davewantsmoore Posted February 12, 2020 Share Posted February 12, 2020 On 07/02/2020 at 6:37 PM, BioBrian said: Any thoughts out there? Low inductance cable is good for speakers covering any/all frequency ranges. On 07/02/2020 at 6:37 PM, BioBrian said: I might be a convert! They're really good. Link to comment Share on other sites More sharing options...
davewantsmoore Posted February 12, 2020 Share Posted February 12, 2020 On 11/02/2020 at 5:35 PM, BioBrian said: I know not everybody has faith in this "worst of all possible designs", but hey they're only subs. Are they the foundations of good sound, or the sewers? Vinyl users might know what I mean. Recordings are improving though. Hopefully, the difference between this build and a real gestation is that the fun part will happen at the end. Noting a bit of EQ won't fix 1 Link to comment Share on other sites More sharing options...
BioBrian Posted February 13, 2020 Author Share Posted February 13, 2020 11 hours ago, davewantsmoore said: Low inductance cable is good for speakers covering any/all frequency ranges. I thought it was a see-saw between inductance and capacitance. As long as the Canare quad-core passes, I'm happy. Link to comment Share on other sites More sharing options...
BioBrian Posted February 13, 2020 Author Share Posted February 13, 2020 We have closure. Last panel on today. Away with the saws and messy glue, and a guilty RIP to the 12 Chickenfeed toothbrushes who so virtuously had their lives shortened by this project. Now begins the big cleanup (still a minefield) and seal. And mount. (Rolls off the fingertips so easily). 3 Link to comment Share on other sites More sharing options...
BioBrian Posted February 13, 2020 Author Share Posted February 13, 2020 11 hours ago, davewantsmoore said: On 11/02/2020 at 5:35 PM, BioBrian said: Hopefully, the difference between this build and a real gestation is that the fun part will happen at the end. Noting a bit of EQ won't fix Couldn't agree more Link to comment Share on other sites More sharing options...
BioBrian Posted February 17, 2020 Author Share Posted February 17, 2020 Both boxes now all trimmed, ready for final sand and varnish. Don't think I'll need DuraTex after all... Worst problem has been lack of handles to move them. 110 kg each, so will be about 125 kg with paint, filter, and driver. Chain blocks have been very helpful, but hard to stop greasy chain making marks. 5 Link to comment Share on other sites More sharing options...
almikel Posted February 18, 2020 Share Posted February 18, 2020 On 17/02/2020 at 4:07 PM, BioBrian said: Worst problem has been lack of handles to move them. look after your back! As a lazy DIYer I don't get why you built such a complicated box, but I remain in awe of your workmanship! cheers, mike 1 Link to comment Share on other sites More sharing options...
BioBrian Posted February 19, 2020 Author Share Posted February 19, 2020 Yes, it's been rather tedious, using slings, ropes, chain blocks, and FEL, but much better than surgery. There is a joy in having done something big, a bit different, and to the best of one's ability. I can't find adequate words to describe it. The end result will be clear to some, I guess. And I haven't even finished yet - carefully saving all the joy for later . That is actually a lie - the denouement is a bit ruined by the frustration of the painting saga. The boxes have sort of shrunk now that they're cleaned up - they are both monocoque and framed, and have a certain bouncy, youthful manner. I had thoughts during the build about the braces being a bit light-on, potentially resonant, but now they are held on all edges by the outside skins, all is integral and working together. 2 Link to comment Share on other sites More sharing options...
BioBrian Posted February 25, 2020 Author Share Posted February 25, 2020 On 21/01/2020 at 2:32 PM, BioBrian said: On 21/01/2020 at 2:32 PM, BioBrian said: The question about stuffing in subs - this is still being asked around the forum, and is still unclear to me. With the previous build, 15" woofers in 240 litres vented, we ended up with basically none, as you considered it unnecessary, and possibly a hinderance. Yet every sub build I read about has carpet or eggshell foam or something on the walls, and various other pillows etc inside. But... Some of this would have a dual purpose, one being damping the panels. I'm working on having a very stiff box which won't need this. Fluffy stuffing alters the apparent air viscosity, makes the air behave like it's in a bigger box? My box is big enough not to need this. I can't test the impedance until all is finished, and adding stuffing will be difficult. I gather there are quite a few of you out there, following this build. Thanks for hanging in all this time; I hope it's worth it at the end. I've been told on a number of occasions "you're not very good at asking for help", and this might be an example. The quote was in a response to our good Dave, but also a question to the wider readership! Please don't be shy about adding your opinion or experience about stuffing and lining. I'm trying to learn as I go, and cannot ignore all the history of subwoofer building I come across around the traps. I lost some sleep overnight worrying about having lost the opportunity to add felt, or egg-shell foam, etc, and came to the conclusion that it might just add a bit of extra roll-off to the high frequencies in whatever LP (hi-cut) filters I end up using. I've never actually come across a sub with no damping, hence my stress. "The conversation we need to have" didn't happen - discussion here is good, but please PM if you're unsure or shy! 1 Link to comment Share on other sites More sharing options...
BioBrian Posted February 25, 2020 Author Share Posted February 25, 2020 (edited) After an unbelievably tedious amount of sanding etc (couldn't believe it, just doing the round-off of the a driver hole, the paper caught and ripped off a piece of the outer veneer, needing another glue repair and re-shape), the last section got its first coat today. The end-grain in the plywood looks much better now. Another question - how would you paint the insides of the vents black, and how would you do it - eg masking the varnished section off, and use spray can? (Maybe white is not so bad). Edited February 25, 2020 by BioBrian missing word 1 Link to comment Share on other sites More sharing options...
almikel Posted February 25, 2020 Share Posted February 25, 2020 6 hours ago, BioBrian said: I lost some sleep overnight worrying about having lost the opportunity to add felt, or egg-shell foam, etc, and came to the conclusion that it might just add a bit of extra roll-off to the high frequencies in whatever LP (hi-cut) filters I end up using. I've never actually come across a sub with no damping, hence my stress. IME ported boxes typically have very little damping, and egg shell foam will have no effect at the frequencies this box will run at. mike 1 Link to comment Share on other sites More sharing options...
BioBrian Posted February 25, 2020 Author Share Posted February 25, 2020 Thanks, Mike. It looks as though the bass acts the same in a box as in a small room - futile to try and stuff it enough to make a difference, and have no room to sit and listen. So I guess the conventional padding is mostly for box wall vibration damping, with the additional benefit of cleaning up any stray HF that gets through the filter, or might be generated by the driver suspension, etc. 1 Link to comment Share on other sites More sharing options...
almikel Posted February 27, 2020 Share Posted February 27, 2020 (edited) On 26/02/2020 at 9:47 AM, BioBrian said: It looks as though the bass acts the same in a box as in a small room just a bit different in your case because you have a tuned Helmholtz resonator as the box is ported...but it will behave like a small room in the context that the box (very small room) is too small to have modal resonances...and you want the resonances created by the port interaction with the driver/box volume (the Helmholtz resonator). A colleague who has built many ported boxes doesn't use stuffing in his ported boxes and his justification (for no stuffing) was that he didn't want anything inside the box interfering with his carefully calculated driver/box/port interaction DataBass did some measurements on stuffing/no stuffing/lining of sealed vs ported vs tapped horn https://data-bass.com/#/articles/5cace1c48c663e0004cd9ce2?_k=1csg8i I hadn't read it in a while, and it was worth another scan: "It is immediately noticeable in the before and after frequency response of the vented system that some of the larger response issues related to the enclosure resonances and port resonances were effectively damped down and heavily muted. However, the system tuning was dropped and the overall port contribution was lowered quite a bit as was total system efficiency." In the specific test DataBass did, with damping added they got a smoother result 100-300Hz - which should be above where you're using your speakers - provided you run a steep enough low pass - but the port tuning was changed significantly by adding the stuffing! DataBass's final takeout was: "In general, there will be a sweet spot for most speakers where the system's response issues are improved with a minimum of material, but further addition of material will only serve to further decrease efficiency and output. Unfortunately, finding this sweet spot probably involves trial and error testing for each speaker design." In my case: I added stuffing to my TD18 sealed boxes, as I thought there might be times I needed to run them high - my mid amp died at some stage and for a while the TD18s were working 50Hz to 1.2kHz until I got a new amp. I was amazed how clean the TD18s sounded up high crossing to my tweeters - the stuffing likely helped up that high, but would have minimal effect at 350Hz where I normally l low pass cross them I don't run any stuffing or lining in my T20 tapped horn sub, which has a 48dB/octave low pass at 50Hz, with its typical tapped horn resonance peak around 90Hz. Tapped horns are narrow band devices - they have an upper limit resonance which needs to be avoided. This is an outdoor measurement of my sub, with the plate amps' low pass filters set as high as possible (160Hz) - the peak around 90Hz is expected behaviour from tapped horns, hence I cross at 50Hz cheers Mike Edited February 27, 2020 by almikel clarification 1 Link to comment Share on other sites More sharing options...
BioBrian Posted March 1, 2020 Author Share Posted March 1, 2020 (edited) Just a quick announcement that twins were painlessly born today, to a badly-presented but relieved BioBrian and his wonderful StereoNetter cohorts. I'd really like to gratuitously thank all staff, but they'd all been given RDOs. There were some more and less (euphemism alert) moments of support from chains, and some heavy grunting and heaving, but all is well, and I counted 10 toes. So far, not quite the "wall of bass" that one might think - after checking the phase of driver, socket, and cables, I played them full-range, which I thought might be illuminating. There are no filters yet - I'm going to do external passive ones to start with - so playing some of a Prokofiev symphony through them was pretty hysterical! I'm not a fan of large drivers doing midrange anyway, but flutes in the region of their breakup spike (~1800 Hz) were definitely not pretty. A good incentive to get on with raiding the coils, caps, and resistors from my boxes of leftovers. Or, hey, they might just need breaking in... Edited March 1, 2020 by BioBrian 7 Link to comment Share on other sites More sharing options...
Sub Sonic Posted March 3, 2020 Share Posted March 3, 2020 Is it just me, or are those enclosures huuuge? Very nice work, and thanks for the thread so far. SS 1 Link to comment Share on other sites More sharing options...
BioBrian Posted March 3, 2020 Author Share Posted March 3, 2020 1 hour ago, Sub Sonic said: are those enclosures huuuge? You are right! Quite cuddly though, in their own sort of way - haven't checked out their "bouncy" qualities too much so far, more by good fortune than design. I did the first measurements today, but there's a lot to process before putting it out for comment/advice. The short story is that some stuffing might be in order. 1 Link to comment Share on other sites More sharing options...
Auracle Posted March 3, 2020 Share Posted March 3, 2020 11 hours ago, BioBrian said: The short story is that some stuffing might be in order. What makes you say that? Link to comment Share on other sites More sharing options...
BioBrian Posted March 3, 2020 Author Share Posted March 3, 2020 The impedance curve, FR curve, and "Bass Decay" all show quite a strong phenomenon at 110 Hz. Too hard to access right now over my network, but this Bass Decay pic might mean something: The mike was 1 cm from the dust cap. Program is Omnimic. To me, it indicates an organ-pipe kind of ringing (related to 1.44 m internal box length, although I can't get the maths to accurately clarify my guess - should be 119 Hz?). I'd like to see what a bit of wool does to it. Link to comment Share on other sites More sharing options...
BioBrian Posted March 3, 2020 Author Share Posted March 3, 2020 OK, here are the Omnimic FR and DATS Impedance pics: Black is nearfield driver and phase. Red is nearfield vent. Both using 0.22 Volts input, 250 ms gating. (Bit of useless gossip: I know it was nearfield, but the conventional 2.83 V produced 99 dB at driver and 111 dB at vent at 20.6 Hz. The back wall was shaking a bit). The 2 blips at 773 and 1842 Hz are of course out of band, but correspond to peaks in the driver datasheet FR, so no surprises there. The 2 minor ones at 258 and 325 Hz are currently a mystery - related to maybe distance from CONE to walls, or the vent itself?? Link to comment Share on other sites More sharing options...
Auracle Posted March 3, 2020 Share Posted March 3, 2020 wavelength = 343m/s divided by 119Hz = 2.88m. 1/2 wavelength = 1.44m. The two minor blips 258 & 325 is probably the holy bracing. This will be verified one way or the other with stuffing. Sorry gotta go. (Doing this from phone in between charters.) 1 Link to comment Share on other sites More sharing options...
BioBrian Posted March 5, 2020 Author Share Posted March 5, 2020 Tried a few variations on a stuffing theme. 2 layers of wool batting across the middle section seemed to work best. More made no difference; batts behind the driver, or in the compartment "above", didn't help anything either. The empty box Impedance shows the 110 Hz nipple; with stuffing it almost disappears (good), and a little lump around 174 Hz moved up to 235. Impedance in the vent area looks to be improved, so I might stick with this. Also, the Bass Decay shows the 110 Hz problem to have gone. I'm impressed... What's a bit more obvious here are the blips either side of 200 Hz. Maybe these would change with something behind the driver? 2 Link to comment Share on other sites More sharing options...
Sub Sonic Posted March 5, 2020 Share Posted March 5, 2020 14 hours ago, BioBrian said: Tried a few variations on a stuffing theme. 2 layers of wool batting across the middle section seemed to work best. More made no difference; batts behind the driver, or in the compartment "above", didn't help anything either. The empty box Impedance shows the 110 Hz nipple; with stuffing it almost disappears (good), and a little lump around 174 Hz moved up to 235. Impedance in the vent area looks to be improved, so I might stick with this. Also, the Bass Decay shows the 110 Hz problem to have gone. I'm impressed... What's a bit more obvious here are the blips either side of 200 Hz. Maybe these would change with something behind the driver? Would it possibly be caused by some resonance from the driver itself, or perhaps a panel? Link to comment Share on other sites More sharing options...
Auracle Posted March 6, 2020 Share Posted March 6, 2020 I recall working with a driver once that had similar bumps. Turned out that the pressed metal basket (budget version) having wide "pillars" was resonating and reflecting. 'Cured' it by covering the pillars with 3mm felt. Not sure if this would help Brian. Link to comment Share on other sites More sharing options...
Wozza_Lee Posted March 6, 2020 Share Posted March 6, 2020 That's a rather impressive change for a small amount of stuffing! Glad to see that you are still improving on your design Link to comment Share on other sites More sharing options...
Auracle Posted March 6, 2020 Share Posted March 6, 2020 Forgot to add: The stuffing has altered the major impedance peaks. You will have to change the length of the port to return to the ideal BR matched peaks. You should find that they have also lowered. 1 Link to comment Share on other sites More sharing options...
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