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Old 20th November 2007, 07:25 AM   #1
diyAudio Member
Join Date: Nov 2002
Location: Sweden
Default Vented alignment for Fostex F200A

Fostex is recommending vented box for their F200A driver
Length of port = 14cm
Port Dia = 8cm

I have seen other solutions, such as Bob Brines MLTL. But, as far as ported Box goes I have not seen anyone tried other Box than Fostex 45L with 14cm port.

Has anyone here tried the F200A in other vented Box alignment? - or did some simulations?. I have used my F200A in a sealed enclosure up to now. But, last week I tried vented alignment according to Fostex recommendation (14cm port, V=45L, port Dia=8cm) which I felt was quite boomy. I have my F200A flush on a wall (i.e the Box built in the wall)

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Old 22nd November 2007, 01:12 PM   #2
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zener_diode's Avatar
Join Date: Nov 2007
Location: Michigan
Did you measure the speaker parameters? Maybe they do not match
the published parameters exactly and hence, the boomy sound.

I was looking at this driver and thinking about buying a couple. How
do they sound?
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Old 23rd November 2007, 10:41 AM   #3
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Join Date: Nov 2002
Location: Sweden
Hello zener,

I think the F200A is wonderful. I bought this unit couple years ago but actually never tried it as fullrange driver. Instead, I have had it in a sealed 3-way application digital active XO 80Hz, 12,000Hz in a built in wall application. It was just last week I finally removed all network, made a port, and tried the F200A as truly single driver, in a vented box as recommended by Fostex. I was quite astonished how thunderous bass it had. The bass is deep and tight. Midrange and treble is very detailed and analytical. Also, I could play at higher levels I thought would be ever possible.

Still, having said that, I have certain issues with the F200A to deal with:

(1) Treble:
In my case and application I am not 100% satisfied with treble. I believe F200A can definitely benefit with a good supertweeter especially in my case since I will always be listening at off-axis position therefore lacking some of the highest treble extension. At same time, I can feel that lower treble can be slightly "sharp" sometimes. I have already Fostex FT96H tweeter in place so I am now experimenting different cut-off values between F200A/FT96.

In Fostex Japanese brouchure that came along with the element, Fostex is recommending three different alignment alternatives for the F200A. Obvioulsy first one is to use the F200A alone as single driver. Then two diffrent XO alternatives are proposed using Suptertweeter T90A+F200A combo along with attenuator R80B. One alternative is to use only 1.5 uf cap over the Supertweeter + Attenuator + F200A running fullrange.

Finally, Fostex writes something like:
...a better XO suggestion for the F200A, is to apply Inductor (0.18mH) in serie with F200A with 1.5uF cap over tweeter, which provides more "sparkling" treble...

For what it is worth, I felt improvement when applying 0.18mH inductor + tweeter as above but only marginal. I now plan to experiment with larger values of inductor- such as 0.2-0.4 mH and see how it goes.

(2) Bass:
Again, perhaps due to in-wall alignment and room gain, I suspect I have some peak at around 60Hz (need to measure it) but anyway very slightly boomy. Don't get me wrong, basically the bass is fantastisc so I am sure this can be solved with another tuning of port. I am now experimenting different port length/Dia.

Having said the above, it is possible that the issues (i.e shortcomings) I am facing - could be related to my very specific application namely where the wall is my baffle & no possibility to direct speaker to listening position.

In any case, I think I can say with some confidence that the F200A is quite spectactular driver.

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