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Old 29th June 2004, 10:17 PM   #1
bzdang is offline bzdang  Canada
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Default Fostex FF series X-max

I fear that many of you are missing out on a fairly nice group of drivers due to misprinted specifications. The 0.3 mm x-max specification is incorrect ( 0.3 mm is the thickness of three sheets of printer paper). I have an FF225K in my lap and can easily displace the cone +/-3.0 mm without any distress to myself or the loudspeaker. I can not push it in far enough to bottom out the voice coil (it is suspension limited). I expect that the FF165 is similar but don't have one here to check.

The FF225K is not bad at all, it is no LE8T but it is affordable and is far more polite than the 208 Sigma in the midrange, according to my wife, who has not blasted a large crater in the center of her hearing.

Some small advice for full-range rookies from a rookie - don't judge a fostex loudspeaker until the driver is broken in. Run it out in the garage for a week or two first. They improve with some time on them but don't corrupt your ears/brain by listening to it while it is breaking-in!
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Old 30th June 2004, 05:20 AM   #2
navin is offline navin  India
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oh no....i have been looking at them however from what i can tell other than the FF85 the rest are suited to horn cabinets. horn cabinets are however very difficult to DIY.
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Old 30th June 2004, 05:42 AM   #3
Variac is offline Variac  United States
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I have the 208EZ drivers and they also have lots of travel- at least compared to spec. I think Fostex rates drivers for their most linear response, not the mechanical x-max.

In fact I wanted the FF225, but was put off by the low x-max Really!!

The 208 also has it's charms, but flat it ain't!!!
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Old 30th June 2004, 03:30 PM   #4
MarkMcK is offline MarkMcK  United States
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Hi,

Just another word on xmax. It is specified by the simple relationship of the voice coil winding length to the thickness of the top plate (or pole disc in the enclosed neodymium designs). So, for example, if the metal that sets the gap length is 6 mm in thickness and the voice coil winding is 7 mm long, then X-max is .5 mm before the amount of voice coil in the gap decreases.

That is all this specification means. Drivers can excurse farther than X-max. The distortion just begins to rise when they do. Excursing just slightly beyond X-max produces a very small increase in distortion. Hitting the excursion limit of the driver produces much more distortion.

If you eliminate a driver just on X-max alone (and you are not planning on using it as a subwoofer), then you have made a mistake. Please do not over generalize. In the realm of a wide-range driver, there are so many other things that matter so much more to the sound of the driver than its X-max. If I was building a high SPL subwoofer, then I would be concerned with X-max.

As I have stated in another thread, in full range or wide range drivers, large X-max is going to limit top end. You cannot have both. Large X-max requires lots of voice coil out of the gap. This adds mass and increases coil inductance. Both decrease the top end of the driver.

Mark
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Old 30th June 2004, 04:04 PM   #5
bzdang is offline bzdang  Canada
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Thanks Mark,
this increases(redefines!) my understanding of x-max. I would now correct my first post to read "The 0.3 mm x-max specification is misleading for many of us who thought that we understood it."


I suspect that fostex makes these drivers for use in small intimate rooms, almost near-field, where the subtleties of music reproduction can be appreciated and high sound levels would be inappropriate.

Dave
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Old 30th June 2004, 05:09 PM   #6
zobsky is offline zobsky  India
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Quote:
Originally posted by bzdang


I suspect that fostex makes these drivers for use in small intimate rooms, almost near-field, where the subtleties of music reproduction can be appreciated and high sound levels would be inappropriate.

Dave
esp. true for the FF series, im my experience (FF165K) . .. a bit rolled of in the higher octaves, .. probably suited to near field listening

The FE series are better for larger spaces, .. also IME (FE166E), .. and have a more extended treble
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Old 30th June 2004, 05:31 PM   #7
Variac is offline Variac  United States
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Most Fostex probably have short coils, for the advantages mentioned above. Unfortunately designs such as open baffle
or bass reflex require a decent amount of excursion just to handle normal bass. In a horn you don't have as much problem

Sa, as has been stated, if not in a horn these are for music at reasonable levels.
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Old 1st July 2004, 07:18 AM   #8
navin is offline navin  India
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Quote:
Originally posted by zobsky

esp. true for the FF series, im my experience (FF165K) . .. a bit rolled of in the higher octaves, ..
the FF85 claims to have usable response well beyond 20kHz..infact I have been looking at the FF85 as an alternate to the JX53 (jordan). at 1/4 the price of teh Jordan it looks very attractive.
BTW has anyone used Fostex drivers (FE103, FF85 etc..) in a line array? Given the cost and limited LF response of the FF85 I was considering using 2 of them in a linear array.
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Old 1st July 2004, 04:02 PM   #9
Rudolf is offline Rudolf  Germany
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Hi navin,
at a recent loudspeaker DIY meeting in Germany Fostex showed a short FF85K OB array. The comment of one auditioner was something like "quite nice".

http://www.audiodiskussion.de/foren/....php?idx=40886

Just go some way down in the picture gallery
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Old 2nd July 2004, 05:33 AM   #10
navin is offline navin  India
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very nice. any published specs? my rational here is to use drivers with a rising top end and then use the "destructive polar interference" to reduce the top end to flat.
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