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Discussion Starter · #1 ·
Can someone confirm that I have my numbers correct before I start my project.

For the Box.

Height: 790mm
Width: 595mm
Depth: 580mm

Internal 221lt less Port, Bracing and Driver = 200lt

For the slotted Port:

Height: 51mm
Width: 559mm
Length: 923mm

The box will made out of 18mm MDF with a double front baffle.

2nd order high pass filter @ 14hz

And the amp will be:

OAudio subwoofer amplifier
500 watt : OAudio
500W RMS into 4ohms @ 0.3% THD
420W RMS into 4ohms @ 0.05% THD
325W RMS into 8ohms @ 0.01% THD
S/N (A-weighted): 105dB
Lowpass Crossover: 40Hz to 120Hz, 4th order
Parametric EQ: 20Hz to 80Hz, 0 to -12dB, variable Q
Continuous Phase Adjustment

The Manual and User Guide
http://www.oaudio.com/docs/subamp_variouseqsettings.pdf

Please, any help or suggestions would be great.

Thanks in advance.
 

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re: Mach 5 18", 180lt, 500watts tuned to 20hz

The box dimension are right but the port is not correct. For a 20 hz tuning (as discussed in the other thread) the inside dimensions should be 50 mm high x 350 mm wide and 545 long. Add the material thickness to the sides and top of the port to get the displacement.

2nd order high pass filter @ 14hz
The O-Audio amp has a selectable high pass filter at 12, 16, 20 and 25 hz. For your application it should be set at 20 hz.
 

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Discussion Starter · #3 ·
re: Mach 5 18", 180lt, 500watts tuned to 20hz

I was hoping to keep the port the same width as the box for simplicity, is this possible?

Thanks.
 

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Discussion Starter · #4 ·
re: Mach 5 18", 180lt, 500watts tuned to 20hz

Thanks Mike, I will go with your Port suggestion, Only had to cut 1 sheet different, I've started the box so it shouldn't take very long to complete. When I modelled the sub in WinIsd I could get the High Pass Filter down to 14hz? Can you explain the 20hz high pass filter, did I model something wrong? Can the 16hz filter be used for this setup if im only using 500watts as compared to your original post of 1000 watts?

Thanks for the replies.
 

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re: Mach 5 18", 180lt, 500watts tuned to 20hz

If you build the port the width of the box then it would need to be 907 mm long. The port length can be made smaller if you reduce the height of the port but then it get to narrow which can cause problems.

You can't get the High Pass Filter down to 14hz on the O-Audio amp. The options are 12, 16, 20 and 25 hz. If I remember correctly he 12 hz HPF has about 8 db of boost, 16 hz has 6 db, 20 hz has 4 db and there is no boost on the 25 hz HPF. The 12 and 16 hz HPF would work on a sealed sub that can handle the boost, for a ported box the 20 hz HPF works best. Although the 20 hz HPF has 4 db of boost, the amp's EQ can cut it since the effective EQ range is 18 - 80 hz.
 

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Discussion Starter · #6 ·
re: Mach 5 18", 180lt, 500watts tuned to 20hz

Thanks Mike. I've started the box and have the panels cut, just need to cut in the window panels into the the 2 bracing pieces. Im very excited to be building an 18" sub as the biggest driver to date is only 12". The Mach 5 18.2.2 is $319 plus $20 shipping and handling which is a good price for such a great sub.

Can you please confirm the slotted port for the 20 hz tune? For simplicity I have kept the width the same of the box and will round of the corners and the end of the port.

For the slotted Port:

Height: 51mm
Width: 559mm
Length: 907mm


Thankyou very much for your help with the modelling and I should have some pic's up by the weekend.
 

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re: Mach 5 18", 180lt, 500watts tuned to 20hz

The port length would be 907 mm long if the height is 50 mm and 924 mm long if the height is 51 mm. The port height and width are inside dimensions. The baffle thickiness counts as part of the length. The port will displace about 35 liters.

For the Box.

Height: 790mm
Width: 595mm
Depth: 580mm
Those are inside dimensions, correct? If so, you'll have a bit less then 200 liters net volume and the port length will have to be adjusted a bit.
 

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Discussion Starter · #8 ·
re: Mach 5 18", 180lt, 500watts tuned to 20hz

I will have to rework the size of the port and bracing to maximise the box size. I've already cut the panels for the box so the volume is already set.

The port entry at the front of the box will be 51mm high (height is set in stone but the width can be adjusted to any size). So if I keep your first recommendation of 350mm, what will be the length of the port if the entry is 51mm?

Can the width be less than 350mm or is that the minimum?

If the box volume drops to 190lt what will happen?

Thanks.
 

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re: Mach 5 18", 180lt, 500watts tuned to 20hz

Then the internal dimensions are 754 H x 559 W x 526 D if you're doing a double front baffle. If the port is 51mm high and the width of the cabinet which is 559 mm, then it would need to be 1056 mm long and that includes the double front baffle thickness. With the displacement of the port bracing and sub subtracted, the net volume of the cabinet is around 180 liters.
 

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Discussion Starter · #16 ·
re: Mach 5 18", 180lt, 500watts tuned to 20hz

Had to laugh when I looked at the photo and the box made my kids 37" lcd look small. Should have the port built by Monday and most of the box together and im sure I will have more questions to follow.

Mike, the port will have two bits of timber to hold the port top in place all the way around the box, so the port will be 51mm high, 523mm wide and ???mm long. :huh: Sorry im not sure how long and how much less the port volume will take up in the box.

I pulled the side panel out to show my wife and asked the silly question, do you think this will be to big for our lounge room? and all i got was :foottap:

She really does not care, just as long as she can turn the tv on and watch a dvd without pushing to many button.:D

Thanks for your help. And a little teaser for you.

Dave.

pdf.jpg
 

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Discussion Starter · #18 ·
re: Mach 5 18", 180lt, 500watts tuned to 20hz

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I've made some progress.

What would be the minimum amount of bracing inside the box be? I have 2 pieces of off cuts that are only 200mm wide and go from side to side, will this be enough or should I go with one window panel?

Its amazing how much sturdier boxes are with having the slotted ports.

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Discussion Starter · #20 ·
re: Mach 5 18", 180lt, 500watts tuned to 20hz

Thanks Mike, Some more progress today.

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My 2 year old daughter was helping with some clever art work.
 
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