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Old 27th September 2005, 09:57 AM   #1
j.burtt is offline j.burtt  United States
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Default Someone please check my calculations

I am leaning towards a 3 way system consisting of a Scan Speak 21W/8555-01 8" woofer (30 - 300hz), 15W/8530K-00 5" midrange (300 - 2000hz) and a LCY ribbon tweeter.

My figures using WinISD Pro in estimating the 21W/8555-01 vented enclosure = 1.5 cu.ft. tuned to 30hz with a 2" port 4.75" long.

The 15W/8530K-00 will be in a sealed enclosure of .4 - .5 cu. ft. .

The back of the speakers will be 12" - 18" from the rear wall and I don't want to want to have issues with a rear port that close to the wall. I don't want to endure port noise or any other issues that may come from a front vented enclosure either. I've never seen this, but could I port them towards the outer walls that are about 8 feet away without any negative effects ?
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Old 2nd October 2005, 06:42 PM   #2
Notax is offline Notax  Montenegro
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Default calc

1.3-1.5 cu. ft. is OK.

Fb = 30 Hz is OK.

I think its better larger port diametar. 2.5"-2.7". Calculate lenght.

For 15W/8530 closed box of 0.42-0.46 cu. ft.
Full dampened it would be about Fc=47-48 Hz.
It is the same as uper freq. od bass-reflex Fg (uper peak of impendance at bass-reflex) for box of 1.5 cu. ft.
With this, you can try it as 2.5 system.
High pass for bass, only high pass for mid and low pass for tweeter.
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Old 2nd October 2005, 09:36 PM   #3
j.burtt is offline j.burtt  United States
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I will be using an active x-over, so I can try many different frequencies to find the best.

Should I front port or rear port the bass cabinet if the back of the speaker is only going to be 12-18 inches from the back wall ?

I have never heard of a side firing port. There has to be a reason. I am 6-8 feet from the side walls.
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Old 2nd October 2005, 09:43 PM   #4
simon5 is offline simon5  Canada
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You can do sidefiring, no problems with that, especially that low.
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Old 2nd October 2005, 11:07 PM   #5
j.burtt is offline j.burtt  United States
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Which would work better 18" from the rear wall and 6-8 feet from the sides.

Front, rear, side or down firing
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Old 3rd October 2005, 06:17 AM   #6
simon5 is offline simon5  Canada
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18 inches from the wall is quite far away. You could do anything, front, side, rear, down, up whatever hehe!

At 30 Hz, bass source can't be localized.

Do what's the best for you. If you were crossing very high, I would say use front port, but you're crossing very low so it doesn't matter at all IMHO.
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