box and WinISD

hi guys. i am thinking of changing my su set-up for more low end bass. I have 2 12" Alpine type E. 250w rms. i am powering them with a kenwood KAC-9102D. 850w @2 ohms bridged.  i know i have plenty of power to push these subs. right now they are in a sealed box with 1 cubic ft of space per sub.

What i want to do is go with a ported box. the alpine manual doesn't give any info on ported boxes with this sub. and i have searched this site long and hard and come up empty. SO is anyone out there who can direct me in cubic feet needed and port size?  I listen to all music mostly old school 80-90 rap, classic rock etc.

the THIEL small parmteres? no idea what that is.

the speaker specs are here https://www.alpine-usa.com/images/products/documents/OM_SWE-1242.pdf

and i know its not intended for a ported box ..but just wanting info about how it will sound and what size etc i need the box and port etc

thanks again

T/S parameters are the measurements of a woofer that define what type and size of enclosure to use.  This sub's parameters indicate an EBP of 44, which defines it as a sealed.  You can change the box type to vented, but be aware that there will be trade-offs involved.  The big trade-off you will find here is that you will need to build a much larger enclosure than you have now.

Ideally, your subs should reside in a sealed box twice the size of what you are using now.  That change in airspace would drop the peakiness down by a decibel and lower the F3 by about 5 Hz.  F3 is -3db down from flat response and is considered the low end limit because at that point it is receiving only half power.

To change to a vented box:  give up enough room in the car to build a box that will have 5 cubic feet of airspace dedicated to the subs (2.5 to each).  The box tuning has to be very, very low to achieve a good response, which means that there will be little if any sound produced by the port.  Because of this, the port itself should not have to be built as a slotted-type with all the extra displacement associated with such a type of port.  Instead, use a round PVC tube.

Here is a look at responses for this sub in WinISD.  I had already had this driver loaded in the database so it was a simple matter of just opening it up and trying a few different things with it.  Open the file, expand it to full size, and refer to the colored response lines that I will describe to you:

swe1242.jpg

Yellow:  this is what you have now.  2 cu ft sealed, F3 is at 43 Hz (follow the line as it crosses the -3 db purple line).

Orange:  this is what I would recommend you change the box to.  It is also sealed but the box airspace is almost twice as large at 3.75 cubic feet.  You see that the peak doesn't go as high and that the F3 is pushed a little lower to about 38 Hz.  Would work well with any type of music and is a better SQ curve.

Teal:  this is what you could do by venting a box for these subs.  5 cu ft of airspace after deducting all displacements (such as port and drivers, and the added braces you will have to use).  The response goes up a little peakier than the orange curve but not as bad as what you currently have.  The F3 goes lower than either of the sealed types, to 30 Hz, which corresponds to the Fs of the driver.  The port is a PVC tube that has a 4" interior diameter and is cut to 14" in length.  This makes the box tuning at 20 Hz.

Now, because the tuning is so low, there will be very little sound emanating from the port structure.  You don't need to build the larger slotted port design (with its inherent larger displacement costs) because port noise will generally not be an issue at this low frequency.  And, tuning to a higher Fb by using a shorter port would result in a bad response curve....it would cause an abnormal peakiness to the sound.  Also, changing the box size to anything less than 5 cubic feet would give you an abnormally bad response.

Bottom line:  I suggest you rebuild your box as I defined above to the larger 3.75 cu ft sealed.  If you want to experiment with vented, and have the necessary space to do so, use what I showed here and nothing smaller.

thats so much more indf othen i needed. thats why i love this site. thanks a million for your time. i will make a bigger sealed box this time and im sure it will sound exactly how i want it to ..fro mthe chart it will be perfect..

thanks again STEVDART

just to update this post.. i made a sealed box with 1.75 ft of airspace per speaker... its like a brand new system. i made the first box as alpine wanted at 1 ft per sub..  NO WAY.. this is so much stronger.

THANKS AGAIN FOR A GREAT SUPPORT SYSTEM.

Well I am not a expert, but I know quite abit about boxes. I know if you choose the smaller req specs on the box volume it take more power to push em. On the other hand if you can beable to fit the max volume its not as hard on the amp.  A sealed box is more cleaner sound then a vented/ported box, and a isobaric is your basic one note wonder.. I prefer slot vented.. Just my 2 cents.. If anyone has a myspace  look me up at sanity0187@yahoo.com and in my picture section you can see the box I made housing 2 12' kicker comp cvr's..

Anyone can quote me if I am wrong on this matter..