Some DIY questions....

Discussion in 'DIY Speaker & Subwoofer Building' started by mr yonex, Jan 31, 2014.

  1. mr yonex

    mr yonex
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    I am due for a sub upgrade and I'm currently considering the diy route. However, I have a few questions.....

    I see most the people that have diy subs have generally gone with 15"/18" drivers in sealed enclosures. Why are you using such big drivers? Are 10" or 12" too small to be effective?

    Also, why is virtually everyone using sealed boxes? Is it due to space/swmbo restrictions? Or are ported subs not a good option for home cinema/hifi setup?

    I come from a car audio background and have designed and built a few boxes in my time, these have been both sealed and ported types. Left over from my car audio days, I have a Crystal CMP X2 15" sub and I'm considering building a box for this. The sub is a d2 configuration and I think is rated for 800wrms, which amps should I be looking at to power it?

    Ed
     
  2. scottthehat

    scottthehat
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    In my opinion bigger is better.

    Most people go for sealed as it others more upper punch and needs smaller cabinets and in my opinion I would rather have 2 sealed which others the same or more low end output as a ported box even if it does cost more it others more.


    Have you got any TS specs of the driver. Power changes when the cabinet size does.
     
  3. mr yonex

    mr yonex
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    I guess with a larger driver in a sealed box, you would get improved frequency extension without losing the punch and impact. You would require a pair to match a ported sub for output though. And this would mean 2 boxes to build, 2 drivers to buy and tons more amplifier power too. Expensive and out of budget unfortunately, though I do like the idea of having a match pair of subs and stereo bass.

    The t/s for the sub.

    Crystal Mobilesound CMPx2 15Subwoofers
    MSRP $579
    Fs
    23.5 Hz
    QMs7.33
    VAS4.2 cu ft / 119 Liters
    CMs.123 mm / N
    MMd12.7 oz / 360 Grams
    Xmax1.10 in / 28 mm
    Qes.56
    Re2.0 Ohms
    Z2.0 Ohms
    BL14.0 Telsa / M
    Pe1600 Watts
    Qts.52
    SPL92.2 dB
    Voice Coil Diameter3.0" Diameter / 76.2 mm
    Displacement.3 cu ft
    Mounting Depth7 3/8"

    I have already modelled the sub for 3cuft sealed box and a 5.5cuft ported box tuned to 26hz using BBP6. The frequency response for both look fairly decent. The sensitivity of the driver would suggest I won't need tonnes of power to get it moving, I was thinking in the region of 500wrms would suffice. I only fed it 400rms when it used to live in the car.

    I know it is capable of good sq and was branded as one of the first "SQL" subwoofers back in 03/04.

    Ed
     
  4. scottthehat

    scottthehat
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    Hi when you modeled did you keep an eye on excursion ported boxes in general need some sort of HP to protect the driver.

    Ported boxes are normally bigger to.
    I will model them later and give you my thoughts.

    What is it you looking for in this sub low end for film or best of both.
     
  5. Member 639844

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    Been a while since a ported design was attempted (I think Im the only one to have actually designed/built any, exept perhaps russells test mule), Ill be interested to see where this one goes :smashin:
     
  6. mojogoes

    mojogoes
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    I know you built / designed Andy's aka 4ccam's twin 240l ported enclosures for his fi Q18s , and the last time I was around at his gaff they shook the whole place to bits and he loves um.
     
  7. Member 639844

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    He certainly seemed to prefer the performance of the ported subs, so Im glad he likes them. They were actually designed to be run in 3 possible modes to, sealed, or one of two tune modes, do you know which tune he preferred in the end?
     
  8. mojogoes

    mojogoes
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    I've only heard them with all 4 ports open ran with the ep4000 but he did say he was going to bung all 4 ports up and try that! but as his room is near on 40' in length he's loosing punch and slam , so after some discussion he's now going to build a wall some 3/4 feet behind the mlp to bring it back and get rid of the null which if I remember correctly was something like a 25db black whole between 40/50hz................but talk about being able to go low and loud into the single digits well!!!!.........with help of course from a bfd.
     
  9. mr yonex

    mr yonex
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    I've played around with the designs the last few days. The ported design is 4.8cuft after port and driver displacement tuned to 24hz. The sealed design is 2.1cuft. The sealed design is the box the sub is currently living in The graphs show the ported design is superior in most departments. One area in which it isn't is group delay, but I guess its unavoidable in a ported design?

    Modelling a larger sealed box, (3.2cuft) shows slightly better low frequency extension but still very similar graph plots to the 2.1cuft.

    I would need a subsonic filter for the ported design, would 15-20hz be sufficient?

    I'm hoping the design is good for film and music.

    What do you guys think?
     

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  10. scottthehat

    scottthehat
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    once an hpf is in place you will need more power, what are you using to drive the sub, what are you looking for from the sub, is it something you wont to add another of looking for an all in one.

    im a person who would rather have 2x sealed to match and better a ported performance , I know it costs more but its the best of both.
     
  11. scottthehat

    scottthehat
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    with those specs, in win im getting the box size for a q of 0.7 needs to be 147l and needs 900w rms and at 20hz hits 106.771db(then add room gain)

    ported is saying 150l box tuned to 20hz with a hpf at 19hz will hit 112.8db at 20hz(and will need 1500w rms)

    both within xmax at 10hz.



    [​IMG]
     
  12. mr yonex

    mr yonex
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    Thanks for modelling my sub. I don't have a amp for it yet though I was considering something like a inuke 1000 or a 500w plate amp from bk though I could go with more power if necessary. The sub will be the only one in my system, so I want it to be a good all rounder with a flat response for best sq, but added good low end output. I doubt very much if I'm able to get hold of another one of these Crystal subs as the company went bust nearly 10 years ago. I won't be looking to a second sub to my system at this time.

    Your sealed design is over 5cuft in size! If I'm building a box that size, I may as well go ported, for better low end output.

    From my understanding of box design, tuning lower won't change a lot from my 24hz design, the response curve would be flatter and the f3 would decrease marginally but you will start to give up output in the 40-50hz range, (where most audible sub bass is).

    Tuning to 20hz would require increased port length, therefore decreasing the box size. To correct this, the box size can be increased, but modelling the box larger results in worse group delay (transient response) which could be portrayed as slower muddier bass, ie worse sq.

    If using a subsonic filter with a 18/24db slope, I'm not too worried about exceeding xmax below tuning,

    Lots of compromises in designing a ported box. All good fun though.
     

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