Another Desktop Speaker Project (FE103E)

[TheGimp]

This is another build for desktop speakers, but I’m limited to 7” wide, 8” deep, and 12” tall (SWIMBO requirements). I’ve chosen the Fostex FE103E as my driver (already ordered them).

The speakers are to be desktop speakers for SWIMBOs computer, and will be driven by a Single Ended Pentode amp with about 4W output. (6P1P-EV).

I'll probably build a second pair to go in the garage for my system out there, and to use with tube amps I build/work on.

I’ve read up to page 50 of the Full Range Reference Project, but that is going a bit big, and as I said I already have the drivers ordered.

I like the Fonken, but again it is a bit too large and I would like to stick with a simple tuned port if possible.

The mFonken (FE127E) looks like it is very close to what I had in mind. How adaptable is it to the FE103E?

It appears to me that the vent in the bottom has a 19/32” X 15/32” port that widens to 15/32” x 5 5/8” in the front. Is this correct.

I would expect the port in the back vent to change dimensions for the difference in resonant frequency of the two speakers (79.5 for the FE103E and 70.4 for the FE127E). How do I calculate the new dimension?


Thanks

Steven

[planet10]

Originally Posted by TheGimp

The mFonken (FE127E) looks like it is very close to what I had in mind. How adaptable is it to the FE103E?

There is an mFonken103. We built a pair so that we'd have something to compare head-to-head with the mMar-Kel70 (CSS EL70).

Looks like i never did any drawings, the email to Chris says an mFonken with ports shortened to 103mm (i didn't see the syncronicity of that till just now, honest)

dave

[TheGimp]

Is that the 152mm dimension that would be shortened to 103mm, and keep the vent opening 19/32” X 15/32”?

I found this site that using the FE103E parameters looks like the volume would be 5.5L compared to the 4.5L of the mFonken.

http://www.ronshaw.citymax.com/f/Des...Enclosures.pdf

How well do these formula follow for design? I put both the FE103E and FE127E in a spreadsheet and got 5.5L and 13.17L respectively, which is way off from the design.

[planet10]

The miniOnkens are not simple BR. I have my own techniques for developing them.

Some drivers will work in a range of miniOnken (ie FE127), some only work in a very limited volume range. With the FE103 I haven't explored beyond the milliSize.

dave

[TheGimp]

I misinterpreted the porting. I see now it is a brace down the middle supporting the deck to make two ports on each side of the brace rather than being the port opening in the back.

How did the mFonken103 sound?

[planet10]

Pretty good. The FE127eN has it all over the FE103eN (certainly much deeper bass), but if you have stock drivers, the lack of 7k peak on the 103 makes it smoother.

dave

[mondogenerator]

Originally Posted by planet10

The miniOnkens are not simple BR. I have my own techniques for developing them.

it looks like a simple, slightly resisitive damped, slot vented BR, as made prolifically in the 70's..........albeit a nice one, theres nothing new in that. Id totally agree with the NOT using a 127 and swapping in a 103. I have no heard the latter but the peak in the former driver is a little unmanagable for me-i would notch it, but that defeats the object really doesnt it?
The Fonkens(generally speaking) do open up possibilities for self experimentation though, rather than mathematical modelling, which is always appealing...that surprises me Dave, I thought you were a modelling type of guy?

[planet10]

All the miniOnkens i design are modeled, then built, After having to redo the 1st few i got the mental handle on the translation between the standard vent (which the modelers deal with) and the high aspect ratio vent i've been pretty much spot on 1st time out.

When i'm done with the FE127 (ie it is an FE127eN) it has no measurable peak, althou you can still hear a hint of it. FE127eN goes lower, higher and is more dynamic than a similarily treated FE103eN.

dave

[mondogenerator]

Originally Posted by planet10

All the miniOnkens i design are modeled, then built, After having to redo the 1st few i got the mental handle on the translation between the standard vent (which the modelers deal with) and the high aspect ratio vent i've been pretty much spot on 1st time out.

When i'm done with the FE127 (ie it is an FE127eN) it has no measurable peak, althou you can still hear a hint of it. FE127eN goes lower, higher and is more dynamic than a similarily treated FE103eN.

dave

Personally i quite like the fonkens. It seems to almost fulfull the OLD philosophy of a port near equal or equal in area to the cone SA, except with a smaller Vb and longer port, which is slightly damped. this i would beleive gives rise to the lower amplitude of the lower BR impedance peak. this in the old port area=cone area tunings would give 2 near equal impedance peaks, if i remember right. with all other things being equal(Fs,T/S etc) id expect an audible difference in bass response from the larger SA of the 127, though ive no idea of the HF response in comparison. personally in a FR design, i would always go for a FAST approach, with as small as possible and as low Mms as possible driver. i would assume, without knowing the Mms of both drivers, that the 103 was lower in Mms and be better transiently. that being said i dont know and could possibly be wrong. after all VC has quite an impact too. to this end i wouldnt opt for a driver of more than 4" for the wideband driver, and an Mms of less than 5g(and as far under 5 g as possible), to preserve HF transient response and reduce the possibility of HF distortion which i feel the 127 has in copious highly audible amounts.but thats my view.

[TheGimp]

I can see that it makes sense that the FE127 will have a broader frequency response and more dynamic range than the FE103.

I'm trying to find a moderatly uncomplicated enclosure design that can be tweeked to suit the FE103. The FE127 is close, and if all that is needed is to change the port length by shortening the bottom shelf, then hopefylly it will do.

Another possibility is the SOLO-103, but it is slightly more complicated with top and bottom tuned ports.