Hey all,

I've read IHC's IB thread and saw his install with 2 15" mounted on the back seat. I'd like to do something different by mounting the single 10" under the rear deck, firing into the cabin.

Right now I have an IDMAXD4 10" in a fiberglass sealed enclosure tucked in the driver side corner of the trunk. I've been dancing around the decision to try Infinite Baffle with my IDMAX. My sealed IDMAX sounds nice in it's enclosure, but I'm just curious about IB esp. since my IDMAX has IB capabilities.

Would you recommend this mounting position? Why/why not? I'm aware that I have to completely seal the mounting area.. How would YOU do it?

Basically i want to show the back of the woofer. Like the pics below, obviously, with 1 sub mounted in the middle.





Thanks

 

The ID Max has proven very good in IB. A 10" will have a higher Fs and you'll probably get a little bump in the 50hz area (no worse than in a box however). A little EQ can flatten that out.

You'll have the same output but it will require less than half the power so be careful the first time you fire it up, start with the gains barely on.

For the rear deck, you're going to need to reinforce it with MDF or something. It rattles with the stock sub, a Max is going to kill it. If there wasn't so much metal to cut I would have put my 15s there and taken up even less space.

Remember, a larger sub will have a flatter response while retaining all of the good qualities of a small sub. With the excursion of the Max I'm sure you will still have good output.. IB makes it so easy to max the sub out with so little power that adding a second one is not a bad idea if possible.

I started a thread in here with a link that explains IB very well. No replies but it's still near the top in this forum.

 

You'll likely lose some volume. Gonna have to reinforce the hell outta that rear deck. I would think of a way to keep it from flexing rather than vibrating.

 

I've actually been curious about this too...
How about building the baffle so that it bolts to the under side of the rear deck with door weather stripping put around it to buffer the direct vibrations from the sub. Then, technically, the rear deck shouldn't be experiencing any more stress/shaking than from the sound waves traveling thru it like a traditional box bouncing off the trunk?

Too easy?

 

Just weatherstriping won't allow that deck to not flex. Even if you bolt a baffle to the rear deck, it would likely act as one unit and move as one. I'm sure it'd help if you built it double-baffled though. Also remember that for cone area is king in sound. Unless you're crossing the sub extremely low, a larger sub will be able to play easier and with less distortion than a smaller speaker. Nowhere is this more evident than in IB. Personally, the bracing, aesthetics, and look would be better like IHC setup. It takes up the same space basically. But you aren't mounted to a flemsy piece of metal

 

Volume should be the same, just much less power required to reach max volume. It will just be much more efficient on the low end so a high pass will have to be used to stop over excursion.
Agreed.

I look at vibration and flexing as lost SPL and added distortion. If something is vibrating, that's energy that is lost. Less vibration equals more SPL and better SQ. I've had thoughts of adding more bracing or another sheet of 3/4" MDF for a total of 2-1/4" for the baffle. Mine has very, very little vibration in the baffle but I'm looking to get zero.

I've got to take pictures of my current setup, the ones I posted are a little embarassing. I installed a lightweight frame work with the stock skipass door and factory looking carpet right behind the subs, touching the magnets. When you pop the trunk it looks like you're looking at the back of the rear seats and skipass. Only a TL owner would be able to tell something is different. I could park my car with the trunk open at the mall and not worry about anyone stealing anything. With the frame work installed I lost a total of 7" of trunk space. If I remove it I can slide large object and even grocery bags under the subs so even less space is lost.

And going a little off topic, I removed the trunk vents and put a screen in their place to lower the Q of the system a little. It definitely works. I love the well damped lower Q sound. It's just so accurate and blends so well with the front stage. Something to consider for anyone going IB, you can still "tweak" the sound a little with the factory vents.

 

I thought it's been proven that ported (and sealed I thought) would be louder at a given volume..

 

Ported and sealed are louder in most cases

 

I stand corrected...I have a lot of theoretical ideas that don't necessarily pan out.

 

Ported will be louder at the same power.

Sealed will require 2x as much power at a minimum to hit the same SPL down low as IB. Sub displacement is all that matters here so with the same excursion and diameter, sealed and IB will have the same potential SPL but IB will do it with much less power. In the 20hz range I've seen IB setups require 10x less power than sealed. As you go up in frequency it evens out. All a sealed box does is limit your low end. IB lets it play more efficiently without cutting off the low end.

Some very good reading by a guy who designs subs:

http://www.mfk-projects.com/subwoofer.htm

"

Why is my sub-woofer bottoming out...and how do I stop it?

I don't know how many times I've heard it...but it doesn't matter how many times...it's still wrong.
Putting a subwoofer in a smaller box does not increase power handling, it simply reduces efficiency and thus requires a larger amplifier. When designing a subwoofer especially one using equalization like a Bi-Quad (Linkwitz Transform) one of the primary considerations is the amplifier power required to drive the cone to it's maximum linear excursion. A bigger number here is a bad thing...not a good thing. The smaller the box, the bigger this number will be so you may want to look at the curve generated by your Linkwitz Transform software and think it is telling you that you have very high power handling but that's not what it's telling you. It's telling you that you have a very high power requirement...not power handling. It's probably telling you that the thermal limitation of the voice coil will be reached long before the excursion limitation. Contrary to popular belief, that's not a good thing. When I 'm designing a subwoofer I'm hoping that curve will tell me that 10 watts will drive the woofer to it's maximum excursion. Of course this is a very unrealistic expectation but it would be a very good thing if it were possible.
"I have +/- 25 mm linear excursion and I get it at 20 Hz with 10 watts"! Not... "I've got +/- 25 mm linear excursion and it would take 25,000 watts to exceed it at 20 Hz so I've got great power handling...I never have to worry about bottoming"! That second statement is just the wrong way to look at it folks! The less power required to bottom the woofer the better!
What your subwoofer can produce at any given low frequency is determined by one thing and one thing only. It is determined by how much air volume the woofer can displace. So, if my unrealistic subwoofer idea above were possible, it would get the most out of the woofer with just a 10 watt amplifier. If on the other hand someone has told you that you can increase your subwoofers power handling by putting it in a smaller box you will likely end up with a subwoofer that can no longer reach its full potential. With the smaller box, you have introduced a second limitation on what your woofer can produce, that is, the thermal limit of the voice coil.
A stiffer restoring force from the smaller box does not, "increase cone control". This is determined by the damping of the system. Qtc is Qtc...and this is what describes the control of the cone motion. Actually, decreasing the box size will increase Qtc and thus increase the chance of ringing...it will reduce cone motion control.
So, smaller box...more power required, possibly beyond the thermal limit...not more power handling. Also, smaller box...less control of cone not more control.
So if all the above is true how do we stop a woofer from bottoming? Well, we stop driving it in such a way as to bottom it! The question is, what is the woofer capable of based on its excursion limits. Once we know this, we can determine what HP filtering can resolve the problem. It could be that this woofer just can not produce 20 Hz at 115 db like you might want it to. That might require several times the excursion limit of the driver depending on what driver you are using. So, if you don't want it to bottom you just can't try to make it do something it can't do. Putting it in a smaller box isn't going to somehow magically enable it to do the 20 Hz at 115 db. The only viable solution is to use a HP filter. Just as with all speaker building this will be based on a balance of trade offs. If you want 20 Hz you will need to settle for less than the 115 db you hoped for or optionally you can keep your 115 db and settle for something higher than 20 Hz. You can't have both unless you get more or bigger woofers. No smaller box will change this. So, the solution is to use a HP filter to limit your woofer to a frequency range it can handle at the output level you desire. That's how you prevent bottoming, you don't put it in a smaller box and thus in a position such that it can never reach it's full potential.
Keep this one thought in mind, Infinite Baffle is better than sealed box. Infinite baffle has always been better than sealed box and it will always be better than sealed box. What is a smaller box doing? Moving farther away from infinite baffle! So, acoustically, a bigger sealed box is always better than a smaller one. The limitation should be based more on space limitations because making it smaller will never be a move toward optimization. Depending on the Q of the driver a very large box might move Qtc below the desired level but this can be corrected using the Linkwitz Transform. So the, "too big" box is still better assuming you correct the Q with a bi-quad. Of course a point of diminishing return can be reached with the box volume as the restoring force of the box becomes very small relative to that of the driver. At some point the large sealed box is essentially infinite baffle so making it bigger beyond this is not necessary."

 

Me too. I think I have 3 times the amount of failures as I do successes.

 

Yup, i read that which got me to post a thread. Very good and informative reading material.

Here is another option to toss into the mix.





This may sound stupid, but I was thinking of a double baffle and weather stripping along the perimeter of the baffle, with a thick foam pad (Maybe Carpet pad) or something. I have a lot of Ensolite and Rammat laying around.

Question for IHC and others: Did you have to seal the underside of the rear deck for your install, or are you only using the trunk lining?

PPI 356CS (Active) - Might upgrade back to DLS Iridium if I can find any (2 or 3-way)
IDMax 10" D4
JL Audio HD900/5
JBL MS8

 

Look at what you said, though.

"down low". You're talking about 1 maybe 2 octaves. the output potential isn't any lower with drivers mounted IB compared to sealed. BUT...the difference is in the response curve.

We have to consider what frequency region is being discussed. IB is wonderful, not the answer for every setup, though.

 

IB doesn't require gobs of additional power to maintain a flat response down low.

The sealed box doesn't affect response much in the upper bass range so efficiency is pretty good but it kills it down low. The sealed box kills efficiency the lower you go. You have to feed the sealed sub anywhere from 2x to 10x the power to have a flat response to the lowest regions. I never realized what I was missing by missing the lowest region when sealed and even ported but when you go IB you realize how much that region contributes to impact and overall SQ.

My thought process is if you have two identical subs and in one setup you can have a flat response and hit full SPL at 150w and the other takes 1,500w to hit the same level down low, which one do you want? Mine is almost dead flat with no EQ between 18hz and 150hz and I'll hit the mechanical limits way before I ever worry about thermal. Those numbers sound way off but look at what a pair of IB15s do with 200w at 20hz and look at what your typical pair of sealed 12s require to hit the same level. You're literally talking nearly 10x more power to hit that level.

I just don't see the point to having a sealed sub *when you have the means to go IB*. It only kills efficiency.

 

when shaking my mirror turns to math it loses it's fun...

Glad to have you back IHC...

 

Thanks. I'm done with the rest of this board but the audio section is still fun since I don't understand it that well.

Agreed on the math. I try not to learn too much lol but this is pretty basic. Excursion*diameter= potential output in IB and sealed. Displacement and nothing else. Assuming two subs are able to hit full excursion before reaching their thermal limits, it's easy to see which one would be louder.

 

I wish you were local, I'd love to hear yours.