BKOLFO4

They are definitely a nice sounding set of comps. Paired with an 18" BTL, I would assume you are looking for loud just as much as SQ. . .Should work great for your application. Brian

Have not taken any. It is the old style and looks "normal". I think just a change to the spider setup. . .

Definitely enough volume. I have run mayhem 15's in less than 3 cuft. . . Brian

If you can not afford the SMD, go with a Mayhem. . .

No way to know. . .too many variables. . . All good subs. The SSA's would be my choice from those 3. The AA Arsenal could also be a good choice, but it is a little more expensive. Brian

#12 Sheet Metal screws (not self drilling) from Lowes. Predrill with 1/8" drill bit. Works great. Easy. . .never broke one. . .use the same holes over and over. Brian

Don't do coil to coil. Run from each coil to the box terminals, or better yet directly to the amp.

Are you stuck on RF Amps? There are nice high powered amps out there that will save you $$$.

Out of control I tell ya!!! But hey. . .Who am I to talk??

I think your calculations for volume are off, unless I missed something. 28 x 7.25 x 17.5 = 2.05 cuft gross, and that is before driver displacement, not after. The picture says 2.25, which is not correct, even if those are internal dimensions. If the Q is .16, you have 1.89 cuft after driver displacement. If you have 1.89 cuft before port displacement, you can use (2) 3" ports that are 20.75" long (measured through the center, since you will have an elbow). That makes the port displacement ~.2 cuft and net volume ~1.7 cuft. 1.7 cuft tuned to 32 Hz with (2) 3" ports x 20.75" long. Brian

CRAZY man. . .

Next questions to answer correctly are: How much power? What does "double port" mean? How big are the ports?? Square ports or round ports? 6.5 after displacement you think, or you know? 6.5 NET is great, 6.5 gross is not that great. . . As already stated, installed correctly the 18 will be louder. But, you still have not provided enough info to determine if the 18 will be installed correctly. . . Brian

I broke my BTL's in with 4000+ watts for ~30 minutes. Decent change in the feel of the suspension and the sound of the lower bass notes. I could tell as they started to break in, since the coils started to rock a little too much and I had to raise the subsonic filter setting

Avalanche is no longer available, so it is not on the website. They run great in 2-2.5 cuft sealed. I had (4) of them in 11 cuft sealed in my home theater. With 3400 watts and 5 bands of EQ, I had nice response down to ~18 Hz. Very nice drivers. If I build my IB and don't like it, I will be sad that I sold the 5 avalanches I had.

If you are going to run more ~2500 watts to a single 18", I would shoot for 6-6.5 cuft, not 8. Your mechanical power handling is going to drop in 8 cuft. . .

You've read before on here that you can just pick up Vance Dickason's Loudspeaker Design Cookbook and you will have "all" the good info, but that I guess you already knew. Great book. Read it cover to cover many times. Have it on my desk at work right now. Problem is that it is too technical for most people. They just want to know how it is done, not why it is done that way My guess - that is why all of these "close enough" estimates came to be. . . Brian

As far as I can tell, that calculator uses the formula. I have never had a problem with it. It gives the minimum diameter for a round port, the minimum area, and the side length if your port happens to be a square. As I said above, I design a lot of boxes with much less port area and they work great. . .In a car, it is normally a trade off due to size constraints. Brian

Why 5 ft? Is that what sundown recommends? Seems small for an 18, but I have never looked at that one.

It is an 18, correct? Did I read you are putting it in 5 cuft? I think 80 to 100 sqin is enough for your application. If you can design a box with more, great. If not, don't lose sleep over it. Brian

On the second part of your question. A drop in comparison to me can be fair if the box is within the specs suggested for both drivers. But you are also correct that some people do not consider it fair since they may not be in the same alignment. You also have to look at the frequency they peak at. The true comparison would not be in a car where the cabin gain of the car may factor into the spl readings due to the two different drivers peaking at different frequencies. In one persons car on the same power in the same box, the BL might be louder than the BTL. In a different box or a different car, the opposite maybe true. A lower peak frequency may make one seem louder while really the other is louder on a meter. There are a lot of factors when making comparisons. Another subject I hate. The assumption that the driver with rated power handling closest to the amount of power you have is the beat choice drives me insane!! Brian

I take each box I design on a case by case basis. The estimates work good. I have used less, and I have used more. If you tune at 32 hz and then you play a lot of music at 32 hz, you may hear a little port noise. Depends on the amount of air the driver can sweep and how hard you are driving it. Normally in a car things are getting really loud by the time you really start compressing the port and it is not audible. The ranges suggested perform good vs the amount of volume required for the port. Large ports get really long in small boxes! At the tuning frequency, sound is radiated from the port. If you want the port to operate 100% correctly with no compression or noise, use the formula. Brian

I was the one who did the calculations that it is 29in^2 per port area, just to see its relationship compared to the "general rule of thumb" which we were supposed to go by. I feel as though companies like Fi shouldnt put that on there website (even if it is a starting point) then others get bashed for something they thought was right from start including me (that is misleading the consumer). Instead for each driver put how much port area is required and stop steering the consumer in the wrong place. Id rather they give the formula so I can do the math then be bashed for information I thought was to be followed since the MANUFACTURER said to follow it. It is to many he say or she say rules in car audio and healthy debates like these help weave out all the bs. I appreciate Duran for passing the formula on and will be using from here on it then the in^2/cube rule we see on a daily basis. I was not bashing anyone. I honestly did not look to see who posted it. Just making a point, since this thread turned into bashing the only person who really knew what they were talking about. Those guide lines work, they just are not hard rules. Learn as you go man. No harm done.

Scott said he returned your email on Friday. . .Did you get the response?

For an 18 like that, I would try for at least 80. . .100 if you can. Brian

That will work, but sounds like it is on the small side. . . Funny how all of this calculating port size based on enclosure volume has become the "law". . . Enclosure size is NOT used to correctly calculate the required port area. Sorry. I wish people would stop making this assumption. Why did someone even calculate Duran's calculation to be 29 sqin per cube?? It means nothing. . . There are also more issues with port area than just port noise. The port will not work properly if there is too much compression. In a car I doubt you would ever notice it as long as you have a subsonic filter (at enough compression, the box looks like a leaky sealed box), since it is normally so loud it becomes less noticable. And what is wrong with designing a "daily" box correctly? What is your definition of "daily"?? Maybe you think SPL boxes need more port area? Ever think maybe that is so the port operates correctly??? Tuning frequency should be the only difference between "daily" and "SPL" if you want the box to actually operate as it is designed. . . I will admit, I know you can get away with less port area in a car system. . .I help people design boxes all the time with less than perfect port area when space is tight. It works, but don't jump on someone's response when they give what is actually the correct answer and then use false info to try to prove it wrong. . .