18" reflex sub ports |
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stalian87
Registered User Joined: 16 March 2015 Location: United Kingdom Status: Offline Points: 110 |
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yep i got around 75 after changing the size.
so basically i've positioned the diamond shaped plate further forward thus cutting the baffles from the rear...that gave me more volume to play with. now i've always wondered whether theres a difference in performance with front vs rear mounted drivers? cos if i can mount them outwards, that'll save some hassle of making sure they can actually fit inside. i was thinking about that last night...to make the diamond shaped panel a port panel! I'll need to measure it carefully though as for now it's just a plate.
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Hemisphere
Old Croc Joined: 21 April 2008 Status: Offline Points: 2272 |
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That'll probably increase the volume to 75 since you can shift the baffle forwards a bit when there's more space to work with.
You can also stuff the enclosure with fibre fill to increase the apparent volume of the box. When you factor that in, you can probably get away with 57.5 height which would give you a good neat square. The mouth of the TH18 is approximately square shaped right? So that would be a good balance. (if it isn't exactly square shape, perhaps work out what ratio it actually is and copy that for the kick bin) We're talking very, very negligible differences in output though (the difference between 80 and 120 litres is only 1dB). A lot of the practicality of the box rests on the weight of the wood. 4x12" could be 14kg, so watch the volume of wood. Assuming a rule of thumb 1g per CC (I think it's something like that for ply?) a single 60x60x1.8cm panel alone is 6.5kg. 5 of them plus baffle and bracing that's 6 is 53kg with the drivers. If you use well braced 15mm ply and 55cm panels it's 41kg So think about the fibre stuffing, and consider that even if it's 30 litres undersize it'll only be about 1dB less efficient, and the stuffing will smooth the response. 40kg is viable then. (not suggesting 30 litres undersize is okay though, as mentioned 80 is really low for 4 12's already, but it wouldn't be a disaster if it was 70 or so) In terms of pure sound quality you'll still be better doing it in halves though. Having 30-35kg or so per half to play with would open up many options. Cheaper/higher quality ferrite drivers, 18mm plywood, better bracing, etc. You really don't want to skimp on the box quality if you can help it. 4 12's running flat out in one box is a lot to handle. Then again you would lose the possible benefits of the exotic angled baffle. Edit: When you say you cut the baffles, do you mean you moved it forwards? It looks like you could move it quite a lot forwards, if you could find a practical way to square off the front of the box. It doesn't need to be so wide open. You can also mount the drivers with their magnets facing outwards, and that will work absolutely fine (and if you can find drivers with well designed magnet structures, potentially look amazing). If you modelled them facing inwards then you'll gain about 8-12 litres from doing that. Something you might want to consider is designing the box so that it can be ported, perhaps even so you could switch it between ported and sealed with a single adaptor mounted to the middle panel. There's always a possibility you would prefer the ported sound, and even if you prefer sealed it would mean if you ever did expand your bass section, you wouldn't need to build new kick bins, you could just open up the port and they would keep up with 2x TH18.
Edited by Hemisphere - 25 August 2017 at 11:56am |
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stalian87
Registered User Joined: 16 March 2015 Location: United Kingdom Status: Offline Points: 110 |
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the volume is unfortunately only 52l and i've already extended the rear to the max and cut the baffles further so look like i can do this with a 50cm high box :( back to the drawing board.
I actually like the look of the 1 box so i'd prefer to keep it as 1 and just extend the height to 60cm and see what the volume ends up being.
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stalian87
Registered User Joined: 16 March 2015 Location: United Kingdom Status: Offline Points: 110 |
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That's the one thing I forgot to measure so in the morning I'll do that. I've still got around 12-15cm of depth to play with if I need more volume which I'll probs will do. I can also cut the baffles slightly more forward to give me more volume as well
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Hemisphere
Old Croc Joined: 21 April 2008 Status: Offline Points: 2272 |
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That looks amazing. Are you sure it's got enough internal volume behind the baffle though? 80 litres is the bare minimum really.
Space in front of the baffle doesn't count towards the enclosure size..but as mentioned it will have some impacts on the sound reproduction which are harder to predict. But will probably be positive in terms of the character of the sound and perceived impact delivered by the box. Appearances are important too and can have a slight placebo effect. It looks loud and punchy. The diamond shape in the middle could be braced to the rear wall if you needed to extend it a few cm back. If you gave it a cross brace behind the woofers, and possibly even some partially decorative braces in front of the baffle (bracing along the middle of the four flat faces ie), it'd be a seriously solid box. It definitely risks getting into impractically heavy/large territory though, even with lightweight drivers.
Edited by Hemisphere - 25 August 2017 at 1:44am |
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stalian87
Registered User Joined: 16 March 2015 Location: United Kingdom Status: Offline Points: 110 |
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well i've given it a go in sketchup and man it was frustrating but got the box down to 50cm tall but i may just end up with doing 2 boxes of around 32cm tall each as you've suggested to save on a design nightmare!
they'd look pretty cool though! to be honest, not even sure there's enough clearance for the drivers....i think they'll just about fit
Edited by stalian87 - 25 August 2017 at 1:23am |
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Hemisphere
Old Croc Joined: 21 April 2008 Status: Offline Points: 2272 |
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Looking at the height of your subs, and considering a midtop could easily be designed to be between 35 and 55cm, even if your kick section was 65cm you'd be looking at somewhere between 200 and 225cm overall stack height, depending on whether the kick is in two sections and how tall your midtop is, which is typical, if not optimal, for a system like this. If it's at the high end of that number and the kicks were in two sections you could adjust the height to 190cm for low ceilings, cosy/intimate gigs, or gigs where the system is going to be raised on a stage already, and you could definitely design the midtops to be pole-mountable so there wouldn't be any situations you couldn't work with. A close commercial equivalent of what you're trying to achieve is the HK Audio Linear 5 system. 'big venue pack'. http://hkaudio.com/products.php?id=400 That's 233cm tall. Their smaller 'rock pack' is 201cm. That's fairly typical. If anything the 'rock pack' is a little shorter than a typical compact ground stack. Another benefit of designing your own midtops is you could give them that unusual 57.5cm wide form to match the rest of the stack. A set up with the TH18 and then 3 matched dimension boxes, all 57.5 x 34cm from the front (with the midtop box being not quite so deep), could look very neat. You'd get a good visual balance of two sections 'the bass', and 'the rest', each approximately 1 metre tall. Something like this ie: And in 'short stack' mode: Edited by Hemisphere - 25 August 2017 at 12:12am |
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stalian87
Registered User Joined: 16 March 2015 Location: United Kingdom Status: Offline Points: 110 |
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Ok thank you both, out now but will research a bit later :)
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Hemisphere
Old Croc Joined: 21 April 2008 Status: Offline Points: 2272 |
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If anyone is the master of squeezing an implausibly large amount of drivers into a small space it's Danley.
It's worth considering that for the 65-125Hz frequency range, the 12" drivers really don't need to be facing anything like straight forwards. The resulting look of a design that works might not look like it will work well at all, so if you can only see one way that they could physically fit within your size requirements, and it doesn't look like it'll work, try it anyway. Hopefully someone can tell just from looking at it. There are a few other unusual loading types for lots of drivers in a small space like push/pull designs, but don't know how they work exactly or if they would be appropriate.
Edited by Hemisphere - 24 August 2017 at 5:20pm |
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kevinmcdonough
Old Croc Joined: 27 June 2005 Location: Glasgow Status: Offline Points: 3751 |
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A good idea of how this possible would be to look at the pic Kyle posted of the inside of the Danley cabs on the "how do Danley speakers work" thread. They have a 4 way angled baffle, which in that case obviously makes the walls of the Synergy horn, but the way it goes together may trigger some ideas on how you could do your own design. K
Edited by kevinmcdonough - 24 August 2017 at 4:56pm |
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stalian87
Registered User Joined: 16 March 2015 Location: United Kingdom Status: Offline Points: 110 |
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I'm gonna go for the 4x12 but looks like I have to make the box higher than wanted cos I can't simply work out how to create the baffles to vertically and horizontally align accurately! Using sketchup and just can't figure out an easy way to do that! If anyone can help that'll be appreciated!
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Hemisphere
Old Croc Joined: 21 April 2008 Status: Offline Points: 2272 |
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Sorry, I've got the numbers way off there. It's 125-129 for 2x12 with the BMS, 131-135dB with 4x12
With a more lightweight driver (50-60g Mms, 8-9mm xmax), it's generally around 122-127 for 2x12 or 128-132 with a 4x12. (with half the amp power required of the BMS, but no more headroom available) That's across the 70-125Hz range with a rising response, 20 litres sealed enclosure per driver. You can get an extra dB gain in the low end of the range with 30 litres per driver.
Edited by Hemisphere - 24 August 2017 at 4:12pm |
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