95Honda

The RMS rating of the subwoofer has absolutely nothing to do with output capability or power requirement. At all... Using the RMS rating to compare drivers is as important as the color of the basket...

I would concentrate more on bracing than 1.5" thick cabinet walls, as the bracing will help much more than wall thickness... What does the response look like modeled at 20Hz vs what you are planning? If you don't loose a lot up higher I would just go with 20Hz tune... Nothing wrong with 26Hz, just curious if the response is any different... If you get the large cone spikes, they will be fine. Port and sub forward will work great. Put the port opening on the bottom.

I am starting a IB build for my H/T in our new house. We finally bought a house that we (wife and I) really like and are trying to keep it very nice inside. I am going to design a complete 5.1 system for the living room with everything being stealth. In walls, no visible components, flat screen flushed into wall, etc... I want to have decent bass and really thought long and hard about this for the last 2 months. IB was the logical choice, but we are going to finish our 1200 ft2 basement next year, so having a big-ass manifold hanging from the floor joists down there would also be a no-no. After carefully laying out a baffle arangment that will tuck my pair of XXX18s into the rafters high enough that they won't protrude below the drywall ceiling when everything is said and done was a a serious undertaking. I think it will turn out perfect. I will add an additional faux HVAC vent into the floor upstairs that the XXXs will fire into. I will probably top it off with a 2-3Kw pro audio amp that will also be mounted downstairs so you won't hear the fan. I will be a while before I get started, but I will post up some pictures as I go....

The room behaves the same. So if you have a huge null in an area you are listening in, IB won't make a difference, especially if it loads from the same area...

And as M5 said NO RATIOS to start with....

The T/S parameters are suitable for a 4th order bandpass. But, as a others have stated, there are a lot of trade-offs if you go this route. Honestly, modeling both choices first (4th order vented and 4th order bandpass) with the power you will have will be the only way to tell you which would be louder. BUT, pay close attention to the passband of the bandpass and see if it is worth it...

Match the tweeter impedance to the specified crossover. I.e., use the 4 ohm tweeters with the 4 ohm crossovers... The impedance presented to the amplifier is primarily influenced by the driver. If you have the 4 ohm drivers and the 4 ohm crossover, the amplifier will be presented with a nominal 4 ohm load. If you use the tweeters with the wrong crossover, the cutoff frequency will be off by one octave... They will sound horrible or you blow them... Those tweeters don't sound very good...

Many are different... A lot are metric...

You are already modeling, so just adjust parameters to keep VV low at your chosen tuning and power level. Also see that bump/ripple in the response of the recommended alignment @ 50Hz? That is what I call the "Best Buy" bump, meaning when you walk into Best Buy and they have a bunch of subs going with some crap music on the radio you notice the one with this crappy response when it sticks out... But after having it in your car for a while it gets annoying because it has stupid emphasis around 50Hz which wears on you... Moral of the story, tune flatter and you will be happier in the long run...

Kind of... It is simple ohms law, when you bridge, you double the output voltage. When you double output voltage you increase the power 4x into the same impedance (E^2/R). If an amplifier is only capable of X watts total, then you cannot get more than that under any condition. Knowing this, when you bridge an amplifier, the overall load must not be any lower than what will draw maximum power at 2X the voltage of the un-bridged mode, i.e. you must have 2x the impedance. So it really isn't really that the each side is 1/2 the load, but that the output voltage has been doubled and when you do that you must also double the load impedance in order to not ask too much from the amp... Additionally, there is no benefit to bridging unless it is to overcome a voicecoil configuration issue. Output impedance of the amplifier is doubled, dampening factor is cut drastically. In other words, the amp performance suffers...

Why only 99%, pretty sure it is way higher than that. I was in a "giving" mood....

The point of test equipment is that it isn't easy to use because it has a vast array of capabilities and limitations...

The RMS rating of the subwoofer has absolutely nothing to do with output capablity, efficiency or power requirments, AT ALL. PERIOD. EVER. SERIOUSLY.

Meh, I think the difference is that 99% of the car audio audio community has no clue on how to properly use individual pieces of test equipment...

No, modeling will cost you nothing and objectively let you know the difference in output.

Ugghhh... #1, there is no such thing as "box rise". There is impedance, it both rises and falls, both above and below the actual driver impedance. #2, not a single person can actually tell you how much power they are actually applying to their drivers unless them have swept impedance curve and measured the output voltage of the amp over your entire operating range. Period. #3, you have no idea how much power it will take to attain full output of your driver(s) unless you model them in the EXACT enclosure they are ACTUALLY in...

Lol, thought you were trying to do this a car. For home, get a 6-7' piece of 10" sonotube and mount the driver in one end and loosely fill the whole thing with polyfill or fiberglass (loose kind) and leave the last foot or so barely stuffed. Mount it vertical and the stuffing will stay in place better. Use something to keep it (stuffing) off the motor structure. Mess with the stuffing density to get it to sound right...

Most of the Transmission Lines you see in car audio actually aren't... they are normally just 4th order alignments with lots of vent area or a bandpass/horn. Transmission Lines don't have ports that resonate and don't have enclosure volume. What they do have is a dampened line. The reason why you don't see many is that they are just too big. They have to be around 6' long if you want to get near 30Hz and the line has roughly the same cross-sectional area as the driver Sd... So a 6' line for a pair of 12s ends up being at least as big as an 8-10ft3 "normal" enclosure... And here is the kicker, a Transmission Line's output capability lies in between a standard sealed enclosure and a standard 4th order vented enclosure... There are some benefits, but they normally don't out-weigh the size and design/testing requirements... If I had a single 8" or 10" woofer and unlimited space, I might consider a Transmission Line... Might...

If I were to go IB and had to buy new drivers, FI IB3 would be my first choice, 2nd choice the Parts Express Dayton 15" IB subwoofer...

IB suitability doesn't really have anything to do with the XBL^2 technology, but the other parameters of the driver. In fact, the (first/second generation) 18" XXX is really the only one that shines in IB due to it's high overall Qts... The 10", 12", and 15" versions won't work quite so well as they all have lower Qts... The higher Qts is needed as the driver won't self dampen and require equalization to remain somewhat flat...

CCA is garbage and purely a marketing gimmick geared towards car audio. There is absolutely no reason, ever, to use CCA unless you like cable that just looks bigger for the same price or cheaper. I didn't read back, but did you model to build the sub enclosure you are using now?

I guess if it is loud enough is relative. I was doing 142db, at the headrest, on the Term Lab, with 180 watts total and 8s in a Full Size Bronco... I would want to get an honest reading, but that is extremely low for any single sub in a bandpass with cabin gain. But, like M5 said, SPL meter is extremely suspect... I have had a few of those Rat Shack meters, but the last time I used one was maybe 1993...

They should read the exact same voltage if they are wired in parallel, assuming you have sufficient gauge wire to not let much voltage drop. Something is wrong.

They do, it would not make any sense to do otherwise. Drivers are designed to meet overall goals with suspension components at a target value. That value is based on "broken in" components that will behave a certain way over the majority of their lifespan.

T/S parameters are given for "broken in" drivers. If they aren't, they are not an accurate representation of the driver.