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About BioBrian

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  • Birthday 06/11/1954

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  1. Hi Sam, great to have you back! Yes, the DIY thing was getting a bit quiet, so I thought I'd expose myself with some public gestation. Just a pair of augmenting subs, but the thread has definitely pulled in some interesting contributions (just wait, says Sam?). I agree, the 'nasties' shown in the graphs are not important - except in that case, to ask the internal reflection question. They don't show up in 'finished' measurements, and I have noticed that placement of the mic, either right next to the dust cap, level with the baffle, at 50mm from the baffle, etc, can show (or get rid of) these extreme peaks. So they can be reflections within the cone space/surround, etc. But I do worry about what happens to all the energy delivered by the back of the cone. It's almost equal to what comes out the front, that gives us silly grins and knocks on the door. But it's stuck inside the box, with the only possible escape being by moving the cone. (Let's forget vents for now). That has to be a lot of distortion, my little brain tells me. I've been tossing around the idea of using lots of baffles with smaller-than-usual holes (an extreme would be like a silencer??), making the air have to 'work' a bit harder, and lose more energy; less large reflections from open surfaces. But I suppose that's just 'stuffing' on a larger scale. If there's any sense to this energy dissipation thing, it would apply to spherical enclosures as well, but this is why I'm here gestating. 2nd trimester is yet to begin.
  2. That's incredible, thanks Russell! What a beautiful thing. Might be a bit thin after all the smoothing, but could be lined, or at least strengthened around the driver hole. It'd be hard to bring myself to cut holes in it though. Painting would be fun. (What were the advantages of a sphere again?)
  3. According to WinISD, the "1st port resonance" is 806 Hz, so I guess not.
  4. I'm still uneasy about this. All waves reflect off a hard surface. Waves of any frequency will have about 2 ms before they crash into the cone again, off the back wall(s), however long the wave is. How can this not have an effect? I dug these up from early measurements of (here we go again) my OTHER sub boxes, which are about 750 mm deep, with a flat, unpadded wall behind the driver. Both nearfield measurement, 250 ms gating, one of driver, the other of one of the twin vents: Can you say what the nasties are at 222 Hz from both? (Not floor reflections, as mic heights were different). Is it just a coincidence that it's the same distance as a 222 Hz wavelength, driver-wall-driver? Sorry if I've asked this a million times before, but I'm not getting it yet. In such a big box, this is not out of the pass-band. There's also a slight glitch in the impedance curve about this frequency.
  5. Maybe that's why I'm interested in this topic 🙃 I would like to try it in a better box, but suspect something else is the problem. Like my amp - it seems to be suffering from 'waning powers'.
  6. A lot seem pretty unhappy with the noisy fans.
  7. This more recent recipe for "plate amp" seems quite highly regarded - have you had a look? https://www.hypex.nl/plate-amplifiers/ Personally, I think subs need to move air to be successful, and 15-18" drivers would be more suitable to get lower frequencies from. I have a 12" Peerless XLS, which is helpful in a small-medium room for HT, but it's really quite underwhelming compared with proper subs.
  8. I've just come across this, and wonder how you went. I have a similar pair (Plinius 2B and 7), and remember once seeing the woofers moving in and out an alarming amount, really slowly. I thought it must the the same speed as the TT rotation. Were you running the TT when you noticed this?
  9. Love it, thanks. I haven't kept up enough with the Munich posts, so will get onto it. I find a lot of these new arty builds would be using skills a bit out of my DIY experience. A bit further from 'au naturel', too. Not a lot of bracing in the Cabasse - could save a bit of work, haha. It brings me to the extreme of my internal reflections question - the sphere would be the worst offender for making a peak at this frequency - I wonder how this is dealt with? The Odeon Audio one is fun. It's kind of saying 'this is what you should have done to make it work'. Looks a bit unstable, whereas mine looks truly rooted 😊. Not sure that the bottom horn could be doing anything useful, but it's attractive. After 15 years of working in the Odeon Theatre in Hobart though, I'm not sure I could live comfortably with the name. (We were rehearsing the 1812 in there once, and some dudes from the army let off shotguns - it was a fairly resonant acoustic without an audience. The performance proceeded with different methodologies. Brings a new meaning to the need for 'bracing').
  10. Would anybody like to comment on any of the artworks above? Are they even legible? I'm almost ready to start sawing, so any feedback would be welcome now, rather than when it's too late. Expensive wood, and it's looking almost like boatbuilding - not such a normal box. I'll probably have to start baffle-down, and build back from there. I've shown the triangular nature of the box, as it hugs the wall and ceiling, but I forgot to say that it's 1500 mm long/wide. If stood on end, that's the same height as my DTQWT-12s, as in my pic on the left. Big. A rough calculation puts the driver cone about 300 mm from the large rear/side walls. That's half a wavelength of 554 Hz, which should be well out of range of this sub. But my question about placement of the driver toward one edge remains - would it help to not have the same reflection from both walls?? Bracing is still in the head, but I'm anticipating 4 cross-braces (about 350 mm apart), and 1 fore-and-aft, right up the middle. It'll probably need some others, to halve the longer open surfaces.
  11. The drawings are threatening Leonardo: That's where they are planned for the room. From above, the "B" distances are planned to be equal, for timing: And the boxes themselves - I have the volume worked out at around 350-360 litres, which will allow 30 litres for driver and vent volumes, plus bracing. At the moment, they look like this, but I wonder about internal reflections, and whether the drivers should be offset from the baffle centre:
  12. And not only in NZ! You really must be on the premium scale - I only get very marginally "English-speaking" people on the Internode help line. I think over-subscription and Netflix are 2 likely suspects here. But the whole thing is apparently un-knowable. Sorry, that's all a bit OT. I did manage to download those files via Russell though, thank you.
  13. I do too, but am lucky to get 10 days a fortnight with more than zero connection. But down here it's with the very inappropriately named "Fixed Wireless".
  14. Not at all, no. We have the same problem as before - these pics should be in the other (4-way) thread. It's going to look much more like the grey, black or green traces, I would think. The black is still only 12 dB/oct from 40 to 80 Hz though, even with big LCLC filter. I know it would be easier with DSP, but my way (not many others to include, alas) might give more even room response, not dropping away too fast. Will have to wait'n' see. And of course the vent output will bump up the output below 40 by a large margin.
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