making a bass reflex box for Fostex FF85K

[Thebrain]

hello everyone

currently my FF85K are used in my setup as rear surrounds.
they are housed in the worst small cabinet possible.
i decided to give them a proper cabinet!
in madisound website there is a plan for
a bass reflex cabinet for these little wonders.
i think im gonna go ahead with that design.


any tips?
should i use MDF or other type of wood?
should i put damping inside the cabinet?
im asking this because this cabinet is planned exactly for this driver.
damping increases the volume.

link to box plan
https://www.madisound.com/pdf/fostexcabs/85kencrev.pdf

the lousy "cabinet" :

An externally hosted image should be here but it was not working when we last tested it.

An externally hosted image should be here but it was not working when we last tested it.

 

[GM]

Greets!

MDF Vs Plywood construction as well as stuffing (damping) has been extensively debated/documented, so a search should give you all you need to know to make a decision as to what is best for your application (app).

Based on its published specs, this driver is ill suited for a HT surround app if not horn loaded, but at least your little sealed cabs protect it somewhat against bottoming out, something a BR can't do and be XO'd at 80 Hz.

GM

 

[planet10]

Some of the Fostex boxes are OK... many aren't. I haven't tried this one.

What we did do that works really well is the uFonken.

http://www.planet10-hifi.com/fonken.html

As a mid-tweeter with an added woofer these drivers are one of my favorites... here is a thread about that http://www.diyaudio.com/forums/showthread.php?s=&threadid=144099

dave

 

[Thebrain]

thanks for the help!

those ufonkens are really nice!
i like them more then the fostex design

the fonkens are more complicated so...
since my friend, the carpenter is doing me a favor, i let him
decide what design to do.

at least your little sealed cabs protect it somewhat against bottoming out

well they are not sealed

i made an opening in the back of the cabinets because i liked the sound
coming out from the FF85K back.
it makes some improvised sort of but not really bipolar sound

GM why do you think they are ill suited for surround application?
i liked them as surround speakers especially in classic music.
they kinda fill the hi mid holes in my huge front speakers.

 

[planet10]

GM why do you think they are ill suited for surround application?

GM likes to be able to play REALLY loud, and the FF85 is somewhat limited in that respect

My experience is that they perform way better than you would respect in that regard.

dave

 

[Thebrain]

GM likes to be able to play REALLY loud,

my kinda of guy

the FF85 is somewhat limited in that respect

oh they are! i connected them directly to my stereo amplifier.
i thought i give them some running time (is that how it's said? )
and i felt that it wouldn't take much to send them to a mars express

i still think they are great as surround speakers.
when i play really loud i just use the fronts.

 

[GM]

well they are not sealed.

GM why do you think they are ill suited for surround application?
i liked them as surround speakers especially in classic music.
they kinda fill the hi mid holes in my huge front speakers.

OK, obviously, I made the reasonable assumptions that since I didn't see a port, it was sealed and that since surrounds are normally only used for HT which in turn normally use an 80 Hz XO, there's no way this driver can meet even the near-field SPL requirements at low distortion, i.e without exceeding Xmax an audible amount.

My personal listening preferences aren't relevant nor does it influence my remarks beyond 'at low distortion', which can be measured. Provide more acoustic gain down low and/or increase the XO point and for most movies I have no doubt this driver would make a fine small HT mains, surround driver, though still a little SPL shy of meeting even the reduced DD/DTS broadcast movie reference level. Still, plenty loud enough for small rooms, HTPC, and/or attached unit homes (apartment, etc.).

You're right though, to get the most enjoyment from a good movie soundtrack or recording, I want to experience it the way it was intended to be, so DD/DTS reference and studio recordings = 'loud' with symphonies, church pipe organs and especially large live concerts = 'LOUD'. Unfortunately, many folks currently don't have this option for whatever reason(s) and the way the world is changing it appears that eventually only the rich will have it, just as they did in the pioneering days of audio and video.

For music other than the surround encoded ones which have ~the same requirements as HT, they are much less stringent since they typically should be just loud enough to add the missing reverberation of an acoustically large space. Still, you need a low distortion BW to the XO point, so an EQ'd ML-horn such as I did for Dave's tweaked RS 40-1197s should be adequate for an 80 Hz XO.

GM

 

[planet10]

... use an 80 Hz XO, there's no way this driver can meet even the near-field SPL requirements at low distortion, i.e without exceeding Xmax an audible amount.

From the sims uFonken is hitting xMax at 100 Hz with 1W in... certainly disguises that well when played full-range in my big room.

dave

 

[Thebrain]

well probably xmax is the one speaker parameter i understand...
well i think...
and i must say the little fellas hit it pretty fast.
i agree that they start distorting pretty quickly.

but... my living room is small and again when i hit the really high volumes i turn them off(and never use 5CH stereo mode it will blow them away).
they are only turned on when watching a movie.

btw i do not cut their low.
i had a bad experience with home theater crossover on a Yamaha receiver. it turned out that when i used the built in XO it made
some unbelievably phase cancellation in the front speakers bass,
even when it was on stereo only mode and the rear speakers were off...


as for the original thread topic i will post some pics when i make some progress