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recon440

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  1. At the moment I'm looking at a pair of Sundown U-12s for my next build and it's nice to see that they posted some DAAS32 measurements. I'm currently designing a series 6th-order and would like to have the best grasp of the driver in terms of TS parameters. Specifically, I design all BP6-series enclosures in Hornresp and I like to work out semi-inductance parameters from the impedance curve but there are some inconsistencies in this trace along with T-S parameters. This is quite critical to know this the most accurately as the impact on a BP6S is unforgiving relative to a simple reflex design. To look at a specific example, take the U-12 D4 (although the same effect manifests itself on all woofer sizes and coil configurations throughout the U-series lineup). This QTS parameters are also consistent with what Sundown publishes on their site. There are several key features below which I'm not fully understanding: 1) The impedance peak for this particular driver is asymmetric and bimodal (40Hz and ~48Hz). This is actually the first time seeing such an effect as though the woofer has two resonant modes... Is there an explanation for this? -Whether it's just down to smoothing? Not sure about this as the lower peak is too pronounced to be deemed insignificant. -Whether there is something inherent to the subwoofer design that causes this? Particularly the alarmingly high Rms value of 24.4kg/s (which effectively damps resonance outside of key nodes, like a high-Q effect). To me it sounds dubious that the subwoofer would have two resonance modes so close together. Ideally you would expect to have a symmetric singular peak and if we were to extrapolate the "ideal" peak it would probably lie ~42-43Hz, rising to an impedance of ~60-70ohms. 2) Ultimately, parameters presented from DAAS32 sweeps are typically bang-on in terms of consistency and yet here there are some strange anomalies. In terms of TS parameters, there is a strong disconnect between the Fs, VAS and MMS. The Fs cannot be 40Hz with the given VAS and MMS but much higher. I would wager to say that the MMS is realistic for a woofer of this caliber so I'm not sure about the VAS. To me, for the QES/QMS to be agreeable the VAS would have to closer to realm of 20L rather than the published 12.9. I'm wondering if the derived QTS parameters are inconsistent due to the shape of the observed impedance curve or if something else is going on. 3) I'm also questioning the very high Rms... I've generally not seen such high losses, even in ultra-low QTS, high-MMS, SPL-oriented woofers which are still typically in the realm of 10-12 kg/s. For mid-QTS, mid-MMS woofers I would expect this to be in the range of 4-7 kg/s. Is this value correct? I would appreciate any insight to try to better understand this before I decide to purchase these woofers.
  2. I was wondering if you guys could give me some ideas on what I could do to get more bass into the cabin. The equipment I'm using is quite humble. -Alpine MRD-605 amplifier (600W RMS @ 2ohms, 900W peak) -Alpine SWR-1043d (dual 4ohm coils, wired down to 2ohms) -The enclosure is 1CF net with 11" of port, tuned to 36Hz as per Alpine's spec I live in Japan and the vehicle is in question is a 1997 Toyota Chaser (think of a turbocharged RWD Camry ) Photo of the my vehicle below: With many Toyota's of that era the gasoline tank was behind the rear seats separated by a double wall of sheetmetal, which obviously doesn't fold down. I know the obvious solution to run 1kW+ power and dual 10s in a large 3-4CF box but unfortunately I need the trunk room and I don't want to compromise on weight since I occasionally would like to drift the vehicle. What I've done so far: - remove the two rear speaker cutouts as well as the factory subwoofer (2 x 6.5" holes and 1x 8" hole in the rear deck) -- this has helped out slightly (+2dB gain from 35-60Hz) - removed the rear seat (temporarily) -- this produced a 7dB gain, however I must retain the rear seats for convenience and the Japanese biannual safety inspection - the optimal position of the box, with the port and subwoofer facing outwards -- +3dB gain - the big 3, vehicle is equipped with a 115A alternator so the relatively small amp is not such a big load on the electrical system but it's nice to have done it anyway. What I'm thinking of doing and maybe you guys could give me some opinions here: - rebuild the box to 1.5CF with 16sq in. of port (tuned to 38Hz). The current box is made out of 5/8" thick MDF and the port is not following the 1:8 ratio (instead 1x11" as what Alpine recommended). I don't have port noise but do you think I would gain with a larger port? Also, would the thicker wood increase SPL? How about flaring the ends of the port? Or maybe just run a 4" aero port? - replace the woofer with a Kicker CompVX 10". I'm seeing that the Kicker has a 86dB sensitivity vs. Alpines 83dB? Opinions on this? - sound deadening the quarter panels. The quarter panels on this vehicle are paper thin. In fact there is no bracing between the inner trunk carpet and the panel. Would this increase pressure? I have a molded duck-tail spoiler on the trunk which is weighing it down but only on the edge. There is still some flex in the central part of the trunk. - I've folded down the center trunk liner (exposing the gasoline tank and bottom of the rear deck) to get direct air flow underneath. Do you think there would be merit in creating a smoothed reflector/vent underneath the rear deck to more efficiently vent the pressure into the holes above? Please excuse the subwoofer box (it doesn't leak but I was just experimenting with aluminum tape on the seams to see if it would do anything (which it didn't)). As I mentioned earlier as well I always have subwoofer facing backwards but I was hauling a few things that day so I put it upward. [see photos for what I'm getting at...]
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