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Old 17th August 2003, 05:47 PM   #11
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Ok, let me run some more simulations with those numbers. Can anyone explain to me why Madisound recommends a 15L box tuned to 45Hz? I ran the simulation on that and the frequency response curve doesn't look so good. It has a bump in the frequency.

Oh I forgot to say that this is the Peerless driver that is on sale at Madisound. specs:

High-end 8" subwoofer. Peerless CC line. Double voice coil. Rubber surround, thick poly cone, extra-heavy magnet system. Great in small bass reflex or band-pass sub.
8 + 8 ohms; Fs 22 Hz; Qts .23, Vas 79.8, 90.5 db, 200 watts
x-max 7 mm

15 liters ported
Port size 1.5" x 5.4" or 2" x 10"
F3=45 Hz
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Old 17th August 2003, 06:22 PM   #12
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For box size 49.8L and tuning point of 22.7hz, the sub shows extremely high group delay. This is a bad thing correct?
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Old 17th August 2003, 07:50 PM   #13
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I assume Madisound either has more accurate specs to work from or is catering to the car boombox crowd. BTW, efficiency is closer to 87dB/W.

Group delay increases with decreasing frequency. Fortunately, if tuned low enough and there's no 'ringing' peak at Fb, it will decay away enough not to be obviously audible due to our poor LF hearing acuity. It can be lowered to near sealed values by 'critically' damping the vent, with reduced vent output being the tradeoff. With this driver though, it will roll it off enough that you might as well stick it in a sealed cab.

FWIW, based solely on the specs presented and its intended app, 20L/27Hz with a 6.35cm diameter vent seems to me to be the best tradeoff between BW, group delay (transient response), low distortion/vent mach, and power handling.

GM
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Old 17th August 2003, 11:59 PM   #14
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GM,

The response seems pretty good. The decay in frequency response starts off pretty early but it is going at a slow rate. I will be placing it in a small/medium type room so room gain should boost the 50-30Hz spectrum by a bit correct? This will give me a pretty decent extension.
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Old 18th August 2003, 01:16 AM   #15
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Should. Since it's for a computer I figured it would be close and probably on the floor against the wall so there should be enough LF to EQ it flat and still be plenty loud.

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Old 18th August 2003, 05:47 AM   #16
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I just noticed that with the 20L/27Hz design, unibox indicates that the woofer will go past peak cone excursion in the 40-50Hz range. Will this be a problem?
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Old 18th August 2003, 06:20 AM   #17
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Well, it's potentially going a little over Xmax if fed a 200W peak, but not nearly enough to cause damage or be audible. Also, assuming it's near the floor there will be a ~ +3dB boundary gain so that more than compensates it. Really, unless you sit it out in the middle of the room there should be enough boundary/room gain to allow you to attenuate some of this BW to flatten out its response down to below Fb.

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Old 18th August 2003, 06:28 AM   #18
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seeing as how I am also talking about a computer sub using 8inch driver(s)... and the "having the last word" thread was closed... I thought I would ask here.. lol
what do ya think of these?
http://www.advanceae.com.au/car/prod4.htm
I was thinking of putting 2 in a 60litre box tuned to 35Hz... looks something like this... lol anyway.. I have no money... but I was wondering what you guys thought of these "subs" maybe I should just finish my towers first...
Click the image to open in full size.
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File Type: jpg dual8inchsubwoofer.jpg (70.0 KB, 132 views)
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Old 18th August 2003, 07:10 AM   #19
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I tried simulating with 2 of the the Peerless, which are cheaper, in a 70L/30Hz and it mimics yours frequency response except giving better extension as well as more SPL. But then I am still learning. Take my words with a grain of salt. =P
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Old 18th August 2003, 07:57 AM   #20
Keith D is offline Keith D  United States
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Is it just me or is that site way more expensive than others? Their Peerless XLS 10" is almost $300. You can probably find better than that venom driver, it only has 5mm of xmax but it looks like they tried to make it LOOK impressive with that big surround. Try ebay and see if there's anything decent on there with the right ts specs. I got my sub driver for $40 off on ebay and it has a return policy and full warranty and all that, there's some good deals to be had if you wait for them to pop up. To lower the Q you could try an aperiodic vent if you do a sealed box, and a bass boost could lower the f3.

Tell us how it sounds when it's all done.
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