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Old 15th September 2004, 05:07 AM   #1
oto79 is offline oto79  Brazil
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Default problem: HUGE (impossible) volume

Hi guys,

In my first attempt to build speaker boxes I bought 170W wookers (40-5000 Khz) and 70W tweeters. Here´s the problem: I´ve cut 25mm(1 inch) MDF for a volume of 83 litres, but it should have been 372 litres - which is huge! Can I go on building my 83 lts box or will they sound awful?
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Old 15th September 2004, 07:26 AM   #2
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Do you have the t/s parameters for the woofers . if you dont have them can you post a link to a web site that has them

How did you come up with the volume of 372 ltrs . does it need to be sealed or ported ?

Is the 83 ltr sealed or ported ?

I am sure there i have not ask for all the infomation needed

Hopefully some else will
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Old 15th September 2004, 11:03 AM   #3
oto79 is offline oto79  Brazil
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Default all the specs

12"
170W RMS
40-5000 Hz
96 Db (sensitivity 1w @ 1m)
Fs - 52 Hz
Re - 5.8 Ohms
Qts - 0.77
Qes - 0.85
Vas - 83 liters
Sd - 510 cm2


That´s it. The box I am building is a closed one, but it doesn´t need to be so.
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Old 15th September 2004, 12:01 PM   #4
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That looks like a cheap or PA woofer. It is not suitable for a ported box.

The box you have cut will be OK. The huge volume you calculated will be because you tried to choose Qtc of much less than 1 and because the Qts of the driver is already very high, it needs a very large box to have negligible effect on the Q.

For the size of box you have, the bass will not (and never will be without EQ) be very deep. It will go quite loud. It's not a great solution for domestic use (needs a midrange, it's too big and poor bass), but should be OK for PA.
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Old 15th September 2004, 12:06 PM   #5
oto79 is offline oto79  Brazil
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Default why cheap?

Well Richie, you seem to be right, I just recalculated everything and got down to around 80 liters again. Guess I was too tired last night. How come you say it is a cheap woofer? The pair cost me over 100 dollars, which is quite expensive in Brazil, and it is made by Selenium,supposedly very good. Also, I´m using a super-tweeter on top of it, so it can be aligned properly.
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Old 15th September 2004, 12:45 PM   #6
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Actually those specs look to be what you'd find in a musical instrument (electric guitar) speaker intended for an open back cabinet. Even in a large enough box to theoretically get any bass the Xmax is probably only a millimeter or so and wouldn't put out much. The response is likely anything but flat too; I'd forget about them as far as woofer usage goes. Put them in a 2 cu ft open back box and sell them to a guitar player.
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Old 15th September 2004, 08:12 PM   #7
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I said cheap *or* PA

Selenium, I think they are a PA brand. Whilst they may be good drivers for PA duty, PA drivers just do not work for home use because they are made to give out high SPL and not *deep* bass.

I agree with Bill's comments.
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Old 15th September 2004, 08:37 PM   #8
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Selenium, I think they are a PA brand.
Based on the specs they are probably the QSL 12P20, a low end brand made by Selenium. US retail $40, definetely a PA/MI speaker, and not a terribly high quality one. Absolutely not a speaker that would work as a hi-fi woofer, but OK for low end PA (vocal only, no music) or electric guitar. Curious that they would cost more in Brazil where they are made than in the US.
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Old 15th September 2004, 09:15 PM   #9
Svante is offline Svante  Sweden
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I think a closed box could be ok if there is enough stuffing in it. That will bring Qtc down. However, fc will be about 70 Hz in the 83 litre box, this is a bit high.
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Old 15th September 2004, 09:44 PM   #10
GM is offline GM  United States
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Yeah, at this Vb I would stick a 3" diameter x ~8" long vent in it also.

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