Box Help on 3 -18s

[jmanjr82]

Vehicle 2010 Eddie Bauer Explorer

Subs 3 Skar Audio ZVX 18s D2

Amp Taramp 8k 2ohm model (yes I know 3 D2 subs is lower than 2ohm) never had any problems for 2 years now

Space I would like to use max is H: 22in W: 44in D: 31.25in for 15 total cubes

tuning 34hz is what im looking for, but which way to do the port to be the most efficient? mobilelabs port calculator says a port h6xw30xd2 would be 34hz that would be 180sqin of port area

goals be loud to the ear, move some air, true ground pounder scores no longer matter those days are behind me.

 

[Triticum Agricolam]

You need more space or less sub. 

[jmanjr82]

I respect the input, however from trial the ZVX line of woofers tend to like smaller space than recommended by Skar. I ran the zvx 12s in a far smaller box with far more power than rms and it yielded great results. I have tried 3 boxes now for 2 18s and so far the loudest and more brutal has been the smallest of the 3. First box was built to spec 5.5 cubes per woofer tuned at 33hz. Second box was 11cubes before displacement  tuned at 33hz. Current box is 10.28cubes before displacement tuned at 34hz. I am all for trying multiple options. I think the subs can be done in this space maybe not optimal on paper, but people have done this with great results for years. From mass reading people tend to favor a smaller box than recommended often when using globs more power that rms to keep the sub linear. I noticed first hand the 2-18s in the recommended 5.5 cubes got very sloppy and smelly real quick using the 8k (yes it was set correct using DD1) there was no distortion nor clip based off the DD1 and clip detector on the amp nor has voltage ever dropped below 12.0 volts. If you say I need more space how much more space? Are you saying I need to do 5.5 cubes per sub? 16.5 cubes? I have more room to spare, but I didn’t want to go above the seats nor did I want to leave NO room for the batteries. Didnt Steve Meade himself use less than recommended box specs for his current build, correct me if I am wrong? I am really just looking for input and trying to find a way to cram this in here without walling it.

[Triticum Agricolam]

There is nothing wrong with using less than recommended net volume, especially when running above RMS power.  In fact I prefer the sound of small-for-sub ported boxes.  There certainly is a limit though to how small you can go and I think you are over estimating just how much space you have.

Based on the dimensions you gave and assuming you will double layer the walls (on 8k you really should double layer), that leaves you with 12.74 cu ft of interior box space.  The subs are going to take up .57 cu ft. and then a 180 sq in port is going to take up at least another 3.5 cu ft (if not more) assuming you want to tune to around 35 Hz.  This leaves you with about 8.5 cu ft net (at best) for three 18's.  That's on the low side even for three 15"s.  

[jmanjr82]

The current box is 2-18s

10.28 cubes (H-16.25, W-43.75, D-30) Tuned at 34 Hz (Port= H-14.5, W-8.5, D-14.5) Which is 123.25 sqin of port.

If my calculation is correct after Sub displacement 0.38cu and port Displacement 0.68cu that would be 10.28-1.06=9.22/2 is 4.61cu per sub?

So again I shall ask where do you think I need to be total for airspace prior to displacement? What If I went the aero port route?

I can probably squeeze a tad more on height and maybe a smidge on depth I was trying to leave some space between the port and the back hatch. Just some random info also if you check the FI Audio website their range for a ported box on an 18in woofer is 6-10cubes clearly we know that’s a 4cube difference, but that massive. The ZVX 18 on paper calls for 5.25 how do you draw the line as to how small is to small?

I really appreciate the input thus far. I am just trying to cram 10lbs of shit in a 5lb bucket!

[Triticum Agricolam]

I think 4.25 cu ft per sub is a reasonable place to be, if you can get that much.  

Looks like you may have done your math wrong in n your current port, no matter what I do I end up at over 1 cu ft of port displacement. Are you including the thickness of the port panels in your calculations?

 

 

[jmanjr82]

I very well could have. I just took the measurements of the port and calculated them like you would for a box to get air space. I could read and read and couldnt really find exact ways to calculate port displacement. If you can shed some light on that it would be a huge help. I think I can get 4cubes per woofer

[Triticum Agricolam]

When calculating port displacement you are basically calculating the external dimensions of the port inside the box. So you need to base your measurements off the walls of the port inside the box. 

[jmanjr82]

Ok so can you show the process of how your gettting over 1 cube for port displacement? The dimensions of the port at taken from measuring the opening, which would be the internal dimension. TO my understanding you measure the port surface area?

[MrSkippyJ]

14.5 * 8.5 * 14.5 = 1787/1728 = 1.03cubes