infinite baffle build

[Spookz1369]

I'm new to this forum but have been a long time follower and sub to Meade916. I want to do an Infinite baffle build from the current system I have but am unsure if I want to add a 3rd 12 inch sub. The build is as follows in a 2012 Hyundai Elantra: 2 B2 Audio Rampage 12D1's on 2 Crescendo Audio Bassclef 4k amps strapped with audio batteries back there as well. I know I want the motors facing the rear with the cones aiming towards the front. Should I add a 3rd or just build it with the setup I currently have now?

[audiofanaticz]

I wouldn't say those are the best woofers for IB, the FS and QTS is a tad too high to be even considered for that use imo.

[Spookz1369]

11 hours ago, audiofanaticz said:

I wouldn't say those are the best woofers for IB, the FS and QTS is a tad too high to be even considered for that use imo.

So buiding a better box for these is the course I should go instead of the IB?

[audiofanaticz]

IMO a good box is the correct path, but again this depends on your wants, needs, and what you're currently unhappy about with your setup. 
Generally you want a sub with a low FS for IB around 15-27'ish hertz.
Usually a QTS of around 0.5, but some people say around 0.7 but you wouldn't want to go much higher than that.
Another thing to look at is the VAS which is usually in the form of Liters so you'll have to convert it to cubic feet. This will tell you how large you want the rear "chamber" of the IB to be. I want to say its VAS x the number of subs x 20 = the ideal rear chamber. so 9.7L = 0.342cf so it would be 0.342 x 2 x20 = 13.68cf.
Your vehicle seems to have a little over 14cf of space so that's no problem, the QTS seems to be fairly ideal at .5, that 34hz FS just seems a little high (at least for my likings), granted you're not me so you may like it depending on what you're trying to change with your setup now. So I wouldn't let my opinion stop you from trying it, and trying a IB is going to be cheaper than buying/building a new enclosure.
The Rampage 18s have a decently lower FS in the 28hz range but that's going to be due to the added weight of the larger cone/surround.
One thing people have done a bunch to lower FS is evenly add weight by covering the rear of the cone with CA glue or Epoxy, this will add strength as well. Typically this is easier done when the woofer is being built and not after it's already built but it can still be done just would be wise to cover the spiders to prevent any excessive glue landing on them while doing it. The reason I say this is because maybe you do like how the IB is but want more low end out of it you could either A) cover the back of the cones in glue or B ) have B2 build you some custom recones with added mass to lower the FS.

[Spookz1369]

On 8/16/2022 at 10:33 PM, audiofanaticz said:

IMO a good box is the correct path, but again this depends on your wants, needs, and what you're currently unhappy about with your setup. 
Generally you want a sub with a low FS for IB around 15-27'ish hertz.
Usually a QTS of around 0.5, but some people say around 0.7 but you wouldn't want to go much higher than that.
Another thing to look at is the VAS which is usually in the form of Liters so you'll have to convert it to cubic feet. This will tell you how large you want the rear "chamber" of the IB to be. I want to say its VAS x the number of subs x 20 = the ideal rear chamber. so 9.7L = 0.342cf so it would be 0.342 x 2 x20 = 13.68cf.
Your vehicle seems to have a little over 14cf of space so that's no problem, the QTS seems to be fairly ideal at .5, that 34hz FS just seems a little high (at least for my likings), granted you're not me so you may like it depending on what you're trying to change with your setup now. So I wouldn't let my opinion stop you from trying it, and trying a IB is going to be cheaper than buying/building a new enclosure.
The Rampage 18s have a decently lower FS in the 28hz range but that's going to be due to the added weight of the larger cone/surround.
One thing people have done a bunch to lower FS is evenly add weight by covering the rear of the cone with CA glue or Epoxy, this will add strength as well. Typically this is easier done when the woofer is being built and not after it's already built but it can still be done just would be wise to cover the spiders to prevent any excessive glue landing on them while doing it. The reason I say this is because maybe you do like how the IB is but want more low end out of it you could either A) cover the back of the cones in glue or B ) have B2 build you some custom recones with added mass to lower the FS.

Great knowledge and info. You've definitely given me alot of food for thought and consideration.

[JerryWilliamson]

On 8/14/2022 at 8:42 PM, Spookz1369 said:

I'm new to this forum but have been a long time follower and sub to Meade916. I want to do an Infinite baffle build from the current system I have but am unsure if I want to add a 3rd 12 inch sub. The build is as follows in a 2012 Hyundai Elantra: 2 B2 Audio Rampage 12D1's on 2 Crescendo Audio Bassclef 4k amps strapped with audio batteries back there as well. I know I want the motors facing the rear with the cones aiming towards the front. Should I add a 3rd or just build it with the setup I currently have now?

 The 2012 Elantra probably can hold the third sub but with everything else going on in the back it would be a tight fit. The D1 subs are effectively an open air (infinite baffle) design. Anything 8 inches or larger will have plenty of open space on the basket design so that it will not matter which direction you point the cones in terms of SPL and sound quality. The only thing a third 12" subwoofer will give you an extra 5-10 db SPL and that is *if* you plan on adding a third amplifier to go with it.

I assume you have each sub (dual 1 ohm voicecoil) wired in series (2 ohms) currently? The Crescendo 4K's are stable down to 0.5 ohms so, regardless of what your current wiring configuration is, the third amp would simply go to the third sub. Otherwise you are running three subs off two amps which makes things much more complicated. You could split the loads up and present 3 ohms to each amp but that reduces your power and defeats the purpose of adding the third sub in the first place. Also, adding the third sub will have very little impact on sound quality at normal listening levels.

Without additional information, given what you have I would recommend staying just with the two subs unless you were planning on adding that third amplifier. Good luck!