Print Page | Close Window

box tuning

Printed From: the12volt.com
Forum Name: Car Audio
Forum Discription: Car Stereos, Amplifiers, Crossovers, Processors, Speakers, Subwoofers, etc.
URL: https://www.the12volt.com/installbay/forum_posts.asp?tid=62203
Printed Date: May 23, 2024 at 1:46 AM


Topic: box tuning

Posted By: dirt_jumper54
Subject: box tuning
Date Posted: September 04, 2005 at 10:02 PM

i have a 1.88ft^3 ported box that has a 3" diameter port that is approx 11.2" long using the port lenght calculator i came up with 27.5hz. the box currently has an older mtx roadthunder 12" sub in it. my question is 27.5hz seems a bit low for me do u think i sould shorten up the port and tune it higher in the 30-40 hz range i listen to mostly rock with lots of bass and some rap/techno from time to time if that helps at all. what is a good tuning frequency for a happy meduim of spl and sq or is there such a thing? Any help is greatly apprieted(sp?) and if it makes any difference in a 04 accent.



Replies:

Posted By: stevdart
Date Posted: September 05, 2005 at 11:02 AM

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.



-------------
Build the box so that it performs well in the worst case scenario and, in return, it will reward you at all times.




Posted By: dirt_jumper54
Date Posted: September 05, 2005 at 5:42 PM
the box is homemade but not for that specific driver. i bought the sub from a friend and wanted a box to go with it so he gave me an old box to go with it so i didn't have to make/buy one for it. it is in and running right now. it is being powered by my kac-6201 at 150w rms. it seems ok right now but when i turn the volume up about 3/4 or more the sub pops(very loud) sometimes on large bass hits i firuge it is the box and the tuning that are making it do that so i measured up the box and came up with the above numbers about it. the 3" port isn't make any noticable port niose so i think i will leave it in.




Posted By: stevdart
Date Posted: September 05, 2005 at 7:26 PM

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.



-------------
Build the box so that it performs well in the worst case scenario and, in return, it will reward you at all times.




Posted By: dirt_jumper54
Date Posted: September 06, 2005 at 8:43 PM
i have the rt1240 sub see link https://www.mtxaudio.com/caraudio/archive/roadthunder.cfm
it is running at 150rms with rather low gain setting (about 1/4ish) but i think i know what is cuasing the poping see in the pic the extra part they glued on that says mtx road thunder it has 2 small creases and i think that is moving under big hits and hitting the cone behind it. i am thinking about trying to carefully remove the part that says mtx road thunder (there is still cone under it its just for looks)any one have the t/s parameters for this sub i tried looking but wasn't very sucessful




Posted By: stevdart
Date Posted: September 06, 2005 at 10:03 PM
Just going with the info in that link, my feeling is that you will get the best performance by using this sub in a sealed box.  Your power is a little high at 150 watts (it's a 125 watt RMS woofer)....it has a sensitivity of 93...and the freq response is listed at 30 Hz to 3.2 kHz...which makes me believe you should seal up that box you have it in.  you should try that before you go trying to take off that center logo.  That sub's not made for major pounding bass, but it should provide good sub bass to complement the rest of your system.  Sealing the box will stop the over-excursion that is causing the voice coil to go past its limits.  The box volume should be fine as it is.

-------------
Build the box so that it performs well in the worst case scenario and, in return, it will reward you at all times.




Posted By: dirt_jumper54
Date Posted: September 07, 2005 at 9:40 PM
my amp is supposed to have 150 rms x 1 at 4ohms but i doubt that as it is a pos kenwood KAC-6201.Im very convident that it is just the badge making the poping now because when i bought it i has a small crease in it and then my lil bro was fooling around with is and the crease got bigger (u know how lil kids poke at the cones) thats about when i started hearing the pop. do u think sealing will be better? its just with my other sub when i was using it a while back before i got the r/t was in a sealed box and u couldn't feel the bass and thats what i want (it was a 10" thunder 6000) the reason i stopped using it was it was svc 8ohms and my amp couldn't get much power to it. only like less than 100 rms so i bought the r/t cuz it was super cheap and worked way better with my amp





Print Page | Close Window