New Martin Login Subwoofer -- Is 3 x 10 as good as an 18?

Discussion in 'Archived Threads 2001-2004' started by Will, Sep 29, 2001.

  1. Will

    Will Guest

    The new Martin Logan Descent, according to http://db.widescreenreview.com/weekn...d=39331&-find=
    "By operating three 10-inch drivers in parallel, the Descent benefits from aggregate low distortion and optimal control,
    achieving the effective cubic displacement of an 18-inch
    driver while maintaining the control and low distortion
    resolution of a next-generation 10-inch driver."
     
  2. Joe Cole

    Joe Cole Second Unit

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    I would guess that at least on music the answer would be yes. I have a Vel RLD THX 18" sub that is too slow for music. I never was satisfied for with it when using in for music. Even in some films it is not quick enough. It is a powerful sub. After I added 2 16-46cs subs from SVS every thing became perfect in the sub department. Since I have Marlin Logan Requests for mains I would have check this sub out, but now have no need. Any more low frequency drivers and my house would collapse.
    Now I have heard an 18" sub that was very good on music but it cost 6K.
    I am sure you know this: listen to your choices before you buy, at home if possible. [​IMG]
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    Joe C.
    quote:Who's scruffy looking?
    My biscuits are a burnin.
     
  3. Miles_W

    Miles_W Second Unit

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    I would be inclined to believe that 3 10" drivers are faster than 1 18". This reminds me of the vandersteen 2wq/w series which I believe uses 3 8" drivers to great effect... fast and very articulate. I'm not sure if they have the absolute bottom end of the big 18" woof but for speed, no contest... needless to say I will borrow one to try as soon as my local logan dealer gets it in. Joe, I'll let you know how it mates with my CLS IIz's...
    Miles
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    Miles
    ************************
    DarkSide Member since(93)
     
  4. Dustin B

    Dustin B Producer

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    You should go do a search in the DIY/Advanced section on this topic. It's a miss conception that smaller drivers are capable of producing faster bass.
    To produce the really low frequencies at any volume the cone has to displace a lot of air. To figure out how much a driver can displace you take its Sd (an accurate spec of the cones surface area) and multiply it by twice the Xmax (or in other words the peak to peak excursion limit of the driver where it isn't starting to distort). This gives the volume of a cylinder that is the sweaped volume of a full stroke of the driver. This is a measurement of how much air it can displace. So if the 10" drivers have a farily long throw and the 18inch driver has a farily short throw then yes they would be capable of equal output or greater output. Since a 10" driver would need over a 60mm p-p Xmax (I don't think any exist that can do this) to displace 2L of air and there are 18" drivers out there that can displace almost 6L with just over a 50mm p-p Xmax.
    The fast response of a sub has more to do with the motor strength of the driver and the design of the enclosure. There are a bunch of Q values that go along with the excusion limits of the driver. They dictate whether a box design with a particular driver will be underdamped, critically damped, and overdamped. I haven't quite got it through my head what overdamped is, but I think it's just means you start to eat away at the drivers efficiency. Ie it takes more power than normal to reach the drivers limits. Critically damped means your boxes Q is 0.5 and the base is as tight, or fast as you can get. Underdamped means your Q is above 0.5. Up to around 0.6 is still considered good for music (or really tight and fast). Once you get up to 0.7 and higher its still considered ok for home theater, although some would argue. And once you get up past 0.8 it just starts to sound sloppy and bad.
    Also you can think about it this way. In order to displace a lot of air that 10" driver really has to move a long way. The farther it moves the harder it is to control. While the 18" driver doesn't have to move nearly as far as the 10" driver making it easier to control. Add this to a well designed box and it becomes possible for the 18" driver to sound faster. Provided the 18" driver's motor is strong enough to stop the mass of the driver quickly. But I think that is easier to do than controling a 10" driver that is way out there excursion wise.
    The final thing I'll mention is that a 10" driver requires a much much smaller box than an 18" driver. Manufactures have to deal with shipping, so very few make the huge boxes 18" subs deserve. This makes it very hard to almost impossible to make an 18" driver sub with that critically damped Q. The only ones that do are either really big and expensive (Wilson's sub) or just plan expensive (Velodyne's top 18" subs).
    My understanding a little simplistic, but it's how I understand the topic from my readings in the advanced section and a bunch of other sites.
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    Dustin
    [email protected]
    My Adire Tempest Sonosub
     
  5. Mark Hayenga

    Mark Hayenga Supporting Actor

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    I'm one of the advanced section lurkers and an occasional poster there, and I just wanted to say Dustin pretty much nailed it. I'll elaborate a little bit more. (For any guys from the advanced section, I'm going to be glossing over *a lot*, so don't hassle me about it [​IMG])
    'Speed' of bass has absolutely nothing to do with the size of the driver producing it. It is very simply the result of the frequency response, phase response, and delay characteristics (all of which are wonderfully related - change one and you change the others) of the final subwoofer system (ie, driver + box). Even things like cone mass and driver strength don't necessarily matter, it's the implementation of the driver in the overall system that does(for example, I could take a high cone mass, weak motor driver and stick it in a sealed box, and come out with a better delay plot than a low cone mass, high motor strength driver in a ported box). It's the system that matters, NOT necessarily the driver size (or even the driver's parameters, to an extent).
    It works like this - any time you have a variation in the amplitude response of a system, there's going to be a corresponding phase shift of the output signal at those frequencies. The amount of phase shift increases with the rapidity of the amplitude variation (ie big peaks in frequency response, sharp rolloffs, etc ==> more phase shift) . If you take the negative derivative of the phase plot, you get a plot of what's called 'group delay' (typically measured in milliseconds). Since this is the derivative of the phase plot, the faster the rolloff of the subwoofer -> more phase shift introduced -> higher delay.
    So let's apply this idea to some sub designs. As most folks (should) know, sealed subs have a rolloff of 12dB/octave below their -3dB points. Vented subs have a rolloff of 24dB/octave below their -3dB points. Because the vented subs rolloff more steeply, they are going to have more delay around cutoff than the sealed design.
    This is really the only thing that can affect the 'speed' of bass from a subwoofer design point of view. Notice in that little discussion, driver size NEVER came into play. It's more the result of the electromechanical parameters of the woofer and its interaction with the box you stick it in (which determines the sub's frequency response), than anything relating to cone size.
    Now, there are some problems with using this as a determinant of bass 'speed'. The first is, that even in a high order alignment such as a ported or passive radiator enclosure, the amount of delay induced by a typical subwoofer is usually less the 50ms or so (sealed boxes sometimes swing less than 10ms depending on box Qtc and cutoff frequency). The amount of delay induced by your *room* is likely going to be in the *hundreds* of milliseconds. This totally dwarfs any problems caused by the subwoofer's delay characteristics.
    This is where the truth comes in. Driver size doesn't matter. Alignment-induced delay characteristics are only marginally important. Room positioning and room acoustics are EXTROARDINARILY IMPORTANT when dealing with subwoofers if you want tight bass. Spend weeks, months, a year even moving that sub around, finding the best spot for it, doing some acoustic treatment to the room, etc if you want the 'tightest' bass. This, along with moderate equalization of the sub with a good parametric EQ, is the key to high quality bass.
    And don't let no one bullshit ya different [​IMG]
    Mark
     
  6. Lewis Besze

    Lewis Besze Producer

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    Wow guys,I tip my hat!
    I found these posts very refreshing,compare to the usual "audiophile" bs,which most has to do with belief over facts.
    Anyhow,good show! [​IMG]
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    "You Hungarians always disagree"
    [Edited last by Lewis Besze on September 30, 2001 at 01:52 AM]
     
  7. Stephen Dodds

    Stephen Dodds Second Unit

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    The other thing to remember is that bass, especially deep bass, is by definition not fast.
    We are dealing with wavelengths in the order of many feet.
    What people confuse with 'fast' bass is in fact mid bass. The attack, for example, of a plucked bass note of 40Hz is not at 40 Hz, but more likely at 80, 160 or even higher.
    Have a listen to your sub with your mains turned off. If you can actually the attack or anything except low rumble, you have problems with your low pass.
    What people call 'slow' bass is usually boominess from resonances in the speaker, sub or room.
    Steve
    P.S. Buy an EQ
     
  8. Joe Cole

    Joe Cole Second Unit

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    Thanks guys for the info. Any one want to buy a couple of SVS subs? NOT. My vel comes in a box big enough to use as an aircraft carrier in our coming war.
    Maybe my room was to blame. But it never was good enough for music(for me). Even after treating the room. But not by much mind you. It certainly fills the room. But the SVS subs are much better sounding to me on music. [​IMG]
    Miles, let me/us know how it works with the CLIIzs. I am very interested in your opinion. [​IMG]
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    Joe C.
    Who's scruffy looking?
    [Edited last by Joe Cole on September 30, 2001 at 06:32 AM]
     

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