Xcons: Infinite Baffle

[ATF 4]

I'm going to try and keep this as short, simple, and straight forward as possible. My trunk's cubic feet is 15.18 ... 2 18" Xcons Vas is 429, resulting in 15.14^3. Good match eh? I hate the idea of having just one subwoofer. I don't know why, but i just do. I want to see what everyone thinks about using Xcons in an IB setup? I read that it decreases power handling, doesn't sound as loud as an enclosure would, but saves space and weight. And hopefully allow me to utilize the amount of cubic feet i have and be able to use 2 18's! I'm just coming up with some ideas, so i don't know if this is just completely dumb or what But i want to keep a lot of options open. So please give me some suggestions on if this would be a considerable thing to do. Also i hope to come up with a design of possibly firing the subs into the rear deck, Maybe the seat if i get new seats. lol Thanks.

[helotaxi 46]

It might work OK. They are not really well suited and power handling would be severely compromised.

[ATF 4]

How much power do you think I could throw at the pair if I did do this? Maybe an AQ2200 at 1ohm. I've read different things about IB such as having drivers with a QTS of at least .5 but also read that it should be fine with a daily sub with lower QTS and more subs, bigger sizes.

[Sir-Lancelot 216]

What is it you are trying to accomplish besides having 2 subs?

[ATF 4]

A little less weight from a huge box with only 1 sub. And maybe a little more of a challenge on install. Just something new besides a sealed box. I just want to see what anyone thinks about the xcon being used in an IB setup. And I wouldnt have to throw 3000rms+ on a pair of subs.

[helotaxi 46]

Not that you wouldn't have to, more like you wouldn't be able to. If you want an idea about how much power they can take model them in WinISD in a 15cf box and see what it says. I'd be surprised if they would like 2kw.

[Impious 1,476]

I've read different things about IB such as having drivers with a QTS of at least .5 but also read that it should be fine with a daily sub with lower QTS and more subs, bigger sizes.

You have to consider the environment as well. If we were talking about home audio, then yes a Qts of >.5 (ideally closer to .7) and a super-low Fs (<20hz) are pretty much mandatory.

In a car, however, things are different. We get significant boost in the lower frequencies from the transfer function of the vehicle, and most times the trunk doesn't act as a "true" IB alignment. So we don't need the drivers themselves to generate flat response down to 20hz....the car helps us do that

Generally there are two routes that work well for IB in a car.....low Q (< .4) and low Fs (~20hz), or mid Q (~ .5) and mid Fs ( high 20's - low 30's). If you go with a low Q/high Fs driver, then the low frequency response is rolled off too much. High Q/Low Fs (like home audio IB subwoofers) can work with appropriate EQ to tame the bottom end....with out it, they'll be too bloated on the low end.

However, you have to consider how the airspace is going to affect the driver. Chances are you're going to get some increase in Q as a result of the trunk. According to Unibox, in a 15cuft enclosure with two 18" Xcons the Qtc would be .63 with an F3 of 43hz......models pretty well for mating with the transfer function of an automobile.

Maximum output is the same as that of a sealed enclosure because peak output is limited by the same factor; peak linear displacement. So the output potential isn't any lower with drivers mounted IB compared to sealed. The difference is in the response curve. Sealed enclosures will usually have a little more output in the upper-subbass (above 40hz) due to the peak generated by the affect of the enclosure.....however, IB drivers will typically have more output in the lower frequencies (40hz and below) due to the lack of enclosure (a sealed enclosure is essentially a highpass filter, so if you remove that you improve low frequency response). So to say drivers mounted IB have "less output" is typically incorrect as you have to consider what frequency region is being discussed And maximum output potential is equivalent between both alignments.

As for power.....don't apply more than is required Mechanical power handling is reduced for a driver mounted IB since it doesn't have the "spring" of the enclosure to aid it mechanically. Unibox says you wouldn't hit Xmax in a 15cuft enclosure with 3500w until 12hz......but I would focus on what personal experience tells you there.

Long story short....go for it Just be careful, IB drivers are easier to overdrive.

[ATF 4]

Thanks for your opinion ! But so i've been reading more and more on IB and i read that the vas of the trunk should be at least 3x greater than that of the subwoofers? I've read a few different things about that, but does anyone still think i could try the 2 18's ? I mean.... i really want to try this but i don't want to put my new subs in a lot of danger of being damaged rather than using a sealed box. I need some FAITH !

[bimmerboy 3]

what about 2 15s?

[ATF 4]

That's what i was initially planning on. But then i seen mark posted on my thread about the sale of Will's 18's for $279 each and i got eager and just bought one. lol If the 18's aren't possible then i could always sell this one and get some brand new 15's.

[jrod1050 5]

Some IB subs would be better suited for this application. I dont think putting this xcon in a IB setup is going to maximize its potential. Believe me 1 18" xcon in a ported box will have huge output and sound great doing it.

[ATF 4]

I think I might just try all options. 1 18 sealed, then ported. Then 2 possibly IB'd. I need to do a little more planning and designing for my car.

[lithium 358]

a fellow member put 2 18" fi ib3's in his car, there is a build log in the forum.

[Notorious97200 339]

OP : try it, just do it !!!

I think you can trust Impious, he seems to know what he's talking about.

You can try a box with wood lighter than 3/4 "mdf , but brace the box as much as you can.

Good luck in your choice

[kryptonitewhite 1]

I've read different things about IB such as having drivers with a QTS of at least .5 but also read that it should be fine with a daily sub with lower QTS and more subs, bigger sizes.

You have to consider the environment as well. If we were talking about home audio, then yes a Qts of >.5 (ideally closer to .7) and a super-low Fs (<20hz) are pretty much mandatory.

In a car, however, things are different. We get significant boost in the lower frequencies from the transfer function of the vehicle, and most times the trunk doesn't act as a "true" IB alignment. So we don't need the drivers themselves to generate flat response down to 20hz....the car helps us do that

Generally there are two routes that work well for IB in a car.....low Q (< .4) and low Fs (~20hz), or mid Q (~ .5) and mid Fs ( high 20's - low 30's). If you go with a low Q/high Fs driver, then the low frequency response is rolled off too much. High Q/Low Fs (like home audio IB subwoofers) can work with appropriate EQ to tame the bottom end....with out it, they'll be too bloated on the low end.

However, you have to consider how the airspace is going to affect the driver. Chances are you're going to get some increase in Q as a result of the trunk. According to Unibox, in a 15cuft enclosure with two 18" Xcons the Qtc would be .63 with an F3 of 43hz......models pretty well for mating with the transfer function of an automobile.

Maximum output is the same as that of a sealed enclosure because peak output is limited by the same factor; peak linear displacement. So the output potential isn't any lower with drivers mounted IB compared to sealed. The difference is in the response curve. Sealed enclosures will usually have a little more output in the upper-subbass (above 40hz) due to the peak generated by the affect of the enclosure.....however, IB drivers will typically have more output in the lower frequencies (40hz and below) due to the lack of enclosure (a sealed enclosure is essentially a highpass filter, so if you remove that you improve low frequency response). So to say drivers mounted IB have "less output" is typically incorrect as you have to consider what frequency region is being discussed And maximum output potential is equivalent between both alignments.

As for power.....don't apply more than is required Mechanical power handling is reduced for a driver mounted IB since it doesn't have the "spring" of the enclosure to aid it mechanically. Unibox says you wouldn't hit Xmax in a 15cuft enclosure with 3500w until 12hz......but I would focus on what personal experience tells you there.

Long story short....go for it Just be careful, IB drivers are easier to overdrive.

spot on! my simple version: you dont lose power handling, you lose power requirement. an IB sub is just as loud as sealed assuming the same FR responce. What changes is FR, a sealed box raises the midbass (depending on size) making it "louder" but simply EQin for the same FR would make it the same SPL but requiring less power to do so.

[Aaron Clinton 2,372]

I think I might just try all options. 1 18 sealed, then ported. Then 2 possibly IB'd. I need to do a little more planning and designing for my car.

Try it in the optimal sealed box and see how you like it.

[Impious 1,476]

Thanks for your opinion ! But so i've been reading more and more on IB and i read that the vas of the trunk should be at least 3x greater than that of the subwoofers? I've read a few different things about that, but does anyone still think i could try the 2 18's ? I mean.... i really want to try this but i don't want to put my new subs in a lot of danger of being damaged rather than using a sealed box. I need some FAITH !

Did you even read my post? I specifically answered your question. Are you trying for a true infinite baffle setup? I don't think you are, and 3x VAS wouldn't cut it if true infinite baffle was your goal. For a true infinite baffle setup, Qts = Qtc and Fs = Fc. You need more than 3x VAS to accomplish this. The 3x VAS rule of thumb is more of a "close enough" approximation to a true infinite baffle alignment.

I think you are trying simply to run "enclosureless", which for the most part is the best we can do in car audio and what we in car audio refer to as "infinite baffle". It's a technicality in definition. Just because you won't be truly "infinite baffle" doesn't mean the enclosureless arrangement won't work. What's the difference between enclosureless in your auto and true infinite baffle? It's easy to model in any enclosure program, and I briefly outlined in my previous post how the drivers will respond to being ran enclosureless in your vehicle.

Any sub can be ran IB. The only fear of "damage" is in the fear of the person operating the controls (you) not knowing when enough is enough....and this can happen in any enclosure, it's just that with IB the mechanical power handlling is lower than a sealed or ported enclosure.

[ATF 4]

Yes impious i read your post. My bad for not reading it more thoroughly. But i understand what your saying, completely. I keep forgetting that it's different between home and car audio. I'm going to try and order another 18 as soon as i can. I'm positive i can pull this setup off. I don't need to completely seal all the leaks in the trunk right? Free air? I just have to make sure to seal the front and rear sound waves completely right..

[Impious 1,476]

No, you don't need to completely seal the trunk itself (and really, you wouldn't want to for other reasons related to the vehicle itself).

Some people get crazy with silicon and expanding foam and everything else to seal off the baffle. I run my subwoofer "IB" firing through the ski-hole and didn't go nearly that far in sealing. I doubt anyone could tell a difference in my car. I wouldn't leave gaping holes of course. But I didn't use any silicon or expanding foam or anything for sealant.

[bawward 0]

Coming in late, and seriously considering running an IB setup in my car, what would an ideal sub be for IB? I guess I'm just looking for a good mix of quality and output, not having to be amazing at either.

Also, as an example, if I had a sub with 1000 RMS ability, I seem to understand that I shouldn't push a full 1000 amplified to it, but rather about 1/2 that or so, reaching my excursion limits before the thermal?

Very basic, and if this is stupid, I apologize, but I am genuinely trying to learn. Thanks!

[Impious 1,476]

Coming in late, and seriously considering running an IB setup in my car, what would an ideal sub be for IB? I guess I'm just looking for a good mix of quality and output, not having to be amazing at either.

Also, as an example, if I had a sub with 1000 RMS ability, I seem to understand that I shouldn't push a full 1000 amplified to it, but rather about 1/2 that or so, reaching my excursion limits before the thermal?

Very basic, and if this is stupid, I apologize, but I am genuinely trying to learn. Thanks!

Read my first post in this thread. It pretty much covers your questions.

Unless you were asking for specific subwoofer suggestions. In which case, you didn't provide enough information for us to assist you.