RE 18s, Box Size

[Captain Stupid]

Hello everyone. I'm new to posting in this forum, but have been a basshead since the late 80s! Been out of the game for a few years and just getting back in. Many things have changed, yet so many others are still the same. Anyway, on to my system:

I just recently ordered a pair of RE SX 18s for my Escalade and plan to build my own box, just as I always did back in the day. This will be my first venture into a ported box, and my first box with 18s. The 1.25" MDF is on order and the subs should be arriving here this week about the same time. On the RE website it recommends a 5.5cu ft box tuned to 35hz as "compact" and an 8.0cu ft box tuned to 34hz as "optimal". I plan to power the subs with a Fosgate 2500@1ohm

I do not plan to compete with the system, just want to rattle the ground and enjoy my music, but I also want to get the most from the system that is possible without sacrificing an unreasonable amount of sound quality. I know 18s aren't exactly built for SQ, so I am not expecting the world, just a decend compromise between deep, low bass and decent sound. I know the 18s are going to give strong, deep base in any proper enclosure designed specificly for them, I simply seek to not sacrifice any more SQ than is necessary. And before you suggest that I can get better SQ and higher SPL from 4 12s or 3 15s or something of the sort, the speakers are bought and paid for and on their way. I chose them because I have always wanted a pair of 18s, since before I could drive. My decision was based on that, as simple, stupid and childish as it may seem to others.

Here are my questions:

#1: Which box size should I build, 5.5 or 8.0 or something in between?

#2: I have always built sealed boxes with a seperate enclosure for each woofer. Would seperate enclosures help my 18s or hinder them? I am assuming for SQ, seperate is better, but SPL would be lost. Am I correct? And what else should I be considering in the seperate vs. community box debate.

#3: When building the box, should I subtract a certain percentage of cu ft per side when using a community box for both subs, or do the recommended box dimensions per sub apply no matter how many subs are in a single undivided enclosure?

I'm sure I'll come up with a few more questions as I get these answered, but I appreciate anyone who takes the time to answer.

Edited August 12, 2012 by Captain Stupid

[Tarball]

1. 7-8^3 @34hz 14-16 ^2 inches of port area
   
2. Shared space is fine. use some bracing
   
3. Just add the requirement for both subs. Remember that the port does not count towards speaker chamber volume.
   

If you port the area you have for a box folks on here will often help you designs the box all the way down to a cutsheet.

First thing you want to think about is supporting electrical system (battery, big 3, alt, wire) .

Welcome to SMD!

[Joe X]

Ok the first step is getting the max dimensions for the box, also some comments on your musical tastes.

[Captain Stupid]

The truck is a 2006 Escalade SWB (Tahoe size) with the third row seats removed. I don't want to go any taller than 26", width is limited by the fenders at 49" and the lenth from back seats to the rear hatch door is +/- 49". I have plenty of space to make the box significantly larger than the optimal suggested size of 8.0cu ft X2. I'm a master carpenter and I've been playing around with numbers on the Torres calculator, so finding the correct dimensions and building the box are not really my concern. No need for you to waste your time crunching numbers on my behalf, I enjoy that part of the project! I really just want to get to the point where I can make the decision on what cu ft size box to build and whether to divide the box or not.

As far as what music I listen to, the range is eclectic. Everything from low, deep screwed bass to quick beat rap, to rock, to ultra-heavy thrash metal. Obviously I need a compromise between all, so one type doesn't always end up sounding like muddy crap. That is why I am leaning toward a slightly smaller 5.5-6.0 cu ft enclosure and dividing it. Am I correct in assuming a ported enclosure will get slightly better transient response with such large speakers if I use a seperate, divided box for each sub?

[Joe X]

I modeled that sub and you will get a lot of group delay with them, if you want even frequency response and low group delay you will have to go sealed (even if RE does not recommend that since you will loose lots of output) otherwise go for a 6 cube per sub ported box (double baffle at least), that will limit somewhat it peaking and will slightly reduce group delay, will also cost you output though.

Separate chambers will grow the size of your ports and therefore the size of your box and will not improve transient response, if the box is sealed then the box size stays the same except for the displacement of the center divider.

[Captain Stupid]

Thanks for the reply Joe. That was the type of information I was looking for. I still welcome more responses if anyone has anything to add to what Joe said. I think I have decided to design the box for what RE calls "optimal". At 8 cubic feet per sub, it will be big, but it will allow me to make a smaller box out of it later if it doesn't suit me. I'd rather start on the larger side and cut it down than start small and build an entirely new box if I change my mind.

I'm thinking of building a shallow box, 49x49x15-ish and taking up the entire rear cargo area. This would mean speakers up and port up. I know speakers up and port rearward is the loudest design, but this seems more practical. This would also allow me a smaller cross section to cut off if I decide to make the box smaller, as opposed to making a 24x24x24 cube. Thoughts?

Also, any thoughts on my pic for an amp? The Rockford Fosgate 2500. It is slightly over powering the 1000 watt speakers, but as long as it isn't cranked up at full volume for extended periods, I should be ok, right?