally very large... typically several times the Vas of the drivers used. Large adjacent rooms, basements and attics commonly represent this large free air space. It is easiest to think of its advantages by comparing it to smaller sealed designs where pressure builds up in the box as the drivers move. To maintain steady output as frequencies drop lower, greater demands are put upon a driver causing excursion requirements to increase at an exponential rate. This effect is greatest in the infrasonic range, which is effectively around 20hz and under. As pressure increases in a small sealed enclosure, the more force it will take to maintain that steady output, which will require more power and result in potentially higher distortion. By enclosing the drivers in a large space the ‘air spring effect’ caused by small enclosures is removed. Ultimately all cabinets introduce coloration in one form or another, and the idea behind an IB is to completely remove this so as to hear only the bass in one of the purest and cleanest forms it can be heard. Additionally, with no damping effect from a 'cabinet', the drivers in an IB are more efficient meaning more SPL per watt than traditional sealed enclosures. Because of the need for this extremely large sealed space behind the drivers baffle, the subwoofers are usually mounted on a wall or ceiling opening into a large area. The rear of the baffle must be acoustically sealed from the front of the baffle, therefore a large baffle like a wall or ceiling works great. Careful consideration should be taken in choosing the placement of an IB system since it can be difficult to move after installation.

The definition of an infinite baffle comes from the idea that the drivers are mounted on a very large baffle (infinite baffle). The rear wave of the driver is completely separated from the front wave of the driver by this very large baffle. To help better understand what a baffle is, the images below show the baffle on a small sealed enclosure and also the wall being used as the baffle, with a manifold recessed into the wall. The drivers are mounted so that they fire into your home theater or listening room.

[CLICK ON THE IMAGE TO ENLARGE]​

There are numerous choices in how you might install your drivers in an IB system. Below is merely a few various examples of manifolds and line arrays that are attached to floors, ceilings or walls.

​

As already eluded to, typically a wall, floor or ceiling is used as the baffle. Think of the baffle being totally infinite, which in reality is impossible since you cannot have a never ending wall between you and the drivers. However, take your imaginary never ending wall, and begin to fold down parts of the wall... basically wrapping it around the person standing on the listening side of the baffle, until it completely encloses the person in a cube. The baffle is now infinite in the same way as the edge of a circle is infinite, in that it has no beginning or end. It is akin to making a sealed sub with the driver mounted the wrong way, but make it so big you can get inside and set up your home cinema in there, and add enough drivers so it works as a bass system. The IB is effectively the inverse of a room sized sealed sub. The outside world is then your subwoofer enclosure (also theoretically infinite, yet very rarely is). The reality is that this outside world is made up of the rest of your house. As such the enclosure is no longer infinite (and the drivers are designed with this knowledge), but it will not affect your IB system as long as the enclosure is not so small it alters the Q of the system. The rear volume (the outside world) should ideally be at least 10 times the Vas of all drivers combined or the point where the drivers Qts equals its Qtc. With an IB driver, the driver is not designed to be loaded to result in a system Q, the driver is made with its system Q native to where it should be already. 10 times Vas is considered the normal requirement, with 4 times Vas generally considered the cut off point at which it will be unworkable.

Vas: Measured in litres (L), is a measure of the free air 'stiffness' of the suspension - the driver must be mounted in free air. It represents the volume of air that has the same stiffness as the driver's suspension when acted on by a piston of the same area (Sd) as the cone. Larger values mean lower stiffness, and generally require larger enclosures. Vas varies with the square of the diameter.

Qts: A unitless measurement, characterizing the combined electric and mechanical damping of the driver. In electronics, Q is the inverse of the damping ratio. The value of Qts is proportional to the energy stored, divided by the energy dissipated, and is defined at resonance (Fs). Most drivers have Qts values between 0.2 and 0.8.

Q (Qtc): The system Q is the characteristic sound of the bass system. Higher values represent a focus on upper bass impact, while lower values focus on low cleaner frequency reproduction. You cant have both in your system, but there is the middle of the road which is considered the optimal balance of upper bass punch and low bass rumble, and that is the .707 value. IB specific drivers are designed to give a good balance in a non loaded system close to the .7 figure, while normal drivers are not, which is why many non IB specific drivers are of questionable use for an IB.

Bill "Collo" Collison gives us this explanation: What is an IB (Infinite Baffle) Subwoofer System?

Check out our member IB installs Finished IB Project Photos, which will give you some idea of different types of IB installs.

 

[Sonnie]

Re: The Official IB (Infinie Baffle) FAQ

Why would I want an IB System?

IB systems can improve driver efficiency. By eliminating the load of the enclosure “air spring” against the driver, it reduces the overall load on the driver allowing it to work more efficiently. This increases the drivers output per watt, therefore, a driver mounted in and IB alignment will be more efficient than a driver mounted in a small sealed enclosure.

IB systems can reduce the cost of amplification and significantly reduce amplification distortion. When power is applied to the voice coil, it heats up and the resistance of the voice coil increases. This increase in resistance means that less current is being supplied to the voice coil from the amplifier and the amplifier is required to put out more power per level of driver output. This phenomenon is called power compression and it can result in as little as half the available current being delivered to the driver. Power compression can be reduced by placing the driver in free air (and IB system) allowing it to stay cooler longer because there is more air to cool off the voice coil (less heat build up due to lack of small enclosed space). The fact that you typically use much less power with each IB driver helps with heat reduction.

IB systems reduce phase shifting since no ports or passive radiators are required. It is worth noting however, that if you space your drivers out to take advantage of the benefits afforded by a multiple sub-driver setup, normal phase issue rules apply, and EQ may very well be required to properly integrate the non co-located drivers.

IB systems are easy to model and usually require less equalization than other systems. When there is no load on the drivers, the Q of the system (Qtc) matches the Q of the driver (Qts), therefore the overall resonant frequency of the subwoofer system matches the Fs of the driver. This makes the IB system easy to model and it performs as modeled. The low Fs also means the low end will need much less equalization than any other sealed sub design. An IB system lends itself to a smooth shallow roll off meaning that once in room, it is quite common to have masses of low end output before any equalization is applied. In most cases your equalization will then only be needed for room correction rather than trying to boost low end performance.

IB systems usually have lower distortion than other systems. One goal of any subwoofer design is low distortion and in an IB alignment this is achieved by using several large drivers. By using multiple drivers (with low power consumption requirements), the excursion of each driver is reduced, thus decreasing the overall distortion of the system.

IB systems are generally easier to integrate into the room decor. They are ideal for applications where a standard box subwoofer is not desired. An IB can be hidden in a wall, ceiling or floor... out of the way and unnoticeable in many cases. If your room is a good candidate for an IB system, you can essentially end up with no visible subwoofers in your room.


Why would I not want an IB system?

IB systems can sometimes create challenging installations. Access to attics and crawl space might be an issue. Depending on its location and the type of baffle you will use, consideration must be taken in getting the materials, drivers and tools to the mounting location. Planning the installation is a significant part of the process of determining if an IB system is right for you.

IB systems can sometimes be cosmetically challenging because they require holes to be cut into the baffle (walls, ceiling, floors etc.) which could require slight remolding of the listening area or home.

IB systems create significant output from the rear of the driver, equal to what is being produced from the front of the driver. Care must be taken to select a suitable location where this rear sound will not be an issue. Care must also be taken to properly decouple the drivers from the home's structure, otherwise vibrations can travel throughout the home and in some cases may even cause structural damage. Timber studded walls with a line array of IB drivers mounted on it will lead to the cone movement of each driver transferring to the wall. The wall will vibrate in sympathy with the movement of the drivers causing unwanted vibrations from the wall, which will likely be audible. In addition, the sympathetic movement of the wall is basically energy from the drivers that should instead be used in the reproduction of the bass, therefore the movement of the wall represents lost output from your IB. The opposed box type manifolds (shown in the illustrations above) are the best way to cancel out transference of these vibrations from your IB drivers to the structure of the home, ensuring you get maximum output from your subwoofer system.

As with any subwoofer system there will be problems to overcome, but most, if not all of the potential problems, can be overcome with good design and good installation practices.

Fs: Also called F0, measured in hertz (Hz). The frequency at which the combination of the moving mass and suspension compliance maximally reinforces cone motion. A more compliant suspension or a larger moving mass will cause a lower resonance frequency, and vice versa. Usually it is less efficient to produce output at frequencies below Fs, though motion below Fs can cause uncontrolled motion, mechanically endangering the driver. Woofers typically have an Fs in the range of 13–60 Hz. Midranges usually have an Fs in the range of 60–500 Hz and tweeters between 500 Hz and 4 kHz.

 

[Sonnie]

Re: The Official IB (Infinie Baffle) FAQ

How do IB systems compare to other subwoofer designs?

There are basically two types of subwoofer systems, sealed and ported, with all other designs being some sort of variation of these two systems. An IB system is different in that it acts as though it is essentially enclosure-less, but it is more closely related to a very large sealed design (think room-size large).

A sealed design (or acoustic suspension) is designed to take advantage of the air spring provided by the sealed cabinet to provide more output above Fc and naturally attenuate low frequencies, which in turn minimizes bottoming out of the driver. A driver bottoms out when it reaches its mechanical limits, which is when the driver cone has reached its excursion limits. The output rolls off at 12dB per octave below the point where output is -3dB (F3), which helps to minimize over excursion of the driver. A traditional sealed subwoofer is a sealed enclosure with a fixed volume of air inside. When the driver moves in and out the air inside is compressed and decompressed, causing pressure changes inside the cabinet that act to control the driver. As a driver moves forward and away from the cabinet, the pressure inside drops and the higher pressure of the air outside the box pushes back on the driver to restrain it, and vice versa, when the driver pushes into the cabinet, pressure increases and the driver is pushed back. This is the damping effect in action, which causes more power to be demanded from the amplifier to drive the speaker to its mechanical limits and high SPL levels. Since there is no dampening of the driver in an IB system, it requires less power than a smaller traditional sealed system and is thereby more efficient. For any given SPL at any given frequency, and IB will need much less input power to achieve a result equal to that of a traditional smaller sealed sub, or you get greater output for any given input wattage compared to a sealed sub. On the flip side, this means it will be easy for the IB driver to reach its limits. There is effectively nothing mechanical preventing the driver from being destroyed if too much power is applied. To protect the drivers in an IB system, an infrasonic/high pass filter can be used, but typically protection is afforded by spreading the power over multiple drivers.

Ported designs take advantage of the energy produced by the back of the driver and redirect it back into the room via a port acting as a Helmholtz resonator, resulting in large gains in output near the tuning frequency. This allows them to have higher output than sealed designs with lower levels of cone excursion (which reduces distortion) and higher power handling up to the point of the ports predetermined tuning frequency. However, the output added by the port is out of phase with the main input signal so group delay is higher. Group delay is time distortion, which is a phase issue related to two identical signals arriving at a set point (in this case the listening position) at different times. Group delay is the mathematical derivative of phase response. Although group delay is measurable, it is thought to be inaudible at very low frequencies where ports do the most work and the sensitivity of the human ear is at its lowest. Ports do have other issues such as compression and resonances that can also effect the sound of the bass produced. Although good design can minimize these issues, with an IB system the possibility of such issues are completely removed. The same can be said for sealed designs, because the back pressure created by the driver's movement can transmit into the cabinet itself coloring the sound, as well as small cabinets will raise the Q of the sealed system which further colors the sound. There are no such issues to deal with in an IB system.

Below is a comparison of a sealed, ported and IB subwoofer driver. The drivers in the model comparison are all 15" drivers from the same manufacturer. Their standard driver is used for the sealed and ported modeling, while their IB driver is used for the IB modeling.

Traditional Sealed = Pink
Large Low Tuned Ported = White
IB = Yellow

Although it is possible to use many different drivers for an IB system, it is best to use IB specific drivers, since not all drivers are suitable. If you do not want to use standard drivers, try to choose ones with a Qts more in line with your desired final system Q (i.e closer to .7) and ideally with as low of an Fs as possible. Drivers with a higher Fs will work, but your IB system will require more equalization to boost the low end. Contrary to what some would believe, all drivers are capable of output below their Fs.

With any system you choose, driver selection and accurate design are critical to the reaching the maximum potential of that system. Careful consideration of both resources and your goals must be taken into account when designing your subwoofer system. Our DIY Subwoofers forum is dedicated to helping you with designing the perfect subwoofer system for you.

 

[Sonnie]

Re: The Official IB (Infinie Baffle) FAQ

What is the best placement for an IB system?

While your room will have no idea what type of subwoofer system you are using, the placement is always critical. With an IB system, determining the location prior to installation is especially critical, since you are most likely about to cut a hole in a floor, wall or ceiling. The lowest bass frequencies, typically under 80Hz, radiate into your room and are omnidirectional, so you should not be able to determine the location from which those frequencies originate. However, the reflections of the bass waves bouncing off of the room boundaries will cause peaks and dips in the response. Therefore, the placement of the drivers will determine the type of room mode interaction you will have. The best method we will suggest is to place a subwoofer (if possible, one capable of the lowest frequencies) into your current or intended primary listening position. Using a program like REW (Room EQ Wizard), with a calibrated microphone, measure about six inches from the wall, ceiling or floor locations you are considering for placement of your drivers or manifold. The location with the best extension and smoothest response... or perhaps the location with the best extension and what appears to be the easiest correctable response, should be your target location, pending no other limitations. REW can be downloaded here for free. If you are using a sub equalizer, you can go one step farther and set it up to see how the corrected response will measure. Here is an older thread of how the potential location for an IB system was determined. This is not an exclusive method, but it is the best method we can suggest due to the potential installation issues. If it is feasible to place the sub at the location you ultimately desire to install the IB drivers, you might consider measuring with the mic at your main listening position, however, keep in mind that the actual enclosure you are using may have an effect on the response. While there is no absolute accurate test method, these should get you very close... and if at all possible, you really want to try your best to get this right prior to cutting holes in your room. If you need help with REW and measuring your potential locations, we will be happy to assist you in our forums. Check out our Equalization | Calibration forums, which include the REW Forum. We also have the most respected DIY Subwoofers forums anywhere.

In determining your location, you will want to make sure you can completely seal the back wave of the driver from the listening room. Something else you may wish to consider is if the floor, wall or ceiling where you intend to mount your drivers or manifold is insulated, the drivers will effectively break the insulation barrier. For this reason, you may choose to use one of the box type manifolds and incorporate an insulated fascia panel that could be put in place when the IB is not in use. Below is an example of a potential fascia design to give you and idea of what we are suggesting.

[CLICK ON THE IMAGE TO ENLARGE]

​

How much space is required behind the subwoofer drivers?

For a true IB system you will need the guideline suggested ten times Vas of each driver (or more) behind the drivers. Increasing the space behind the drivers to more than ten times Vas has no effect on the system, so external venting or leaks extending outside the home with an infinite volume is perfectly acceptable. For a multi-driver array, multiply the Vas of each driver by the number of drivers you will use, and multiply that figure by ten to determine the total space needed behind your drivers. The ten times Vas figure is the point where the Q of the system (Qtc) is normally equal to the Q of the driver (Qts), which is one of the definitions of an IB system.

Smaller spaces behind the drivers can be used, but as space decreases, the system begins to take on the characteristics of traditional sealed boxes with a faster roll off at low frequencies and a raised system Q. If you do not have sufficient space, it is recommended to model an IB system with the space you do have available and compare the results to ten times Vas or more. If you are trying to decide between a traditional sealed or ported design and an IB system, you may want to model all three to determine what is most desirable for you. As mentioned previously, as your space behind the drivers decreases, the system Q will begin to raise and low end output will reduce, however, this happens on a much slower scale with IB systems than with traditional sealed boxes. Even if your space behind the driver is limited to as little as four times the Vas of your drivers, an IB system may still be practical and sufficient. There are more drivers available today that are built for IB systems and will model better for small spaces behind the drivers, so choose your drivers accordingly and model your potential IB system. For help with modeling... see our DIY Subwoofers forum.

You can reverse engineer the mathematics by calculating the space behind your drivers and use it to figure out how many drivers you need. Take the calculated volume, divide it by ten, and divide that figure by the Vas of your driver. This will give you the exact number of drivers required to yield ten times Vas. If the result is as low as two drivers, you will want to determine if an IB system is feasible... or if you will be able to add more drivers to the system, creating the less than optimal ten times Vas. A lower number of drivers can result in the drivers reaching their mechanical limits before producing sufficient output into the listening room, especially if you use lower Xmax drivers. After calculations, if you end up with a result that suggests a large number of drivers, then four drivers is a common number for an IB system that will perform admirably in a typical sized listening room. If your room is extremely large or opens up into several other rooms, you may want to consider more drivers. You can always start with less drivers and add more later, space permitted.


How do I measure the area behind the subwoofer drivers?

The volume of most areas in a house can be calculated by totaling the volume of the cubes and triangles in that area. Square and rectangle spaces are very simple to calculate, while odd shaped spaces can sometimes be more challenging. The image below is representative of most attics or spaces under stairs. Volume of a cube is Length X Depth X Height. Volume of a triangular section is half of the length X depth X height. Sum (or subtract) the volumes of each part to get the total volume of the space.

[CLICK ON THE IMAGE TO ENLARGE]


Total Volume = (Length*Depth*Height1)+[(1/2)*(Length*Depth*Height2)
​

We also have an enclosure volume calculator here at HTS to help you determine the volume of space you have to work with:

HTS Enclosure Volume Calculator

As always... help is merely a New Thread away.

 

[Sonnie]

Re: The Official IB (Infinie Baffle) FAQ

How do I model an IB?

Modeling an IB can be accomplished in a couple of different ways. A sealed enclosure can be simulated with a volume of either infinite size using the maximum figure your preferred modelling program will allow, or by using 10 times the Vas of the driver(s), which essentially equates to the same thing. If you should happen to know it, the actual volume of the space you are using can be used as well.

WinISD is a free subwoofer modeling software that can be downloaded here. There is also a video guide on inputting driver parameters into the WinISD database here, with a more in depth guide on using WinISD available here.

The Vas of the driver(s) is one of the TS parameters of the driver and you can find it with the information that comes with a new driver, or from the manufacturer of the driver. If you have downloaded a WinISD driver file from this website, you can click on the “Parameters” tab at the bottom left side of the model’s window and look for the Vas spec. Multiply this number by 10 and enter it in the “Volume” box in the “Box” tab. Remember, if you are using multiple drivers... and you really should... you will multiply the Vas figure times the number of drivers first, then multiply that figure by 10.

As always, we are more than happy to help you model an IB system. See our DIY Subwoofer section of the forum for more help.

What kind of drivers are recommended for an Infinite Baffle system?

Once upon a time, there were no specific drivers designed for IB systems, but there were several subwoofer drivers that were sufficient. Today there are now plenty of IB specific drivers on the market that are available for consideration. Typically drivers with higher Qts and lower Fs will work best, as will drivers with more xmax. So why not use any ole driver? The problem with non specific IB driver is that it is designed to go into a loaded system, which drives up system Q and causes the low end performance to reduce, which is what helps protect your driver in a traditional subwoofer design. Hence, their Qts is usually very low... so low that when you use these drivers in an IB system which is unloaded and the driver Q remains native, it will be almost all low end rumble and no upper bass punch, leaving many with a reaction of 'where has all my bass gone'. True IB drivers are not going into a loaded system and their Q values are closer to what the final system Qtc should be, making them a much better choice for use in IB systems. Furthermore, a driver in free air has no resistance to work against and less motor force is needed, therefore smaller and less expensive motors can be used. This makes an IB specific driver less expensive in most cases. This also helps when your subwoofer is totally reliant on just the drivers for all of the output of the low end system output.

Larger drivers work better! 15" and larger drivers are recommended, although there have been some very good IB systems built with 12" drivers. Not only can the larger drivers displace more air per mm of excursion (which leads to easier reproduction of those difficult infrasonic frequencies), but they do not have to move as far as smaller drivers to produce the same output. This keeps them in the linear range and in line with the philosophy of the IB as a low distortion design. One common misconception is that large drivers will be slow or sloppy, but a properly designed IB system will prove otherwise. There are application specific IB drivers from several companies, so there is no longer a shortage of good IB driver options.


How many drivers are recommended for an IB system?

There is no exact definitive answer to this question as performance is dependent on room acoustics and listening habits/expectations, as well as variation in driver performances. Typically you do not see many IB systems with less than two drivers. If you know the enclosure size, you can determine how many drivers will give you your 10 times Vas figure. If your enclosure is extremely large, then use modelling software to see how many drivers are needed for your desired output levels. Enclosure volume of more than 10 times the Vas is acceptable for an IB, so if your enclosure size exceeds that figure, but your model shows the desired output performance and all drivers are within xmax, you have enough drivers.

What happens when you start adding additional drivers? Sensitivity increases every time you add another driver along with better power handling. For every doubling of drivers 6db of additional output is gained. (3db from sensitivity and 3db from the additional power supplied to that driver). 4 drivers will have 12db of extra output and less excursion over a single driver, and when you compare SPL levels, a multi-driver array has a massive amount of reduced excursion. Performance increases dramatically as you begin to add drivers, but there comes a point of diminishing return, so buy as many as you need or can afford up to your desired output performance.

Below an example of the maximum output of a single driver vs. 4 drivers in an IB system. Notice that 12db of output is gained while excursion is reduced.

 

[Sonnie]

Re: The Official IB (Infinie Baffle) FAQ

What is the best design and use of multiple drivers in an IB system?

The answer to this is really up to you and your preference based on the research you have completed thus far. The design depends on each individual installation... your room, your budget and your listening goals. You may end up with a simple line array, which can be fairly easy to design and build, but it also depends on your situation. A manifold system can take up less space on the wall facing your room and will help hide multiple drivers. A manifold allows the drivers to mounted opposite of each other, which might help cancel mechanical vibrations that may otherwise be transmitted to the structure of the room. If you build a manifold, make sure the opening of the manifold is no smaller than the total combined area (Sd) of the drivers being used. Another benefit of the line array over the manifold is the acoustic radiation of the drivers are not limited.

Here are some examples of how multiple drivers can be used...

​

Also referenced earlier is our Finished IB Project Photos thread where you can see several member installs.


What kind of wood is recommended for building a manifold?

Usually these are made with plywood or MDF, but any sturdy, stable 3/4" or thicker material will do. Below is a list of the various options and their pros and cons.

Cabinet grade plywood / Baltic birch plywood is the top of the line in terms of sheet goods. Usually one face is of premium quality (smooth, no defects, ready to paint/stain) and the other is still of good quality (possibly a knot or unmatched grain pattern). It comes in many hardwood varieties for the face sides. If you are matching trim this would be important. If you just want to paint it, go with a maple or birch. Cabinet grade has more ply layers than the cheaper plywoods, which accounts for their superior stability and screw-holding ability. A very specific type of cabinet grade ply is Baltic birch, which has many more layers (usually 13 instead of the typical 7 to 9 layers). This adds to the stiffness and makes it a very nice material for cabinets. The main downside to Baltic birch is that it only comes in 5ft x 5ft sheets instead of the normal 4 foot x 8 foot. This may affect your particular installation.

Pros:

• Stable
• Very few, if any voids
• At least one side is high quality in the event you need to paint/finish it to match the room.
• Holds screws well

Cons:

• Expensive
• Availability - not usually available at the discount home centers. Most lumber yards, hardwood suppliers, and construction supply houses carry or can order it.

MDF (Medium Density Fiberboard) is a composite material consisting of mostly wood chip waste ground into a pulp and a formaldehyde resin as a binder. It is denser than plywood, is easy to machine, but chips easily and does not hold regular screws well. Special confirmat screws are recommended for assembly, especially for heavy large boxes like an IB manifold. The dense random grain/chip pattern damps resonances, which make it a favorite for speaker cabinet construction. It is important to note that while this will lessen ringing, an un-braced MDF side panel will still resonate at lower frequencies (as would any plywood or drywall panel of similar size and mass). Finally, while a dust mask is recommended for any sawing or routing operation, it should be considered a requirement with MDF. The finer particles and the formaldehyde binder make MDF dust a severe irritant and can cause respiratory problems in some people.

Pros:

• Stable
• Less resonant
• Cheap and available at home centers
• Easy to machine

Cons:

• Heavy (good for stability, bad for transporting, setting up, and cutting).
• Dust can be an irritant
• Does not hold screws as well as premium plywood

Regular Plywood is more expensive than MDF, but cheaper than its premium cousin described above. It typically has fewer but thicker core layers, which makes it less stiff and more prone to having voids. For many applications this is not a problem, but if the project requires a screw into the side grain (the plys) where a void is, the screw will have very minimal holding power. The veneer faces are usually of a lower grade, meaning they can have knots, imperfections, and are usually not grain matched. That being said, this variety of plywood is readily available, comes in many species (again, go with birch or maple if painting) and is generally a good choice for building a large box, especially if it will be hidden or otherwise covered.

Pros:

• Stable
• Cheap and available at home centers

Cons:

• Voids
• Appearance (if this is a priority)

Not mentioned is solid wood panels or framing lumber. These are generally not good for baffles (where drivers are mounted) due to wood movement during humidity and temperature changes. The metal driver frames do not move much from temperature (and not at all from humidity), however the wood can expand enough to make this a problem. While not good for the carcass or driver mounting, framing lumber like pine or Douglas fir is fine for bracing and securing the box to the wall studs or ceiling joists.

 

[Sonnie]

Re: The Official IB (Infinie Baffle) FAQ

Will an IB system vibrate my wall?

Yes... your wall is going to vibrate. How much vibration will be dependent on the framing of your wall along with the quality of bracing and build of your mounted IB system. A line array is typically going to cause more vibrations in your wall than a manifold, but again this will ultimately be dependent on your overall construction. As the drivers move back and forth they can create a significant force and make your wall flex. Your wall can be excited by its natural resonance at certain frequencies. This could easily cause pictures and windows to rattle and create unwanted distortion in the sound... even in other rooms. These are things that have to be considered when designing an IB system. As mentioned earlier, manifolds with opposing drivers can help reduce resonance if built properly. Consider the wall you are thinking about mounting your IB system. If you want to get an idea of how your current wall might vibrate, AT YOUR OWN RISK take your forearm (with a folded towel for cushioning) and hit the wall with a bit of force (again, careful not to break your arm or the wall). How much are things vibrating? Now figure if you had about four times that much force shaking your wall. You must make sure your wall and your IB system are structurally solid and even then it will not be possible to completely eliminate all vibrations.


Will I need equalization for my IB system?

It is certainly possible and likely. How many subwoofer systems do you know that don't need at least some equalization? We are not talking about the exception... we know there are a few out there that don't need equalization, but those are in the minority... and not everyone can doctor their room with fifty-eleven acoustic treatments, especially those needed to tame low frequency response below 80Hz. It may be that you have a processor or receiver with Audyssey or some other type of built-in EQ system that can take care of any equalization issues you might have. Our recommendation is to download RoomEQ Wizard and measure the frequency response of your IB system when it is finished. Check out the various options available for equalizing your subwoofer and apply as needed. There is no replacement for a properly equalized subwoofer system and there is plenty of help here in the forum to get you fully equalized if needed.


The Official IB FAQ is authored by current and previous staff members of Home Theater Shack. We appreciate all of those who participated. If you see anything that needs correcting and/or have anything that might be good to add, please let us know.

 

[ksrigg]

I am trying to determine the best use for a Parts Express "buyout" driver. It is the 6 1/2" Poly mdbass driver found here.

https://www.parts-express.com/6-1-2-poly-cone-midbass-woofer-4-ohm--299-609

I don't know if I could mount them in a line aray with an opn back (infinite baffle) design or not. I do know that a single driver requiring a 3.6 cu.ft. enclosure for a vented enclosure doesn't work very well, nor does a sealed box needing 1.5 cu. ft. to plumb the depths of 50 hz. isn't a great project either. No wonder they are less than five dolars each in quantity. I know they came from the venerable B652 Bookshelf speaker and are likely cosmetic rejects as most have glue and other evidence of sloppy workmanship. BUT, I want to do something ith them. Any one have any brilliant ideas? I really thin this might require a little thining outside the BOX...to get something tht is truly untstanding..I currently own 30 of them but I'm sure I could get more, or use less.....Thank you again..

Thank you in advance for any ideas....

 

[Savjac]

Brilliant write up Sonnie.
I have heard two, both at Mikes house in Tampa, they were nice.

My new home has a perfect place for an IB, the HT is directly over the garage which is completely insulated, dry walled and painted, top and all sides with insulated doors. It would be a snap to build something in the garage then cut a hole in the ceiling/floor and voila. Might want to do some learnin here first.

 

[Rob41]

Very nice write up Sonnie! I'd like to build either an IB or Ripole system using Dayton's IB385 drivers.

I am trying to determine the best use for a Parts Express "buyout" driver. It is the 6 1/2" Poly mdbass driver found here.

https://www.parts-express.com/6-1-2-poly-cone-midbass-woofer-4-ohm--299-609

I don't know if I could mount them in a line aray with an opn back (infinite baffle) design or not. I do know that a single driver requiring a 3.6 cu.ft. enclosure for a vented enclosure doesn't work very well, nor does a sealed box needing 1.5 cu. ft. to plumb the depths of 50 hz. isn't a great project either. No wonder they are less than five dolars each in quantity. I know they came from the venerable B652 Bookshelf speaker and are likely cosmetic rejects as most have glue and other evidence of sloppy workmanship. BUT, I want to do something ith them. Any one have any brilliant ideas? I really thin this might require a little thining outside the BOX...to get something tht is truly untstanding..I currently own 30 of them but I'm sure I could get more, or use less.....Thank you again..

Thank you in advance for any ideas....

Those 6 1/2" drivers would work great.......down to about 60Hz where they begin to roll off sharply. Not really suited to the intended purpose of providing the lowest of bass.

Those 6 1/2" drivers do work exceptionally well in an Open baffle line array when the system is augmented with bass. You can look up You can see my build of these by googling "Rob's OBLA-33".

 

[Raymonk]

Hi,
the slope below f3 for a sealed box is 12db/octave.
But what is the slope for an IB. Is it 6dB/octave?

Thanks,
Thierry