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DIY Sub - Advice Needed Please....

Discussion in 'Home Cinema Building DIY' started by theritz, Jun 23, 2004.

  1. theritz

    theritz
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    Hi,

    I've got a BKElec 100W panel and 12" Speaker on their way - intending to make a Q100e/RTP12/RELinquish/Relax/etc clone (take your choice......). One small fly in the ointment, the depth of the design isn't exactly ideal for the location in my movie room, something nearer 300m would be handier. Can I maintain the other dimensions of the sub enclosure and use polyfil to make the enclosure "appear" bigger, or do I have to adjust the dimensions to maintain a 50 litre enclosure volume ? If the volume is smaller than 50l, what will the effect be ?

    Thanks in advance,


    Sean G.
     
  2. rob_w

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    If it's a sealed sub then polyfil will lower the box Q a bit. Have you modelled the driver at original volume, and newer volume. ? If it goes from say, a Q of 0.7 to 0.75 then I doubt you'd notice the difference.


    Cheers,

    Rob
     
  3. theritz

    theritz
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    Rob,

    Thanks for the response........... unfortunately your talking to someone who will have absolutely no prob constructing the box, but who is mystified by the terms (Q, Qts, Vas etc) which accompany the dark art of subwoofery. I've tried modelling it (it will be sealed) using Winisd, but as the BK site doesn't list Xmax (which I understand) I fear that I haven't all of the parameters correct. It recommends something like a 67l box when I try it.......... definitely out.

    As far as the stuffing was concerned I was operating under the impression gleaned from lots of Googling that I could get the box to appear about 25% bigger by using the correct amount. This is not a "mission critical" issue, really, but I don't want to go down this path if the result is going to sound "choked" or if it limits the low frequency performance of the sub.


    Would be grateful for any further advice.


    Sean.

    Any further
     
  4. ShinObiWAN

    ShinObiWAN
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    Hi,

    I've too recently built the q100e clone. Not bad at all for £150 worth of parts.

    Is it possible to build the box say 32cm (w) x 32cm (d) x 55cm (h) and downward fire the unit? Or you could still forward mount it near the bottom, may look a little strange though. These are external dimensions and the final internal volume will be approx 50ltr. With this sort of shape you will have something that resembles a Rel Storm.

    If I were you I wouldn't worry terribly about the volume if its 45ltr then I think you'll be fine, less and you may start to notice.
     
  5. theritz

    theritz
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    Shinobiwan,

    Thanks............. I thought about having it that shape, but I don't think the driver is suitable for down-firing ( vague recollection of Retro posting something about this in the dim distant past...). If anyone would have a look at the specs of the driver and say whether they think it would perform ok down firing I'd be interested - I tried writing a spreadsheet based on an Adire paper, but found it rather difficult as I wasn't familiar with the metrics used in the specs.

    Funny you should mention the Storm, I had one on extended loan from another member and it really rocked..... the sound stage is a bit (!) anaemic without it, now that it's returned to it's rightful home, hence the DIY route. I'm not gone mad on having that shape front-firing..... I may just end up sticking with the proven volume/shape.

    The big downside is it would mean losing my current arangement - the screen wall in my movie room is false, made with black velvet covered panels and hides variable masking for the screen, with the hcpc, amp etc and front L C R speaker all out of sight and we really like it that way. The Storm fitted out of the way behind the screenwall (just !), but there's just a little over 12" clearance which means the Q100e dimensions won't fit.

    Love your work on the sub and the vistathon speakers, btw, class workmanship....... :smashin:

    Sean G.
     
  6. IronGiant

    IronGiant
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    The specs for the BK driver don't easily fit into WinISD as they are labelled up differently. With some lateral thinking you can get most of them in, but WinISD will still suggest a bigger box. I figured that if I'm building a clone and know less about subwoofer design than REL, I'd stick with their internal dimensions (outer dimensions were adjusted for the thicker MDF I was using). So long as you stay to the same internal volume I doubt it will matter if you change the actual dimensions of your box to fit your space (within reason)

    Dave
     
  7. GaryG

    GaryG
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    Yes, up to a point.

    http://www.win.net/audtatious/audio/fiber.html


    The response will have a slight peak just before the corner frequency at which it starts to roll off, for HT use this is probably beneficial. Most people prefer the sound of a high Q sub for HT use, it has a 'punchier' sound. Also, the output below the corner frequency will be lower as the 'roll-off' is steeper. In other words, the bigger the box, the more output you will get at the lowest frequencies for a given amount of input power.


    If you feel that you need the lower Q response provided by a larger cabinet here are two possible options you can do.

    1. Use electronic equalisation

    2. Use 2 drivers and go for an isobaric design, which requires half the cabinet volume for a given Q compared to a single driver (at the expense of lower efficiency).

    If you have bought a BK amp with bass boost that will probably be sufficient.
     
  8. rob_w

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    What drive unit are you using ?

    Rob
     
  9. theritz

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    Dave,

    Thanks for that...... I think I'll have a play with the dimensions and see how close I can get.....

    Gary,

    That link was the one which prompted the idea about the filling.......

    I'm very grateful for the rest of you're reply, but must confess that most of it went gently whooshing over my head....................:blush:

    I'm assuming that this means that a smaller enclosure will mean that it won't have as good a response at the lower end of the scale as it would with an appropriately sized enclosure.

    Any view on the suitability for down-firing ??

    I'm heartened by the response and advice of the sub "regulars" - I'll reflect on this a bit longer, hoping the panel and sub might make it here by the weekend, (fingers crossed). I think I might go for the smaller enclosure (screwed together temporarily) with filling; if it doesn't perform as well as I might hope, I'll make a new enclosure - I'll be able to re-use the back, front and brace....

    Thanks again for the advice, guys.........


    Sean.
     
  10. GaryG

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    No offence, but given the low cost of that driver I wouldn't worry about down firing. It's most likely you will have moved onto bigger and better things before you will notice any sag in the cone.

    For testing the difference in cabinet volume try and get hold of a big cardboard box from a retail park (discarded appliance box) and cut a hole in it for your driver and add mass (bricks, magazines etc) to it to lower the volume to get a feeling for the difference it makes. You will need to keep the amp volume down to stop the cabinet vibrating too much but it will give you an idea of what the final cabinet will sound like.
     
  11. theritz

    theritz
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    Gary,

    Missed the question about the driver in your earlier post, soz, and no offence taken - I know it's the lower end of the foodchain, but selected on the basis that the match of components is well proven from diyérs experience here. I wouldn't have a clue about picking a driver (and there's bugger all available here - would always have to import....) and for a first try this seems like a reasonable approach.

    As for moving onwards, if this produces a decent result, I'll be keeping it, pursuing audio perfection etc is not on my upgrade path, more interested in upgrading the projector and doing some room improvements - fabric panneled walls etc.

    I might give it a go in a sealed Storm-sized enclosure firing downwards...... I can see a couple of sheets of MDF disappearing into this :D


    Thanks again


    Sean.
     
  12. theritz

    theritz
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    Rob,

    Sorry, only noticed that it was your post asking which driver - it's a BSB-12 from Bkelec, specs here - as used in the Q100e and clones mentioned above. I incorrectly thought GaryG had asked........


    Sean G.
     
  13. ShinObiWAN

    ShinObiWAN
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    Glad you've got some plans laid down now, its always a pain when your unsure how to progress to the next stage, but you sound like a man with a purpose now :thumbsup:

    If you get stuck then pop back here and I'm sure we'll all chip in with advice. Don't forget to post some pictures of your progress too!
     
  14. theritz

    theritz
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    Shin,


    "A man with a plan" - more like a man with three plans !!!!! I'll think more about it tomorrow, and I'll come back and report the results when it's built. I intend to get the parts pre-cut by my local suppliers, they're brill at cutting stuff to spec, so it'll be a bit of routing and assembly. I might run it for a few weeks in it's chosen format before finishing it - particularly like the effect you got with the black/veneered sides, but I'm inclined towards a painted finish all over - it'll be out of sight so a classy finish is not necessary.


    Thanks again,


    Sean.
     
  15. rob_w

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    I wouldn't worry too much about the smaller enclosure. Just use the polyfil.

    I've attatched a pic with the response for 40L, 50L, winisd recommended vol. 67L, and my fav. - Q=0.5 (ish)

    See how as the box gets bigger the low end comes up ? notice how it starts to roll off earlier higher up though..

    Cheers

    Rob
     

    Attached Files:

  16. theritz

    theritz
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    Rob,

    That very useful, thanks...... the difference between the 40l and 50l graphs is obvious - the roll-off point seems close enough in both cases, but the effect at 20hz is plain to see. I think that the 40l with polyfil seems like a good compromise in my situation - it's 20% less volume and going by the site quoted earlier I should be able to make that up with the appropriate amount of filling.

    Now if only BK would tell me if it's been shipped and the tracking number.......... getting a little tired of making phonecalls......... Grrr.


    Thanks again,

    Sean.
     
  17. Mat-Moo

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  18. theritz

    theritz
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    Mat,

    Thanks.......... this is the thread you're referring to about down-firing - I though I recollected Retro saying something about it.

    Speaker and panel confirmed in stock and ordered on Monday - not being shipped until today :confused: , a bit disappointed TBH, had hoped to get it together this weekend.

    Will come back once it's done - I think I'll get the MDF cut and ready for assembly this weekend in any event for fun and games during next week (hopefully).

    Sean.
     
  19. IronGiant

    IronGiant
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    Regarding the polyfill:
    "How do I use it? Per the CSR article, there are a few rules of thumb that may be followed: For enclosures that are a maximum 3cf of internal airspace, using 1.5lb of fill per cubic foot of internal airspace should net a 30% increase in box volume without any major performance issues. For larger enclosures, using 1lb of fill per cubic foot can boost the enclosure by about 25%."

    Doesn't 1.5lbs sound like rather a lot? The stuff hardly weighs anything. I just lined the walls with a single layer, should I have used a lot more?

    Dave
     
  20. theritz

    theritz
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    Ok, a quick update.............

    Sub and panel arrived yesterday, this morning I faxed a cutting list to my local wood yard and picked up the MDF for the sub (cut precisely to size, the whole lot came to €16 - less than £12)...... 400mm x 400mm x300mm internal dimensions, about 50l by my reckoning. taking account of the volume of the speaker and the amp panle it should be still well above 45l internal volume. The only cutting I had to do was the holes in the internal brace, holes in the two front pieces for the speaker and the cutout in the back piece for the amp panel.

    Assembled in a few hours (half day off for the occasion !), a mate (Vexorg) dropped by around tea-time to assist with final assemby. Packed it with polyester filling (No data on exact weight of filling - Mrs. Ritz donated an old pillow to the cause), and was careful at the back near the amp panel to staple it in such a way as to keep it well clear of the internals of the amp.

    We hooked it up quickly for a test-drive (in a rush of enthusiasm, like an idiot I connected it to the subwoofer IN, instead of the sub out, you should have seen my face as it stood there mute instead of pumping out lots of lovely bass..... :blush: :blush: ). WE quickly sorted that out that moment of madness and............................

    Well folks you can believe all you've read about this diy sub formula............... it sounds smashing - tight controlled bass (and plenty of it. I haven't even started trying to locate it well or mess with Avia tones, I just set the Low Level Gain to 12 o'clock, the frequency to LFE, and ran through ATOC (opening and Asteroid Belt), FOTR (Ring Drop - Whoa !!) and Master and Commander - Cannon Balls out of the Fog (CH. 4).

    Vex and I sat there with very silly grins all over our faces (including wondering what it would be like with two subs of this design...... OMG...)

    Later playing the Eagles Hell Freezes Over it was superb, there is no dominance in the bass, it's there (in spades if you want) but compliments the rest of the soundtrack perfectly. I know practically nothing about the esoteric side of subwoofery but I would describe this as "well integrated". I will be interested to try Avia and a sound meter on this and see what it shows up.

    To say I'm pleased would be an understatement..... I'm very well chuffed.
    The cabinet needs to have countersunk screwholes filled and some sort of finish applied (black of some description allover, it doesn't really matter, TBH, I hope to have it out of sight behind my screenwall). This was a very effective way of spending four hours, no mistake about it.

    I'd like to say thanks to the originators of this DIY project - RTP, take a bow.... and also much thanks to the members who've posted on this thread with advice and encouragement.......... I know I said this would be a one-off, but I've gotten a serious buzz out of the result and am off to have a little think about what I might concoct next.......

    :smashin:

    Sean G.
     
  21. Mat-Moo

    Mat-Moo
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    How about some pics!!
     
  22. GaryG

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    None of use believed you anyway! :D

    The 'DIY Club' will be catching the 'SVS Club' at this rate.
     
  23. ShinObiWAN

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    Congrats on the finishing and sounds like you'll be building another soon.
     
  24. theritz

    theritz
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    Thanks, guys.............


    Mat - no digicam..... and probably just as well; plain MDF with lots of countersunk screw holes isn't that attractive. Had difficulty fitting the sub in it's intended position so this evening I hope to do some surgery.... I intend to move the amp panel from the back of the sub to the side... it'll prolly be a bit messy to do but necessary to get the thing to integrate physically with my movie room.

    DIY vs. SVS..... Mmmm.... how about building this combination into a 110l cylinder (400mm diameter, about 1000mm tall ) ???............ Only joking... :D

    My room is 13' x 8', I think two of these subs in there would be overkill (yeah, I know some of you would love it.....!!)


    Sean.


    Sean G.
     
  25. GaryG

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    I have such a cylinder sitting in my loft, along with a suitable 12" driver and a suitable amp. :D

    All you need is the dosh and they're yours!




    Same size as my room, minimum requirement for me is:

    2 of these
    http://www.adireaudio.com/Files/cut sheets/Tumult Sales Brochure.pdf

    with 1 of these (K2)
    http://www.crownaudio.com/pdf/amps/136713.pdf

    and 1 of these
    http://www.marchandelec.com/wm8.html
     
  26. vexorg

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    This sub is a super piece of work, considering the woofer and amp were still in their boxes, TheRitz was covered in mdf dust with a couple of sides still to be attached to the enclosure to something the produces some lovely tight bass the wipes the smirk off a rel storm in under an hour and a half, (including the obligatory - OH Crap why is there no sound coming from it?- moment). This using super cheapo interconnects, I can see this little baby just getting better as it runs in.

    Congrats Sean, I think you should figure out how to squeeze its twin in behind your variable masking, and then onto the SVS clone project.... maybe 2 for the back of the room behind the lazy boys. I wish I had the patience and ability to make something like it... GaryG has a tasty sounding spec for a sub there!....:)

    V
     
  27. rob_w

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    Job done :smashin:

    Rob
     
  28. theritz

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    Surgery done, amp panel now located on the side of the enclosure....... and it juuuust about fits behind the screenwall - if it were 20 mm less deep it'd be perfect.

    A twin for this sub ?? becoming more attractive, but frankly, with the gain half way turned up, it moves plenty of air (with a very naff interconnect and no running-in). I'll think further on a having another though.

    Vex, thanks, it was brill to have assistance firing it up first time out. If you want a clone for the Velo, I think we could have some fun cooking something up !!! Two CHT 15s........ there's a thought........ :devil:

    I just ran the sweep on the THX optimiser through it (having enjoyed lots of air and earth moving in The Phantom Menace..... I could "feel" the Light Sabres in the air..... yum...) and I reckon there's two "valleys" in the response. Some work with a sound level meter will give me more detail, and I reckon that the room response could have a lot to do with it - too much plain plasterboard walls.

    Oh well, onwards and upwards..........


    Sean.
     
  29. GaryG

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    Not everybody's hearing is the same, however, if you're likely to use the subs for music sticking the subs behind you will make integration with the mains very difficult.



    It's not a spec, it's my sub. :)
     
  30. theritz

    theritz
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    Gary,

    I think Vex was joking about the SVS clones........ we had discussed making a "sonotube" type diy sub, but it wouldn't really fit in with my room (I think two of them would look really groovey in Vex's room - then he could get rid of the Velo "dishwasher".......... :D )

    That's a serious spec - two Tumults........ Are they in two enclosures ? what way have you got them set up ? One way or another I presume your dentist has lots of fun replacing your fillings from time to time... Is the Bassis gizmo similar to the Behringer Feedback Destroyer ? I may end up trying out that kind of equalisation........ from memory I had a "hole" in the frequency response when I had Vex's Rel Storm running in the room also.

    I swore that if I made something that made a satisfactory "thump" at the appropriate moments in movies I'd be happy.......... now you lot have me itching for more... must resist... must resist.....


    Sean.
     

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