box tuning

First, I'd like to say what a great pleasure it is to be able to use this site again.  Big kudos to 12volt for saving the database and getting the site back up.  We wish him and his family/friends good fortune and health when this is all said and done...

dirt_jumper54...are you using a box that was premade, or used for a different driver, and switched over to the MTX?  And, is the system up and running and you are able to make some observations about the performance?

Answer those questions, but otherwise here are some of my observations about this:  I would find the parameters and whatever other info I could on the MTX woofer you are using.  Try the website and use tech support if you need to.

If you look at a 12" RoadThunder like this one, you could do a comparison between what you have and what this one recommends for a ported box.  If you look at the ported box specs in this link, you'll see what the port size is and how it relates to tuning frequency vs. the driver's Fs.  In this case, the driver's Fs is 31.3 Hz.  The box tuning frequency....if you do some calculations......is about 43 Hz.  You'll also notice that the square inches of port opening is 28 compared to the the 7 sq inches you have with your 3" port.

Two things to observe about this example:  the box tuning is higher than the Fs of the driver, and the port opening is large enough that there wouldn't be a chance of getting port noise.  If you want to use a vented enclosure to boost the level of volume, you want that extra 3 db of sound to be as clean as the sound that the driver would make in an otherwise UNvented box.  That is, you don't want the box to ruin the sound.  So, if your driver has specs that are similar to this one, your current box would be insufficient.

Cutting the length of the port tube would indeed make the frequency higher, but you would still be left with the specific box volume and small 3" port opening.  A redesigned, new enclosure for that driver should be the order of the day...but you have to first get the parameters for it.  If you use that box in the interim, then yes you should get that tuning frequency higher than the driver Fs.  And using a subsonic filter is a good idea, too.

Ok, I'd say the tuning freq appears to be too low.  Shorten that port tube up to about 7" or so (check with the calculator) to tune the box higher.  (At least, start with 7" and you can make some further cuts if you still get that popping).  It could be that the woofer is over-excurting on some of the bass hits because of the low Fb.  Make sure you figure out the displacements of the sub and the port tube when you're figuring the net internal volume.  It would still be a good idea to get the T/S parameters for your sub so you'll have something better than guesswork to go on.  If you don't know the specific model just look at like woofers as I did in the post above to get your best idea of what it's Fs might be.  Between 35 and 45 Hz would probably be the best box tuning with what you have to work with.

Again, a subsonic filter that will cut at 30 Hz and below is in order as well.  And bear in mind, also, that excessive amplifier gain will cause that kind of problem too.