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ported boxes want to learnPrinted From: the12volt.comForum Name: Car Audio Forum Discription: Car Stereos, Amplifiers, Crossovers, Processors, Speakers, Subwoofers, etc. URL: https://www.the12volt.com/installbay/forum_posts.asp?tid=65516 Printed Date: June 08, 2024 at 5:48 PM Topic: ported boxes want to learn Posted By: steezs Subject: ported boxes want to learn Date Posted: November 03, 2005 at 1:00 AM ive been reading a lot about ported boxes and im getting really confused about all kinds of different info. one really weird thing was one site said you should use high pass filters on these. so my first question is on your amp when you got a ported sub box in it do you set it to HP or LP i thought all subs were to be on LP. and when your calculating port length do you put the Fb from the original formula fb =Qts^-0.9 *.42*fs or do you put the frequency you want cause the column says desired frequency and what effect is it if you put a value higher than the fb you get from the formula. and i also would like to know what f3 does is it a boundary that you cannot tune your box lower or higher than this number?
------------- THE DUCE Replies: Posted By: stevdart Date Posted: November 03, 2005 at 7:33 AM steezs wrote: Start with this: what program are you referring to? And I'll add some to this. For the first question, a vented driver needs a subsonic filter, which is actually a highpass. You have to set the crossover on the amp on lowpass so that you can crossover to the mid drivers, but the additional subsonic filter will control the cone movement below the box tuning frequency. Some amps have a subsonic filter available. A sealed enclosure doesn't need one. For #2, here's a quote from https://www.diysubwoofers.org/prt/ported1.htm that you may have already read:
Posted By: steezs Date Posted: November 03, 2005 at 11:45 AM OK so i got it now i the amp is on low pass which i figured. And im not building a box just want to learn about it more so when i do i can make a good one i was using the calculator on this site and the program WinISD. Ya i was up a while last night reading and figuring out more of this program so hopefully maybe you can answer me these quick questions the F3 is the point where if you want to tune your box below that mark it wont work properyl right? and when your tuning your box with that program it is generally better to try and get a smoother wave correct and the drivers i was practicing were some JLaudios like the jlw6 2 12 incher found on thier site. And also when your tuning your box is it better to try and get it as low as possible (frequency) and this number how is it incorporated when you hook it up like for say i made a ported box with jl audios w 6 12 inch the box is tuned to 27 hz (you can check it if you want) www.jlaudio.com find 12 w6-2 info if you have the program i tuned it to 27 or so a box of 4.6 cubic feet, retangle port of 4 by 6. you can see the results ive compentated for the area of the port in the box you get a box of like 21 by 33 by 13 inches used 19mm thick wood all included. maybe try it see what you think if i did it ok or not. That driver isnt included with the program so i added it form website here ill give you what i used Qts=0.45 VAS= 2.82 cubic feet Fs= 25 Hz Xmax=16.5mm Qms=7.1 Qes=0.48 and Pe= 400 watts (Rms) ok i dont really have time to go through all the links right now but if you can message me with how to make a subsonic filter or a link with how to understand it that would help . ------------- THE DUCE Posted By: steezs Date Posted: November 03, 2005 at 12:06 PM Ok forgot a few things and hopefully learned a few things reading on subsonics forgot to mention the f3 in that equation above it came out to 19.9Hz and the Fb came to 21.54Hz originally but i modified the tuning frequency in the program to get a workable port length (was too long at that frequency). ok the amps usually come with crossover so if theorectically i made this box with that sub and connected it to the amp i would set the amp on LP i guess amps start at higher frequencies like 35-40 Hz or if possible get it closer to the FB i used to tune my box 27-30 right (usually see on amps crossover begins at like 35Hz). and if i got subsonic filter on the amp i would set it to 20 Hz to prevent it from going under my f3 point right? if you could answer me this please ------------- THE DUCE Posted By: stevdart Date Posted: November 03, 2005 at 5:50 PM steezs wrote: I found the time to post them for you though. And I believe you DO have the time. Those are just a beginning. With some diligence, links from this site and others, and Google searches you can find all the information you want or need. Read through the entire help section of WinISD. It speaks volumes. It's not uncommon to spend more than a year learning about designing vented boxes. A sure way to speed up that learning curve is to get started on a project, whether it be for car or home audio. It's like OJT, and everyone knows you learn faster on the job than with your nose in a book. And please....use punctuation in your posts. Capital letters, periods, commas, sentences, paragraphs.... Major headache time trying to work our way through your writing. ------------- 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: steezs Date Posted: November 03, 2005 at 6:23 PM AHAHAHAH ya i do, but the thing is i've read all that already im just trying to ask you questions to see if i understand what i read. Thanks, some helped didnt know about subsonic filters and stuff. I just have a few things to clear up here. First F3 this frequency is the frequency that you cant tune your box under and it should be the frequency you set your subsonic filter to right? Secondly if i tune my box to 27 hz for example will it sound good when i play with the crossover frequency on my amp? (most amps i see crossover frequency begins at 35Hz) or is it better to tune the box higher than that, buy a crossover, or make one out of caps and coils? Sorry about the grammar been out of school a while. ------------- THE DUCE Posted By: stevdart Date Posted: November 03, 2005 at 9:34 PM A definition of F3 is that it is the -3db point where the output power has fallen to one half and so is considered to be the low frequency limit of the loudspeaker. (https://www.highefficiencyloudspeakers.com/user/Alignments.pdf) When you put a speaker into a vented enclosure you know you are (or at least you CAN be) extending the low freq response by using a port. So, knowing that, you know that if you change the tuning frequency by manipulation of the box size or port size, the F3 will change along with it. Keep the Fb above the driver Fs when finding a tuning freq. You probably shouldn't be worrying about F3 so much. In that link above they show 3 formulas to use with a driver (of your choice) to see if it will suit your application. By using the formulas, you will find F3. If it is too high for what you want, choose a different driver and start over. You can use the T/S parameters given for each one and choose your speaker that way. Or you can use a nifty program like WinISD Pro or Unibox and let them do these calculations for you, like I do. If you try to manipulate the low end (F3) of an enclosure too far you'll get problems in other areas. As you work with different drivers you'll see there is a limited range of changes you can make and still have a good sounding loudspeaker. As far as a subsonic filter goes, you just want to make sure it is set just slightly below Fb so that you still maintain the full complement of the port but the filter controls the cone movement at freqs below the tuning freq. Which leads to your second Q: it is often desirable to tune an enclosure below the point at which you will start crossing it over or filtering it out. You don't get the full effect of the port at Fb because it is crossed out, but you can sometimes extend the low freq response by doing it this way instead of using a sealed box. And drivers are, you know, made to work better one way or the other, although there are a lot that can go either vented or sealed. As you will read over and over, it depends on what you want to accomplish, what your working with, the driver, etc. ------------- 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: steezs Date Posted: November 03, 2005 at 10:05 PM Thanks a lot man, ported boxes can get real complicated to understand and perfect them. I dont even want to know about bandpass :(
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