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Best chassis for G-Sub with 28-80 Hz ?

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ElsaEcomo View Drop Down
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    Posted: 03 April 2017 at 6:52pm
Hello everyone,
since I am new here - first let me give you a big thanks for all the helpful plans and discussions in this community. I have been reading here especially about the g-sub and also the 184 sub. I guess for most people here its more about professional usage - in my case I am interested in building one or two subs which can deliver bass for music inside and outside - and home cinema inside. So this is only for private usage and about making a compromise - since from what I understand, people would rather build something like an infra sub especially for cinema content.

I dont want more than two subwoofers, and maybe the g-sub is a solution. Is there a suitable driver to make it theoretically possible to achieve -3dB to -6dB around 28Hz?

I simulated with WinISD 0.44 , tuning for 33Hz and (if correct) 333 liters for volume. And it was close but maybe you know a more suiteable driver Smile?
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Post Options Post Options   Thanks (0) Thanks(0)   Quote mobiele eenheid Quote  Post ReplyReply Direct Link To This Post Posted: 03 April 2017 at 7:49pm
IIRC the G-sub is more or less tuned to 40 Hz. Without altering the port (making it longer) there's no way a driver will go as low as you'd like. From the designs on here the X1 would be much more suited.
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ElsaEcomo View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote ElsaEcomo Quote  Post ReplyReply Direct Link To This Post Posted: 03 April 2017 at 8:17pm
I would like to avoid band-pass enclosures, since I have been told, that band-pass systems tend to deliver somewhat unprecise bass. Also I think I may need less skills to be able to build e.g. a g-sub compared to the X1.

So I looked into what you just said. I fired up WinISD 0.44. Put in the data of the RCF L18P300. Since its the second recommendation and the "old" pd186 is not produced anymore.

If I didnt fail calculating the volume, the gsub has 333 liters. With 2 drivers and a tuning freq of 33Hz I get -7dB at 30Hz . The Port would be 0.12m x 0.464m with a depth of 0.239 meters.

This is close but maybe there is a suitable driver which has an even lower Fs than the RCF?

Also I fear somethings wrong with the calculation of the port. If I put 40Hz for tuning then WinISD sais it should be 0.094m depth. But the plan sais it should be 0.118. So yea... :/


Edited by ElsaEcomo - 03 April 2017 at 8:20pm
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DMorison View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote DMorison Quote  Post ReplyReply Direct Link To This Post Posted: 04 April 2017 at 10:30am
The Net volume you need to use for modelling the G-Sub is about 290l, because you need to account for the space taken up by the drivers, bracing, port and handles etc too.

With the longer port the tuning ends up about 37Hz IIRC.

That, plus the fact that the port isn't particularly big in the first place, means that trying to tune it another 10Hz or so lower isn't going to let you get the best out of most drivers that have any chance of being happy tuned that low in the first place.

Your net volume will get even lower as port length increases, and the kind of drivers that are happy going down to 30Hz or lower tend to want bigger box volumes.
If you'll be pushing them anywhere near full power, you'll also want a larger vent cross sectional area to minimise artifacts from vent airspeed being too high, and any time you make the vent area bigger, the required length to maintain your low tuning frequency goes up even more, further eating into the available cab volume.

In short, you need a bigger cab to start with if you're serious about going that low at any real volume.
Have a look at 18 Sound's dual 18 vented cab as an alternative starting point: http://www.eighteensound.com/Portals/0/EnclosuresKits/18sound_18_dual_subwoofer_kit.pdf

There's a good thread about building cabs very similar to this over at soundforums.net: https://soundforums.net/forum/low-earth-orbit/diy-audio/11488-no-compromises-front-loaded-double-18%C2%94-cab

PS don't worry toooo much if winISD predicts longer vents than in plans - it's often the case that when a vent is built in adjacent to the cabinet wall, it behaves as if its tuned lower than just the physical length of the shelf. That's because part of the walls of the port are extended backwards by the cabinet walls. 
WinISD's calculated lengths are only valid if you keep the internal end of the vent well away from the side or back walls of the cabinet.
If you're not building straight off a plan from a trusted source, you're best to build a prototype with some method of measuring port tuning and adjusting it if needed before building your final box.
For example, make one whole side of the box removable (held on with screws only for testing) and use low strength adhesive like silicone sealant rather than wood glue to hold the vent panels in place so they can be removed and replaced with longer/shorter ones as needed until you're sure the tuning frequency and overall response of the cab are what you want.

Good Luck,
David.


Edited by DMorison - 04 April 2017 at 10:38am
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