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Subwoofer for electrostatic speakers

Discussion in 'Archived Threads 2001-2004' started by Javier_Huerta, Jan 7, 2003.

  1. Javier_Huerta

    Javier_Huerta Supporting Actor

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    I'm having some doubts here...

    The sub I'll be designing will be used on a small room (around 15 x 12 x 10 feet). It will be paired with a couple of MartinLogan Scenarios, powered by a 125 watt per channel Adcom amp.

    The sub driver will be a Tempest.

    The MartinLogans have a woofer (they are hybrid electrostats), 8" in a sealed enclosure. I'm thinking what kind of sub would go better with them: an EBS ported enclosure, or a Q=0.577 sealed enclosure. I think the sealed enclosure will have too much roll-off in the low end, and the EBS will never sound as quick in the transients as the MartinLogans will.

    I could use an UltraCurve to automatically flatten the frequency response, though.

    Any opinions on which design would go best with the speakers?

    Thanks!!!
     
  2. ThomasW

    ThomasW Cinematographer

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    Critically damped "Q" of 0.5 will give you the tightest bass available in a 'box' sub.

    I have big electrostatic panel/planar magnetic array mains. The best match for them is either IB or dipole subs.
     
  3. Javier_Huerta

    Javier_Huerta Supporting Actor

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    Thomas, unfortunately an IB is out of the question (or maybe not, now that I think about it - I have an unused attic space that could be used for an IB. do you think it would work?).
    I'd rather use the Tempest driver, though, since I'm sure one single Tempest on an IB wouldn't simply be up to the task. There is actually a way I could end up with 4 15" subs which have a Qts of around 0.6 and 17 mm Xmax, so if I end up with them, I might build the IB.
    I do like the idea of a Q=0.5 sealed box, but I feel there is too much rollover on the low end for it to be a good idea.
    OTOH, Adire Tech support told me that the closest to a sealed box with high efficiency would actually be an Adire Alignment box! [​IMG] I'd think the EBS was closer to my design goals.
     
  4. ThomasW

    ThomasW Cinematographer

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    Javier

    Either IB or dipoles will give you bass quality that IMO is the best match for the electrostatics.

    For years I used a sealed critically damped 0.5 subs with my arrays. They sounded OK, but the IB/dipoles are in a league of their own. I don't think that 'normal' ported designs are a good match with ESL's.

    If you have a place for an IB (attics are the most popular placement), I suggest going that route. I recommend using at least 2-15"s or multiple 12"s.
     
  5. Jack Gilvey

    Jack Gilvey Producer

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    I'd try the Tempest in a dipole like Thomas mentioned first.
    Maybe leave one VC open. Just mount the driver on the biggest piece of wood you can manage. Then enjoy. Really the best bass I've heard by a large margin. Better, even, than the IB I've got in the same room since the IB, being a monopole, is still at the mercy of my room while the dipole is (for the most part) not. Someone with a more forgiving room (mine's almost a cube) will likely find less of a gulf between a dipole and the other types than I have.
     
  6. Stephen Dodds

    Stephen Dodds Second Unit

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    I used dipole subs (Celestion SL6000) with my Martin Logan CLS a few years ago. Dynamic limitations aside it was the best quality of bass (and overall sound) that I've had until my current DIY dipoles.

    Besides, the construction is so simple that if it sucks you can always just bung the drivers in a box.

    Steve
     
  7. Javier_Huerta

    Javier_Huerta Supporting Actor

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    Dipoles... I'd assume I need two Tempests two create a dipole, am I right?
    How can I build a dipole subwoofer? I'm very confused about it. Is it like an Isobarik box with the subs wired out of phase? Is it like an IB with two drivers? Can I create a dipolar driver with only one driver?
    Stephen, I am very interested in this. How can I start simulating a dipolar array? Can it be done?
    [​IMG]
     
  8. ThomasW

    ThomasW Cinematographer

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    Javier
    A dipole can be created with a single driver but the output will be quite low
    here's a link to a bunch of links about dipole sub design
     
  9. Stephen Dodds

    Stephen Dodds Second Unit

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  10. Javier_Huerta

    Javier_Huerta Supporting Actor

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    OK, I have seen the dipole designs, and I now realize why MartinLogan's best system uses 8 dual 12" dipole subwoofers (mainly, because extension suffers when using a system like this one!).

    I think a dipole is not for me... yet. Maybe I'll try to build one later.

    As for IB's, I think I found the perfect driver. The specs are:

    Qes: 0.640
    Qms: 11.470
    Qts: 0.606
    Fs: 20 Hz
    Vas: 332.60L
    Xmax: 17 mm
    VAS: 332L

    If I mount a pair of these and power them with a PE 250W amp, simulating a 1,400L enclosure (the approximate space I have in my attic - it's very small), I get a system with an FRC of 24.8 Hz, a Qtc of 0.687, an F3 of 23.6 Hz. So far, so good. But 250W send the cone excursion flying upwards. If Xmax is indeed 17 mm, it seems the system can only handle around 180W, maximum (I could wire the subs to produce an 8 ohm load, so the amp could only produce 180W, though), at peak levels of 113 dB.

    Hmm. Do you think this will be enough for a room that is about 16 x 12 x 14, completely irregular in shape? The subs are costly, around $110 each, so for the time being, I can only buy 2 of them.

    One thing I noticed is the incredibly low group delay at 20 Hz (11.6 mseconds), which is much less than half of a sealed box design.

    So, what do you think? Should I wait to be able to buy 4 subs, or will 2 suffice for a music only listening system? The numbers seem very promising.
     
  11. ThomasW

    ThomasW Cinematographer

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    Javier

    Go with the IB, but make the box a cube that can hold 4 drivers. Add the two additional drivers when the budget permits
     
  12. Stephen Dodds

    Stephen Dodds Second Unit

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    Javier,

    I got the Adire DPL12 driver for $75 each from Adire because I bought four of them. By all accounts it is also an ideal IB driver. You might want to contact them.

    Steve
     
  13. ThomasW

    ThomasW Cinematographer

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    Steve

    The current price in USD for the DLP12 is $145
     
  14. Jack Gilvey

    Jack Gilvey Producer

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  15. Stephen Dodds

    Stephen Dodds Second Unit

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    ThomasW,
    Yeah, that's the cool thing. If you buy 4 or more you get a very nice discount, ie 50% off. Or maybe they just liked me.
    [​IMG]
    Steve
     
  16. Javier_Huerta

    Javier_Huerta Supporting Actor

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    Jack, I do have one Tempest. Do you think it will be enough for an IB? Everywhere I've read it states that I should try to build an IB only if I have 2 - 4 12"-15" drivers to maximize efficiency.

    The thing is, I'm building a new house, and there's a small attic-like space on top of one of the rooms. I intended to leave it as-is, and to add maybe a bunk bed, but my fiancée insists we should close it (she fears spiders will crawl up there in no time, and she might be right). I'll take some pictures of it today and post them tomorrow, to see what you think about it.

    Thanks for all your help!!!
     
  17. Javier_Huerta

    Javier_Huerta Supporting Actor

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    Hmmm... so it's all about the VD. I'll try to find out more, since apparently Cerwin-Vega is having very hard times at the moment (distributors tell me they can't get any new products at the moment) so I can't get any of their drivers -at all (and the rest of the drivers they sell around here are all cr*p).
    [​IMG]
     

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