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Old 28th March 2012, 11:08 PM   #1
Rick R is offline Rick R  United States
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Default Fostex F200A center channel?

I am currently using a pair of rear ported BR cabinets with Fostex F200A drivers and Hi-Vi RT2-Pro ribbon tweeters for either stereo or home theater use. These speakers are 13" wide, 17" deep and 40" tall. I either use a 300B amp for stereo, or an Onkyo receiver for HT, by swapping speaker cables. I am hoping to do a center channel with the same driver and tweeter. The space below the big screen TV is 22" wide, 22" deep and 16" tall. I only need the center channel to go to 60 - 70 Hz.

I have seen a Fostex recommended BR for the F200A that is 45 l., 11.8" wide, 11" deep, and 21.6" tall, ID. There is no info on low frequency limits. As the design would need to be fudged to fit the space, any suggestions on alternate designs? I would need something like 16" of height to just fit in the drivers. The back of the space is open, so a rear port could be used.

Also, does anyone out there have experience using either of these drivers as a center channel? I did a search, and could find no specific info on this combo. Any suggestions or ideas would be appreciated.

Last edited by Rick R; 28th March 2012 at 11:28 PM.
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Old 28th March 2012, 11:10 PM   #2
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I'd make the center the exact same speaker as the left right.

Norman
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Old 28th March 2012, 11:24 PM   #3
Rick R is offline Rick R  United States
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I am sorry I did not put the dimensions of the L&R speakers in the post and will insert that info. These speakers are 13" wide, 17" deep and 40" tall. So, they are big, tall cabinets that would not fit under the TV.
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Old 29th March 2012, 01:28 AM   #4
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ahhhhhhhhh......................

I'm suprised the f200a could not be in a smaller sealed box (given speaker setting to small).

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Old 29th March 2012, 04:37 PM   #5
chrisb is offline chrisb  Canada
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Rick - the F200A is not a budget driver, nor a tiny one, and there are likely few folks with the wherewithal to play with them for this type of application.

That said, as the center channel is both the most important of the 5 or 7 mains in a surround system (responsible for up to 60% of the total soundtrack), and its bandwidth can easily be restricted through surround processor's bass management into the low 100-150HZ range, there's likely no reason that a small(ish) sealed enclosure couldn't be devised as Norman suggests.

However, while sharing the same tonality of the L&R mains, that approach might not maintain the same dynamic signature. How wide is the TV? - Would the existing enclosures laid on its side fit under? Or you could reduce cabinet dimensions and retune venting for higher cut-off - just don't ask me how
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Old 29th March 2012, 07:08 PM   #6
Rick R is offline Rick R  United States
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I already have the drivers and ribbon tweeters, I got a great deal on them used. The L&R speakers are big, with a volume of about 140 l. The TV is a 70" Sony, rear projection and sits on a custom made stand that includes spaces for various electronics. The space in the center is 22" deep, 22" wide and 16" tall. In theory you could put a 120 l. cabinet if you filled the space. If I built a cabinet the same width and depth as the L&R's, and the full 16" available in that space, I could get about 65 l. of volume. Because the drivers would be taking up most of the front, it would have to be rear ported. Of course, the AV receiver can cut the signal off from 60 Hz or higher, to match the cabinet frequency.

That assumes the ribbon tweeter is set above (or below) the F200A. If I were to but them side by side, I could have them higher up from the floor. I have tried using two way monitor speakers horizontally as center channels and it worked fine. I also tried a pair of monitors head to head horizontally, and that was even better. However, in this case, I don't have the horizontal room to do so.

Since I have a pair of drivers and tweeters, I suppose the best would be a single ribbon in the center and one F200A on either side. Since these are 8 ohm drivers, the receiver should be able to run them both. Wow, now this is really getting crazy.
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Old 29th March 2012, 07:54 PM   #7
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I'd just do a sealed box, given placement there should be some room gain to get response below a 60-100 Hz cutoff. I also did a 50 litre reflex sim, tune 35-39 Hz. The vent would likely needto be a slot wraped around the box. You do not want to use 2 F200A in the centre, that will just ruin things.

dave
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File Type: gif F200A-sealed-sims.gif (21.7 KB, 146 views)
File Type: gif F200A-50L-vented.gif (20.8 KB, 142 views)
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Old 29th March 2012, 09:40 PM   #8
Rick R is offline Rick R  United States
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More isn't always better? I guess that's why they are called single driver speakers. A closed box it is.

Given a set volume for a closed box, are the ratios of the dimensions flexible? Would making it wider and less deep change the sound quality, for example. I was thinking of perhaps 12 x 20 x 18, which would be around 65 l.
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Old 29th March 2012, 09:45 PM   #9
chrisb is offline chrisb  Canada
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Quote:
Originally Posted by Rick R View Post
More isn't always better? I guess that's why they are called single driver speakers. A closed box it is.

Given a set volume for a closed box, are the ratios of the dimensions flexible? Would making it wider and less deep change the sound quality, for example. I was thinking of perhaps 12 x 20 x 18, which would be around 65 l.

well, for our own reasons we try to keep aspect of 3 dimensions at GR (Golden Ratio - .618 / 1 / 1.618 ) but at the very least try to avoid cubes except for "subs"

what are the dimensions of the ribbon?
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Old 29th March 2012, 10:27 PM   #10
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Quote:
Originally Posted by Rick R View Post
More isn't always better? I guess that's why they are called single driver speakers. A closed box it is.

Given a set volume for a closed box, are the ratios of the dimensions flexible? Would making it wider and less deep change the sound quality, for example. I was thinking of perhaps 12 x 20 x 18, which would be around 65 l.
Ignoring potential doubling up of standing waves (2 dimension the same) and keeping in mind that the front has to be large enuff to accomodate the driver, you are free to change the aspect ratio.

Given the placement i would recommend trying to push the baffle to close to filling the cavity it will be in, with enuffspare to get it up on something that will isolate it from the cabinet (ie a chunk of foam or isolation feet)

dave
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