Subwoofer Questions

Discussion in 'Computer Audio' started by Neapolitan6th, Feb 13, 2018 at 12:40 PM.

  1. Neapolitan6th

    Neapolitan6th Limp Gawd

    Messages:
    242
    Joined:
    Nov 18, 2016
    Hello all, I am a two channel user who is looking into subwoofers and I have a few general conceptual questions.

    I have a really solid pair of floorstanding speakers that extend down to 35hz. (JBL 590)

    My question is if an 8 inch driver can reach 35hz at the same spl/dB/ect. as say an 18 inch subwoofer, is there any perceptible difference in bass quality? Is a bigger driver going resonate/fill up a room more fully than a smaller woofer will with all other factors being equal?

    (I want to know if a subwoofer can feel "bigger" without actually being louder in dB)

    Thanks, I'm trying to see if a sub would be much of a value add for me. I'm more interested in music, but I plan to integrate into a home theater at some point.
     
    Last edited: Feb 13, 2018 at 12:46 PM
  2. John721

    John721 [H]ard|Gawd

    Messages:
    1,574
    Joined:
    Mar 8, 2006
    The trouble with that 35hz spec is that it doesn't mention a +/- db value. Which means a person should be at least mildly skeptical of it, despite the dual 8" drivers. Moving on from that though, I do think a good ported sub that can hit down to 20hz with proven authority would add to your listening experience. My older B&W 600 series with three 7" drivers definitely benefit from my SVS subwoofer - especially in movies and some kinds of music.
     
    Neapolitan6th likes this.
  3. rive22

    rive22 [H]ardness Supreme

    Messages:
    4,532
    Joined:
    Mar 10, 2004
    The smaller driver in the right enclosure can hit low notes just fine, but no it won't sound the same as an 18" at all, nor will it play those notes as loud. Yes the bigger driver will resonate and fill up the room much more fully and let you play it substantially louder before distortion. Basically if you're in a living environment where other people are in the same building like an apartment/condo then get the 8" and even that will get you in trouble. If it's a house get bigger for sure and even consider dual. What size room is this for? Is this for music or movies? What genre of music? Keep in mind 18's are hardcore, common in dance clubs and used with professional soundproofing, albeit lots of them. Dual 12" or Dual 15" in a typical house living room is nice, depending on what you're going for.
     
    Last edited: Feb 13, 2018 at 8:16 PM
    Betaboy1983 likes this.
  4. Neapolitan6th

    Neapolitan6th Limp Gawd

    Messages:
    242
    Joined:
    Nov 18, 2016
    Thanks for the input. This is more of a theoretical question really.

    I suppose I'll put it this way. I am cautious of my hearing as it is important for my career.

    I'm not wanting to increase volume to high values as my space isn't huge and I want to mitigate the risk of hearing damage.

    So I am curious of the importance of a larger diaphragm subwoofer if I have dB limitations.

    Given my constraints of room space and dB levels, lets for the sake of discussion assume a 12 inch and an 8 inch subwoofer are capable of producing an equal level of decibels at 30hz.

    With those factors being equal, what variable accounts for the difference in perceived sound favoring the larger subwoofer?

    I'm curious about the science of it. The wavelengths must be the same if they are both producing 30hz at the same volume, no?

    I wish to quantify the difference, but I'm not sure what that would be.

    I suppose I will just have to audition one and hear the difference for myself. Quality bass is important to me so I would like to gain a better understanding of it so that it will allow me to make a more informed purchasing decision at some later date.
     
  5. B00nie

    B00nie [H]ardness Supreme

    Messages:
    6,518
    Joined:
    Nov 1, 2012
    The answer is a solid yes. A large driver moves air much more efficiently. Think of trying to peddle your boat with a pencil vs a paddle. The difference is present especially in the dynamics. A small driver can't 'grab' the air as well as a large one. That's why bigger is (once again) better. You don't have to play any louder to hear the difference.

    There is one caveat though. It's not enough to have a large driver but also the driver must have an engine strong enough to actually move that 18-32" cone - and it needs to be in an enclosure suitable for the driver.

    A superb solution would be a hole in your wall and stick a 18" Dayton audio ultimax through the wall. Cheap and you get bass extention close to 10hz.

    Edit: And your wife or mom will absolutely LOVE the idea. lol.
     
    Last edited: Feb 14, 2018 at 6:25 AM
    Neapolitan6th likes this.
  6. Pandur

    Pandur Limp Gawd

    Messages:
    307
    Joined:
    Apr 4, 2000
    30Hz is a 30Hz sine wave no matter what size the speaker is. So yeah they have to produce the same wavelength. And the 8" will have to work harder to do so than the 12". But there are plenty of 8" subs on the market that will do 30Hz. Personally I'd lean towards something in the 12" range because your main speakers already claim to do 35Hz and you want something to fill out below those properly.

    There are many variables to this though. Magnet size, how far the stroke of the membrane is, membrane material, electronics quality: both crossover filters and amplifier. Type of enclosure: with or without a bass port. So bearing this in mind, a well designed 8" sub can outperform a 12" sub. But that also means you are likely looking at a higher price tag as well. Because the basic physics of this is in favour of a larger speaker.
     
    Neapolitan6th likes this.
  7. SineDave

    SineDave Limp Gawd

    Messages:
    223
    Joined:
    Jun 9, 2004
    The real reason most subwoofers use larger drivers is that it's more efficient, which means lower distortion. When you produce 35hz with an 8" driver, you have to get the driver a lot closer to xmax (limit of excursion before sound degrades), which distorts the sound somewhat. Larger drivers driven by larger amps will have more headroom, less required excursion and lower distortion, which you will hear as "cleaner" or "tighter" bass.
     
    Last edited: Feb 18, 2018 at 10:36 AM
    HammerSandwich and Neapolitan6th like this.
  8. Neapolitan6th

    Neapolitan6th Limp Gawd

    Messages:
    242
    Joined:
    Nov 18, 2016
    Thanks you guys, some really quality responses here. It gives me a lot to think about and has helped point me toward areas of research that will help me better understand what solution will best meet my preference.

    I've been a bit wooed by what I've heard of Rythmik followed by SVS. I have heard of Dayton and a few others as well. Always open to new suggestions.

    Thanks b00nie, Pandur, and SineDave!
     
  9. B00nie

    B00nie [H]ardness Supreme

    Messages:
    6,518
    Joined:
    Nov 1, 2012
    Xmax is not the mechanical limit, Xmech is. Xmax is the air gap minus the height of the voice coil (i.e. the length the voice coil can travel without leaving the magnetic field in the air gap). Most drivers can handle way larger excursion mechanically but the distortion and compression rises rapidly.

    For example the 18Sound 21" 1400LW has an Xmax of around 18mm but an Xmech of 57mm. So you can really punish it without the danger of bottoming the voice coil.
     
  10. Commander Shepard

    Commander Shepard Proud Brony

    Messages:
    2,331
    Joined:
    Apr 12, 2016
    I'm a big fan of SVS subs. Have an SB-2000 on my PC audio system. Love it!
     
  11. Stoly

    Stoly [H]ardness Supreme

    Messages:
    5,447
    Joined:
    Jul 26, 2005
    While its basically true that a 12" subwoofer will deliver a deeper and louder bass than an 8" driver, it is possible for a properly designed and placed 8" driver to deliver good bass that rivals a subwoofer.

    That said, its will certainly cost a lot more. So you are better off just getting a 12" subwoofer.
     
  12. HammerSandwich

    HammerSandwich Gawd

    Messages:
    1,020
    Joined:
    Nov 18, 2004
    The Daytons offer crazy value with free shipping from Parts Express. Hsu is another good company to look into.

    And I believe you'll learn a lot by comparing various subs at Data-Bass.
     
    Neapolitan6th likes this.
  13. HammerSandwich

    HammerSandwich Gawd

    Messages:
    1,020
    Joined:
    Nov 18, 2004
    Oops - forgot to add:
    It's specced at -6dB. This is JBL, so you have to ignore the normal, "consumer" site & dig better info from either jblpro.com or jblsynthesis.com. They still don't have spinorama charts for all of their products, though...
     
  14. DoubleTap

    DoubleTap [H]ard|Gawd

    Messages:
    1,594
    Joined:
    Dec 16, 2010
    I have an M&K 12" sub that goes down to about 24hz (I tested it with tones) and an 8" that starts dropping way off around 32hz

    I'd prefer to use the 12" sub, but it was just too much for my 10x10.5' office and even at a very reasonable volume, it was almost giving me a headache and making me feel.... not good. (and I like loud music and bass)

    I'm not an expert, but I do read and try to understand room acoustics, but I can't explain this one - I ended up putting it in the living room and using the 8" sub in my office (the only place I listen to music)

    So that's just anecdotal and some might poo-poo it but the level of compression was just physically uncomfortable YMMV.
     
    Neapolitan6th likes this.
  15. HammerSandwich

    HammerSandwich Gawd

    Messages:
    1,020
    Joined:
    Nov 18, 2004
    Rooms increase deep bass. When a wavelength's longer than 2x the room's longest dimension, the entire room will pressurize or rarefy right with driver movement. There are no modes, and bass boosts at 12dB/octave as Hz drops. (This is why you shouldn't use an anechoically flat sub in a car, at least with the windows rolled up.)

    So, smaller rooms boost from higher frequencies than larger rooms. And because the boost keeps growing, small rooms REALLY boost deep bass. In reality, you won't have that much boost, because your room leaks a bit. Put your subwoofer in, say, a small submarine, and theory should match closely. (I wonder if anyone's ever tried that one!)

    The typical speed of sound is about 1130fps, which means your room becomes a pressure vessel below 53Hz or so. Unless you have a very odd ceiling height, of course.
     
    Last edited: Feb 15, 2018 at 5:26 PM
    B00nie likes this.
  16. John721

    John721 [H]ard|Gawd

    Messages:
    1,574
    Joined:
    Mar 8, 2006
    Neat. Handy little resource there.
     
  17. B00nie

    B00nie [H]ardness Supreme

    Messages:
    6,518
    Joined:
    Nov 1, 2012
    Most likely you had a nasty reverberation in the room (bass notes stay 'alive' and bounce around). This makes it extremely uncomfortable. The solution is (reason defyingly enough) to add one or two more subwoofers on other walls or apply a good amount of acoustic treatment.

    The extra subwoofers help because the sound waves coming from multiple subs cancel eachothers out and act like a powerful acoustic treatment. You can simulate how it works using Room Eq Wizard.
     
  18. DoubleTap

    DoubleTap [H]ard|Gawd

    Messages:
    1,594
    Joined:
    Dec 16, 2010
    Yeah, that's possible, but I managed to find a good spot for my 8" that reduces the 42hz null by a decent amount and it sounds good. I might make another run at the 12 as I'm going to go with all new living room HT gear in the next few weeks and my wife keeps making the stink eye at the giant black cube...
     
  19. HammerSandwich

    HammerSandwich Gawd

    Messages:
    1,020
    Joined:
    Nov 18, 2004
    Paint it white.
     
  20. Wyodiver

    Wyodiver [H]ard|Gawd

    Messages:
    1,404
    Joined:
    Aug 15, 2004
    If the local urban crowd aren't impressed, den you doin' it wrongly. Even on yo' birf' day, ya gots'ta represent, no whut I sayin'?
     
  21. SineDave

    SineDave Limp Gawd

    Messages:
    223
    Joined:
    Jun 9, 2004
    Yes, good catch. That's what I get for trying to dumb it down :D

    I think the point in either case is that you don't want to use tiny drivers that have to come close to xmax to achieve reasonable output at lower frequencies. That also doesn't address the issue of power - so many cheap subwoofers are criminally underpowered. It takes roughly double the power for every 3dB of output you wish to add. Then you account for the fact that most subs roll off around 30 Hz, so if you want to play clean down to 20 or the teens, you need thousands of watts instead of hundreds.
     
  22. B00nie

    B00nie [H]ardness Supreme

    Messages:
    6,518
    Joined:
    Nov 1, 2012
    The old saying there's no replacement for displacement is valid also with subs. You can go only so far with a small driver. Even if you have an insane amp to run it, the drive will die either to heat or overexcursion and still do a poor job before it dies. A small piston is ineffective in pumping air and that's basically all what a bass driver does.

    Of course a good quality bass is possible also from a 8" driver, especially if it's servo driven. You just won't get a whole lot of it.