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Old 18th August 2003, 01:39 AM   #1
Fabiano is offline Fabiano  Brazil
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Default Will this sub sound good?

Dear All,

I am trying to design a DIY Subwoofer for my HT. I have got a Brazilian subwoofer called Bravox Endurance DVC , 15 inches, its T/S parameters are as follows:

Impedance : (x2) 6,0 (ohms ± 10%)
Sens. : 89 (± 2dB/m/2,83v)
Fs : 20 (Hz ± 15 %)
Pot. máx : 700 Wmax
Qts : 0,29
Qms : 4,46
Qes : 0,31
Vas : 270 liters
X máx. : 10,1 mm
Re : 2,68 Ohms
Sd : 881 sq.cm 15"

Using WinISD and SubSim, I came up with a 116L box with a port tuned to 25.6Hz. Will it be boomy?

I am planing to build it with 15mm MDF (double walls), according to the attached sketch, do you guys have any comments? I am a newbie , and this is my first DIY.

Fabiano
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Old 18th August 2003, 03:52 AM   #2
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Your plans sound good, but I can't see an attached sketch... did it not attach correctly?

Your plan sounds great...
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Old 18th August 2003, 03:52 AM   #3
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I much prefer the look of the driver in a 200litre box tuned to 20Hz should get nice and low and nice and loud.. :d hehe... but.. abit big... lol
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Old 18th August 2003, 05:01 AM   #4
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With a +/-15% Fs spec, any sim is going to be a 'crapshoot', but based on the specs, ~135L net/20Hz with 15.24cm diameter vent looks to be a good tradeoff between BW, power handling, and acceptable vent length/mach.

WRT sub cab design/material, the object is to get it stiff enough to raise its resonance to above the passband, so a well braced 11 or 13 ply 19mm Baltic Birch is the better performer even though the 30mm MDF walls probably have ~the same MOE (stiffness factor) due to its much lower resonance.

HTH,

GM
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Old 18th August 2003, 06:35 AM   #5
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Opa! Ae Fabiano um conterrâneo Bem vindo ao forum, olha só acho que essa caixa com esse volume você não vai poder aplicar muita potência no sub.. toma cuidado com a excurssão..


Translation:
Hello Fabiano.. Welcome to the board, look IMO I think that enclosure with that huge volume you won't be able to apply much power to the driver.. be carefull with cone excurssion


Cya!
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Old 18th August 2003, 04:26 PM   #6
GM is offline GM  United States
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Hey Arthur,

What do you know about this driver that we don't? At 10.1mm, neither Fabiano's nor my alignment will exceed Xmax, though the 200L one will somewhat. Still, at the low frequency it occurs at it I doubt the extra distortion would be audible due to the room dominating below 80-100Hz. The vent's so large on this one though that PR's would be required.

GM
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Old 18th August 2003, 06:59 PM   #7
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I Simulated these enclosures and for me it showed that they have an enormous fall in the amount of power u should apply to driver without exceding it's cone excurssion.. IMWO if you pretend to build that enclosure You'd be shure not to apply more than 300watts..
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Old 18th August 2003, 11:57 PM   #8
Fabiano is offline Fabiano  Brazil
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Hey guys.

Thank you very much for all your comments.

I really do not know whether it was clear in my sketch (sorry folks, I am not very good with AutoCAD). To increase the WAF I need to make the enclosure a kind of a table, with the driver and the port firing downward (she wants to place some things, aka: vases, on the sub enclosure). To save space of the cross sectional area I had to use a rectangular vent (30cm x 5cm) and apply the correction factor from the JLAudio.com tutorials.

Arthur: As a matter of fact I plan to apply no more than 150 to 180 WRMS. This is what I have available anyway.

GM: You said 135L / 20Hz. I simulated this in WinISD Pro Alfa, with a power input of 180W and it showed a cone excursion greater than 10mm from 23Hz to 52Hz. As a matter of fact even with 116L / 25.6Hz it showed a cone excursion greater than 10mm from 30Hz to 53Hz (I haven't seen this before). I haven't quit understood WinISD and the difference between "Maximum Power Graph" and "Cone Excursion Graph". Can someone explain it to me? Anyway I liked the Transfer Function Curve of the 135Hz / 20Hz option, but I would have one BIG problem: to fit a Ø152.4mm x 922mm port in such a "small" enclosure

Bes Regards.

Fabiano
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Old 19th August 2003, 02:48 AM   #9
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Just to know Xmax is a linear measure.. The excurssion in winisd shows both-ways
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Old 21st August 2003, 04:48 AM   #10
GM is offline GM  United States
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Well, I double checked the specs I inputted/simmed and *based on the published specs* all three programs I have (Lspcad Pro, BoxPlot, Margolis-Small) say it can handle 700W with a minor/inaudible overshoot beyond Xmax right above Fb in 135L/20Hz Fb, so all things considered, this is my recommendation.

WRT the vent, I would cobble together a ~135L prototype cab with one side being 50.8cm wide and leave a 1.9cm open slot for the vent opening. Make and clamp over the opening a 50.8cm x 1.9cm x 50.8cm long (all dims are i.d.) vent and use some gasket material to seal it.

Test as best you can. In theory it should be too long for 20Hz, but with this high an aspect ratio they don't work as the math predicts. Anyway, make it longer/shorter as required and once satisfied figure out the cab Vb that allows you to fold it around the interior walls (the length is measured down the center), or leave it external as some folks do.

GM
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