Madisound BK-20

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I am going to build some speaker using Fostex FE206eN drivers.

I noticed that Madisound sell a flat pack BK-20. I can't find any reviews of them. Has anyone heard them, and what do you think.

I am also considering building a pair of Sachiko's. My only concern with the Sachiko's is that I my room is on the smaller side and they would have to be placed near the wall. I understand they work best in a larger room away from the wall a bit. My listening distance is about 9 ft.

Any thoughts would be appreciated.

Thanks
Debra
 

rjbond3rd

Member
2007-01-24 2:28 pm
Hi Debra, well since -any- thoughts are appreciated, I'll hazard an opinion even though I'm a newb.

For what this is worth, the BK-20 looks to be a somewhat antique design to my eyes. By comparison, the Sachiko was computer-modeled to get (among other things) deeper bass. I would vote for the design with more engineering behind it, room size aside.
 
Deb,

Your room is indeed a bit tight for Sachiko. Have you looked at the RonHorn Dallas II? Plans are a bit sketchy due to the originals being eaten by Windows. It has always been my intention to redraw them thou.

As RJ says, BK20 is a bit of an antique and didn't take advantage of modern tools. It was designed for the FE206 that predated the FE206e (the driver that FE206En just replaced). 206e & 206En are quite similar, but few here have experience with earlier 206.

It works but will not squeeze as much performance out as more modern designs that take advantage of the advances in modeling horns.

dave
 
There are 2 primary issues. 1st is that you won't be able to get far enuff away for the 2 mouths to integrate, so the transition from midrange to bass will not be as seemless as if you can get further away. This may not be as big an issue as we make of it. The other is that you may end up with too much bass. This fortunately could be fixed with a filter that attenuates the bass. Said filter should make bass even more effortless.

dave
 
Hi Deb,

I built a pair of Half Changs with FE206e after hearing Bob Trancho's:

http://www.diyaudio.com/forums/full-range/109576-half-chang-build.html

Although the HCs were designed for the FE207e, the FE206e work quite well. We added a BSC of 1 mH air core inductor and 5.5 ohm Mills resistor (IIRC).
The 207 should have a bit more bass extension, but I find the 206 to be quite sufficient--no need for a sub woofer. By all reports the FE206e should be a bit better--i.e. more refined.

Cheers, Jim
 
BSC lowers sensitivity. MF/HF are reduced sto bring them in-line with the bass that is being put out. In your small room you will probably only lose on the order of 3dB max. An 8 w SET should still drive you out of the room if you crank it.

Something like Sachiko has bass gain, so that the lowest frequencies are brought up to the level of the mids so you loose nothing.

More of concern with a SET is the affect of the impedance on the amplifier. That said, Jim uses a SS amp with low output impedance, your SET will have much higher output impedance which will naturally boost the bass. That along with significant room gain (ie small room) may mean that you can actually get away with little to no filtering.

dave
 
Thanks for the information. I think the best way to go at this time would be to build the HC's. With the SET amp I will try it first without the BSC filter, it will be simple to add it later.
If I want or when I move the system to a bigger room, I can always take the drivers out and put them in a Sachiko cabinet.

Again thanks everyone for your input.

Deb
 
I wanted to build the Sachiko's, but the workspace I would use to build them is unheated, and not usable till later in the year. So, to have something now I built a pair of the Madisound BK-20's, with Fostex 206eN^2 drivers ( still want to build a pair of Sachiko's later in the year as time permits). I am diving them with a 300b SET amp. They have 100+ hours on them.

The bass is quite adequate, and the mids are incredible. When listening to solo piano music it sounds like a the piano is in the room.
The issue I find is that voices tend to be a little shrill especially when listening to them straight on.

Would a BSC or Zobel help with the shrillness? Any ideas would be appreciated

Thanks
Debra
 
Pictures Debra?

You can try the 98 cent whizzer trick.

You can also play with toe-in. Try it such that the axis of the drivers cross a bit in frnt of you.

A Zobel's effect will depend on your amplifier. Given that the copper cover on the pole piece of the 206, it is unlikely to have much effect.

BSC shelves down everything aove a certain frequency, in essence lifting the levels of the bass.

I'd let them get another couple hundred hours on them before firming up any filters.

dave
 

rjbond3rd

Member
2007-01-24 2:28 pm
The issue I find is that voices tend to be a little shrill especially when listening to them straight on... Would a BSC or Zobel help with the shrillness? Any ideas would be appreciated

Hi Debra, the usual remedy is to make sure you're listening at least 15 degrees off-axis. If you check out the Fostex PDF for this driver, you'll see a diagram which shows the frequency response (a) straight on (i.e., zero degrees off-axis), then 15, 30, 45, 60 or something like that.

You want to pick the degrees off-axis where the driver starts to flatten out. Too much off-axis and you lose the highs (of course).

If you still feel the treble is rough, or too beamy, in addition to being X degrees off-axis, you might want to experiment with a rear-firing tweeter which can add some air and sparkle.

Any tweeter you get would have to be fairly efficient, e.g. Fostex F17H which are about $40 each (if I recall correctly).

If you still aren't satisified, the next step is to roll off the 206 with a single inductor, and then roll in the tweeter (by changing the value of the cap) letting the tweeter do more and more work. I know you can get a much smoother treble this way, and it will be less beamy (more dispersion) which many feel is pleasing.

None of this is really -necessary-, but it's just taking the next step to perfection if you feel like it.
 
My experience w/ FE206e is limited to building a pair of Half Changs using the 206. BSC is a real hot botton issue, but I have used it to good effect on the HCs, FE108eSigma Metronomes, and FE127e Fonken Primes.

With the HCs I used 1 mH air core inductor and 5 ohm Mills resistor. Without the BSC they were rather 'shouty' and fatiguing.

I didn't finalize the BSC until I had 500+ hrs on the drivers. If you only have 100 hrs, then you can still expect some significant changes.

Almost forgot to mention: your choice of amp will significantly affect your decision on BSC. I use 1970's vintage SS receivers. If you are into tubes, then things could be very different.

Cheers, Jim
 
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Purple Heart Veneer with a shellac finish. Turned out ok, finishing is not my forte.
 
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