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Subwoofer venting question

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pike

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Hey guys,

I just built my 100watt stereo amp (2x 50w mono), i've connected the subwoofers up in series because each driver is 4 ohms to get 8 ohms.

The recommended venting of each driver is 35mm pipe 57mm long. Each box is recommened at 6.5 litres.

Heres the problem: If i have 2 drivers in the same cabinet, what should happen to the venting (double or halve length??). I'm pretty sure the volume of the cabinet should double.

Ive also heard from some sources saying that i should put his white speaker damping material inside the cabinet. Do i need to deduct the space taken up by this foam/damper from the original volume of the cabinet??

thanks in advance.
 
pike said:
Hey guys,

I just built my 100watt stereo amp (2x 50w mono), i've connected the subwoofers up in series because each driver is 4 ohms to get 8 ohms.

The recommended venting of each driver is 35mm pipe 57mm long. Each box is recommened at 6.5 litres.

Heres the problem: If i have 2 drivers in the same cabinet, what should happen to the venting (double or halve length??). I'm pretty sure the volume of the cabinet should double.

Ive also heard from some sources saying that i should put his white speaker damping material inside the cabinet. Do i need to deduct the space taken up by this foam/damper from the original volume of the cabinet??

Double the volume of the cabinet, and add the TWO ports - essentially making the two boxes into one. You should add acoustic wadding on three adjacent sides, not on opposite ones - you don't generally need to worry about the volume the wadding takes up.

As you have 4 ohm drivers, presumably they are in-car ones? - you should be aware that such drivers are usually pretty poor quality, not much use for home systems, and are vastly over specified!
 
**broken link removed**

Thats the driver, its listed in the website as a hifi driver.

So what will happen to the power rating when they are put in series?? Its rated at 40watts RMS. Does that mean the rating doubles??

heres the tweeter: **broken link removed**
 
The power rating will double, both in series or in parallel (only the impedance changes), two 40W drivers give 80W handling.

I presumed you were talking about much larger drivers?, these aren't really sub-woofer material, more like mid-range drivers?, or bass/mid in very small systems.

Notice that it's a screened speaker, so it's intended for TV use, and suggested as a centre speaker - where there is no bass!.

I'm also rather confused about the tweeters?, you've mentioned a sub-woofer, and tweeters, but nothing else?.
 
I think that two woofers in series result in a terrible boom-box sound. At the resonant frequency (the vented cabinet causes two high impedance peaks in frequency, above and below the box tuning frequency) each speaker needs to have the extremely low output impedance of an amplifier's output connected directly to it to damp the resonances. With an identical speaker in series and resonating at the same frequencies then the damping is non-existant.
The speakers are small at only 5 inches so maybe their bass output is low anyway (their Qts and Xmax are low) and the undamped booming sound might be better than having no bass.
 
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