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Old 22nd January 2004, 07:42 PM   #1
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Default Aperiodic vented subwoofer(s)

I want to have the smallest possible box for my subwoofers and still have them sound descent. So I was looking to build a aperiodic vented enclosure.

I ran across this article http://www.elitecaraudio.com/article.php?sid=18 seaching on the web. It states you can build an AP enclosure with fiberglass and some flat sheet material that has holes in it, such as aluminum sheets with 3/8" holes. And the fiberglass is sandwiched between the sheets.

What worries me is that the vent is designed for a car. And in the article it states that the vent cannot be firing into the same enclosure as the sub. So vent has to fire outside the car or into the trunk. So I guess the vent causes descent SPL to cancel out the subs sound waves. Infact it sounds like this is a dipole sub almost.

Also the article states that you only need enough space behind the sub, only to enclose it and the rest is a big AP vent about half the Sd of the sub. I figure I can leave about 1.5 cu. ft. in the enclosure and build a smaller vent and this will cause negligable ammount of cancelation. Is this a correct presumption? This is why some AP designs have small vents is it not?

Is this a bad way to build a AP vent? Are there any good ways to build one? Note I don't care too much about losing low end perforance cause my sub amps output goes up as frequency goes down to around 25 Hz.
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Old 22nd January 2004, 07:54 PM   #2
sreten is offline sreten  United Kingdom
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The reason the world isn't full of small aperiodic loaded
subwoofers is that it doesn't work well, and I severely
doubt you have a high Q driver where such loading
could be useful.

In car audio its one way of using so called "free air" subwoofers.

sreten.
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Old 22nd January 2004, 11:29 PM   #3
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Nice to hear from you again sreten . . . . I can never get away with using the "" smiley face and still look .

Anyway, the woofer I have is similar to a car subwoofer that I used to have (in my car). It's designed to go in a 43.2 liter (1.5 cu. ft.) sealed box. I figured 43.2 liter sealed would sound descent [I get Qtc of 1.08, don't know why that's the recommendation, maybe car applications are different when it comes to Qtc ], but 43.2 liter AP vented box would be better, no?

The man who wrote the article said (I guess I can't cut and paste, so I'll summarize, it's on the second page of the link) that a sub with a Qts of .45 or less is good for this design and not subs designed for sealed enclosures. With their stiff heavy moving mass and stiff suspensions. But my sub is designed for a sealed enclosure and has a Qts of .404. It's EBP is 51, pretty close to 55 for a vented recommendation in WinISD.

Here are the sub specs (don't know if they make or break an AP design):

Fs =21.57 Hz
Qms=9.101
Qes=0.4231
Qts=0.4043
Vas=263.27 liters
Cms=0.2562E-03 M/N
Re=3.79 ohms
BL=16.060 Newtons/Amp
Sd=0.085530 sq. mtrs
Mms=0.212463 Kilograms
Hvc=1.250"
Hag=0.500"
Xmax=0.375
Xlin p-p=.750
Ref Efficiency=0.6001%
Predicted Output=89.982 Db/1W/1M
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Old 22nd January 2004, 11:51 PM   #4
sreten is offline sreten  United Kingdom
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The article may be correct for an in car response to give a very
overdamped aligment suited to the pressure region in car.

Nevertheless a sealed box of circa 100 litres is indicated
for a normal in room sealed sub if you want real bass.

sreten.
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Old 23rd January 2004, 12:07 AM   #5
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Quote:
Originally posted by sreten
The article may be correct for an in car response to give a very
overdamped aligment suited to the pressure region in car.

Nevertheless a sealed box of circa 100 litres is indicated
for a normal in room sealed sub if you want real bass.

sreten.

Real bass means the quality or transient response of the bass or the SPL at low frequencies? Cause remember my amp has that peak at 25 Hz, if it's SPL I don't think it will be a problem.
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Old 25th January 2004, 10:46 PM   #6
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Quote:
Originally posted by Jimmy154
I want to have the smallest possible box for my subwoofers and still have them sound descent. So I was looking to build a aperiodic vented enclosure.

I ran across this article http://www.elitecaraudio.com/article.php?sid=18 seaching on the web. It states you can build an AP enclosure with fiberglass and some flat sheet material that has holes in it, such as aluminum sheets with 3/8" holes. And the fiberglass is sandwiched between the sheets.

What worries me is that the vent is designed for a car. And in the article it states that the vent cannot be firing into the same enclosure as the sub. So vent has to fire outside the car or into the trunk. So I guess the vent causes descent SPL to cancel out the subs sound waves. Infact it sounds like this is a dipole sub almost.

Also the article states that you only need enough space behind the sub, only to enclose it and the rest is a big AP vent about half the Sd of the sub. I figure I can leave about 1.5 cu. ft. in the enclosure and build a smaller vent and this will cause negligable ammount of cancelation. Is this a correct presumption? This is why some AP designs have small vents is it not?

Is this a bad way to build a AP vent? Are there any good ways to build one? Note I don't care too much about losing low end perforance cause my sub amps output goes up as frequency goes down to around 25 Hz.
No one can tell me anything more about aperiodic vents (Plant10 maybe)? I can't find too much on the web about them, do they suck? Is that why not many people build them or is it the higher f3 and 18 db/octive roll-off?
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Old 25th January 2004, 10:57 PM   #7
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You've probably already seen most of this stuff, but here are some threads
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