# Infinite Baffle mounting a sub designed for vented enclosures will lose output.



## AtlasMick (May 24, 2014)

I've been trying to get my head around infinite baffle designs recently. I've talked to a few shop owners and they tend to admit their lack of knowledge with infinite baffle setups due to not having performed many of those installs. 

I also can't find anyone who can straight up tell me WHY they believe IB is either A) never going to be as loud as ported or B) a sub designed for vented just "wouldn't" work IB. 

Here is what is going on in my head:

A woofer cannot tell if it is in sealed, vented, dual band-pass, free air, or even in mineral oil. It is simply a motor that does work on the moving parts (cone, spider, etc.)

The motor is working on the moving parts of the woofer while ALSO at the same time fighting whatever resistance the air provides (enter, the type of box, or fluid if you want to be super scientific, to establish HOW much that air provides resistance)

The motor also has to fight its own impedance depending on the Hz being played, which changes it's efficiency at that note. In this respect, the efficiency of the sub is constantly changing while playing music. This impedance can be affected by the resistance to movement the AIR has at that particular frequency as well. 

These assumptions I have may be wrong, please pick them apart. Having an infinite baffle is more complicated than just xmax and cone area but how much more complicated... I can't really see it being that extraordinarily more, especially if you are using EQ to level out everything. 

Why would you go vented or sealed instead of IB?


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## BuickGN (May 29, 2009)

With all else being equal, IB and sealed will never be as loud as ported. 

With IB and sealed, for low frequency output, displacement determines output. How much cone area and how much excursion. If you take two identical subs, one in an IB setup and one sealed and they have the same excursion, they will have the same output even if the IB one requires 100w to hit xmax and the sealed one requires 1,000w. That's why IB not being able to physically take as much power as sealed is not a bad thing, it's a good thing. The less power it takes to hit xmax (or xmech) the better.

Ported has port gain or whatever they call it. You have output from the cone and from the port. I believe the majority of the output comes from the port around tuning frequency. It has the benefit of reducing excursion and increasing efficiency which can lower distortion. Output is no longer a matter of cone size and how far you can move it. You can get a +3db gain to more than a +6db gain over sealed with ported. To put that in perspective, you would have to double the power and add a second sealed sub to get the same output as a decent ported setup.

If space were not an issue I would most likely go ported or bandpass over just about anything. Second would be infinite baffle. Over sealed, you get higher efficiency in the range where it matters the most, a flatter response, the obvious increased trunk space and to me, IB just sounds more effortless and digs lower easier than just about anything else. It allows you to use multiple large subs that you would otherwise not be able to fit ported or sealed. I believe it has the advantage of wider bandwidth over ported.

Sealed is my last choice, I don't know why anyone would go that route unless they can't go IB and don't have the room and/or eq for ported.

I typed this in about 2 minutes so excuse the many mistakes I probably made. Not time to re read it.


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## Fetus (Apr 14, 2011)

On a somewhat related note, didn't you try porting your IB setup a while back, Buick? How did that turn out?

Apologies if I'm thinking of someone else...


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## mikey7182 (Jan 16, 2008)

I'll echo what BuickGN said. There is additional gain with a vented enclosure because of the port. Typically, a vented enclosure will net a 3db gain over sealed. Anticipate the same over IB, more or less. This is why you'll find the majority of posts about IB mentioning "cone area is king" or something to that effect. Without the constraints of enclosure fitment, many guys run more/larger woofers in an IB configuration than they would be able to in a sealed or vented alignment. This is part of the appeal of IB. And you can make up for the reduced output by adding cone area, so where you might have only been able to fit a single 12" ported, you can squeeze a pair of 15s on an IB wall and have 3x the displacement on tap. 

As for woofers "optimized for vented/sealed" I wouldn't get terribly caught up in that. There have been a lot of guys having awesome results with a variety of traditional subs mounted in an IB setup, ranging from the JBL W15GTi to the Alpine Type R 15, to the Stereo Integrity Home Theater 18" I just ordered. Treat the sub of choice like an air pump- find the one(s) that displace the most air (Sd x Xmax) as a good place to start, and worry about the other parameters after.


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## cajunner (Apr 13, 2007)

my theory on this phenomenon, is that air pressure coupling from the vent, being added to the woofer in a vented configuration, allows the sound wave to do double the work, or 3 db of gain, based on the simple principle of congruent wave formation.

Where the woofer and the vent combine at resonance, I'm not sure whether you can say the driver is contributing since it's visibly motionless, while the vent pumps mad air.

So it's a theory. 

But going to sealed configuration, means that you remove that air doubling, you can only get out what is being put in, there's no free lunch here. As long as the box is solid, the loss will remain at 3 db in comparison to vented.

However, I differ from others here, and say that IB is a configuration that loses, even when the excursion is the same as sealed.

It's not about the watts, it's about the mechanical losses involved. When you build the box, it's basically keeping all the energy in it, and the cone moving as an air spring, builds against the internal atmosphere of the box in a static, defined fashion.

An IB install has no containment, except for the leaky trunk with it's much less of an air spring, and the return wave that added to the cone's force in a sealed and vented, is extremely weak and helps the cone hardly at all, to redouble the cone's physical force against the air inside the cabin.

At best, you'll get a standing wave that usually hurts more than it helps, and not much else, but it also is the cleanest, most pure representation of the bass note based on the distance from the first rear wave return, or reflection acting on the cone.

Less muddy, less circles in the pond.

But, a few db less output.


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## mikey7182 (Jan 16, 2008)

cajunner said:


> my theory on this phenomenon, is that air pressure coupling from the vent, being added to the woofer in a vented configuration, allows the sound wave to do double the work, or 3 db of gain, based on the simple principle of congruent wave formation.
> 
> Where the woofer and the vent combine at resonance, I'm not sure whether you can say the driver is contributing since it's visibly motionless, while the vent pumps mad air.
> 
> So it's a theory.


I like this. Perhaps the total output of a vented alignment is the sum of the respective outputs from the vent and the cone displacement in a complementary relationship, where the percent contribution from each varies by frequency? Or whatever the equivalent of "complementary" is when discussing percentages rather than right angles.  So given a flat response "Fr" at any given input: Xmax + vent output= Fr. Where the cone moves less, the vent picks up the slack, and vice versa. Thoughts?


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## AtlasMick (May 24, 2014)

I've also come across somewhere on this forum people saying that since the vented enclosure becomes very efficient around its tuning frequency, and the woofer barely moves, you can start pumping far more power into it to make it get closer to xmax at that range of frequency. 

If this is possible, where would you want to tune the box to peak at so that you could essentially make the 3-6db hump a vented box typically gets at the bottom end into a dbmountain right before you want to cut off for subsonics?


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## cubdenno (Nov 10, 2007)

cajunner said:


> but it also is the *cleanest, most pure representation *of the bass note based on the distance from the first rear wave return, or reflection acting on the cone.
> 
> Less muddy, less circles in the pond.
> 
> But, a few db less output.


I find that portion of the statement interesting. It gets thrown out there a lot in reference towards sealed and IB configurations.

Since we are less sensitive in our hearing the lower in frequency you go. to maintain the same output level, everytime you halve the frequency the cone excursion increases 4 times, the more cone movement increases IMD and other harmonics that can definitely degrade the sound quality, it's interesting that people claim sealed/IB is cleaner. When the lower in frequency one goes, the more excursion is required to mantain the output level you are trying to achieve.

It just is interesting in a search for trying to achieve the most accurately reproduced sound, we willingly introduce more distortion because of this "cleaner" claim.


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## mikey7182 (Jan 16, 2008)

cubdenno said:


> I find that portion of the statement interesting. It gets thrown out there a lot in reference towards sealed and IB configurations.
> 
> Since we are less sensitive in our hearing the lower in frequency you go. to maintain the same output level, everytime you halve the frequency the cone excursion increases 4 times, the more cone movement increases IMD and other harmonics that can definitely degrade the sound quality, it's interesting that people claim sealed/IB is cleaner. When the lower in frequency one goes, the more excursion is required to mantain the output level you are trying to achieve.
> 
> It just is interesting in a search for trying to achieve the most accurately reproduced sound, we willingly introduce more distortion because of this "cleaner" claim.


That is an interesting thought. Approaching my first personal IB install, and being a huge proponent of vented enclosures, I am eager to see how the IB works out. I would venture to guess that the reason so many guys counter the output reduction with increased cone area is to keep excursion (and therefore distortion) limited, so where someone may have done a single 12" ported, they install a pair of 15s (or in my case, a single 18") in IB.


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## 94VG30DE (Nov 28, 2007)

cubdenno said:


> Since we are less sensitive in our hearing the lower in frequency you go. to maintain the same output level, everytime you halve the frequency the cone excursion increases 4 times, the more cone movement increases IMD and other harmonics that can definitely degrade the sound quality, it's interesting that people claim sealed/IB is cleaner. When the lower in frequency one goes, the more excursion is required to mantain the output level you are trying to achieve.
> 
> It just is interesting in a search for trying to achieve the most accurately reproduced sound, we willingly introduce more distortion because of this "cleaner" claim.


I think that's part of why we tend to recommend "max cone area" for IB, because this effectively lowers the excursion/IMD for a given "perceived output level" (according to FM curve, which I assume is what you are referencing).


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## cubdenno (Nov 10, 2007)

94VG30DE said:


> I think that's part of why we tend to recommend "max cone area" for IB, because this effectively lowers the excursion/IMD for a given "perceived output level" (according to FM curve, which I assume is what you are referencing).


Don't get me wrong, I understand the IB approach with cone area and agree that to boost the sensitivity with a given amount of power, in using IB as a solution, cone area has to increase.


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## Hanatsu (Nov 9, 2010)

Don't overcomplicate things. Max output with sealed/IB = Xmax * Sd (cone area).

Sealed or IB don't differ much in terms of output, if we assume the backwave is sealed from the front then output is equal, efficiency (not the same as sensitivity) and non-linear distortion are aspects that will change between IB/sealed depending how large/small enclosure you use.

A sealed box will raise Fs(c) and Qt(c) while true IB will retain the driver's free air T/S parameters.


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## Hanatsu (Nov 9, 2010)

94VG30DE said:


> I think that's part of why we tend to recommend "max cone area" for IB, because this effectively lowers the excursion/IMD for a given "perceived output level" (according to FM curve, which I assume is what you are referencing).


There will be an increase in distortion around resonance, depending how good the driver is - more or less. 

With IB, Fs is lower than in a box. It's likely that the audibility of distortion changes as you alter the resonance frequency (and Q). Other than that - non-linear distortion is heavily dependent on excursion. Less excursion = less distortion, that's why vented boxes designed correctly is cleaner than both IB and sealed. Bandpass boxes are even better in this regard.


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## mikey7182 (Jan 16, 2008)

Hanatsu said:


> Don't overcomplicate things. Max output with sealed/IB = Xmax * Sd (cone area).
> 
> Sealed or IB don't differ much in terms of output, if we assume the backwave is sealed from the front then output is equal, efficiency (not the same as sensitivity) and non-linear distortion are aspects that will change between IB/sealed depending how large/small enclosure you use.
> 
> A sealed box will raise Fs(c) and Qt(c) while true IB will retain the driver's free air T/S parameters.


This may be another reason IB guys prefer it over sealed, as with an unaffected Fs, there is no bottom end drop off or less EQ needed.


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## AtlasMick (May 24, 2014)

Are there two schools of thought on IB? One being have a stiff suspension and powerful motor and the other being light suspension and moving mass to increase efficiency? 

Which case or combination of things would help to control the changing of frequency found in music (transient response?) A stiff suspension that would dampen the moving mass at the expense of efficiency shouldn't matter if the efficiency is already higher due less fighting of the air spring, right?

Also, when you see people putting 15's or 18's IB in their car wouldn't 8-10x VAS be like 100cu ft0?. One of the VAS i looked at for a 15 was over 150L, making 8x come to 42ft3. I doubt anyone has that kinda airspace in their trunk, meaning some kinda air spring is still going to be in effect.


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## mikey7182 (Jan 16, 2008)

If you model 2x Vas vs 4-6x Vas, the difference is virtually negligible all the down to 20hz. Plus most trunks aren't "sealed" as there are pressure vents, leaks, etc. As long as you're at or exceeding Vas, I would think the effect is minimal.


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## AtlasMick (May 24, 2014)

mikey7182 said:


> If you model 2x Vas vs 4-6x Vas, the difference is virtually negligible all the down to 20hz. Plus most trunks aren't "sealed" as there are pressure vents, leaks, etc. As long as you're at or exceeding Vas, I would think the effect is minimal.


What are you modeling that on?


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## mikey7182 (Jan 16, 2008)

AtlasMick said:


> What are you modeling that on?


It's been awhile since I've done it. I usually use WinISD. I read some comments a week or two ago as well (I can't remember if it was here or AVSForums) that discussed modeling 2x vs 4x Vas for a particular driver and the difference was something like [email protected] I think the reason guys model high multiples of Vas is to get a good look at how true IB models. IB in a car is not true IB, but a 15cf leaky trunk isn't going to add a whole lot of spring either.


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## BuickGN (May 29, 2009)

cajunner said:


> my theory on this phenomenon, is that air pressure coupling from the vent, being added to the woofer in a vented configuration, allows the sound wave to do double the work, or 3 db of gain, based on the simple principle of congruent wave formation.
> 
> Where the woofer and the vent combine at resonance, I'm not sure whether you can say the driver is contributing since it's visibly motionless, while the vent pumps mad air.
> 
> ...


i don't know if I understand your post entirely but in IB and sealed, there is nothing else that determines output other than cone area vs excursion. Power doesn't matter, Qtc, Fs, none of that matters for output, just excursion. 

Sealed reduces cone control (damping) which causes overshoot which can raise efficiency. So with a higher Qtc you can have more excursion at a given power level which means higher efficiency. This is usually in the upper bass frequencies where power requirements aren't as great. Plus, I don't want to attain my efficiency by cone overshoot which might be considered distortion. 

IB increases efficiency where it counts, in the sub bass range by eliminating the air spring restriction. The backwave is a near nonexistent contributor to efficiency. The air spring on the other hand kills efficiency. On the inward stroke the cone has to compress the air. On the outward stroke rarification, vacuum, or whatever you call it restricts cone movement and it gets worse with more excursion.


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## BuickGN (May 29, 2009)

AtlasMick said:


> Are there two schools of thought on IB? One being have a stiff suspension and powerful motor and the other being light suspension and moving mass to increase efficiency?
> 
> Which case or combination of things would help to control the changing of frequency found in music (transient response?) A stiff suspension that would dampen the moving mass at the expense of efficiency shouldn't matter if the efficiency is already higher due less fighting of the air spring, right?
> 
> Also, when you see people putting 15's or 18's IB in their car wouldn't 8-10x VAS be like 100cu ft0?. One of the VAS i looked at for a 15 was over 150L, making 8x come to 42ft3. I doubt anyone has that kinda airspace in their trunk, meaning some kinda air spring is still going to be in effect.



Cone control is better IB than sealed so you're already ahead of the sealed game. The suspension is a very small contributor to damping. The motor is responsible for the vast majority of damping. The "IB specific" IB15s have an extremely soft suspension and they obviously work very well without the airspring. My Max 15s are the opposite and they also work very well IB. It really doesn't matter that much as long as th Qtc works out. 

My Max15s have 3x higher moving mass, a much stiffer suspension, but more motor strength. Qts is .5 vs .46 for the AE. The AE is better damped with a soft suspension , weaker motor, and lighter cone. However, the Max15 is less affected by box size or trunk size so it may end up with a lower Qtc which is what ultimately matters. The Max 15 would most certainly be better for smaller trunks or multiples because Q will be less affected. 

The Max has better punch and a tighter and quicker sounding bass which goes against what many believe. They sound better to me which is awesome but they require about double the power for the same output which sucks. 

I wouldn't worry about achieving 8x Vas or 10x Vas or 100x Vas. You have to ask yourself why you want to achieve that in the first place. After 1x Vas, the changes are small. You've got 90% of "true" IB right there and you retained your trunk space. 

And once again I have to say that people stress about Q and Fs and cone area so much when it comes to IB when it can be argued that these parameters are less important when going IB than sealed.


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## sqshoestring (Jun 19, 2007)

Far as I know the difference in a 'vented sub' is that they are made to handle a lot of power and have less xmax (or a normal xmax), because the vent reduces xmax. If you use it IB you don't need big power handling, you may need big xmax depending on how you run it. More power handling could be less efficient, though it should work.

I like IB for a few reasons, mostly because in a trunk(ed) vehicle I can have my cake and eat it too. I can have big low bass and a nearly empty trunk and no big heavy box. What is not to like. I can even get nice results with these cheap pyle subs, since I don't need to bow the roof that much for my needs.

Another issue is what kind of bass you want? For high bass a sealed can be ideal as they are small and easy to do, they control xmax. A ported can also be tuned high for huge output. However if you want low bass that is a different story now your sealed and ported boxes just got huge or your sub got really inefficient, but it can work that way. With IB it does not matter as much, if you want more output or to get lower then larger and/or better subs will do that.

I would also look closely at the FR you are getting out of a box, back to that tuning high thing. You tune sealed or ported high and the peak is huge, you get a lot of output. But at 30hz that box will suck. I never ran numbers but I feel that advantage is diminished the lower you tune. Not saying a huge ported can't kick it out, but then it gets to where the IB install with twice the cone area is actually a much smaller install.

Last issue is tuning with IB, you can tune it to where you hardly need any EQ at all. While we have piles of EQ power these days it still makes the system easier to tune and less likely to peak out/distort with too much EQ.

My pair of pyle 15s are at 1.5X Vas and I lose 1db at 20hz because of it. I can handle that kind of loss lol. That is with Fs 20 and Qts 0.7. I could use one good sub with huge xmax, but it would cost me a lot more. Cheap speakers can work great, long as you use them within their capabilities. These will get tighter sounding if I push them really hard with the 500rms on them (where they are hitting xmax), so if you want more you need better subs. Below that they will pull down to 25hz and xmax is pretty low at my usual listening levels. I have the subsonic filter turned off. The ironic part is these are '1000w' subs lol, but that should be 500rms and typical to half your rms for IB so then 250rms each....is what I have on them and it actually seems to match up right.

In the end your cone area times xmax will determine output of your IB install, period. Its tuning will affect the sound/tone when run with no EQ. The lower you want it to play the more cone area/xmax you will need. It should be loud as a sealed long as you run a SS and/or EQ to keep it out of xmax. A higher tuned box may peak at higher output, but only in that peak range.


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## captainscarlett (Mar 15, 2011)

Can I flip this around and ask what are the characteristics of an IB sub in an enclosure? 

For example: been looking into Legatia L8's and everyone suggests IB. What would happen if I shoved them into some sort of over-sized enclosure, sealed or ported?


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