Need help tuning my Fostex BK-16 - diyAudio
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Old 4th October 2006, 06:25 AM   #1
Neville is offline Neville  United States
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Default Need help tuning my Fostex BK-16

After reading some of the posts here and elsewhere, I embarked on the BK-16 kit from Madisound. I have completed one speaker and am waiting for the glue to dry on the last piece. I have not glued the remaining side panel as I read from posts and then listened to it and can confirm that it needs some tweaking.

Without any filler or damping behind the driver, I listened to it for an hour or so. I already had been running the drivers for over 100 hours on its own, before putting it in the cabinets. Using the standard FF165K and NO tweeters yet, I was impressed with the overall sound , however bass seemed bloated or overdone and although mids were sweet there was also delayed mids coming through as well. I corrected the delayed mids this by putting Polyster filling around the driver but not blocking the passage.

Now I still have the bass somewhat uncontrolled. I dont know the correct term but "boomy" comes to mind. Madisound sells the HP reflector. Does anybody have experience with this or can recommend something cheaper ? There was talk of using a a Deflex panel or even putting on bathroom caulk on the once side of the panel but that thread was never completed, hence this thread..

I really want to keep this tweak at a minimum and was also wondering if damping the sides of the "throat" in the top part of the cabinet with $1 floor tiles from HD or Lowes would help ? I also feel quite a bit of vibration on the side panels and wondering tif this tile would also help damp that?

I am a newbie when it comes to full range and diy speakers so please go easy...

Thanks
Neville
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Old 4th October 2006, 03:55 PM   #2
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Try elevating it 4-8 inches off the ground.

This helped in my case to reduce the large bump at 150hz that "bloated" the bass for me.

I did not like stuffing the compression chamber heavily. I applied some foam to the back of the chamber and was reasonably happy, at least until I built my austin 166s.

Sean
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Old 4th October 2006, 08:02 PM   #3
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Default stands...

THE BK-16 was designed specifically for the 165k. the 166e has totally different specs, especially in the q region. in the abby, we do both drivers, with the 165 putting out a little more bass, at the expense of treble region. super abby fixes this.

I have heard the BK-16 well set up extensively. it was VERY impressive. pleasing, powerful bass response. high speed. fairly flat overall, good tweeter implimentation. somewhat of a monitor tone...

the only real tweak I can recommend is perhaps a small dot of black adhesive foam, a little tiny bit of wool damping in the coupling chamber, or if all else really fails, hp sound reflectors (in the right spots though) (and if your room placement calls for them). I do not think that a BK 16 really needs any of this, but it is where I would start.

I have to say that the angled stands are very important. just buy them, and use them. also, what did you use to clamp the last panel with while you were testing it? was it air tight? the absence of a glue joint might change the acoustic characteristics of the enclosure.... Was it a (close to perfectly) square build?

if it were my enclosure, I would go ahead and glue the last peices. the only areas you will need access to are accessible by removing the driver. (and also the horn mouth.)

most back loaded horns need to be glued with healthy pressure and then after completed, playing, etc. to sit at ambient humidity in YOUR room for quite a while (a month plus) before impressions are taken. usually the honk simply goes away over time. this is caused by the warps in the panels being "clamped" out during construction into a shape they were not used to taking. it takes those panels a while to recognize their new shape as the one they should be holding and to "destress." as you might imagine, the REAL process takes years and years, and simply will evolve over the rest of your life. it is a musical instrument. however, the amount of settling necessary for the honk to not detract from the music is usually around a month or two (or less, depending on where you live and the amount of warp, glue, construction technique, etc.) I remember touring the paris workshop once and seeing their steam room and storage rooms. I asked alot of questions about their wood curing processes. they placed a heavy emphasis on humidity and warping/dewarping/shaping/etc. and noting that an instrument simply tends to age gracefully, assuming it does not fall apart from shoddy construction. anyways, you can stuff it in the mean time, and the honk will probably go away, but so will the speed and quantity of your bass. it will probably needs very little if any stuffing after several months of playing, and you might find yourself taking alot (if not all of it) out. but your tastes and enclosure might end up varying. who knows. the only frequencies I find myself trying to clean up in a BLH are the midrange bumps (250+hz) which come out of the mouth. sometimes these are a problem, sometimes not.

---I really cannot emphasize this enough though. every pair of horns I have built I hook them up and say "damnit I messed something up!" "there is no bass, there is a honk at 150 hz, and the midrange sounds distorted!" "what a waste of cash" I have finally learned to simply wait and play them for a while. things eventually settle down in a well designed and built enclosure. researching the japanese audio hobby websites, they are well aware of this process of waiting for the enclosure to cure. also, they damp to taste. so I am not really saying "don't use damping." I am just trying to say that things change overtime after the enclosure is built with absolutely no effort on your part. it takes more patience to wait for this to happen than most americans are willing to have...it is well worth it though. it can be particularly frustrating from a design standpoint, having to wait so long before really taking impressions and even reconsidering another cut and try... there are quicker ways, but that take more cash...

understand that I am hardly the holder of truth here. it is just alot quicker to express opinions without the use of conditionals in phrasing.
good luck and enjoy!!!

Clark
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Old 4th October 2006, 09:29 PM   #4
Neville is offline Neville  United States
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Seanzozo, i also read and thank you for confirming that I need to elevate the speakers. Madisound has a "skeleton" stand for either angling and lifting it up or just lifting it up. I am leaning towards making my own elevation stands filled with sand and adding spiked to the botton of that for the angling. Would be intrested in hearing your thoughts on this.

Bluemenco, you touched on somehting thas has me curious, when you said a touch of foam or the the HP sounds reflectors. How can such a small piece of "something" make any positive changes to the way it sounds ? From what I have read these would have to be placed on opposite facing walls but how do you know where do put them ? So I put them in the opening or along the compression chamber ?

I have read in other threads that some folks used a lot of stuffing and damping and then eventually ended up removing some or all of it - i guess their kits settled down/broke in.

I have read the specs for the BK-16 as having 55hz. but the FF165K goes all the way down to 39hz if I am not mistaken, so my question is where did all the bass go ? I currently have Quads that go all the way down to 30hz and I find that too much for me, so no major loss for me if its really 55hz.
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Old 4th October 2006, 11:22 PM   #5
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Quote:
Originally posted by Neville
Seanzozo, i also read and thank you for confirming that I need to elevate the speakers. Madisound has a "skeleton" stand for either angling and lifting it up or just lifting it up. I am leaning towards making my own elevation stands filled with sand and adding spiked to the botton of that for the angling. Would be intrested in hearing your thoughts on this.

I have read the specs for the BK-16 as having 55hz. but the FF165K goes all the way down to 39hz if I am not mistaken, so my question is where did all the bass go ?
I built some lead/sand filled stands for mine out of a chunk of cheap luaun plywood. IIRC they were about 6 inches high. They got the drivers level with my ear and cleaned up the bass a little without the congestion and lack of low bass that resulted from over-stuffing.

I got about 60hz out of mine which were fe166 based, the ff165 probably will go a little lower but the mouth is just too undersized to extend much lower. The 39 hz is the resonance of the FF165. Since the 165 is such a low q driver it does not resonate strongly at 39 hz and thus requires a horn to couple the driver to the air, since the horn is small in mouth area it does not couple well below 60hz and thus produces little bass near resonance. The bass it does produce both because it is horn loaded and because it is largely above fs has great punch (for lack of a better word) and though more coloured and lumpy than my Austins it has a liveleness all it's own, I think this is what blumenco means by "monitor" sound. Indeed I tended to use the BKs less farfield then i currently use the Austins.

I hate to contradict bluemenco (with whom I agree on many things) but IMHO The BK-16 is a generic horn that fostex designed be small (this is where most of the compromises are) and designed to work roughly well with all of its 6 inch drivers. Madisound tends to prefer the FF165, I want to get some now that my 166s have moved on to the Austins and my BKs are empty.

Sean
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Old 5th October 2006, 02:07 AM   #6
Neville is offline Neville  United States
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Sean, I just learnt a few things

OK so what does the compression chamber do for sound apart from channel it out the front of the speaker ? Would enlarging the CC and the mouth give lower bass or would you have to move to a higher Q driver within the 6.5"size for that to become effective ?

Why do some horn designs have the mouth at the rear or even on the sides ? Is to to be placed closer to the corner or wall to help emphasize the bass ?

Apart from wood glue did you use bathroom caulk to go over the edges of all joints or would that be overkill ?

Thanks
Neville
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Old 5th October 2006, 03:10 AM   #7
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Quote:
Originally posted by Neville
Sean, I just learnt a few things

OK so what does the compression chamber do for sound apart from channel it out the front of the speaker ? Would enlarging the CC and the mouth give lower bass or would you have to move to a higher Q driver within the 6.5"size for that to become effective ?

Why do some horn designs have the mouth at the rear or even on the sides ? Is to to be placed closer to the corner or wall to help emphasize the bass ?

Apart from wood glue did you use bathroom caulk to go over the edges of all joints or would that be overkill ?

Thanks
Neville
NOTE- all of this is IMHO

The compression chamber acts as a low-pass filter. The larger the chamber the lower the low-pass frequency. It will not increase the extension. I believe from my few simulations that the compression chamber is not that far off.

The lumpiness in the response and the low frequency pole are largely due to the undersizing of the horn. A higher Q driver might increase the low-end extension very marginally but the horn will not properly load the driver at those frequencies and so dynamic capability will suffer, additionally a high q driver will probably not produce the dry and clean bass of the fostex.

Rear firing BLH like my Austins are generally meant for corners. The corner acts as an extension of the horn smoothing the response and generating measurable increases in both extension and dynamic capability. Unfortunately it also means you need corners or a wall and it also loads the modes of the room which gives up some of that smoothed extension. Front firing BLH like the BK-16 can be fit in small rooms without uniform corners they generally have some floor-loading so they dont give up as much as you might think to the rear firing.

Fostex factory designs tends to almost exclusively use Front-firing BLH. I'm not sure why, small Japanese rooms maybe?

The BK sounds good. I agree with blumenco. Make stands, play with placement, listen for a long time (200 hours+) and then get to tweeking.

Sean
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Old 6th October 2006, 12:32 AM   #8
Neville is offline Neville  United States
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I know have completed both speakers but still have not glued on the final side panel, but I reread your posts and decided to clamp down the sides while listening to it and it made a HUGE difference. The "boomy" overbloated bass has been tamed by quite a bit. I suspect the rest will clear over time as I let them break in for another 100 hours.

I just love the sound of them, but am wondering how much high frequency I am missing...I dont want to have to pay for FT17H tweeters, caps and an L-pad and only find it too bright after laying out that cash.

Currently, the sound is warm and very much too my liking. Maybe after a few weeks I will revisit the tweeter addon, but it already looks like I will have to sell my Quads
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Old 2nd February 2007, 12:35 AM   #9
celt is offline celt  United States
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Well, I've been looking at these for awhile as well and decided to pull the trigger on the kit, sans the tweeters. (I can't hear a blasted thing above 12.5kHz anyway.) Have been busy with other projects, but will try to post some pics of them soon.
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Old 5th February 2007, 10:53 AM   #10
Neville is offline Neville  United States
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I am very happy with my speakers. Instead of buying their recommended and very costly super tweeter I ended up getting their $18 tweeters with a cap and lpad so I can adjust. It is certainly one of the better speakers I have had. I just need to finish up with the look of it.

Good luck
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