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Old 5th April 2005, 06:47 PM   #1
htgeek is offline htgeek  United States
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Default Comment on my DIY Sub Design

Please feel free to comment on my design.
It is my first DIY home theater sub, although I have built several for car audio.
Its based on a Lambda Acoustics PB-15.
The power will come from a Rythmik Audio 350w plate amp.

http://img.photobucket.com/albums/v1...rev2Model1.jpg

Ben
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Old 6th April 2005, 12:07 AM   #2
simon5 is offline simon5  Canada
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It's nice but it seems to be tuned flat anechoic, remember that room gain will lift the lowest frequencies so you could tune your subwoofer even lower and stay flat in room.
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Old 6th April 2005, 02:42 AM   #3
mike.e is offline mike.e  New Zealand
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Also most modeling programs are 2pi
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Old 6th April 2005, 03:02 PM   #4
htgeek is offline htgeek  United States
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mike.e

What do mean by "Also most modeling programs are 2pi"?
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Old 6th April 2005, 03:38 PM   #5
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It means that almost all simulators, simulated as if the enclosure is placed in half space.

Half space would be the enclosure placed on the floor, full space way up in the air, quarterspace against a wall and on the floor (or two walls, etc.), eight space on the floor in the corner of your room.

Mvg Johan
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Old 6th April 2005, 08:21 PM   #6
htgeek is offline htgeek  United States
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So according to WinIsd the easiest to lower the tuning frequency is to lengthen the ports. Keeping the same heigth I could make the ports 33" long and tune to about 14.75 hz. Of course I would need to take into account the added volume of the new port lenght and adjust my total enclosure volume. Does that sound right?
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Old 6th April 2005, 09:36 PM   #7
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Quote:
Originally posted by htgeek
So according to WinIsd the easiest to lower the tuning frequency is to lengthen the ports. Keeping the same height I could make the ports 33" long and tune to about 14.75 hz. Of course I would need to take into account the added volume of the new port lenght and adjust my total enclosure volume. Does that sound right?
Unfortunately in all modeling programs this is a catch 22, every time you adjust the net volume to account for the port volume it will tell you to use a longer port, so when you lengthen the port you must recalculate the new net volume and again it will tell you to lengthen the port, it never ends. The only way I've found to accurately tune the port is to cut it long and play test tones while feeling the cone movement, when you hit the Fb the cone will barley move compared to just 1Hz above or below. In addition, I agree with others, tune a little lower, say 17-18Hz
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Old 7th April 2005, 03:45 AM   #8
DcibeL is offline DcibeL  Canada
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The added volume from the port will make such a little difference I'm sure you'd never be able to tell the difference if you did change the box volume accordingly anyways.

Nevertheless, that's a mighty fine sub you have there. I am also working on my first home sub after making several for the car audio. I have to wait for the driver I want to use to come available though (Peerless XXLS), so it will be a summer project.
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Old 7th April 2005, 03:57 AM   #9
spots25 is offline spots25  United States
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well, if you made the box bigger to compensate for the volume of the port, wouldn't the box still be the same size internally?
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Old 7th April 2005, 11:15 AM   #10
simon5 is offline simon5  Canada
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If I look at your drawing, you need to stay under 32 inches to have one port diameter distance for breathing.

I would make them 32 inches long if you can. Could you post a graph with 32 inches long pipes? If you get a shallow rolloff, ruler flat, with around -5 dB at 20 Hz compared to 0 dB at 100 Hz, that's about perfect, IMHO.
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