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Old 3rd July 2012, 05:09 PM   #1
Shpilev is offline Shpilev  Estonia
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Default F3 and Fb significance

Hey,

I'm in the middle of deigning an enclosure for a Audes 75w104-8. The subwoofer would be used in a room. The room itself is about 35 cubic meters and in the shape of a rectangular prism.

Here is what I've come up with so far :

Click the image to open in full size.

The parameters for the driver are as follows:

10''
8 Ohms
RMS: 130 W
Max: 200 W
Range 30 - 2000 Hz
Sensativity (2,83 V/1 m) 92 dB
Fs 31 Hz
Mms 37,5 g
BL 12,37 Tm
Q ms 2,83
Q es 0,31
Q ts 0,28
V as 100,5 ltr

This driver is also available in the latest BassBox pro 6 database with all the parameters.

Now is the fact that my F3 is higher than the Fb a problem? Are my F3 and Fb too close to each other? Are they too high at the moment for good SQ? I'm looking more for SQ than SPL.

Any assistance would be great. Thanks.
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Old 4th July 2012, 12:54 AM   #2
OscarS is offline OscarS  United States
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it's not a problem so long as you are happy with the predicted frequency response. OTOH, I personally would try modeling it with a tad more enclosure volume and slightly lower tuning to extend the low-end a bit more.
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Old 4th July 2012, 01:27 AM   #3
bjorno is offline bjorno  Sweden
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Quote:
Originally Posted by Shpilev View Post
..Now is the fact that my F3 is higher than the Fb a problem? Are my F3 and Fb too close to each other? Are they too high at the moment for good SQ? I'm looking more for SQ than SPL...
Hi Shpiley,

You've done a good simulation job, No worries, everything is in order ..Will post a MJK:sim. tomorrow to prove my statement.Have a look at this:

b
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File Type: jpg Audes-75W104-8.JPG (311.5 KB, 198 views)
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Old 4th July 2012, 07:15 AM   #4
Shpilev is offline Shpilev  Estonia
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Quote:
Originally Posted by OscarS View Post
I personally would try modeling it with a tad more enclosure volume and slightly lower tuning to extend the low-end a bit more.
Well... I wouldn't dare doing that. Although I agree that the tuning might want to be even a little lower - 55 liters is big enough as it is for this 10'' driver. Actually people usually recommend about 45 liters for this driver, however I did not achieve satisfactory response with an enclosure of that size. Hence I went up to 55, but that's probably as high as I'll go. If I remember correctly - a bigger enclosure than this actually tended to increase the F3 again.

Quote:
Originally Posted by bjorno View Post
Hi Shpiley,

You've done a good simulation job, No worries, everything is in order ..Will post a MJK:sim. tomorrow to prove my statement.Have a look at this:

b
Haha... well thank you. I'm really trying to model the best box I can. It is my first project.
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Old 4th July 2012, 01:17 PM   #5
bjorno is offline bjorno  Sweden
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Quote:
Originally Posted by Shpilev View Post
..It is my first project..

As promised:

b
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File Type: jpg Audes_75w104-8_Ported-Box_55L_Cont.JPG (340.9 KB, 169 views)
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Old 4th July 2012, 08:05 PM   #6
djk is offline djk
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36hz box design.

Driver Properties
Name: 75W104-8 (2003)
Type: Standard one-way driver
Company: Audes
No. of Drivers = 1
Fs = 31 Hz
Qms = 2.83
Vas = 100.5 liters
Cms = 0.689 mm/N
Mms = 37.5 g
Rms = 2.633 kg/s
Xmax = 4.5 mm
Xmech = 6.75 mm
P-Dia = 202 mm
Sd = 320.5 sq.cm
P-Vd = 0.144 liters
Qes = 0.31
Re = 6.4 ohms
Le = 0.933 mH
Z = 8 ohms
BL = 12.37 Tm
Pe = 130 watts
Qts = 0.28
no = 0.931 %
1-W SPL = 91.84 dB
2.83-V SPL = 92.81 dB
-----------------------------------------
Box Properties
Name:
Type: Vented Box w/ Active HP Filter
Shape: Prism, square (optimum)
Vb = 1.141 cu.ft
Fb = 33.21 Hz
QL = 6.983
F3 = 35.84 Hz
Fill = minimal
No. of Vents = 1
Vent shape = round
Vent ends = one flush
Dv = 2.75 in
Lv = 10.48 in
-----------------------------------------
Active 12 dB/oct. HP Filter
Fx = 35.54 Hz
Qx = 1.93
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Last edited by djk; 4th July 2012 at 08:09 PM.
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Old 4th July 2012, 08:09 PM   #7
djk is offline djk
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Alternate 31hz box design.

Driver Properties
Name: 75W104-8 (2003)
Type: Standard one-way driver
Company: Audes
No. of Drivers = 1
Fs = 31 Hz
Qms = 2.83
Vas = 100.5 liters
Cms = 0.689 mm/N
Mms = 37.5 g
Rms = 2.633 kg/s
Xmax = 4.5 mm
Xmech = 6.75 mm
P-Dia = 202 mm
Sd = 320.5 sq.cm
P-Vd = 0.144 liters
Qes = 0.31
Re = 6.4 ohms
Le = 0.933 mH
Z = 8 ohms
BL = 12.37 Tm
Pe = 130 watts
Qts = 0.28
no = 0.931 %
1-W SPL = 91.84 dB
2.83-V SPL = 92.81 dB
-----------------------------------------
Box Properties
Name:
Type: Vented Box w/ Active HP Filter
Shape: Prism, square (optimum)
Vb = 1.5 cu.ft
Fb = 31 Hz
QL = 6.983
F3 = 31.2 Hz
Fill = minimal
No. of Vents = 1
Vent shape = round
Vent ends = one flush
Dv = 3 in
Lv = 10.74 in
-----------------------------------------
Active 12 dB/oct. HP Filter
Fx = 31 Hz
Qx = 2
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Old 4th July 2012, 08:21 PM   #8
Shpilev is offline Shpilev  Estonia
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Thanks for the help.

djk the first option - maybea 2.75 in vent might be a little small ? Could it start causing vent noise ?

I'll definitely consider the second box tough.
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Old 4th July 2012, 08:36 PM   #9
sreten is offline sreten  United Kingdom
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Hi,

For the bass end in general its not best to optimise F-3dB. F-6dB
is a lot better and sometimes even F-10dB for some drivers.

This allows room gain to work properly and low frequency vent
tunings help prevent overloading below the vent tuning frequency.

Ideally you would add a peaking high pass filter at around
30Hz for AV use, probably not needed in a music context.

The red alignment has near the same -3dB, better - 6dB
much better -10dB. It will sound deeper and tighter.

rgds, sreten.

I'd tune 55L to 30Hz, but reckon 40-45L 33Hz is about right.
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Last edited by sreten; 4th July 2012 at 08:55 PM.
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Old 4th July 2012, 10:20 PM   #10
djk is offline djk
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"maybea 2.75 in vent might be a little small ? Could it start causing vent noise ?"

The computer calculated the minimum vent size based on the Sd, x-max, and Fb of the design. On the 31hz design I forced a larger vent than what was the minimum required.

As suggested by sreten, you might be able to reduce the Q of the high-pass filter if you have a lot of room gain in the 30hz region.
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Last edited by djk; 4th July 2012 at 10:24 PM.
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