Fostex FF125WK BR box build

Hi all,
After brief discussion and getting tips, I went ahead and build a FF125WK BR enclosure using datasheet measurements for enclosure provided by Fostex in Datasheet/Manual.
I was looking for a better midrange reproduction for vocals ,violin and male voices.I have to say I have not been disappointed with first few hours of listening.
As expected it has slight harshness at around 7KHz region but can avoid by keeping speakers off axis. Bass response is not bad for the tiny enclosure but may need help with BSC filter.
Very mellow to listen to vocals,not good for plays with lot of instruments playing and not for heavy rock.
I am wondering what should be the baffle step correction to use?
Please see the SPL response 1/1 octave smoothed for easy interpretation.
 

Attachments

  • avg spl.jpg
    avg spl.jpg
    80.5 KB · Views: 571

ultrakaz

Member
2004-10-20 11:32 pm
Honestly, I haven't had much luck using any type of Bsc filters before, but you can try an inductor (around 1mH) and resistor in parallel (around 8 ohms) to flatten the treble response. Or for a more notch type filter to cut around that 7kHz region add a cap (around 4 mF) in parallel, so Lcr type filter. Perhaps, worth a try if you have the parts lying around.

However, I prefer to let the driver run unimpeded by any crossover components in the electrical path. Instead I would run a woofer at 700Hz as recommended in the Fostex lit that comes with the driver. Quite clever I may add for Fostex to sell more drivers, but with the smoothish response of the 165wk or 225wk plus the single inductor albeit largish, it should sound pretty good. Also, I do like how they leave the "main" driver unmitigated/pure. Overall a pretty good compromise for "singlish*" driver type speaker.
 
Hello there :D. I have had 2 ta 3 pairs of this driver. I would say look at the paper work that came with the drivers. It's all in Japan but, there is a 3 way speaker in there for cabinet plans. They use a Fostex FT17H Horn Tweeter using a cap and a inductor. A 0.47 uf cap and a 0.18 mh inductor. FF 125WK Drivers running fullrange not cap or anything. Then for the bottom end the FF 225WK Drivers crossed over using one inductor at 3.8 Mh. I hope this helps. Also this driver has a better snap with drums and a higher range then my Fav. Fe 126en drivers. Enjoy N.S.
 
Last edited:

ultrakaz

Member
2004-10-20 11:32 pm
where did you find that 700Hz in literature?I totally missed it.
I am against any inductors or resistors too,but may be it needs it.
I would rather go with a Sub.

Yes, it is in Japanese. But, you can see 700Hz in the text, see the frequency traces (unfortunately no transfer function plots) and see the solitary 3.5mH inductor in series.

A "Sub" is not going to help that 7kHz rise/spike and the elevated mid/treble range. More likely to cause a dip in the lower mids.
 

ultrakaz

Member
2004-10-20 11:32 pm
Hello there :D. I have had 2 ta 3 pairs of this driver. I would say look at the paper work that came with the drivers. It's all in Japan but, there is a 3 way speaker in there for cabinet plans. They use a Fostex FT17H Horn Tweeter using a cap and a inductor. A 0.47 uf cap and a 0.18 mh inductor. FF 125WK Drivers running fullrange not cap or anything. Then for the bottom end the FF 225WK Drivers crossed over using one inductor at 3.8 Mh. I hope this helps. Also this driver has a better snap with drums and a higher range then my Fav. Fe 126en drivers. Enjoy N.S.


Hello N.S., I'm curious to know if you have tried this? And if so, did you build the enclosure as described in the instructions?
 
IG,
Thanks for the link to the very simple line-level BSC circuit. I have all those small signal level parts already - saves me from buying a pair of pretty hefty speaker level inductor coils and high power resistors (which would end up costing more than the drivers) - not to mention fact that amp power is being wasted on heating the resistor at higher frequencies.
 
a few observations:

I've built more than a couple of Fostex "recommended" enclosure designs over the years, and with the exception of the larger BLH for 6" & 8" FE series, most have been remarkable in their shortcomings in LF extension - which will certainly exacerbate the need for BSC in this size range.

Certainly there's no argument that as many things as a 3-4" FR driver can do very well, there are few that couldn't benefit from HP filtering and bass augmentation (call it FAST, or just 2 way with low XO - whatever you like)

Fostex FR drivers are beloved / notorious for long break-in periods ( as much as SEVERAL hundred hours) before they fully "open up / smooth out", but even then, for many folks the 4" size particularly retain some issues of narrow band peakiness / harshness in the upper midrange that are not well addressd by wide band BSC or EQ. While there are some physical cone treatment regimes that can mitigate those issues, in many cases narrow band digital EQ is the most expeditious method of correction.

BSC "balances" FR response works by attenuating above selected frequency, and certainly can't improve the driver's basic excursion limitations - regardless of whether at line level or passive, you'll lose overall SPL capablity

If kinku's application precludes larger enclosure volumes than the 9 liters of the "factory" BR design, there may be little option but careful EQ (i.e. more than just the BSC) with the resultant reduction of maximum SPL / excursion capabilities, which in very near-field situations is not necessarily a deal breaker.

If on the other hand there's space available to accommodate larger monitor size or even floorstanding enclosures, there are many designs that could substantially extend this driver's LF performance:


Floorstanders:
- MLTL similar to the Pensil for A7.3
- Woden Venom
- BLH such as the FH3 or Steve Deckert's interesting little DNA design that's currently getting some attention on another forum thread ( I'd suggest buying the plans and building with plywood, not foam-core, but that's just me)

"desk-top" / stand mounted monitors;
- any of several variants from

http://p10hifi.net/FAL/downloads/CGR-dFonken125-free-090612.pdf

I've heard the FF125Wk in a couple of the above designs, and they are certainly capable of delivering well below 60Hz
 
Last edited:

IG81

Member
2008-02-22 1:21 pm
Paul Joppa (of Bottlehead fame) article on PLL BSC

dave

Missing link? I'll assume you meant that one: Passive Line Level Baffle Diffraction Step Compensation

I've had success with adjustable line-level correction before, it's a neat way to do it. I integrated it in a small inductively-coupled op-amp based preamp I built. Here is the plotted effect:

[IMGDEAD]http://img850.imageshack.us/img850/3/preresponse.png[/IMGDEAD]

IG
 
Last edited:
Hello N.S., I'm curious to know if you have tried this? And if so, did you build the enclosure as described in the instructions?


Hello there. The answer to your question? No I have not built this speaker yet? I was planning on it but, loss of a second job cut it short. I was going to follow the Enclosure instructions and add a few braces here and there to help out with deading the box. Just been thinking about it. N.S.
 
Yes, it is in Japanese. But, you can see 700Hz in the text, see the frequency traces (unfortunately no transfer function plots) and see the solitary 3.5mH inductor in series.

A "Sub" is not going to help that 7kHz rise/spike and the elevated mid/treble range. More likely to cause a dip in the lower mids.


Hello there. I have talked about the Dip in the FF 125Wk Drivers. I see it but, I never heard it on this driver nad I have had 3 sets of them. Also the 8 inch woofer is Crossed over between 350 hz and 400 hz and the 700hz would not be getting to the driver if I am correct. I would build the boxes buy everything you need and then make the ajustments to the drivers with the Caps and inductors. One day I will build this speaker but, not anytime soon. N.S.
 
Last edited:
there are many designs that could substantially extend this driver's LF performance:

Add to that list the Cornu spiral horn. They are actually somewhat bass heavy. Perhaps the extension is not record breaking but the quantity is more than other enclosures.

Chris and Dave you will hear them in August.
 

IG81

Member
2008-02-22 1:21 pm
Thank you guys.I am wondering which one would be better line level BSC or outputlevel correction or Digital EQ which will take care of slight peakiness around 7kHz.
PlanetM ,IG any more details like a circuit diagram with opamaps available?

Here is what I built.

Schematic.png

I started with a TL074 and then switched for an LME49740. The 100K pot is the volume control and the 10K pot is the adjustable BSC control. The 10K and 22nF are calculated with Rod Elliot's method, depending on your baffle width. The output transformer was there because I had it for a while and had no other use for it. It solved a hum problem in that specific system though and boosts impedance for the BSC circuit, but is not necessary. A 2:1 or 1:1 would have been better in any case, as I barely had enough voltage swing to drive the amp. I ended-up using a mains power supply as batteries did not last very long.

IG
 
Last edited:
Thanks IG. But the circuit is still complex for me to assemble.Will it be possible to get something detailed to the final level like where input /pot goes ,where the power goes? I have never been good working with basic level ideas.hope you can help?
I saw MJK zobel+ BSC for Lowther,which will be better,working at line level or at speaker level?
Dougbo there is a post about using Zig glue on the surround to tame harshness down by 3dB. I have not tried it but worth consideration?
 
Last edited: