winisd

Yeah I have been studying that sticky alot the past few days, plus searching other posts related to it, but my poor lil brain just isn't grasping it! I am getting a little more familair with that program though, so guess that is a good thing, I just need to understand what exactly I am looking at and what some ideal results should be. Only plan on building the box one more time! (Wasn't structurally sound enough the first time)

Ok, guess it helps if my dumb butt would have put the crossover points into the program! No wonder my graphs looked so strange. *sigh*

tdsteele, you will need to look at several charts while you manipulate Fb.  Make sure you have entered the RMS power this sub will likely be getting at highest volume in the input power window under the signal tab.  You will want to:

• make sure that the port opening is large enough for reduced port noise.  With rear port - air velocity chart set to feet per second, rms, keep port noise under 100 in the frequency range of 30 Hz and above.  Ideally, you should show no more than 50 ft/sec in that range.
• watch the cone excursion.  If you are using a rumble filter with the amplifier, enter that under the EQ/Filter tab.  The high point crossover is not important to add, in this case, as this is a box for subwoofer only.  Cone excursion graph shows a colored line at Xmax, and a rise over that line indicates overexcursion.  This will change as you alter tuning frequency, power input...maybe other things.  Your goal is to keep excursion at or below that  Xmax line across the entire audio spectrum.
• there are always tradeoffs.  The flattest response may need too large of a box, too large of a port structure, and may go into overexcursion.  Work from flattest to peakiest and find the compromise that will work for your situation.  If you are stuck with having no larger a box airspace than 1.7 cu ft, you will have to deal with that and possibly settle for some peakiness in the mid-sub region.  Avoid 3+ db peak if at all possible.
• with low tuning you might see that the response line shows a slight dip, then a slight rise at the lowest freq before it severely drops off.  That should be okay because the vehicle's gain will fill in the "saddle".

Is it the Soundspinter sub?  Dual 2 or dual 4?  Are you building slotted port or tube?

haemphyst, I have room for mail.  Ask away, but remember, I'm more of a meat and potatoes kinda guy...not sushi and caviar.  Your system's that Ess-O-Terr-ick stuff!

Ok, here is one model. 2 ft^3 @ 28 hz, slot port 1.25X12.5, 23" long. (If i go slotted it will be 12.5" wide as the box will be 14" wide). Crossover set at 100hz, subsonic set around 19hz, no idea if these are good points but this is what I typed in.

Cone excursion stays within limits. Port air velocity peaks at 64 ft/s rms @ 26.88 hz. The function magnitude graph (wish I knew how to save and post the graph on here) shows as follows to give you an idea of the curve:

-6.5 db @ 25hz

-2 db@ 30 hz

0 db @ 35 hz

+.57 db @ 40 hz

+.6 db @45 hz

+.5 db @ 50 hz

+.06 db @ 60 hz

-1.15 db @ 80 hz

So, am I on the right track or am i looking at this wrong? I'm hoping to gain alot of knowledge on this. I was always used to just buying the subs, throwing them in the manufactures suggested set-up, and going on with life, but what fun is that, especially with programs like winisd around, and with the12volt.com as well!

EDIT:  posted as you were posting, so I'll look at what you just said.

This sub is hard to model.  You notice that WinISD will, by default, give it a tiny box and a super huge port.  The program is trying for the best Q but you can't get a real strong low end extension with this sub.  The recommendations Soundsplinter makes look like sort of a compromise...giving it a more normal-sized airspace in exchange for a smaller port, but creating a dip "saddle" in the response.  The very low end that you see in the model is all port;  the driver isn't outputting low freqs.

This sub looks like it functions on a limited scale, more SPL than SQ.  It models easier when tuning high than low, such as 1.1 cu ft tuned to 40 - 50 Hz.  It doesn't seem to like going as low as 40 Hz unless you tune high enough so that the port takes over the function of sound production at 40 Hz.

I don't know how you are getting anything that resembles flat ("I can get a pretty flat line...") .  I'm looking at a one note wonder here.  But right now, looking at it, I'm inclined more toward smaller box airspace at 1.1 cu ft, tune higher to 40 Hz, slot port 15 square inches.  Round the edges of the port slot.  Port resonance (see "first port resonance" under the vent tab) goes up mostly out of range at 345 Hz with this higher 40 Hz tuning.

EDIT:  Okay, I read your post and I'll look at it some more, but first thing I want to mention is port opening size.  While square inches is sufficient, what is wrong is that the ratio of width to heigth of the proposed slot is 10:1.  You will get more noise and less precision with this high ratio.  Keep the ratio at less that 8:1 even though it means that with a 12.5" width the slot will grow longer.

I'm not sure how you got those db numbers you listed.  They should all be on the minus side throughout the entire range.  Employing the filters brings the whole scale down.  Click your cursor on any freq along the curve and read what it says at the top right of the chart.  OR, left click and hold, then drag the white crosshairs along the curved response line.

Ok originally when i got the pretty flat line, I had not put in the crossover points, so I assume it was looking at it like a full range. When I put in the crossover point, it had the big sweeping curve. Still figuring out how to work this program properly.

I know presently, if I put in a test tone cd, it puts out best from 30 to 50 hz, over 50hz it drops off rapidly. 20hz just makes the truck shake with little sound output.

The numbers I listed where by running the cursor along the graph and reading what it had in the upper corner, so, unless I have something wrong, I dunno.