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Kevin, I'm definitely looking to tune lower than that. My design goal is a freq response that's reasonably flat to the 10hz region, combined with very high SQ and output (which I haven't quantified yet, but it will probably be about 130db at the listening position). The SQ will be achieved by selecting a driver with a linear BL design like the LMS or Sicko, and not running it past the linear limits. I'll use as many drivers, amps, and as large an enclosure as needed to achieve that. The enclosure will be located behind the theater in its own room, so I've got virtually no size restrictions, even for silly numbers of drivers. I've done some modeling using the LMS-5400 which has bad issues with ported designs when modeling 1 driver enclosure sizes. The port resonances are unworkable, leaving PR as the only option. I'm guess the Sicko might have similar issues. But it appears that once you start getting into REALLY large enclosures, ~100 cu ft, using multiple drivers (8, in this case) those issues fade as you get lower tuning with shorter ports. At least if WinISD can be believed, anyway. Because of that, I was able to create an EBS model using 8 LMS-5400 drivers in 100cu ft that looks quite workable. When I scale this same model down to one driver (12.5 cu ft), the 1st port resonance comes in at an appalling 19hz, but with 8 drivers and 100cu ft, it's a very acceptable 218hz. The only parameter that looks iffy in this model is the air speed through the port, but the highest speed (68 m/s) is way down at about 9hz. However, there isn't a whole lot of signal that low, allowing leeway there. At 14hz the air speed is at an acceptable 30m/s. So, again, if WinISD is to be believed, I'm wondering if the same kind of design couldn't be applied to the Sicko to put together a monster sub. Even if it requires a PR alignment in single driver configurations, would larger designs allow lower tuned ported options? Maybe I'm totally out in left field here and just don't know it. If that's the case, I'll just build a huge IB and not worry about it. Just exploring the options here.
For your application, which doesn't seem to have a budget, just run them sealed and use a bunch of them. That gives you great low frequency extension and you can get as much output as you have space and money.
Quote from: Kevin Haskins on 29 Apr 2008, 04:41 pmFor your application, which doesn't seem to have a budget, just run them sealed and use a bunch of them. That gives you great low frequency extension and you can get as much output as you have space and money.Kevin,Since you think sealed is the better way to go, would you advocate using an LT circuit?
You are borderline nuts davepete. You are the perfect guy for the Sicko!
Ports are not going to work. They get too large, and have too many port resonance/airflow issues. PRs will work, but have limits to how much mass you can put on them. In the smaller sane sized enclosures, it becomes tough to load the PR with enough mass to tune much below the 15-16Hz range that I'm targeting for a 9-10ft^3 application. If you double the box size, you will be able to go deeper. I won't know exactly how deep until we build some PRs and see what they will take. Even then, I tend to estimate on the conservative side so that I don't have customers ripping them apart.For your application, which doesn't seem to have a budget, just run them sealed and use a bunch of them. That gives you great low frequency extension and you can get as much output as you have space and money.
Hi Kevin,Why the complex basket structure - would a cast basket not have been feasible?
pardon the thread jack . This is surely a sick project no doubt . But please check this out . A true 22 inch monster with a 900 OZ. magnet And a 6.5" voice coil setup http://www.mtx.com/caraudio/products/subwoofers/jackHammer.cfmcityjim
Kevin... do you have an estimated cost for the end user? I know you previously estimated the cost to be about $1000 for the active woofer, but since then you jumped from a standard 18" size to a much more custom 21" size. I would have to think your cost went up.
Quote from: cityjim on 29 Apr 2008, 06:31 pm pardon the thread jack . This is surely a sick project no doubt . But please check this out . A true 22 inch monster with a 900 OZ. magnet And a 6.5" voice coil setup http://www.mtx.com/caraudio/products/subwoofers/jackHammer.cfmcityjimIt isn't usable..... notice they don't list parameters. It is a competition sub for burps and that is pretty much all it's good for. I'm out to create a truly USABLE subwoofer with the inductance of a midrange driver, usable in sane sized enclosures that is as linear as anything ever made. That is the design goal... not a car audio competition product although I'm sure there will be a couple guys wanting to use it as such.
Out of curiosity, how much does it cost?
You don't need T/S parameters to get one-note bass...
