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Old 2nd January 2008, 01:23 PM   #1
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Join Date: Jan 2005
Location: Argentina
Default sub-woofer "coffee table"


I'm moving from my parents house to an small apartment. I have one room (4x3m) that will be for the home theater.

Actually my sub woofer is a bass-reflex 55cm x 45cm x 75cm, really big box for an small room.

I had the idea of making a sub-woofer box that acts as a table too, something like this:

Click the image to open in full size.

so, I don't have to use extra space for the sub, and it's quite cool idea to build a sub-woofer cofee table.

What I want to know is what type of subwoofer box is better for small rooms. Closed? vented? bass-reflex?

my speaker is a 18" RCF L18540P with this specs:

350W RMS
sens: 99.5db
max x-over freq 250hz
Fs: 34hz
Qms: 8
Qts: 0.34
Mms: 0.14kg
Cms: 0.00013m/N
Vas: 0.228m^3
Le (1khz): 1.23mH
BL Factor: 22.7 Tesla m
Reference efficiency: 3.34%
Peak linear displacement of diaphragm: +-4.5mm

of course, I wont be using it at 350W RMS,... but, I dont want to buy a new speaker, this is really good one.


a basic drawing:

Click the image to open in full size.
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Old 2nd January 2008, 02:02 PM   #2
AndrewT is offline AndrewT  Scotland
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Join Date: Jul 2004
Location: Scottish Borders
the VAS and Qts indicate it will work better as a vented rather than sealed.
But vented will end up as a bass speaker not a sub.

If you can get it to work sealed then you have the option to use Linkwitz Reilly to extend the bass below resonance and get sub performance out of it, but this method requires a lot of equalisation and uses up power and Xmax resulting in lowish maximum output levels.
This may not be noticeable in a smallish room with the speaker quite close to the listener and there could also be some room gain to help with the lowest frequencies.

Let's see what other say.

there is another way, fit it to a vented box that is by convention far too big and tune it low. This gets sub performance but only upto lower volumes. You need to do a lot of modelling in WINisd to find a combination that achieves the frequency response you want with adequate SPL and in a box that fits your table.
regards Andrew T.
Sent from my desktop computer using a keyboard
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Old 4th January 2008, 06:08 PM   #3
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Join Date: Jan 2005
Location: Argentina
andrew, thanks for your reply.

After reading lot of pages, I decided to build a fourt order bandpass box.

My lower -3db frequency will be 30hz.
Vas = 228 liters
QTS = 0,34
FS = 34hz
18" speaker, Xmax = 4.5mm

after calculations,

volume of sealed box: 138 liters
volume of vented box: 52 liters
port diameter: 3" (76mm)
port length: 30mm

Can anyone tell me if this values are normal? I don't want to waste my money & time building something that is incorrect

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Old 5th January 2008, 04:47 AM   #4
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Join Date: Jun 2004
Location: Indiana
If you are going to put it in a coffee table you might want to consider Transmission Line or Tapped Horn to get more low bass out of it.

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Old 5th January 2008, 11:05 AM   #5
djk is offline djk
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Location: USA
"volume of vented box: 52 liters
port diameter: 3" (76mm)
port length: 30mm"

T/S parameters for that driver do not indicated a BP4 enclosure. Vented size is too small and a cheap 10" driver will play louder.

"If you are going to put it in a coffee table you might want to consider Transmission Line or Tapped Horn to get more low bass out of it."


Candidates for the Darwin Award should not read this author.
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Old 5th January 2008, 12:52 PM   #6
Eva is offline Eva  Spain
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One more vote for attempting tapped horn
I use to feel like the small child in The Emperor's New Clothes tale
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