Finding subwoofer parameters

[Trizzly]

Hello All,

Long time reader, first time poster. I have decided to attempt to build a ported subwoofer using a spare driver I have. Its a Rockford Fosgate 12 inch Punch HE2 - model # RFP2212. I downloaded the owners manual via RF's website but the manual does not include all the parameters needed for WinISD. The manual does include box dimensions for a ported box tuned to 35Hz but I was hoping to go a little lower. Any ideas or suggestions?

[salvasol]

First of all Welcome to the forum ...

Trizzly wrote:

I have decided to attempt to build a ported subwoofer using a spare driver I have. Its a Rockford Fosgate 12 inch Punch HE2 - model # RFP2212. I downloaded the owners manual via RF's website but the manual does not include all the parameters needed for WinISD...

Contact the manufacturer and ask for that information, or you can do a google search and see if you're lucky to find the info

[Mike P.]

Everything you need is in the PDF except Sd and Re. Those you can get from similar subs, Sd being 480 cm2 and Re being 1.7 ohm for a parallel wiring.

300 watts input power, a high pass filter at 18 hz, and two 4 inch flared ports 21 inches long each for the tuning.

[Trizzly]

Mike, thanks for modeling. That looks real nice. I am actually going to be making two of these, one for each corner of the room. I was planning on using the Dayton HPSA1000-R to power them both. Do you think that would be overkill? You modeled the sub based off of 300 watts input, but the pdf suggests 400 rms. Perhaps the 400 is grossly over rated? Also 42 inches worth of port in each box seems like alot. Is that because this driver really is not suited for the application?

[Mike P.]

The Dayton Dayton HPSA1000-R is 1000 watts into 4 ohms. The RFP2212 is a dual 4 ohm sub, so a parallel - series wiring will have a final load of 4 ohms. The modeling was with 300 watts as that is when Xmax is reached. Going over a bit shouldn't hurt. The HPSA1000-R would be a good match for 2 of these subs. The amp has a high pass filter at 18 hz, perfect for this application as shown in the cone excursion graph.



As for porting, a single 4 inch flared port would have a air speed of 30 m/s at 19 hz which is doable. Port noise shouldn't be a problem. With two 4 inch ports the air speed would be 15 m/s, well under the 26 m/s point where port compression starts.

[Pinhead-227]

Forget my WinISD noobness, but why not run a 7.5 cu ft box tuned to 22 Hz? The graph shows that the higher tuned box has an SPL advantage from 20 Hz on up. It is, in fact, exactly the same at 20 hz.

[Mike P.]

The bigger box and higher tuning will reach Xmax with less power, the smaller box and lower tuning have a 3 db advantage at 18 hz. For a HT application, the goal is to get the most out of a sub at 20 hz and below.

[Pinhead-227]

Hmm, strange that your graphs look different than mine do using the same parameters. Is there a modeling difference between WinISD Pro Alpha and WinISD Beta?

[Mike P.]

It looks like you're using the Transfer Function Magnitude graph while I'm using the SPL graph after power input corresponds to maximum Xmax and the specific HPF of the amp has also been applied to the model.

[Trizzly]

Alright Mike, it's settled. A 7 cu ft box with dual 21 inch ports. Perhaps another noob question, but do the ports have to be a straight? Is it better for them to be straight? Feel free to ignore me as I am now taking up entirely to much of your guys time.