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Here are some more pictures of the rearload "K" slot horn.
My friend finished them down to 600, all- and hand rubbed at the end.The fostex bullet is quite a step above a JBL- expensive, but they are very smooth.
Bill
Goto Gallery/RCA Fan/Anyone to see pix
Follow Ups:
Wow those a nice! Do you get good lowend with the backloaded horn. Do you need a sub??Thanks
Bill: while the graphs are very interesting and most instructive could you share your impressions and those of your trusted ears on the actual sound of the different drivers tested in your back loaded horn. I am interested in knowing how the low x-max ff225k compared to the longer travel fe207e and fe208sigma. I guess that the pm6a is also a fairly low x-max driver. Was there a sense that the longer throw drivers had any advantage in terms of playback level or bass extension in your cabinet? The graphs do not seem to indicate the differences in driver sensitivity that I would have expected, did you find that you heard differences in efficiency between these drivers?Was there a clear favorite between these drivers in this cabinet? Your comments would add a human component to the great measurements.
Thanks so much for posting, your efforts are sure to have a significant impact a lot of DIYers. Best regards Moray James.
Can you mention why you chose the 208sigma rather than the 208Esigma? thnx...
Sorry, I ment the FE208EZ 8" full range Sigma.
I picked this speaker to see how the distortion was compared to a regular cone. It is a little better. It also has nice bass.Bill
Hi Bill,Thanks for sharing more of your cool design! I was about to start my own version this May but my cabinet/speaker builder friend was out of commission for some months =(. Hopefully we can start by mid August.
Anyways, if the 208ESigma have very good bass. I bet they would have a more hefty bottom end with the higher up 208ESII (pict above) which can be bought from a certain Japan seller who export (stock has been deplted AFAIK), with double lanthanum cobalt ceramic magnets and truly fullrange up to 20kHz.
I haven't heard it... But looks nice. BTW, I know what you are talking about, when it comes to the papery character with its upper mid spittines of some lower costs fostex like the 207E, I was thinking of maybe doping 'em with some violine laq or even some natural oil stain to tame it a bit. I still have to try it with a friend's 166E's.
More magnets: http://www2.plala.or.jp/takatsugu/doit/image200203301.jpg
Sorry guys...Their stock has been depleted as I have mentioned. They only got a pair left that got sold early this year... But if you go to Japan I'm sure there are some shops that still have some. EIFL had an earlier 208ES version (Im not sure but I think there's no difference actually, just a second limited edition run *mkII* coz of higher demand AFAIK), but I think "jusbe" (AA member) got the last pair from Koji!? Better shoot email to EIFL Export if they stil have stock.
fred
Fred: I wa thinking the same thing with respect to magnets. If you have a 208 sigma why not experiment with a bucking magnet salvaged from some old dead driver? I would be most interested to hear of your results if you give it a try. Regards Moray James.
Hi Fred76
Can you pass on the source for the 208ESll drivers?
I will be traveling to Japan in October.
Thanks
Hi Fred76,
Would you please give the Email contact information regarding the cool Fostex 208esII drivers from the vendor in Japan?
You can send me an Email with that information if you prefer.
Also, if you have any specifications on this driver would be nice too.
Thanks
Norris Wilson
Fe208 sigma has the most bass extension and definition. By definition, I mean from 90Hz to 120hz - it sounds more life-like than the others.
The ff225k is very similar to a JBL le-8 it is a good replacement for this driver. It does not have the rising characteristic of the other drivers. It is a very smooth sounding speaker. If the Lowther 2kHz zing is offensive to you- this ( ff225k) would be a better choice.
The fe207e is similar to the Lowther in it’s tone quality- but in my opinion sounds too “papery” (I.E. not enough magnet) to my ear.The Lowther PM6a is my choice, as I like the super crisp voice quality. While the voice really jumps out at you, I like this sound.
As far as x-max goes- it does not take much to drive these drivers into distortion- but they are very load when this occurs ( 115dB). The Lowther has an underhung vice coil, so the x-max is better than it would seem.
X-max also infers that you would want a rear chamber- it is quite a bit less when used this way.You loose the main benefit of a backload horn with a rear chamber. Like all designs, there is a trade off.
In short if like classical music- pick the ff225k.
If you like jazz, or “souped up” life-like presence-choose the PM6 or Fostex Fe208 sigma.Bill
What if you like Doo-Wop music?
It is very good on this and rock.
If you like accurate classical music- might not be the right choice.
If you were to EQ up from 2kHz to 8kHz ( +4db) this is what you get. You can build a notch filter to witch this in and out.
They are the be all to end all on DVD movies.Bill
very sharp! which tweet is that? and is that the 208 or the 168? what did you do for a crossover?thanks and enjoy!
It is the fe208 sigma and a T900 tweeter.
see my "Gallery" for T900 x-over.
Looks like some great development work on that T900A crossover. What were the final values you used for R1? Overall, what was the goal - smoother roll off, lower crossover point, etc? I have a pair of these, but was thinking to just use a 1uf cap on them, but it seems that that may not be the best choice? Thanks for posting the graphics and any info you can provide re: your thought process on the development of that crossover.thanks
-Ed
I have sent graphs of what happens when you vary the components of network. The way
this network functions is that the .13mh inductor is very small compared to the capacitor.
This causes a gentle peak at the rolloff point which causes the upper dips to smooth out. By
varying the resistor connected to the coil, it allows the rolloff to become more gradual. In
this way you can "go between" a 12dB and 6dB slope allowing you match up with mating woofer. I
have also shown what happens when you vary the other components. You made have to
add an "L pad" to correct level. Do this with resistors, not a potentiometer.
Note this network is only good for an 8" high efficiency type driver in a backload horn.Bill
Just curious -- have you tried a front baffle that has the Karlson slot facing in the opposite direction?Christopher Witmer
Tokyo
If you were to view this horn unfolded- the slot is widest at the mouth, getting smaller as it goes towards the throat.
i kept changing area and shape until i got the best response.Bill
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