Port change for Fostex DBR for FE207E - diyAudio
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Old 2nd January 2007, 07:48 PM   #1
no xo is offline no xo  United States
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Default Port change for Fostex DBR for FE207E

I am getting ready to build a pair of the Fostex recommended DBR cabinets for the FE207E. I usually try to study the plans before I start cutting the wood, and I had an idea. Could anyone advise me on possibly chaning the square port in the lower chamber, to a vent at the bottom of the cabinet. I am not handy with design software or computer modeling. My question is, would a vent at the bottom, with the same volume of air , give similar results as the square port in the plan. I feel this would make an easier build and a better looking cabinet. I plan on putting alot of time finishing these with veneer and hardwood trim to give them a retro look and I don`t want to ruin the sound with an idea that is mainly for cosmetic purposes. I understand that it is difficult to design a DBR, and most of my expirience has taught me that the engineers at the factory do things for a reason. Thanks, NOXO.
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Old 2nd January 2007, 07:56 PM   #2
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Maybe play it safe and put the square port on the rear of the cabinet. This way you can play with the distance from the rear wall to tune bass to your taste. Firing the port out the bottom might sound great but will require experimentation with distance from the floor. I'm sure it can be made to work firing out the bottom tho.

But my suggestion - assuming you will be putting these near a wall - is to port out the back and keep the front clean looking. Tune bass to taste with distance from the rear wall and stuffing.

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Godzilla
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Old 2nd January 2007, 07:58 PM   #3
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Do you mean move the vent onto the base, and then lift the cabinet up with a plinth? Or simply lower the vent to nearer the bottom but still keeping it on a vertical panel?

In the latter case you should be fine to shift it to whereever you like in the lower chamber. In the former, you can probably get away with it, but it might be an idea to make it fractionally shorter as chances are you'll get some additional loading via the gap between cabinet and plinth.

Hope this helps
Scott
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Old 2nd January 2007, 08:04 PM   #4
no xo is offline no xo  United States
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Thanks for the quick answer and solution. That would keep the front clean looking and not potentially mess up the sound. They will be only a couple inches from the back wall. Thae are going in my bedroom system. Thanks, NOXO
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Old 2nd January 2007, 08:07 PM   #5
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I wouldn't be surprised if they sound better with the port on the back. The frequency chart seems to need a bit of reinforcement in the bass/midbass anyways. Good luck!
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Old 2nd January 2007, 08:16 PM   #6
no xo is offline no xo  United States
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Scottmoose, the arrangement I had in mind is similar to the vent in the Klipsch Cornwall. It would be a front firing vent, but it would be positioned below the port in the plans, at the bottom of the cabinet.I am concerned that the positiion and dimensions of the opening would change the frequency response in the bass. I think my idea has some merit, but I feel more comfortable moving the port to the rear and leave everything else the same.
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Old 2nd January 2007, 08:25 PM   #7
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Rear-firing should work fine and give an additional boost to the LF as Jeff says. Let us know how you get on

Scott
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Old 2nd January 2007, 08:34 PM   #8
no xo is offline no xo  United States
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Thanks to you both.A rear firing port it is. I have a friend coming over tonite to help me wrestle the 5'x5' baltic birch. I have 2 sheets of 19mm and will adjust hte plans for the difference. Does anyone think I`ll notice any difference in sound with the thinner panels? ( I have 2 left over from the horns I built for the FE206ESR's I built a while back, which should be enough for these.)
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Old 2nd January 2007, 11:05 PM   #9
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Probably not. The panels aren't huge, so resonance issues should be relatively minor compared to some boxes. Plus, you have the internal divider helping brace them.
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Old 19th March 2007, 06:16 PM   #10
no xo is offline no xo  United States
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Thanks for the good advice Scottmoose and Godzilla. Last week I finally finished the double BR boxes for the FE207E and put the port on the back like you recommended. I am getting strong response to 50HZ and usable output to 40HZ. The bass is not as fast or defined as the horns I built, but for a bedroom system, they sound womderful. Thanks again, NOXO
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