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cabinet build - from scratch

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14 hours ago, Phil Starr said:

Couldn't resist it I've modelled your cab tuned to 55Hz and compared to my 30l cab It will give you just over 2dB more bass from 100hz down to 40hz (fundamental of bottom E). That extra box volume will give you noticeably more bass in other words, at the cost of a little power handling but power handling is still good, there's a dip to 300W at 90Hz and it handles 180w at bottom E which is pretty good, way better than the Eminence you started looking at. In practice you don't get a lot of fundamental from the pickups so unless you start using stupid power and an octaver you won't have problems at all in any normal use. There's still a bit of extra 'punch' at 120Hz but it's not a bad frequency response at all.

Use one port of 110mm (plastic waste pipe) 15.5cm long or two 64mm (guttering downpipe) vents at 11.2 cm long. (or 3 at 19.2cm) You'll get a little wind noise at full power but you probably won't notice it in practice.

Phil, out of interest I tried firing up WinISD to see the graph you get with these numbers (46l box, 55Hz tuning). To get the same port length I needed to take the box volume down to just over 40l - so I assume the 6l difference is you taking account of the driver and port volume?

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ok, thanks. I'll convert them at work tomorrow. But for now I have taken a photo of them.

DSC03780.JPG

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DSC03782.JPG

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1 hour ago, RichardH said:

Phil, out of interest I tried firing up WinISD to see the graph you get with these numbers (46l box, 55Hz tuning). To get the same port length I needed to take the box volume down to just over 40l - so I assume the 6l difference is you taking account of the driver and port volume?

Yes that's right I assumed 40l, speaker ports and any bracing

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Insulation. The board I'm using is leftover from a friend's flooring, and has around 6 mm of pretty solid sound insulation glued to one side of it. Will this help, or should I remove it ?

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If there is room to fit the 110mm port, it will handle quite a lot more power than two of the smaller ones - although it looks a bit tight from here and you don't want the port right in the corner.

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You could mount the port in the rear of the cab, that way you could fit the bigger port in.

.

Edited by Phil Starr

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The area of 1 x 110 ( 9.5 cm2 ) is 1 1/2 times that of 2 x 64 pipes ( 6.5 cm2 ) Is this how it handles more power ?

A 110 will fit, if I move the speaker down a few mm, but it will be close to the edge - around 12 mm. Or I could put the port in the back ? Or I could use four 50 mm pipes which will fit in the front ?

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It's the extra area and the reduced friction from the port sides (odd though that may sound). I'd put it at the front if you can - I'm not a great fan of rear porting for bass guitar cabs. 12mm spacing from the edge should be fine.

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having read the '1x12 cab to replace 410' thread, I assume not. I will stick to the Beyma.

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+1 stick with the Beyma, you will be really pleased with it's performance. I'm a real Basschat  1X12 Mk1 Fanboy having built two slightly different designs they deliver a performance that is a match for many big brand cabs. Phil & Stevie really know their stuff and have expanded the knowledge of many who follow Basschat. 

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Just realised that I need to add battens in the front, to fix the grille to. I will need to squeeze the driver and the port away from the edge. 

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If you're struggling for space, you could always put the port at the back as Phil suggested. If you decide to stick with a front port, try to get it as far from the corner as you can.

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Yep there are arguments for and against putting the port on the back. The main argument for is that ports produce noises at mid frequencies due to all sorts of resonances, putting them round the back means the noises can't really be heard. Against is the thought that you can't ram the cab hard against a wall and potentially block the port, but even a few cm away it won't be a problem. With compact cabs it's always a bit of a problem fitting everything on the baffle without weakening the panel.

The other solution might be a slot port, you'd have to form it in timber so there is extra woodwork but it's a nice tidy way of creating a port, another more complex method is that used by some manufacturers of building triangular corner ports like Mesa 

 

Edited by Phil Starr

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On 02/06/2018 at 15:37, Phil Starr said:

... The other solution might be a slot port, you'd have to form it in timber so there is extra woodwork but it's a nice tidy way of creating a port, another more complex method is that used by some manufacturers of building triangular corner ports like Mesa 

 

I've seen triangular ports in some designs, but never seen any guidance about how to calculate them. Are they calculated as square ports and built in two halves, or is there some correction factor needed to compensate for the extra resistance of the additional wall, and the effect of the cab walls close by?

David

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Essentially you just need to know the cross sectional area.Add the ports together and then calculate the length. pretty much all the programs  let you calculate assuming a circular port so you can just work out what diameter port would have the same area as your four triangular ports. WinISD lets you use rectangular ports which makes it even easier.

Yes in theory you ought to allow for a different end correction but the change is tuning will be small. the manufacturers figures for speaker specs are rarely spot on so that's all academic. In practice you'll usually find what you have is close enough. I tend to build, check after and then if the tuning is too far out adjust the cab If it is too far out. It rarely is in practice often you are talking less than a cm of port length and a few Hz in tuning

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