Fostex FP203 in bass reflex, tuning? - diyAudio
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Old 19th July 2011, 03:10 PM   #1
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Default Fostex FP203 in bass reflex, tuning?

I've just bought a pair of used Fostex FP203 as a first step into the full range/wide range world.
I cannot make space for horns or OB at the moment so for now I want to try them out in a bass reflex cab filling up the bass with an active DIY sub (SEAS SLS12). Also good to get more wood working skills on a simpler design.

I hope to get some support on what tuning frequencies and volume to aim for.
Could for example 70Hz work well together with a sub? I suppose I should make a experiment box first but it would help a lot to first narrow it down some.

I am thinkin of making it a slot port, or what it is called.

Thanks...
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Old 19th July 2011, 06:02 PM   #2
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Snippet from Japanese catalog attached.

ML-TL project

Click the image to open in full size.

T/S data. Scott has a suggestion for an ML-TL and remarks that the driver should work in Chang/Curvy Chang/Half Chang.

dave
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Old 19th July 2011, 07:38 PM   #3
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thanks for the links! in Swedish and all

the Chang et consortio models seems something to try further on. For a more boring shoebox BR it seems 48L and 40Hz tuning is standard for FP203. A question is what happens with higher tuning frequencies?
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Old 19th July 2011, 11:15 PM   #4
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Quote:
Originally Posted by slackweather View Post
Could for example 70Hz work well together with a sub? I suppose I should make a experiment box first but it would help a lot to first narrow it down some.
Agreed, without knowing actual specs. Making some assumptions, a ~ 0.7 Qtc sealed is ~18.54 L/~92 Hz F3, Fb, so might be one to try first and go from there if not satisfied.

GM
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Old 20th July 2011, 10:19 AM   #5
kaktus is offline kaktus  Sweden
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Hi, I don't think I understand.

But as a suggestin I could start with trying 70Hz tuning freq in a 48L box that I can use also for trying lower tuning frequencies?

That would mean, if I get it right, for a box of 48L (1.695cubic feet) a slot that is 8 inches x 2 inches x 1.89 inches long for 70Hz tuning (or 20.3cm x 5.1cm x 4.8cm). Well around that, my cicular saw isn't very precise.

Please correct if wrong...
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Old 20th July 2011, 01:01 PM   #6
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Hmmm, using the same 48L box and tuning it differently will not produce 'flat' results in the bass. I am not at my usual pc so don't have the software to simulate, sorry. Tuning to the lower frequencies will require a smaller box. I believe what GM is suggesting is a sealed box of 18.54L which will result in a 92hz rolloff frequency... quite possibly optimal when partnered with a subwoofer. Personally, if using a subwoofer i'd go with a box smaller than 48L... I'd also consider putting these on an open baffle around 2' x 4' and use the subwoofer to fill in the bass.

If you do not plan on using the sub, then i think a 48L box, Half Chang or BIB will work great with that older fostex. It's probably a wonderful driver... i'd love to have a pair.
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Old 20th July 2011, 05:07 PM   #7
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An 80s model I think(?). They sure look good. It was very nice surprise when i got the package. I didn't know they were so well built. Very sturdy. I hope they work nice.

should have understod that, but if I make a "mock up" I can make it 48L and fill it partly to try different volumes.
I think FP203 works better with BR than closed box?
Perhaps say 30L could be a start with 70Hz tuning?

For the current set up I want to put it on a deep shelf at the TV, so not a floorstander. I have furnished myself into a corner...
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Old 20th July 2011, 08:48 PM   #8
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Yes, you can use scrap wood or whatever solid material[s] to reduce the cab's net volume [Vb].

It can work in either and the sealed alignment is better overall when a sub is used if the XO point can be made to work well in the intended application [app].

WRT a typical vented alignment, even a 48 L box is a bit too big based on guesstimated T/S specs [~41.2 L/~48.7 Hz Fb] which makes it even smaller than the recommended cab.

Regardless, small vented cabs tuned well above Fs tend to be 'one note' boomboxes and won't protect the driver through the XO BW nearly as well as a sealed alignment, so typically must be bigger, tuned lower.

GM
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Old 21st July 2011, 10:18 AM   #9
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GM wrote: Regardless, small vented cabs tuned well above Fs tend to be 'one note' boomboxes and won't protect the driver through the XO BW nearly as well as a sealed alignment, so typically must be bigger, tuned lower.

Thanks!, thats just the kinds of things I like to know. I thought BR with high tuning would mean a fast and nuanced bass and also make life easier for the cone. How wrong of me. Perhaps I should make a test cab with 48L and see how FP203 is in full range as i have never tested BR before and then try to seal it filled with bricks down to ca 30L for use with sub.
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Old 21st July 2011, 09:32 PM   #10
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You're welcome!

Partly right, 'fast' typically means a rising response alignment, so an undersized cab with a low tuning designed to emphasize the driver's upper harmonics, typically to Fs or even below it depending on driver specs, i.e. no real bass to speak of unless the room boosts it up. Using my guesstimated specs, this would be a ~26.4 L/45.5 Hz alignment.

GM
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