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Dual AE AV15-X sealed subwoofers DIY Build

Discussion in 'DIY Speaker & Subwoofer Building' started by Arendal - Russell, Sep 24, 2009.

  1. Arendal - Russell

    Arendal - Russell Well-known Member AVForums Sponsor

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    I thought I would start my own build thread, although there will be obvious similarities with at least two other adventurous (fool hardy?) builders on here....

    The plan is to build a 75L sealed subwoofer around an Acoustic Elegance AE15-X driver, that will take the place of an Ikea Lack occasional coffee table and look much the same as if it had a box built under it. The main difference will be rounded edges, a real oak veneer and solid oak legs will be used. The end result (veneer colours excepted) should look much like this:

    [​IMG]

    and here's another view:

    [​IMG]

    For those sad enough, here's the full Google Sketchup to spin to your hearts content. For those even sadder, here's proof it can be cut from one sheet of 25mm MDF.

    [​IMG]

    The whole shebang will be powered from a Behringher EP4000 PA amplifier which will deliver about 1200w into 4Ohms. The originally planned EP2500 would (according to WinISD) result in the driver reaching Xmax at 800w@10Hz. Xmech is higher still but with 1200w on tap, I will still have to keep an eye on bottoming the drivers, but based on 800w this should result in 103dB(SPL) at 20Hz, before you factor in 6-12dB of room gain. Factor in the additional 3-6dB of running two subs, destruction should only happen if I'm actually trying to kill them.

    I may yet downsize to a 65L box to give a bit more driver protection, with the added bonus that effective box size and system Q can then be adjusted by adding fibre fill - a trick that does not work in reverse with too large a box to start with.

    Just for a comparison against the predicted figures for a single AE AV15-X, the forum favourite SVS PB-13U when run in sealed mode is 'only' producing 99dB @ 20Hz and doesn't produce similar SPLs unless running the 15Hz tune, below which it rolls off twice as steeply as the proposed sealed box.

    The Behringer has been bought at £244. The six drivers (two each) got us a quantity discount and resulted in much cheaper shipping, so each driver weighs in at about £181 each which is frankly, staggering. The Govenment will of course ruin this pleasant surprise with import tax and VAT, but even still, this is good stuff.

    Any thoughts or input welcome, especially from anyone into DIY subs, speakers or furniture.:)

    18/10/09
    -----------


    Pesky Homebase.:mad:

    I got their wood cutting service to dice me up panels for the second 106L box; the first is 65L. I had a Google Sketchup of the panels to show how they were to be cut from a single sheet of MDF. All of the dimensions were displayed to make it easy. There's one row of 550mm panels and another of 514mm. Unfortunately, the second row was cut at 509mm thus leaving 5mm gaps all over the shop. Grrr!

    It's a shame, because all of the cuts are absolutely square and the rest of them millimetre perfect, so when offering up the panels to each other, the fit is extremely tight with nice clean edges. At £28 for the 18mm MDF sheet, plus 50p per cut after the first two, it's pretty good value and takes the heat off getting one of the most critical stages of construction right.

    I guess that's a trip back to HB during the week as I'm hopeful the drivers will turn up this week and would like to have both of the boxes ready for next weekend. Which reminds me; I must get the Neutrik connectors and appropriate cables sorted.

    I've decided to go speakON rather than traditional 4mm/5-way binding posts because they're a rock solid connector that cannot vibrate loose like spades or banana plugs. They're cheap too at £1.99 for the plug (4 required) and £1.74 for the chassis connector, plus gaskets at £2.90.

    I'm guessing the the de rigure Van Damme Studio Series Blue 2.5mm cable should suffice. I'm going to make a pair of 10m cables (although I'll need one of 4m and another of 7m) to future proof the cables for any other 'smart' ideas I have. Any better suggestions gratefully accepted.:)

    21/10/09
    -----------


    The drivers have arrived.:eek:

    The pictures can't convey the loveliness, or the fact that each one weighs as much as a bag of cement.

    Some teasers:

    [​IMG]
    [​IMG]
    [​IMG]
    [​IMG]

    Me? I'm unnaturally excited by metal in a way that hasn't happened since I last owned an Italian Motorbike.;)

    21/10/09
    ----------


    They are quite large. About 7" across, but heres some more [-]porn[/-] pictures to illustrate:

    [​IMG]

    [​IMG]

    For you Sir? Of course:

    [​IMG]

    [​IMG]

    Russell
     
    Last edited: May 16, 2010
  2. Arendal - Russell

    Arendal - Russell Well-known Member AVForums Sponsor

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    24/10/09
    ----------


    Spent a very productive day with Adam (AngelEyes) finally shaping up his cabinet and refining up my 106L cabinet. The point of interest raised during the day that was inspite of having panels cut to exactly the dimensions calculated by Google Sketchup, that we both found that certain panels were 2-3mm larger than they needed to be.

    For instance, my sub is 550mm across which means the internal brace should be 550mm minus 18mm x2 for it's internal dimension. The internal brace was thus cut to 514mm (confirmed by a steel ruler) and yet when offering up the panels, there was a clear overlap of 2mm.

    Luckily, the presence of a Festool track saw made it the work of moments to trim the extra couple of millimetres off, but I'm still a bit confused given that the panels were cut and latterly measured to be millimetre perfect.

    Anyhow, here's the pictures from todays work. The awesome Festool Track Saw being operated by the extraordinarily hung-over Adam:

    [​IMG]

    I promise you you WANT this £1500 tool:

    [​IMG]

    It makes cutting straight lines so easy that even idiots like us can do it. I won't explain why, just Google it. Here's me pillar drilling the small cut outs in the internal baffle. Bear in mind that the camera is cruel and adds at least four stone to anybody pictured: :rolleyes:

    [​IMG]

    Okay, maybe I meant four pounds...

    Originally posted by AngelEyes:

    These photos are a little out of sync as I was under the impression I had deleted them, anyway these are from a couple of weeks ago when we started on Russell's 'rough' box. The infamous Festool track saw, Russell's Router and in the background a biscuit jointer, yet to be used in anger.

    [​IMG]


    The woodmaster himself! We learnt a lot from this early build, mostly how not to do things but it was well worth the effort as the latest boxes really are spot on. Simple things like nailing down the baffle cut-out as well as securing the baffle itself during routing helps prevent any movement when you finally cut through the final piece.

    [​IMG]


    It was a real struggle lining the baffle and end piece up because we measured and cut them seperately. For the next ones we plan to centre drill through both pieces, so the circles will exactly line up. We even discussed gluing the two pieces before making the cuts but are not quite convinced it is necessay. You live you learn.

    The observant among you will note the proximity of a forklift truck, having moved up to 26mm MDF, this may become quite useful once my box is finished. I can't help thinking Graham could do with it more than me though.

    [​IMG]


    It was surprisingly fiddly to glue and assemble the pieces and keep everything located correctly. I am probably going to use biscuit joints to make this process much easier. It is another job but will add to the strength and make the gluing together a bit easier. I also think we learnt some lessons about the amount of glue required!

    [​IMG]


    I quite enjoyed watching this part and trying to work out how Russell got so much glue on his face, worth another shot methinks:

    [​IMG]


    Kudos to Russell for going first, someone had to do it and we both learned loads. It might seem wasteful financially to build a 'rough' test box but the lessons were invaluable and have given us greater confidence to move forward with the other boxes.

    I think we may well build several versions each to test performance as well as aesthetics. It does help having a skilled professional a few yards away who is only too happy to offer advice.

    Adam

    27/10/09
    ----------


    Response stuff as promised. The first image is the predicted response curve as modeled in Unibox which I must say, is a much nicer program to use than WinISD. Yes the roll off looks steep and from quite a high frequency, but this will be EQd to flat along with any peaks introduced by the room's contribution.

    To appreciate what this actually means as an in room response, you have to look at this graph like this. Say you want a solid 20Hz roll off (which means -3dB at 20Hz) then pick a point on the dark blue line 3dB above 20Hz and try to EQ everything to flat at that level. As the predicted output at 20Hz is a maximum of 103dB, then that means everything else is Eq'd flat to about 106dB. Effectively, even if you're boosting at 20Hz to bring the bottom end up, or cutting like hell to bring the mid bass down you are giving yourself a maximum SPL of 106dB across the range as that is the limit imposed by the driver and it's excursion at lower frequencies.

    By this graph alone this means that however you boost the bottom or cut the upper bass, you're looking at a 16dB boost at the bottom, or a 16dB cut higher up to get to flat.

    [​IMG]

    Except you're not, because that would be the response without the contribution of the room which, when EQing you can't ignore and to a greater degree, you are relying on to help you out. It's dependent on the size of room you are in, with bigger rooms helping less, but from here on I'm only relating things to my room. It also doesn't take into account the processor imposing an 80Hz roll-off (-3dB at 80Hz) which actually means that the natural response peak will be flattened as the crossover starts kicking in from about 50Hz. This means less boosting/cutting already.

    In the graph below, the test tone (Pink Noise) has been calibrated to about 75dB with EQ and so the graph below shows the un-EQd response to see what the room is actually adding. Room gain only kicks in below the lowest room mode (27Hz in my room) and adds from this point about 12dB/octave, co there is no boost at 27Hz, but 12dB extra gain at 13.5Hz. This is particularly important with a sealed sub, because they naturally roll-off at 12dB, so from just below your lowest room mode, they perform more or less flat naturally.

    And there they are; Those room modes, loud and proud and exacerbated by the sub's humped response. There are (if you look carefully) 27Hz, 32Hz and a huge second harmonic 64Hz of the 32Hz mode, the latter being particularly reinforced by the sub's mid-bass hump. I prefer the waterfall graphs, because where you see a hump extending from the back of the graph to the front, you know you are dealing with a real room resonance; These are the peaks you need to hit accurately with EQ filters of exactly the right frequency, the right cut and the right filter width (Q) to deal with them effectively.

    These are the frequencies that 'ring' and so sustain for longer in the room and it's as important to shorten the ringing, as it is to achieve a flat response. The ear is poor at discriminating a response peak from an extended ringing and so it's as important to achieve a short response as a flat response, even if that means creating a bit of a dip in the frequency response to compensate.

    [​IMG]

    So when you look at the EQ'd graph below (look at the back) you will see dips in the response that when dealing with 2D graphs you might try to avoid, but in the 3D waterfall are required in order to ensure a short response which to the ear sounds more even and altogether tighter.

    I should point out that having meant to reproduce this graph at a relative 75dB like the one above. I forgot to save that graph and so you should mentally subtract 5dB from this graph which was a resulted after some tweaking whilst listening to music to confirm results. What can I say? It was nearly 11 o'clock and the brain was fuzzy; Sorry!

    [​IMG]

    The point is, even given a relative 5dB boost, not only is it significantly flatter, but look how much shorter it is. By the front of the plot, the energy still ringing (resonating) in the room is clearly massively reduced. According to REW the RT60 (the time taken for the original signal to fade to -60dB, the limit of audibility) has been reduced from 0.58sec to a shade over 0.26sec. This is very nice, but as EQ can only be truly optimized for one listening position, it should be noted that this result probably isn't true for elsewhere in the room, although it's likely to improve to a lesser degree. A more even result for all room positions would require room treatment (diffusers and bass traps) that most people wouldn't consider visually acceptable in a living room.

    I finally had a chance to listen with music tonight and its clear that the 65L sub offers a very different type of bass to what I'm used to. With the sub's Qtc of 0.8(ish) it is extremely tight and possibly a touch more damped than I would like. Lower frequencies are extremely well differentiated in tone, but perhaps lack a touch of impact, that the higher frequencies (50Hz+) deliver like the proverbial mule kick. The double bass of Harry Connick Jnr's A Nightingale Sang On Berkerly Square was tonally very well differentiated, but lacked a little of the body/resonance and therefore weight to make it sound truly satisfying. By comparison Gwen Steffani's If I Was A Rich Girl kicked so hard it hurt and had me grinning like schoolgirl, with the right balance been the basso drops and chest thumping rhythm. If I was a pure dance/club music listener, I'd probably stop here.

    I suspect that a more even balance between the two, from experience, is probably closer to what I would be looking for to suit my taste for not only music, but movies too. Adding some stuffing to the box should help drag the Qtc down toward the more theoretical ideal of 0.707 if not all the way. The 115L box being built should not only achieve this ideal more closely, but also flatten the natural response peak, plus add a couple of dB lower down too, so comparing this, to the stuffed smaller box should be interesting.

    Looks like I'll be frequenting the haberdashers this weekend for some long fibre box stuffing.

    29/10/09
    ----------


    I decided to use the side panels to position the front sub-baffle, but experience from the 65L box showed me that it was very hard even with lots of pencil marks to reposition, glue and clamp the sub-baffle accurately. I decided to carefully remove the panels and drill a couple of 2mm pilot holes to help with positioning when clamping. Thing was, I noticed that the screws pulled up the baffles really nice and tight, so I decided to do away with clamps altogether and use a lot of screws to pull the panels together with an even pressure over the entire surface:

    [​IMG]

    Again, based on the previous box I used a very thin smear of the dreaded, but very effective Wurth saBesto to minimize excess being squeezed out all over the shop. It's hard stuff to clean off, so best to use no more than is needed. The end result after removing the tiny excess:

    [​IMG]

    The side benefit of this method is that even whilst curing, the baffle assembly is absolutely rock solid and so I could get on with fixing the side panels too it. By now, I've noticed that even if the saBesto doesn't need the reinforcement of screws, they make the job a lot easier than trying to keep panels in line as you tighten up multiple clamps. Offer the panel up, drill a 2mm pilot hole and a No6 x 1.25" screw nips it up nice and tight exactly where you want it, without the panel sliding around on the glue. Lurvely. The clamps are still used just to make sure the corners don't 'spread' whilst curing, but only two were needed rather than four:

    [​IMG]

    A lttle detail to show that the extra time spent measuring, adjusting, remaeasuring and adjusting again makes for a really tight fit when you do commit to glue and screws. Planing/sanding a little extra wood off isn't too bad, but adding/filling a panel cut even a millimetre too short is a real sod:

    [​IMG]

    A couple of pictures of the internal brace, which Adam posted pictures of me drilling on the pillar drill earlier. Already having the round-over bits for the plunge router, it was too much to resist 'airflowing' the cutouts. If nothing else, it looks lovely even if in reality it will make little, if any difference to the performance. Here's the internal brace presenting it's best side: ;)

    [​IMG]

    [​IMG]

    Running out of screws stopped play for the evening, so that's where we are for now. As I rebated the screw heads in, I realised that I will need to fill the rebate holes, plus any other dings and chunks where the edge of the MDF is less than totally clever. Does anybody have any suggestions for a top notch product for the job?
     
    Last edited: May 15, 2010
  3. Arendal - Russell

    Arendal - Russell Well-known Member AVForums Sponsor

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    31/10/09
    ----------


    Tonight, I decided to unscrew the top and bottom panels that had been effectively used as jigs whilst the side panels cured onto the baffle, so I could re-use the eight screws to glue and screw the centre brace.

    I wanted to fit the brace as it would add stability to the structure and allow me to offer up the driver and drill holes on the sub-baffle to fit it. I decided this would be easier as I could stand the box on end and still have two open sides through which I could reach to position and hold things in place whilst holding the t-nuts until they had fully bitten into the MDF.

    I may yet apply some adhesive to the the t-nuts, but they seem to have bitten tight exactly where they need to be. I used the driver (sans gasket) as a jig to drill 2mm pilot holes, then after the driver was removed I re-drilled with a 5mm bit. This is a tight fit for the 5mm bolts, but I see no reason to remove more material from the baffle than is necessary. Once drilled, I replaced the driver, pushed the bolts though (with a bit of force) and finger tightened the t-nuts as far as I could. Then, whilst gripping the t-nuts with pliers, I torqued the bolts up until the t-nut was nearly flush with the rear of the sub baffle. The t-nuts seem remarkably secure, but paranoia means I may yet apply a dab of saBesto to each anyway.

    So, Pictures. First a couple of views of the secured driver and brace from behind:

    [​IMG]

    [​IMG]

    A view of a t-nut screwed up tight with the 35mm bolt. 35mm seems about right given the 18mm of MDF, thickness of the driver basket and gasket:

    [​IMG]

    Driver porn:

    [​IMG]

    View from the front:

    [​IMG]

    And finally, a close up showing the slight extra depth allowed to recess the the driver a little deeper than the gasket. The idea is that after applying an extra millimetre ot two of veneer to the baffle, I'll use a round-over bit on the router to radius the edge to 'exactly the front edge of the gasket for a really neat finish, even if it'll make no difference what-so-ever to the sound of the sub:

    [​IMG]

    I must remind myself to let some magnets into the baffle before I veneer, so I can have invisible fixings for the grill which I've yet to figure out.

    03/11/09
    ----------


    Tonight, I spent some time playing with stuffing the 65L box and the relative quantities of it.

    I'd seen the various 'How much?/Where to buy?' threads and thought that the prices being charged for what amounted to cushion stuffing, seemed a little excessive.

    I dropped into the nearest shop I could think of to where I work (that supplied the curtain blackout cloth and black velvet for my original DIY projector screen) and they were flogging the long fibre, hollow core polyester stuffing for £2.50 for 0.25kg. That doesn't sound like much, but the bag it came in was about the size of a well plumped pillow, so I bought four.

    The theory goes that stuffing the box absorbs the rearward radiation of the driver by vibrating the threads of the stuffing, that whilst rubbing against each other dissipate the energy as heat. This tricks the driver into thinking it's housed in a larger volume of air than the one it is in. Basically, you're replacing that larger volume of air and it's greater number of molecules to absorb the energy, with a medium of greater density that is more efficient at absorbing energy and hence, 'tricking' the driver into thinking it's in a larger box and therefore giving a flatter, deeper response.

    What follows below is the measured responses generated from adding each 0.25kg bag to the box in turn and measuring the response of the sub in the near field (1cm from the centre of the cone) in order to render the room's contribution irrelevant.

    The purple line is the empty box, the blue line is with 0.5kg, the green line with 0.75kg, the yellow line is with the full 1.0kg added. I missed out the 0.25kg line as it was near im possible to spread it out thinly enough to occupy the entire box volume. It simply collapsed under it's own minimal weight into occupying about 2/3 of the box. I've never opened a speaker of any sort to see stuffing of that style, so I ignored it.

    The graphs with the axis scales exaggerated (compared to the usual 45-105dB, 15-120Hz scales) to emphasize the differences between the resultant curves:

    [​IMG]

    Now, I should explain that I've normalized the graphs to the same output at 15Hz in order to emphasize the changes, but in reality, the lines all cross at around 50Hz which is about the F3 (-3dB point of the sub's roll-off) of the sub. The reality therefore is that the peak in output above F3 is reduced, with the response below gaining a slight boost, rather than a simple flattening of the graph as it would appear. The reality is that relative to 15Hz, the sub's response is flattened by about 3dB.

    That this would happen to one degree or another, was never in doubt. After all, this is a long established principle by minds far greater than my peanut. What was interesting was to see the point at which you could stuff the box too much, or to put it another way; The fibres would become so tightly packed that they could no longer vibrate in order to dissipate energy and thus the box would start to become (effectively) smaller again.

    As can be seen above the first 0.5kg makes a huge difference, with the jump to 0.75kg making less than an additional 50% difference. This shows the tighter packing is starting to offset the desired energy absorption. Adding another 0.25kg, to total 1kg, actually makes things worse, so the line has clearly been crossed at this point.

    What does this mean? Well it means that the greatest difference is made with 0.5kg or more and above 0.75kg starts to tend toward worse. If you want a seat of the pants suggestion, then I reckon that 0.75kg may already be slightly more than optimal and that 0.65kg maybe about the mark. I may be making a bit of a leap, but dividing 0.65kg by 65L means that 100g of material per 10 litres of box volume may be a good place to start for optimal stuffing.

    I shall try and extract stuffing to measure 500g, 650g and 750g when I get the time and the quiet necessary to do it. It will also be interesting as whatever I discover will be used as the starting point for the 115L box.

    05/11/09
    ----------


    More graphs.

    This time, the graph below shows the 65L box with and without stuffing and the 115L box with and without stuffing. Any guesses which is which?

    [​IMG]

    The yellow and blue lines are the 65L box with and without stuffing in that order. The pink and purple lines are the 115L box in the same order. The stuffed 65L box was the slightly reduced 650g (10g/L as suggested earlier), whilst the stuffed 115L box used the full 1kg of stuffing I had available. All measurements are normalized to 200Hz where all versions gave the same SPL at the same input level.

    I've now realized that the yellow (65L stuffed trace) shows a bit of an unnatural lift below about 21Hz, probably because of a passing car or some such. By placing the mic 1cm from the cone to remove the room's influence, achieving 75dB involves playing at very low levels. So low, you can't actually hear most of the test tone sweep and equally inaudible background noise can therefore affect the plot in a way that it wouldn't with a normal in room, mic-in-the-hot-seat measurement. I'll be more careful in future.

    Still, there's some interesting info to be gleaned. Although none of it is exactly 'news' as it's all predicted by programs like WinISD, or my favourite Unibox, but it's nice to see it in practice.

    Stuffing clearly flattens and extends the response of both boxes, but it's effects are more marked in a smaller box. The boost at 20Hz in the larger box is about 1dB whilst the small box musters more like 1.5dB, whilst the peak is flattened by 1dB and 2dB respectively.

    The bigger box gives an increasing boost in efficiency with descending frequency. From precisely no difference at 200Hz, there is a healthy 2-3dB gain by the bottom end although the increased effectiveness of stuffing the smaller box means there's less of a difference between it and the unstuffed larger box. If I had to guess, the stuffing has given the 65L box an effective volume of closer to 90L and the 115L box an effective volume closer to 135L. That's a 30%(ish) increase against 15%(ish). I'm left wondering at what point stuffing becomes irrelevant. When Vb=Vas?

    Although the bigger box only extends about 4-5Hz deeper, once EQd in room it feels and sounds like a lot more. It doesn't sound quite as dry or overtly damped as the 65L box (although stuffing did help here) but either with or without stuffing, it simply sounds a lot deeper and a lot more powerful, without relinquishing any of the stop-on-a-sixpence control of the smaller box.

    The way bass transients appear out of nowhere is absolutely bloody awesome and as such, it delivers that "Is the sub on? Holy crap! Yes it is." moments in spades. Equally, the super clean top end I'd hoped for is as good as anything I've heard or rather, not heard, because unless there is deep bass present it simply doesn't sound like the sub is on. The crossover region really is seamless. I haven't managed to try out any serious reference level movie stuff yet, but Mrs. Williams is already "hearing noises" outside the house, so she's convinced by the low down deep ambient effects the sub is delivering, even from mundane rubbish like Eastenders.

    I see no reason not to expect the figures modeling in Unibox suggests, simply because every other box has been ticked so far. 6-7dB headroom over my Monolith at 20Hz, without the roll-off beneath is starting to become a mouthwatering prospect when I can dig out the movie demo favourites.

    The best bit? This is with only one sub. The bad bit is that I've got to build the other one yet so I'm going to have to wait a bit longer. Still, at least I can start looking at veneers and materials for the legs and table top.

    07/11/09
    ----------


    Okay. I'm sure those with a BFD can probably work it out for themselves, but for the benefit of those wondering how you make a DIY sealed sub deliver a flat response given the graphs above, here you are:

    This is the natural response of the 115L sub at it's maximum SPL of 124dB @ 68Hz:

    [​IMG]

    It looks like it's dropping off like a stone, but it's worth noting the figures involved. This is a sealed sub, so 106dB at 20Hz isn't to be shirked at, but 124dB at 50Hz and up is in all practical terms, useless. Note that the 75dB reference line is way down at the bottom of the graph. This is because I want to illustrate the maximum output after EQ. This frequency response is a result of output limited by the driver's capability within its Xmax ie, it's excursion within -10% of the motors force limits. It's mechanical limits are considerably higher, but the point of this game is low distortion bass, right?

    We need to EQ the response into something useful. A BFD has ten filters. I shall use one to approximate to the 80Hz roll-off that a receiver/processor will employ, so from here on in, remember that out of the ten filters available on a BFD, there will still be eight left, not seven. So, after the receiver/processor does it's bit, the response (the dotted line) looks like this:

    [​IMG]

    Note how the theoretical +/-3dB points have already shifted downward as the 80Hz crossover bites from about 35Hz up. This is a point worth noting because the filter employed by the receiver/processor is not a brickwall filter, but starts acting much lower than most people will suspect.

    Now, what we need to do is EQ the response flat within the maximum output (the solid purple line) so the sub delivers a flatter response. First, we need to suppress the response peak with a wide 16dB cut, which results in this:

    [​IMG]

    It's looking flatter already, but clearly were not taxing the limits at the bottom end as described by the solid purple line, so we need to boost in order to compensate for the broad cut at higher frequencies that clearly has an impact far lower down the frequency range. The result is a broad 6dB boost at 20Hz and the resulting response looks like this:

    [​IMG]

    So, because you cant exceed the low frequency capabilities of the driver alone (there's no port here) we've maintained the 106dB @ 20Hz capability, but cut the upper bass to compensate and so the maximum mid-bass output is now circa 108dB.

    Remember, the benefits of using sealed subs are not measured in pure SPLs alone. If they were, we'd all be building ported subs, but the interesting point is that the AV15-X driver in a 115L sealed box is delivering 8dB more than an SVS PB13U in sealed tune at 20Hz which is not to be sniffed at. The response bears greater comparison to a 13U in 15Hz tune, but it has a much slower roll-off than the ported box so it punches lower too.

    For those of a technical bent, here's the EQ curve relative to the 75dB reference that REW allows:

    [​IMG]

    The eagle eyed will note that it looks much like a Linkwitz Transform and indeed, were it not for the BFD's 20Hz bottom limit, it would be possible to EQ an even greater approximation.

    So basically, measure your DIY sub in the near field, use two filters to shape the response to flat and use the remaining eight to tune out any room induced effects over and above the subs response.

    15/11/09
    ----------


    Right. Tonight was the night that I finally made up cables, dragged them all under the carpet, drilled a hole in the wall, installed the EP4000 in another room where it can't be heard and took the time to EQ the subs as a a pair.

    I can assure you there was more than a bit of trepidation involved because with very little control over global phase, never mind the individual phase of each sub any massive phase cancellations would be there for ever more. That means I had my fingers crossed that not only would there be no phase cancellations between the subs, but between the subs and the speakers too. I'd noted during the ancient 'Dual Subs' thread that I needed to not only use the phase controls on the subs, but also a global phase control available on the Velodyne SMS-1 EQ that I was using at the time.

    During the time I was building these subs, the fact that I had long since flogged the SMS-1 and it's phase adjusting abilities was not lost on me. C'est la vie; This is supposed to be a no cost build funded by the things I've sold, so this was a risk to be run.

    So, the results. First the left sub:

    [​IMG]

    The usual room lumps and bumps are in evidence. Next, the right sub:

    [​IMG]

    Much the same lumps and bumps below 40Hz, but a big ole dip just above and clearly shown, above that dip and up to 80Hz the response is quite different.

    [​IMG]

    At this point, the penny dropped and I dropped my original plan. I have wired the room (and the one the amp is in) to allow the subs to run as separate stereo subs. The idea being that if you're going to run one cable, you may as well run two, thus future proofing the Blu-ray promise of 7.2 soundtracks and the ever present possibility that I get sick of this multichannel madness and regress to vanilla stereo. As such, I have cabled up for each sub to be run off and be EQ'd independently from each channel of the BFD I'm using for EQ. It is, after all, a stereo device.

    However previous experience has shown that the individual responses of two subs in the same room does not match the averaged response (that REW allows you to predict) as the combined response is not a mere average of the individual SPLs. REW cannot predict the combined response PLUS the phase cancellations which cannot be EQ'd, so as it currently stands with mono LFE and bass managed mono bass from stereo, the only sensible option is to EQ the combined response as if it were a mono sub.

    So, with that out of the way, best get the speakers involved as EQing a sub is pretty pointless unless you involve the speakers it (they) is going to combine with. The combined sub plus speaker response:

    [​IMG]

    And lo and behold, the one obvious dip is ameliorated to a large degree. It should also be noted that (and maybe I should have done a 'before' graph to illustrate the point) that in this graph I have reduced the overall level of the subs by 6dB. I had hoped for a 3dB gain by using two subs, but below 40Hz and prior to EQ, I am getting the best part of a 6dB gain.

    This is excellent because it virtually removes the need for the 20Hz boost I speculated on earlier in the thread and Nimby correctly identified as a potential factor. I was speculating based on the need to apply a Linkwitz Transform in order to flatten the sub's response based purely on near field measurements.

    The reality is has less to do with boosting the bottom end and flattening the upper bass and much more to do with simply equalizing the response in much the same way as my previous ported sub. Sure, there's less cutting low down and a fair bit more cutting of the room modes higher up, but there are no wide and deep/high boosts/cuts employed to shape the response. Result. Further more, it means no need to waste two of the available ten filters in response shaping. In the end, I only used nine anyway.

    So the combined subs plus speakers response:

    [​IMG]

    As I am now accustomed to, I've EQ'd as much for a short response as a flat response and I think I can safely say that the ringing sub 60Hz is massively reduced. Incidentally, I listen to a couple of reliable 'yard stick' music tracks to fine tune the results and hence what looks like a dip in the power response between 30 to 40Hz, is as a result of shortening the response.

    There is nothing I can do about the response above 60Hz as the speakers are contributing additional energy in this area but it's actually pretty much in line with the rest of the speakers power response above this point so it's not quite the issue that it looks to be.

    How does it sound? With more than a hint of relief, I can honestly say pant wettingly good. Not only is it delivering a seamless musical integration with the speakers I cherish above all else, but the few movie clips I've had the chance to try simply blow my wildest hopes out of the water.

    There is something staggering sudden about big sealed subs that even really good ported boxes only hint at. It's a bit like the description you give to people when they go from their fart box to their first real sub and they then wonder where the 'bass' went. Only in this case it's not distortion that's missing, it's overhang.

    Unibox (I really don't like WinISD anymore) allows you to tune your box to the drivers parametres and then allows you, if you take the time to optimize each alignment (sealed, ported, bandpass, etc) to compare the impulse response of each box. That is, how quickly the sub stops after the signal has passed and for the case of a sealed sub, it's at least twice as quick as the next best option.

    In use, the initial impression is of a much quieter sub, but when the big bass hits happen, they hit far more suddenly and then leave again even faster, which initially makes them sound a touch reduced in impact. However, sustained effects seem just as mental but have far, far more texture and a more impressive sense of grip.

    Whilst listening to Adams dual driver sub, I was put much more in mind of the Velodyne style of bass as opposed to the fatter sounding SVS bass, but in my room at least, it doesn't suffer the Velodyne limitations at the bottom end as the volume goes north. To put it another way, it sounds like I have the HUGE Velodyne that Velodyne haven't made. Effortless, very deep, clean and fast. Everything I had dared hope for and a bit more besides at the bottom end. That makes me one very happy bunny.

    I shall have to wait for the rare occurrence of the wife and son being absent and then I shall try and measure some absolute figures for the in room repsonse as regards SPL and extension at those SPLs.
     
    Last edited: May 15, 2010
  4. Arendal - Russell

    Arendal - Russell Well-known Member AVForums Sponsor

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    28/12/09
    ----------


    It was always the intention that these subs were to double as furniture, rather than just look like another piece of AV. I could just paint, or veneer the cubes as they are, but that wouldn't really cut it as far as I'm concerned. No, because of where they sit, they are going to have to look and perform like the tables they're replacing, so today I started Phase 2; That is the prettification process.

    After a bit of a hunt, I settled on some 70x70mm kiln dried French Oak, but got them to produce minimum lengths of 500mm which cost £103.50 delivered. That's £25.87/m so cock ups are not allowed.

    When it turned up, it came in lengths varying between 510 and 760mm:

    [​IMG]

    Not very convenient and never having worked hardwood before, I wasn't sure whether my 24T blade on my el-cheapo mitre saw wouldn't rip the crap out of my lovely oak. A quick test on one of the longer lengths gave a lovely clean cut, so it was the work of minutes to get all eight lengths within +/-1mm of each other:

    [​IMG]

    Next up, was to use the 6mm round-over bit on the router to round the edges and start the oak looking more like furniture. Tested the cut depth on a spare piece of leg and then did this:

    [​IMG]

    And that's where I stopped because now I have a bit of a conundrum. I had planned to 'scallop' out the back of the legs to accept each corner of the sub, leaving a 50mm bit uncut at the bottom. However, the more I think about it, the harder it looks as I can't run a cut through from one end to the other plus, it's very hard to cut straight with a circular saw on something only 70mm wide that stops you from clamping on a straight edge to saw against.

    The alternative is to cut a 50x50mm corner out of the sub and then plug the holes with the legs. Doesn't sound ideal, but as most of the joints in the entire box are only 18mm wide butt joints, nothing has really changed. The new hole/leg interface could be strengthened using some 25mm angle fillet internally and some screws recessed into the legs with the rebate plugged with some oak dowel to give it that rustic 'pegged' look.

    Any thoughts welcome.....

    30/12/09
    ----------


    I decided to get on with routing my lovely oak. First I tried a few test cuts to check things which I had no idea about such as RPM, feed speed, cut direction and pass depth. The results are being used as the wedging piece on the jig I made out of some gash MDF. Turns out not all 70mm are the same and some legs fitted a touch more snuggly than others, but dumping a handful of sawdust inbetween took up the slack. The jig and leg wedged:

    [​IMG]

    The first three passes and the eagle eyed will spot that I hadn't quite thought about what to do when reaching the line at the end. Turn off in situ, or try and withdraw the router from the cut? Hint, the former; I chose the latter:

    [​IMG]

    Plain sailing after that. Each side required 6 passes in 5 or 6mm increments in two rows on each side. 24 passes later and you're left with 13mm square to chisel out:

    [​IMG]

    The chiselling turned out to be by far and away one of the most satisfying processes, because it's the first one that doesn't involve a machine and actually allows you to feel the wood and it's grain. Mallet out the bigger chunks and use hand pressure to weadle out the details like corners and for shaving fractions of a millimetre here and there. I was dreading it, but I'm actually looking forward to the chiselling more than the, repetitive and noisy routing. The finished result:

    [​IMG]

    The first leg including building the jig, experimenting and pondering, the first leg took nearly three hours. The second took a shade under an hour even in the closing darkness.

    And now some pictures (using the redundant 65L cabinet) of the 'look' I'm trying to achieve:

    [​IMG]

    And some close ups of the fit:

    [​IMG]

    [​IMG]

    I'm pretty happy and any errors are clearly small enough to be hidden by the thickness of the veneer as Dave correctly pointed out a few posts back. About this, I am doubly happy.

    Only another 6 more to go...

    24/01/10
    ----------


    A bit more progress. I bought myself some Forstener drill bits to drill out the recess and mounting hole for the spikes in the bottom of the legs. The 30mm diametre recess was a real sod with frequent breaks required to stop the bit getting too hot and burning the wood. No pictures because I forgot.

    Using the 20mm bit, I drilled out a 3-4mm recess for the 20mm Neodymium magnets. Turned out to be a nice press fit in terms of diametre, but I needed to allow a bit of extra depth for the epoxy resin I was using to fix them. I then wiped over a bit of wood filler to account for any inaccuracies that may have been a result of the bits.

    Piccies. The frames, which I forgot to mention I made today. Opps! The grill and its magnet:

    [​IMG]

    The cabinet and magnet:

    [​IMG]

    All together:

    [​IMG]

    Grill in place. Note that I used 18mm MDF for the grills and rounded over the edges so it sits behind the cabinet legs. Once I've bought some cloth and felt for the rear of the grill (I don't want to scratch the veneer) it should look quite smart:

    [​IMG]

    31/01/10
    ----------


    Todays progress. First I finished filling and sanding the sides of the boxes so that they are ready for the veneer when it arrives. I then sprayed the driver rebate so no MDF will be visible:

    [​IMG]

    Likewise, I don't want the grill frame MDF showing through the grill cloth (when I remember to buy some) so I sprayed that too. This is after only one coat and it won't be seen anyway, so I'm not looking for an automotive standard:

    [​IMG]

    Now, the oak tops. Here they are after all of the edges have been rounded over with the router and sanded to remove any circular saw marks:

    [​IMG]

    And a bit of close up detail on a corner:

    [​IMG]

    Each one weighs in at 12kg, or to put it another way on 1.4kg less that an entire BK Gemini II.
     
    Last edited: May 15, 2010
  5. Arendal - Russell

    Arendal - Russell Well-known Member AVForums Sponsor

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    04/02/10
    ----------


    All four faces veneered and trimmed with router and I have to say, I'm quite chuffed. The only mistake was thinking a side was the back and starting there first. Thus, the least clever join is on a side, but it's not that noticeable. Piccies:

    [​IMG]

    [​IMG]

    [​IMG]

    [​IMG]

    The plan was to veneer and then trim the edges back to overlap the join between the legs and the cabinets. Having just allowed the legs to ovelay the veneer, Im not convinced I can create a neater edge and the thought of a Stanley knife slippage are too much to bear, so I'm going to leave as is. I'm also quite pleased with the driver rebate, particularly the way the black spray (with a bit of touching up from a felt tip!) gives a really nice crisp edge:

    [​IMG]

    Only one more to go.

    13/02/10
    ----------


    I'm determined that these things get finished this weekend. They're taking up too much time, so today I pressed on veneered the second box, tidied up the edges and stuck the legs on.

    Some glue detail. The idea is that the glue will fill the corner without squidging out onto the veneer:

    [​IMG]

    The clamps are only lightly tightened so as no to mark the legs and are only there to keep the legs true. Note the drivers doubling up as ballast to ensure they all glue level as well as square.

    Somebody earlier in the thread asked me to do a piccie with a CD in the frame for scale so I did it here:

    [​IMG]

    The eagle eyed will spot a finished grill in the background.

    I also bought some Sadolin Worktop Oil just to test on some offcuts of the solid oak and the veneer. I didn't mind if it darkened a little, figuring that was unavoidable anyway, but I wanted to maintain the hue of the wood. I think the Sadolin oil does that reasonably well, plus it seems to equalize the slight colour difference between the two samples and brings the grain out really nicely, so I'm not going to mess any further and just use it:

    [​IMG]

    Once the tops go on tomorrow, I'll just oil the damn lot. I can't be arsed to try decoupling the top, as the subs weigh a tonne and don't move anyway. After all, the top is a 58mm thick oak/MDF sandwich.

    14/02/10
    ----------


    The end is nigh!:eek:

    In a good way though and what follows is the final steps toward that end.

    So, today's progress was a grim determination to finish the build. After gluing the legs last night, the next step was to fix the tops, but as large lumps of wood sliding around on glue would introduce another delay (albeit, about an hour) I decided to glue 'n' screw again. Thus, I could work on the subs whilst the glue dried. Keeping the glue well inboard of the edges, I could slide the tops around on the glue until I was happy with the position and then drill four quick pilot holes for some 1 1/4" No.8 screws. The really interesting glue:

    [​IMG]
    With the legs in place, I could finish the second grill which I forgot to photograph earlier. For anybody trying similar, I stretched the fabric to the midpoint of each side and stapled. I then stretched the cloth to the four corners and stapled. This simply left stapling the intermediate points in place and trimming the excess. On the first grill, I stapled a point and then worked my way round the frame. The end result was similar, but seemed to involve a lot more arsing about so I'd recommend the technique used for the second if asked. BTW, I was going to back the grill with felt as I was worried about staples scratching the veneer, but hammering the staples with a small hammer (every workshop needs several hammers) has submerged them into the MDF below the level of the cloth, so I shall probably leave it there:

    [​IMG]
    Next, onto the oiling. Nothing more complicated than pouring some oil onto an old cloth and rubbing it in. The butchers block tops seem to drink the stuff and in non too even a fashion, compared to the legs which took a once over and seemed happy. All oak is not the same. Here's the halfway house. Note how the grain is brought out in all it's glory:

    [​IMG]
    As that is the final stage, all that is left is some gratuitous subwoofer porn.

    A nice perspective shot:

    [​IMG]
    The backs, for people who worry about such things (I do - hence the veneer that no-one will ever see):

    [​IMG]
    Driver fit and finish:

    [​IMG]
    I nearly forgot! The grills which I've yet to show. I'm really pleased with these - Jam them under the table top, let go and plop! They're in place. Nice:

    [​IMG]
    And finally an in-situ shot passed the right sub toward the left sub:

    [​IMG]
    I should at this point hand out some thanks to two co-conspirators. Even if they hadn't jumped on-board once I'd chosen these drivers, they wouldn't have rendered the project impossible, but it would certainly have been made it a lot more expensive by their absence. So thankyou for that leap of faith in trusting my judgment chaps - I could have been very wrong.

    Adam (AngleEyes), many thanks for you patience, support and 'finding' a well equipped workshop to get this underway. Dan (Moonfly), thanks for sending me free glue, magnets and gaskets - I salute you. Thanks chaps.:thumbsup:

    The End.

    What did it cost?
    ------------------


    Right, the real question is what has this all cost?

    This can be split into three parts. The build to get a pair of working subs that could accept a utilitarian paint finish and that's that; The extras to make them look like tables and finally; The tools I had to buy in order to do this. I will ignore the brilliant, but extravagant Festool Track-saw from earlier in the thread, as I have since bought a clamp on edge that with care, gets pretty much the same result from a normal circular saw.

    1. The Necessities.

    £432 - Drivers
    £244 - EP4000 amp
    £15 - Silent fan upgrade
    £54 - MDF
    £6 - Screws
    £10 - Glue. Actually free with a massive thanks to Moonfly.
    £10 - Neutrik Plugs & Sockets
    £30 - Cables
    £801. Sub Total

    2. The Special Stuff

    £115 - Solid European oak legs
    £95 - 40mm Butchers block oak worktop
    £75 - Real oak pre-glued veneer
    £12 - Magnets. Again free thanks to an overly generous Moonfly.:)
    £12 - Grill cloth.
    £309 Sub Total
    ==================
    £1110. Running Sub Total

    3. Tools I bought, but that you might have already and/or could buy cheaper if you weren't a tool fetishist like me.

    £130 - Makita 190mm Circular Saw
    £155 - Trend T5 1/4" Router and bit starter set.
    £30 - Additional Router Bits
    £27 - Really nice 1" flat wood chisel
    £12 - Quick locking guide bar
    £64 - 8x 900mm sash clamps
    £418 Sub Total
    ==============
    £1528. Grand Total

    The big surprise there is that the basic build cost less than a pair of BK Monoliths. Wow. The shock was that I'd spent a BK Monolith in tools before even starting the build and so everything I told the wife about my old Monolith paying for the Behringer amp was really a lie. An eyebrow is raised at the knowledge that the "prettification" materials nearly cost a BK XLS200.

    So I could have just gone and bought an extra two Monoliths, plus an XLS-200 and saved myself four months of labour. But then I'd have missed out on a pair of subs that knock an SVS PB13 Ultra into a cocked hat for just over half the price and impose less on the front room.

    Me like.:)
     
    Last edited: May 16, 2010
  6. micb3rd

    micb3rd Active Member

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    I am looking forward to hearing this !
     
  7. gperkins1973

    gperkins1973 Banned

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    Russel

    Is that all the PB13 produced. Very surprised at that especially as mine will be chucking out 120db without room gain.

    Good luck with your build. That 2D drawing showing the cuts, is that an add on in sketchup cos I couldn't get mine to do that.

    cheers graham
     
  8. AngelEyes

    AngelEyes Well-known Member

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    As you know and true to form I still haven't decided which route to take.:clown:

    My room is a pain so 2 subs should give me more options. I suspect I will build 3 cabinets and see which works best. One set like yours, probably at the smaller end of the scale and a single larger (130L) one similar to below, although I will probably be finishing in Walnut to match my speakers.

    [​IMG][​IMG]

    I am interested in how you will be joining the corners/legs? I am considering a few options but I think I will try cutting a rectangular section from each leg that the 'box' will sit in. This will involve some chiselling to finish off but it should fairly straightforward using a bench saw to do the main cuts.

    The reason I am favouring this approach is that if my 65L test box doesn't work then I can use the legs on the bigger box as they won't be integral to the construction. That is the idea anyway, I am pretty new to this stuff. :suicide:

    Adam
     
  9. Arendal - Russell

    Arendal - Russell Well-known Member AVForums Sponsor

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    That's exactly what I was thinking for the legs. It would also neatly side-step rough joins in the veneers, or rough cuts on the upright corners.

    As a result of chatting on the Acoustic Elegance board, I'd also changed my mind to go with front firing for two reasons:

    1. Driver sag - Big drivers don't much like hanging on the suspension as it reduces travel in the downward direction and eventually results in needing the suspension replaced. AE are certain this won't be an issue with their drivers, but why tempt fate?

    2. If the driver is on a vertical face then, given the 55x55x45cm (WxDxH) dimensions of the sub the driver can effectively be moved from against the wall to 55cm from it and 55cm up or down the room, simply by turning the sub on the spot.

    To do this I would make the legs stand out an extra 30mm on the driver face, and insert a grill fixed with magnets hidden behind the veneer.

    Russell
     
  10. Arendal - Russell

    Arendal - Russell Well-known Member AVForums Sponsor

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    So am I.

    Mic, can you post that link to that glue you mentioned. IIRC this was a glue that rather than expanding to fill gaps, it gripped and contracted to pull surfaces closer together.

    Russell
     
  11. Member 639844

    Member 639844 Former Advertiser

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    Looking good guys. Ive been pondering starting my own thread, but Ive no camera at present, couldnt be bothered to invest much time on google sketch up so Ive nothing really to put in such a thread a present.

    One thing which may interest you though Russell, Ive decided to build 2 cabinets so I can test 2 designs to hopefully find which is the best of the 2. Murphy's law will probably dictate both have pro's and con's, and I'll end up being forced between the 2 though :suicide:

    @ Angel, out of interest how did you come about the 65 litres per driver figure. Its a touch smaller than Russ and I were looking into, so are you perhaps thinking of using more wadding? I ask because I was only intending on using it to re-coup a bit of lost performance due to lost volume due to driver and brace displacement, bu it loks as if you may be taking that one a step further, I dont know?

    I have also been pondering if I should pad out the inside of the cabinet with foam to improve things a little, but remain undecided. Thoughts?
     
    Last edited by a moderator: Sep 26, 2009
  12. AngelEyes

    AngelEyes Well-known Member

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    I think winISD suggested my twin driver enclosure be 134 litres and as I am keen to keep things as small as possible the use of wadding seems ideal. What concerned me a little is when I ran simulations of EQ to boost the bottom end a little it had a dramatic effect on how easy it is to exeed the driver excursion, so I thought a slightly smaller box might protect the drivers more.

    When you introduce EQ it really becomes a balancing act with Group Delay, -3dB point and Cone Excursion. I still have a lot to learn in this area so won't be making any snap decisions.

    There are so many parameters, I will probably opt for a 'safe' design and then tweak in-room with wadding and EQ if necessary.

    Adam :)

    EDIT: The interesting thing about EQ is the effect it has on the group delay. For instance although it dramatically raises the GD at the frequency you add the boost it reduces is at lower frequencies. Maybe this is a bit of a reach but it may be possible an EQ of say +4dB at 25hz reduces the group delay in the more musical end of the spectrum? It also improves the -3dB point by 10 hz. As I said, loads to think about...
     
    Last edited: Sep 26, 2009
  13. Member 639844

    Member 639844 Former Advertiser

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    I see where you going, and I guess if your trying to keep size down then thats the route you'll be forced down.

    Ive been trying to keep things as simple as possible (despite a push pull design), so have accepted a larger box to try keep this simplicity. Ive basically pushed the box to its limit size wise to get max performance but keep within xmax. I did notice a few things, like how much you can actually reduce box size and power without dramatic performance reduction.

    Be interesting to see if your smaller box is just as good as my larger one, or perhaps better, it'll show the value of putting in a little extra effort with some in built eq.
     
    Last edited by a moderator: Sep 26, 2009
  14. micb3rd

    micb3rd Active Member

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    This is what I use.

    Polyurethane Glue

    Bear in mind it has a 1 year shelf life so does not last forever.
     
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  15. Arendal - Russell

    Arendal - Russell Well-known Member AVForums Sponsor

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    Thanks Mic. Moonfly has sent Adam and I a skeleton gun cartridge of an adhesive he uses at works and that's Polyurethane too, so we're all working along similar lines.

    I still seem to remember someone send me a link to an MDF adhesive that penetrated the hard MDF surface and then pulled the surfaces together to create an air tight seal, rather than expand to fill the gap. Mmm....I shall have to Google to make sure I didn't dream it.:confused:

    Russell
     
  16. gregmcquaid

    gregmcquaid Active Member

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    Gripfill by any chance?

    Gripfill 350ml - Screwfix.com, Where the Trade Buys

    Regards,
    Greg
     
  17. gperkins1973

    gperkins1973 Banned

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    That's what I got in the end. Gripfill.

    cheers

    Graham
     
  18. AngelEyes

    AngelEyes Well-known Member

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  19. gujuboy

    gujuboy Standard Member

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    :thumbsup:

    Keeping myself updated on this thread...
     
  20. Member 639844

    Member 639844 Former Advertiser

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    Its worth bearing in mind that I intend to use screws on my cabinets with the glue. The saBesto stuff is designed to bond surfaces and create an air tight seal, but its designed to last a very long time and resist vibration. As such it retains a certain amount of flexibility (although not obviously soft) so I'm not sure if its use is as appropriate for a non screwed cabinet.
     
  21. IronGiant

    IronGiant Moderator

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    Good point :thumbsup:

    Dave
     
  22. AngelEyes

    AngelEyes Well-known Member

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    I was thinking the same thing, it should be good for glueing the interior beading to reduce leaks though.

    Adam
     
  23. Member 639844

    Member 639844 Former Advertiser

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    I cant think of anything better to create an air tight cabinet. I would use it to seal the box inside even if you dont use it as a bonding, this stuff will hold an incredible amount of air pressure its that good. Its main use for me is to ensure ventilation systems are airtight so as not to lose pressure, and those systems can run hundreds of meters. Its even used on high pressure systems, and we use it outside as its totally weather proof.

    I would say test it though, with any 2 materials. Leave it overnight and try separate the 2 materials the day after. We use self drilling tek screws to fix ductwork together, but once this stuff goes off you dont need them and the system remains solid, so it may well work very well for a non screwed cabinet. It cures like hard tire rubber.
     
    Last edited by a moderator: Sep 30, 2009
  24. leedude03

    leedude03 Active Member

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    i use a non acidic silicon sealer like the bathroom sealant stuff to seal all the internal joints on the cabs i build, seals almost anything air tight.
    Just run a bead around all joints then drag your wet finger end over it to smooth into position, works for me,
    i do not use internal beading on the joints as i find if you have enough bracing in the correct places there is no need although it wouldnt harm in doing so.
    The glue i use on mdf is just the plain old resin w have been using it for years and had no probs, this of course would depend on how close of a fit your joints are.
    Hope this is of use.
     
  25. IronGiant

    IronGiant Moderator

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    I just used good old fashioned PVA wood glue with biscuits (and screws to hold it together while the glue dried) on my last MDF box. Makes the MDF go black for some strange reason.
    Dave
     
  26. gperkins1973

    gperkins1973 Banned

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    Dan,

    How much is the stuff your talking about and where can you buy it?

    cheers

    Graham
     
  27. AngelEyes

    AngelEyes Well-known Member

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    Anything to report Russell? ;)
     
  28. Member 639844

    Member 639844 Former Advertiser

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    Its not that cheap, PM your address and I can send a couple tudes.
     
  29. AngelEyes

    AngelEyes Well-known Member

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    Just be aware 'Bond & Seal' is minging stuff to work with, very much like oldschool mastic. Gloves and some parafin might be useful but don't use the parafin to clean the MDF unless you like stains!

    I am just about set on using biscuit joints (thanks Dave), you need to be careful that you make accurate cuts but they will make locating the various pieces much easier than glueing and screwing IMO.

    Adam
     
  30. Member 639844

    Member 639844 Former Advertiser

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    You certainly need something to protect your hands if you dont want to get them dirty, but its not that bad. Good to see you tried it then Adam :D, what do you thin of it?
     

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