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Old 31st December 2001, 07:03 AM   #1
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Exclamation (Poor) Box design

Thanks to everyone who has responded to my previous post (Quad Drivers...), the information has been greatly appreciated. The box dimensions are 19x19x29 (I know it's not even near perfect, but..) with the 4 drivers mounted firing towards the ground on the box like so (as seen from transparent arial view):


19"
____
19 | O O|
| O O|

- to my best calculations it's about 6 cubic feet and the sealed rear (or in this case upper) chamber will be about 2.5 cubic feet with the additional 3.5 cubic feet going to the vented enclosure. Speakers are paltry 8"ers with a 45HZ-3800HZ range. 93db sensitivity 300 watts (peak) per at 4 ohms.

Three questions - will firing towards the ground really do anything to detract from performance? And is 6 cubic feet too large to get decent sound? Assuming I port it right, (on a level of 1-10) what quality of sound am I looking at?

Thanks everyone


Oh yes, I know I may sound like an idiot, but what's the 'tuning frequency' all of these port calculators seem to be wanting? =p Thanks again
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Old 31st December 2001, 07:50 AM   #2
JoeBob is offline JoeBob  Canada
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Well, there was a long thread on down firing woofers just recently, maybe you could give it a look. Alot of people say they'll sag with age... As for the tuning frequency I do believe that this sets to resonant frequency of the enclosure when you're working with ported cabinets.
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Old 31st December 2001, 08:11 AM   #3
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Your 4 x 8" drivers will have a combined Sd equal to that of about a 15" driver ........ but what is the Xmax specified for the drivers you'll be using? Also, what is the Fs of the drivers?

I cant see you getting much usable bass out this. You'll also probably need to use active EQ.
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Old 31st December 2001, 03:20 PM   #4
Super is offline Super  United States
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I would tend to agree with AF. It might be suitable for filling in the void between a sub/satellite system though, perhaps being used as a bridge before a 12 or 15 inch driver?

Also, if I'm picturing this right, you're having two of the drivers in a sealed enclosure, and two in a ported enclosure? I think you would yield better results and lower f3 if you kept it all ported. Perhaps you could make 4 separate chambers for each driver, to keep driver interaction to a minimum.

But in any case, it'll likely be fairly tight bass, but not too deep.
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Old 31st December 2001, 03:39 PM   #5
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We could not begin to tell you how well this would work unless you give us the Thiele-Small. (T/S), parameters of your 8 inchers.

These are:
Qts
Qes and Qms-optional but useful
Fs
Vas
SPL @ 1Meter/1Watt
Power handling
Xmax-specify one way (+ or -,), or peak-to-peak. If you don't have that, give us the length of the voice coil, or VcL.

If you cannot find these numbers, give us the make and model of the speaker-we MIGHT be able to dig them up.

As a general tendency, 8 inch woofers are designed for speakers that are not meant to go that low. But there are exceptions. I'll tell you this-a sub with six cubic feet internal volume ought to put out big time bass, if it is designed correctly.

One more thing. Your quote: "The box dimensions are 19x19x29 (I know it's not even near perfect, but..)"

Perfect for what? You build your box any shape you want, especially a subwoofer. If you build it tall and skinny, you might run into resonances, above a certain length. For instance, if the box is six feet high, you will get a "spike" at 187 Hz or thereabouts. If it is four feet high, the "spike" is at 281 Hz. This only happens if the woofer has not crossed over to a midbass by before it meets these frequencies.

With these measurements, the internal volume of your box is 4.5 cubic feet, assuming you are using 1" building material. Still plenty of volume to make one heck of a subwoofer.
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