so i am building a ported box for two 15's. i am seperating them and each side will be 3ft^3. i am going for db. forum answers have told me to tune it to 35-40hz for best results but winisd tells me somewhere near 80hz. am i missing something here? what am i doing wrong?
You left no specifics on your woofers or amp(s) so I can only answer generally.
Tuning it lower will sound better per say. There is alot of "information" in 30-40hz region, especially if you listen to current music. (although classical is more dynamic)
Tuning the box higher will give you a higher SPL at the expense of the lower frequencies that a large sub can reproduce very easily in a vented enclosure.
So base the decision on if you want to win contests, or enjoy the sound for daily usage.
It will still be plenty "loud" tuned lower (35hz for example) but you would be at a disadvantage if competing in DB drags etc.
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WinISD doesn't really "recommend" anything. What they do is design the enclosure for a certain type of alignment, usually for a flat anachoic response. However that alignment might not be best for your needs. The vehicle has it's own effect on the subs response that needs to be taken into account.
I would suggest you go very carefully over the specs you've entered in the database for your sub. Check also the unit of measurement displayed for each of the specs. I've never seen a case where WinISD (at least the alpha Pro version currently available) has defaulted to such a high tuning frequency. Once you've verified and/or corrected the parameters, click through the dialogue boxes and see what it defaults at. Once there, you can always make whatever changes you desire.
For example, change to a 40 Hz frequency per the advice you said you got. (BTW, WinISD usually defaults to a much lower tuning frequency to achieve the flattest response, like around 24 Hz or so, for comparison's sake...). When you raise the Fb like that, you'll notice an increased bump in the response above the red line. Oftentimes in car audio, suggestions like this come from real world experience, and should be taken seriously. If this is the case where SPL is of greatest concern, that peak will help provide it at the right frequency for a lot of vehicles and modern music material.
Post sub models and links to specs (if possible) for more detailed help. State also your goals: SQ or SPL.
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Build the box so that it performs well in the worst case scenario and, in return, it will reward you at all times.
Question: How can the speaker manufacturer have a clue to the vehicles resonant frequency?
If this was really a problem, especially with a competition or SPL vehicle, would not you use deadners and bracing to deal with this?
I can't imagine to keep changing the reccomened air space and port volume to satisfy the vehicle, shouldn't it be the other way around or am I NUTZ??
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