Several subwoofer questions for the newbie!

Discussion in 'Archived Threads 2001-2004' started by John_Berger, Sep 20, 2002.

  1. John_Berger

    John_Berger Cinematographer

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    Okay, okay. I've done some searches on the forum, but either I'm searching for the wrong thing or I'm just not seeing the answers.
    I don't have a subwoofer. Put the pitchforks DOWN!!! I've been trying to read up on them to determine what I should look for. Unfortunately, I'm seeing several different terms thrown around for which I know the technical definition but not how they relate to subwoofers.
    So, I'm just going to lay these questions out one-by-one. Feel free to answer or point me to threads/articles where this has already been answered. [​IMG]
    1. How does "phase" enter into the quality of a subwoofer?
    2. How does "crossover" enter into the quality of a subwoofer?
    3. What determines whether a subwoofer is good or not? (An open question, I know, but I'm eager to read the responses.)
    4. I am not afraid to build my own subwoofer; in fact, I think it would be a fun and interesting challenge as well as give me bragging rights if I succeed. I need to stay at or below the $100 mark if I ever expect my wife to let me touch her again. [​IMG] Can a decent subwoofer be built with those financial constraints? (BTW, I'm talking about $100 for the internal components, not necessarily the enclosure itself.)
    5. Assuming that the answer to "4" is "Yes", where would I go to find out what I need to do and what to look for?
    6. What is the average air-speed velocity of an unladen swallow? African or European - doesn't matter.
    7. I understand that placement of the subwoofer does matter. What is the best way to determine where and how a subwoofer should be placed?
    I'm sure that I'll have more questions as I go along, but these should be good to start. [​IMG]
    P.S. I just found www.diysubwoofer.com, but they still throw around technical terms and acronyms that make it a bit difficult for subwoofer newbie like me to follow. :b
     
  2. Joe Szott

    Joe Szott Screenwriter

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    I'm kind of a newbie too, but here's what I know from my recent purchase of a subwoofer:
    Phase and Crossover are interchangable terms for the same thing. The phase crossover point is set between 0 and usually 180 degs to filter out the high pass tones the subwoofer receives from the receiver. Basically, you are setting the frequency (in Hz) where the subwoofer 'kicks in' with the big bass.
    Usually the main speakers have a drop off point for the low sounds, let's say it's around 40 Hz. A subwoofer usually goes down to ~20 Hz, so you would set the crossover to activate around 50 Hz in this situation. So as a sound is getting deeper, around 50 Hz the mains are tapering off and the sub is just starting. When it gets down to 40 Hz, the mains stop delivering bass and the sub is ready to take the sound all the way down to 20 Hz if need be. You want to set the crossover point so that the sub picks up the low sound smoothly from the mains when they give out.
    The rest of the stuff you'll need to get from someone else here [​IMG]
     
  3. john_focal

    john_focal Agent

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    1 and 2 dont really enter into the quality of a sub per se. Any decent sub will have controls for both.
    #3: a loose definition would be a sub that can accurately and musically handle everything thrown at it, be it explosions on a movie, or music passages. This is many things to many different people, and many ways to achieve it.
    #4: I dont think that is a reasonable limit for a DIY sub, as just the amp you get for it will cost close to that. I think it would also be a nice challenge [​IMG]
    #5: http://www.partsexpress.com is a start, as well as http://www.adireaudio.com/diy/diy.htm There are lots of others though.
    #6: Your guess is as good as mine [​IMG]
    #7: USUALLY in a corner is the best place to at least start. A lot of this has to do with the room you're using, so experimentation is really the way to go. (Some subs actually sound better along a long wall in the room, for example). I tend to place my sub where it sounds the most balanced from most listening positions, and the least "boomy". Also I try to keep it from rattling things like windows as much as possible.
    And actually, "The phase crossover point is set between 0 and usually 180 degs to filter out the high pass tones the subwoofer receives from the receiver." is misleading. The phase of a subwoofer needs to be set so there is no cancellation of bass tones when other speakers are brought into the mix. This has nothing to do with the crossover point, which determines the level of higher frequency signals that will be blocked from the sub.
    And while most speakers will go below 50-60 mhz, you'll want to (usually) set the reciever to treat your main speakers as "small", which will usually cross them over at 80-100 mhz. Higher end recievers have an adjustability to this feature (mine does not), but then everything below 100 mhz will automatically be sent to the sub.
     
  4. Cees Alons

    Cees Alons Moderator
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    Cees Alons
    Uhm, no (to Joe; sorry, john_focal, we apparently worked in parallel [​IMG] ).
    (1)Two drivers getting the same signal are "in phase", when their voice coils both move to the front and to the back at exactly the same moment. If you change the connection wires (switch the poles) on only one of them they are 180 degrees (also called "totally") out of phase, meaning the first one would move inward while the other was moving outward. They would more or less cancel each other's sound in your room if they're out of phase (one of them tries to higher the air pressure, while at the same time the other wants to lower it). If they move to the same signal, but not even exactly equal (one going in, the other going in, then the first already going out, but the second still going in, etc.) it's also called out of phase, but now another number of degrees (not 180).
    It doesn't actually add to the quality of the woofer: it's just handy if you can influence it on the cabinet (either fully 180 degrees or else a dial for intermediate figures as well).
    (2) The turn-over frequency is the frequency (say: 100 Hz, or even better: 80 Hz), below which all sound ceases to go to your main speakers but start to go to the sub. So the sub will get less of it above the turn-over and the mains will get less of it below that.
    The best subs have turn-overs between 60 and 100 Hz, but because you'd better leave it to the receiver (decoder) to handle this, a sub without a turnover or one that can be set to "no turn-over" is generally the best.
    (3) Oh, no. Well, a few points: How low can it get. How much power can it handle. Does it "bottom out" easily. Does it distort the signal. Is it "direct" (drivers in closed boxes generally cannot go as low, but are thought to sound more "direct" or "precise", i.e. have a low "group-delay"; sorry cannot go into that now, but it's thought to be better for hi-fi music).
    (4) I'm not familiar with the American market. Someone else has to answer this.
    (5) Same answer.
    (6) Don't know. Have to look that up, but won't.
    (7) Put the sub in your main listening position. Walk around the room listening where the bass sounds greatest (also switch the phase and do it again). When (and in the phase position) it sounded best: there should be your sub!
    Hope this helped. Good luck,
    Cees
     
  5. Brian Bunge

    Brian Bunge Producer

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    John,
    Up your limit to $300 or so and you'll be cooking with gas! [​IMG]
    Brian
     
  6. Geno

    Geno Supporting Actor

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    "Phase and Crossover are interchangable terms for the same thing" -

    John, This is definatley not true. Phase has to do with the actual sin wave of the sound. It has little to do with the crossover. but yes the crossover point helps determine phasing. Long explanation, wait till I get home, but im sure someone else will beat me to it.

    ps, you forgot #8. what is your favorite color?

    edit, wow, while i was typing, three others beat me...Cees has a great explanation
     
  7. John_Berger

    John_Berger Cinematographer

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  8. Geno

    Geno Supporting Actor

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    "Oh, my. Based on all of the responses, it's obviously nohwere near as easy as building a standard speaker. This will definintely be put into the category of "challenging." "


    Id say its easier tha building mains, only one driver to mess with, only one crossover point [which might be done thru your receiver anyway].

    subs are what ppl usually start diy with
     
  9. Lew Crippen

    Lew Crippen Executive Producer

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  10. Garrett Lundy

    Garrett Lundy Producer

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  11. Joe Tilley

    Joe Tilley Supporting Actor

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    Jhon, man do I feel sorry for you[​IMG] If my wife was that tight on money I would be well beond my grave right now.
     
  12. Dustin B

    Dustin B Producer

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    Subs are way easier to design than speakers. Crossover design scares me, sub design doesn't.

    Do you have an old receiver or two channel amp you can power this thing with. If so then all you really need to buy besides the enclosure is the driver. The rest will add up, but it won't be bad. $100-$145 for the driver. Then if you need to buy an amp it will be $90-$225.
     
  13. Frank Carter

    Frank Carter Screenwriter

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    Why don't you check to see if anybody still has one of the old SVS driver that everyone was unloading for around $40. You won't stay under $100 but you can get closer.
     
  14. John_Berger

    John_Berger Cinematographer

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