Enclosure troubleshooting

[bunningswarehouse]

Hi all,

Recently built a box for 3x Skar Audio SDR 18 D2s. Wired to 1.34 Ohm on an RP2000.1D.

The box is 15.19 cubic ft after woofer displacement, which equates to approx 5 cubes each. Recommended is 4.6. Don't ask how, cocked up a cut and made do. 

Port was made using Triticum's calc, recommended minim area is 109 square inches, mines a 118 square inch square port between two of the subs (see below for layout):

  O [ ] O   

      O     

Subs facing forward, as I will be sealing it off for a wall in the future. Apparently, the box is tuned to 29 Hz, according to those slightly botched measurements. Skar recommends 34Hz. Here's the thing. Running a frequency sweep, the box is extremely peaky at 50hz. Is this due to:

a). The slightly larger volume per sub, or

b). The lower tuning frequency, or

c). The box design (port placement etc.), or

d). All of the above, or something different entirely...

All in all, looking for any solutions. Considering they are 3 18s, I'd like low bass, obviously haven't got the highest of expectations due to the sub quality, but certainly wasn't expecting 50hz rattlers...

Any help would be greatly appreciated.

[ckeeler11]

A.) doubtful

B.) No if anything you would get some distortion down low.

C.)Possibly. Depending on how the port is inside the enclosure you could get some unloading.

D.) Resonant Frequency of the vehicle. Probably a big part of it.

 

Did you do any modeling of the subs and enclosure before hand? How does that plot line look? It wont match in vehicle response but it should tell you if it is inherent to your design or something else.

[Triticum Agricolam]

So those subs suffer from the same weakness that most inexpensive large (15 -18") subs suffer from.  They don't have a big enough motor for the amount of cone area they have.  This situation arises when a manufacturer uses the same size motors on all the different size subs in the same product line.  A motor that is great for a 10" & 12" sub isn't enough for the 15" and especially 18" versions.  The result of this is they have a high QTS.  High QTS subs will have a peak in output usually around the 50 Hz area and then output will roll off below that.  Depending on your vehicle cabin gain can help boost the lower end, but if its a sedan or other smaller vehicle the cabin gain is going to boost at higher frequencies and make the problem worse.  Sounds like that may be what you are running into.  

Unfortunately there aren't really any great ways to solve the problem.  One thing you could do would be to get a DSP for your sub amp.  With a DSP you could cut down the 50 Hz to give you a flatter frequency response.  Its not going to make your lower frequencies any louder, but at least you can get rid of that annoying mid bass peak.  Other than that your only other option is different subs that have appropriately sized motors.