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Showing content with the highest reputation on 08/22/2018 in all areas

  1. 1 point
    Here on earth, and elsewhere in real life, physics do actually follow those generally accepted rules. Big objects no longer supported fall down, and in the process makes a lot of sound, and the bigger the object, the more low frequency energy it creates. Because there is gravity, and there is air. Like when this glacier brakes loose a quite significant piece of ice (see below for appropriate BEQ): This clip has decent sound, only 2 channels obviously, and it rolls of around 30hz, most likely due to the mic+recorder. A BEQ something like this restores enough to get an idea of what this was: sfm 22hz q=1.4 gain=+12dB sfm 14hz q=1.4 gain=+8dB If you expand to 5.1 you get more headroom and can retrieve even more below 10hz, by moving the low frequencies to LFE.
  2. 1 point
    Moar!!, I used measured driver specs with complex inductance parameters. I have them so those are what I use. Of course there is correlation between harmonic distortion and large spikes in response. This is a well known phenomenon affecting any speaker (vented resonances for example). In this case the 3rd harmonic isn't high enough to worry about. The second harmonic accounts for nearly all the THD 100-120Hz but it doesn't break 10% until it is producing 134-135dB at 2m outdoor ground-plane which is extremely loud. A typical low pass filter would decrease the output and power demands in that range quite a bit. I've not noticed it in use. Low pass filtering does increase delay. However with less low pass filtering slope your putting more power into the cab at higher frequencies. The same holds true at lower frequencies as well. I think the issue with many of the worst sounding bandpasses or higher order cabs is that as designed the bandwidth is extremely narrow, perhaps an octave or an octave and a half and they have ringing and other energy storage issues. You end up with what is described as the one note sound. Then you throw the filtering and other EQ on top of that and you end up with a smeared mess before you ever put them into a room, which further makes a huge mess. I've tried very hard with the Othorn and Skhorn to make subs that have an extended & smooth response over a large range and that have very well damped behavior. They are not as absolutely loud as they could be because of it. However I think the tradeoff is worth it because they sound nothing like the typical higher order cabs I've had experience with. I think a lot of others would agree. When I say "room" in this context I don't mean someone's living room. I mean everything from a church to a night club to an auditorium to a theater to a huge arena. Most of the time subs will not be operating outdoors or in a huge stadium or arena, but will be in some sort of small / medium venue. These are still rooms with boundaries. In a lot of cases the subs will be back up against a back wall or corner, under a stage, flanking the stage, part of the stage even, flown up near the ceiling, ground stacked etc. There's a lot of variation. Vents and maximizing output at the low frequency corner...If you assume that we have enough upper and middle range output and efficiency and need the most output at the tuning area and follow this thought process you will end up with direct radiating vented subs. They will always have maximal use of cabinet volume for the vented chamber and maximum vent area versus an alignment which loads the front of the drivers. It should also be simpler. Assuming you keep the cabs the same total size of course. I thought the advantages of this alignment overall outweighed the slight loss in maximum output near the tuning frequency and the extra build complexity. If you want maximum vent loading and output near tune go standard vented. ELC and is a whole other area of discussion that should probably be handled elsewhere. It's a study of how our hearing perception works not how we should be hearing things. We don't need to correct for it. 30Hz is not supposed to sound as loud as 500Hz. It's been covered in some good discussions on other forums like AVS and DIYaudio.
  3. 1 point
    I looked at the sim and it is quite close below 80Hz. This one should have less efficiency and less output above 40Hz on paper. It should have a bit more output near tuning. I'd say the original sims as being the slightly bit louder cab overall for music apps or live sound (kick drum, percussion fundamentals, most of the content being above 40Hz etc.). I've found over the years I like smoother responding wider bandwidth systems vs systems optimized for more sensitivity over a narrower band of operation. This is part of the reason I decided not to do a straight slot. I wanted extra upper bass output and extension well beyond 100Hz as part of the design goal. Often times you'll see guys using subs for 30-70Hz and another set of kick bins for 70-140Hz or whatever. Usually due to sub bins with degraded upper range behavior or just not enough output. I'm not a fan of that approach. I'd much rather have one cab that can handle everything. I think the sim you proposed would be fine. I tried to get the top end as extended as possible on this one. Another reason I didn't choose a large straight slot was to more fully enclose the drivers inside the cab. Most of the time I notice non harmonic mechanical and operational noises before HD gets to be offensive. The acoustic roll off of the slot above 100Hz should help lower HD a bit, but with the driver cone edge only 10" from the end of a large slot with line of sight to the outside world I'd expect there to be more operational noise leakage, though HR doesn't show too much of a difference. I'd like to see that tested actually. Also the drivers would be a little more susceptible to rain or a drink spill, but either arrangement is safer than a direct radiator cab! I didn't go with a push pull driver arrangement due to the minimum clearances needed for the drivers (10.5" driver depth + a large dustcap and +40mm excursion worst case scenario minus some for the baffle thicknesses and depth to the dustcap below the frame plane) and the fact that most high excursion sub drivers make quite a racket from the motor and suspension when pushed hard. Even more of a reason was the uneven loading it would present on the drivers. It would be much more involved and difficult to design the cab to evenly load the drivers with one inverted. Not impossible but it would complicate things. I'd give a rough guess that there would be about a 25-30L difference in the vented air volumes seen by the drivers. Tuning would be slightly different unless compensated for and the throat area would be a concern. I know this has been done in plenty of cabs before but I don't know if I trust it with the kinds of pressures that can be developed inside something like these. I didn't think the potential lowered even order distortion outweighed the concerns with uneven loading and possible mechanical noise from the inverted driver motor. The forces inside these can be pretty ridiculous. The force cancelling works really well on it. It's not like the drivers are 90deg rotated from each other or even 45deg. It's only a 12deg offset and it's a 250+ lb sub. In use the cab has no perceptible rocking from the driver operation. That small amount of offset from exact opposition plus the sheer size and mass just doesn't add up to any real rocking forces fore and aft. Technically I'd guess a perfect driver opposition would measure a bit lower with an accelerometer but in practice it worked like expected and it's a complete non issue. Regular old panel vibration and bracing is a much bigger concern. The Skhorn has been quite good as far as that is concerned when compared with most other large cabs, but this is always a battle on big subs with tons of output. About Edge and directivity. Keep in mind that the math is simplified and goes back to the point source mic placement method. If the radiating points are spread on one sub and focused on another you can never truly get the same mic distance from the two. In practice there is a very large area that one is trying to cover usually inside of a room with boundaries. It's complicated. One sub is more diffuse but that's not necessarily always a bad thing. Edge is a good tool but I don't get too caught up in an apparent half dB advantage here or there. Most of that directivity happens above 80Hz unless the baffle area starts getting truly large. One way I like to think about this is with 2 different philosophies. The first would be maximize the baffle area for the cabinet (think DTS-10 shape or similar) and get as much out in front of the cab with the drivers and design as possible. However at what point does this become impractical? Let's say the cab has a 60x60" baffle and is very shallow and gets some extra forward gain over a very similar design with the same driver which has a baffle of 30x30" but is much deeper. At some point you run into limitations in available depth to use and/or available baffle area. How many 60x60" baffle cabs are going to be able to be arranged? In a lot of cases not too many and eventually you just need more cabs and drivers. You could fit 4 of the 30x30 subs into the same baffle area as the 60x60 that would outperform it. The best case as far as potential output density per baffle area goes is that one entire face of the sub is radiating surface area. That's not going to be the best for directivity control though. You also end up with deeper cabs to get your cab volume. Tradeoffs. Vent area is vent area I'll give you that as an advantage for sure. This is the #1 priority I would have when redesigning the Skhorn. Mostly to work better with the lowered tunings. I try to avoid turns in vents when possible though. The reduced area of the slot for the drivers would increase air velocity over the horn expansion type though. I have some new thoughts on designing vented subs that I haven't gone to far with yet but I'll share once I think it through a bit more. Anyway that's part of the thinking behind not doing the straight slot or push pull drivers originally. It all comes down to tradeoffs and design choices. None of it is black and white it's all grey area and what makes sense for each case.
  4. 1 point
  5. 0 points
    I'm gonna break my geek out and say that they were orbiting a planet and even at that distance there is still minuscule amounts of atmospheric drag, so technically a ship without any propulsion could slow down.