Fostex FF125K mini-reflex - diyAudio
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Old 24th May 2011, 01:03 PM   #1
IG81 is offline IG81  Canada
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Default Fostex FF125K mini-reflex

You don't see many using this cool little driver. I've had them for some time; actually these are the last pair Solen had in stock before the model was discontinued. I wanted something smaller than the proposed ~8 liters in the Fostex literature, so went for 4 liters tuned to 60Hz.

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Nothing fancy about them; 11mm BB-ply, most interior surfaces lined with open-cell foam, triangular corner vent for simplicity and slightly different look. I measured the actual tuning frequency to be ~55Hz, which results in a ~4-5dB bass shelf alignement, close to what I was aiming for. They will need BSC, which I did not implement yet. I might go for a variable line BSC like Rod Elliot suggests. BSC point is ~660Hz in my case.

Quick listening test suggests they will sound prettty good once the brightness is tamed, bass sounded nice, considering the driver's and enclosure's size, and certainly not boomy. They should perform well within their limits, beneath which they should comfortably stay with their intended ~nearfield, low-SPL, late-night use.

IG

Last edited by IG81; 24th May 2011 at 01:05 PM.
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Old 24th May 2011, 04:33 PM   #2
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I like the look and wonder if the triangular vent has other applications.
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Old 24th May 2011, 04:41 PM   #3
IG81 is offline IG81  Canada
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Thanks!

Although not part of the original design, the triangular vent, placed as it is on the baffle, put in a room corner could nicely help the LF, although would really not be a good place for the midrange/highs and imaging...

The vent is small-ish, but I simulated ~8W before reaching 34m/s vent air velocity; a power level these will likely never see in their intended application. Cone motion will be absurdly non-linear before this happens in any case.

IG

Last edited by IG81; 24th May 2011 at 04:47 PM.
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Old 24th May 2011, 06:36 PM   #4
chrisb is offline chrisb  Canada
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elegantly simple

yup, the FF series are/were rather under-appreciated by most folks

too bad the silliest good driver (FF85K) in the line was discontinued in the replacement series - but that UDR surround must have been one of the more costly parts in the whole piece, and without huge market demand for such a niche product, sooner or later the bean counters will have their way
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Old 24th May 2011, 06:54 PM   #5
IG81 is offline IG81  Canada
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Browsing through the Audio Database website, I came accross the Coral 4B-1AV, which I fould quite elegant and cool looking; it gave me the necessary push to build these small speakers.

The FF-series really looks cool IMHO, like a long-lost cousin to LE8T.

IG
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Old 24th May 2011, 07:49 PM   #6
adason is offline adason  United States
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nice built IG81!
I fancy the same driver, altought I use it in 3-way on open baffle
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Old 24th May 2011, 08:11 PM   #7
IG81 is offline IG81  Canada
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Quote:
Originally Posted by adason View Post
nice built IG81!
I fancy the same driver, altought I use it in 3-way on open baffle
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Nice speakers you built there!

It'll be my first serious listen with the FF125K. I hope I end-up liking them fullrange; at least I'm aware of their limitations, so it might help. If in the end I'm not happy with them, using them as midrange might be the ticket.

IG
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Old 24th May 2011, 08:21 PM   #8
chrisb is offline chrisb  Canada
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Quote:
Originally Posted by IG81 View Post
Nice speakers you built there!

It'll be my first serious listen with the FF125K. I hope I end-up liking them fullrange; at least I'm aware of their limitations, so it might help. If in the end I'm not happy with them, using them as midrange might be the ticket.

IG

would probably need some help in the bottom couple of octaves or so for anything other than very near field use

I tried them full range in the FHMk1 and "Brynn" a couple of years ago, and FWIW found they couldn't quite keep up with the FE126E and late FE127E in those 2 designs respectively - but they could be a sleeper for mid-range.
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Old 24th May 2011, 08:40 PM   #9
IG81 is offline IG81  Canada
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Quote:
Originally Posted by chrisb View Post
would probably need some help in the bottom couple of octaves or so for anything other than very near field use

I tried them full range in the FHMk1 and "Brynn" a couple of years ago, and FWIW found they couldn't quite keep up with the FE126E and late FE127E in those 2 designs respectively - but they could be a sleeper for mid-range.
Yeah, not expecting thundering bass from 0.15mm Xmax in sucha tiny box! They should be decent with sparse acoustic stuff and chamber music. But I'll still try to push some metal and techno, albeit at more than polite SPL.

I hope the EBS alignement I have going was the right choice. I much hesitated as for tuning frequency, while aiming to reduce cone motion to avoid too much IMD; on the one hand I don't want to tune extra-low because, well, because it's a 12cm driver with 0.15mm Xmax; OTOH I didn't want to tune it so high that the driver would already be unloaded at like ~80Hz. I feel that 60Hz is a good choice since, if I want to try to add a small bass boost, the ~60Hz slider on most EQ's will do it, plus there is not much cone motion at Fb, so it's not too harmful to do so IMHO. But it did end-up tuned lower, Fb~55Hz. Might pass on the EQ afterall; it will be wiser to balance the tone with the variable line BSC.

IG

Last edited by IG81; 24th May 2011 at 08:51 PM.
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