question before building

Discussion in 'Archived Threads 2001-2004' started by JasonS, Oct 9, 2002.

  1. JasonS

    JasonS Stunt Coordinator

    Joined:
    Sep 5, 2000
    Messages:
    107
    Likes Received:
    0
    Trophy Points:
    0
    I'm thinking of building my first sub, but have a question regarding direction of sub/port. What differnce will the sound be in a down-firing as opposed to a front-firing position? Also, should the port be on the same baffle as the driver?

    Thanks in advance for your help.

    ~J
     
  2. Geno

    Geno Supporting Actor

    Joined:
    Oct 1, 2001
    Messages:
    637
    Likes Received:
    0
    Trophy Points:
    0
    Hey, there are alot of posts already on this forum with that info. do a search for down firing fron firing in the diy section or the speakers section and you will find out more than you want to [​IMG]
    also down or front depends on driver also. have you got the driver? or I guess where are you in your designing stage?
     
  3. JasonS

    JasonS Stunt Coordinator

    Joined:
    Sep 5, 2000
    Messages:
    107
    Likes Received:
    0
    Trophy Points:
    0
    Thanks for the advise.

    Yeah, I have the driver. It's an old JBL car audio sub (GT122). WinISD says to put it in a 2.255 ft. cubed box tuning it to 38.05 Hz.
     
  4. Jason...with a tunning of 38.05hz, I'd hardly call that a subwoofer. That driver may have been good for a car, but you will be disappointed with it's performance for HT or music.
     
  5. JasonS

    JasonS Stunt Coordinator

    Joined:
    Sep 5, 2000
    Messages:
    107
    Likes Received:
    0
    Trophy Points:
    0
    Thanks for the help. I was just thinking of building it since I have the driver laying around. I'm obviously new to the diy thing. What should a decent powered sub be tuned to?
     
  6. Geno

    Geno Supporting Actor

    Joined:
    Oct 1, 2001
    Messages:
    637
    Likes Received:
    0
    Trophy Points:
    0
    jason, look at this thread
    http://www.hometheaterforum.com/htfo...threadid=98921
    scroll down until you see the response graph. thats the THX intro for the phantom menace i believe. It gives out signals as low as 10Hz. yes it would be very hard to reach but it gives you an idea of how low they can go. Id say around 20 -25Hz if sufficient. Im also designing/building a sub and Im reaching for 20 HZ myself. just have to go thru more testing of my drivers. Kinda neat knowing there are more HTFer's out in Lenexa [​IMG]
     
  7. JasonS

    JasonS Stunt Coordinator

    Joined:
    Sep 5, 2000
    Messages:
    107
    Likes Received:
    0
    Trophy Points:
    0
    thanks for the input. I'm just thinking of getting into the diy thing since I have the speaker sitting around. Still don't know whether to try or not just to see what it sounds like (probably terrible). I have a 6-month old baby and a wife that always thinks whatever electronics we have is more than enough, so it's hard to come up with money for new stuff.

    I have to be honest, I don't live in Lenexa anymore. The wife and I had a house built in Spring Hill last year. I still have family in Lenexa though. Guess I ought to change my profile someday.
     
  8. Chris Tsutsui

    Chris Tsutsui Screenwriter

    Joined:
    Feb 1, 2002
    Messages:
    1,865
    Likes Received:
    0
    Trophy Points:
    0
    It'll probably sound good for rock music and have some nice punch to it. I've built a JBL GT series sub before in a 3CF sealed box and it does pretty well in a car.

    Instead of telling you to do a search I'll just post:

    Front firing sounds the same as downfiring, just about all drivers are front firing while only some are capable of downfiring due to the sag gravity may cause. There is no audible difference with low frequencies, you are only changing the position of the subwoofer for perhaps safety or cosmetic reasons.

    The driver and port position can vary depending on the box's design. If you would like to maximize SPL, then try and position the driver with port(s) towards a bottom corner of the sub box so the driver and ports can be as close to the corner of the room as possible. If you want to minimize corner gain yet still have the sub in a corner then put a FF driver as high on the sub as possible and away from the corner.

    Also keep in mind that it is recommended to keep ports from the side walls inside the cabinet. Perhaps at least one port diameter distance from any walls inside the enclosure should be fine.

    Which way the port faces in relation to the driver doesn't really matter as the woofer generates air pressure changes within the enclosure which simply pushes and pulls air.

    Honestly I would let cosmetics determine the position of the ports and the decision between a FF and a DF sub.
     
  9. JasonS

    JasonS Stunt Coordinator

    Joined:
    Sep 5, 2000
    Messages:
    107
    Likes Received:
    0
    Trophy Points:
    0
    Thanks, Chris. I had followed Geno's advise and found out that it shouldn't make that much a difference. So, I was probably going to go down firing since my daughter will be mobile soon.

    Any other advise before building?
     

Share This Page