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Old 18th July 2003, 08:04 AM   #1
rabbitz is offline rabbitz  Australia
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Default Subwoofer project

Hi guys. I am going to build a modest subwoofer and just want to check if I'm heading in the right direction.

The goal is for this sub to add a bit of extra bass (to hear a thud in movies but doesn't need to shake - maybe a little rattle) to a system in my daughter's room (small to medium) and will be used with some 20+ year old Yamaha NS10M's which start rolling off at 150Hz. This will be powered by a Jaycar 80W (60W @ 8Ohm) sub amp which has a boost of 4dB at 35Hz and the crossover will be set at about 100Hz. Corner loading with room boundaries will give extra gain.

I'll be using a Vifa M21WJ-09-08 (8" coated paper cone woofer)
*note Xmax=4mm, Vas=136Ltr so there are limitations. Specs below:
Qts 0.36
Vas 136L
Fs 29Hz
Re 5.8Ohm
Le 0.90mH
Xmax 4mm
Z 8Ohm
Qms 1.20
Qes 0.45
SPL 91dB
Pe 80W
BL 6.5Txm
Sd 239sqcm

I've done some calcs with the assistance of the "Loudspeaker Design Cookbook" and Winisd and have come up with:
Vented:
Calculator: 83L box, 72mmD x 89mmL port @ Fb=32.2, F3=40.11Hz
Winisd ideal: 93.4L box, 72mmD x 68.3mmL port @ Fb=32.58, F3=33.66Hz
Winisd 45L: 45L box, 72mmD x 165mmL port @ Fb=35, F3=45.46Hz
Closed:
Calculator: 47.6L box, Qtc 0.71, F3=56.94Hz
Winsid: the same (strange - vented are different)
Vifa's data shows this driver intended for vented enclosure of 20-60Litres so I am aiming for 45Litres vented. A closed box rolls off too early.

I know the port entrance has to be a least 76mm from a wall but I don't know about distance of a port to a driver and to side walls. Port will be flared with 6mm R (inside) and 12mm R (outside)- matches my router tips.

Any assistance, suggestions or opinions would be greatly appreciated before I start cutting the MDF.

Thanks Peter (Rabbitz)
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Old 21st July 2003, 11:59 AM   #2
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il chuck it in winisd pro see what i get

unfortunately il have to later like tomorow ,day after,but anyway.

seems like uve got it under control


the rule of 3inches from ANY wall i think it isnot just the back wall i think....

dont forget to minus bracing from usable volume.



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Old 21st July 2003, 02:03 PM   #3
rabbitz is offline rabbitz  Australia
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Great.

I've allowed for everything inside the box - bracing, driver, amplifier, corner cleats and port.

The only thing I could find on ports to walls was in the Loudspeaker Design Cookbook which only referred to 3" from the back.

Thanks for your help.

Peter
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