Fostex FE107E in open baffles? - diyAudio
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Old 22nd July 2004, 11:18 PM   #1
Fuling is offline Fuling  Sweden
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Default Fostex FE107E in open baffles?

Good evening.

First, let me introduce you to how my audio system looks at this very moment.

Speakers: Open Baffles with Scanspeak 8545 mid and 9700 tweeter, woofers are cheap MGR 12" units (one per side)
The baffles measures about 50 x 120cm with some kind of frame around the woofers (we could call them U-baffles i guess).
All DIY of course.

Crossovers are passive for the mid/high section (6/18dB with very high quality components) and active 12/12dB Linkwitz at 120Hz for the low/mids. A bit of shelving EQ is also added to the LP filters.

Amps: for the moment I run the woofers on a pair of Mini-Aleph monoblocks and the rest is fed by a small SE triode amp.
Better (and bigger) amps are under construction

Source: A heavily modified Pioneer PD-S707.

So, whatīs the problem?

Well, nothing really big except that my room doesnīt seem to like dipole subs all that much. But letīs forget this and focus on the subject: Fostex FE107Eīs in open baffles.

Has anyone tried? If I would be the first one to try, can I expect any degree of success?
I realize immediately that I cannot expect much output below 100Hz or so, so this is where my Scanspeak 8545īs would enter the game.

My idea is to build an (well, two) enclosure that would look like a "d" seen from one side. A closed cavity for the Scanspeaks (I really like those drivers in closed boxes) with prolonged baffles that sticks up and holds the Fostex drivers.
So: Closed subs up to 120Hz and dipole Fostex drivers from 120 and up.
The 120Hz comes of course from the active crossovers that i already have (the shelving EQ would have to be bypassed of course). Changing the crossover frequency would be easy if necessary, Iīd only have to replace four identical little caps.
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Old 23rd July 2004, 08:35 AM   #2
Rudolf is offline Rudolf  Germany
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Default Good morning Fuling,

FE 107 E seems to be a rather poor choice for Open Baffle. As the Fostex Spec sheet and the low Qts (0,38) suggest, output will be down ~9-10 dB @ 80 Hz. This is regardless of baffle size! Xmax too is WAY too low to get reasonable SPL lower than 200 Hz. So you will have to equalize or xover at least @200Hz - more would be better.

How your room doesnīt like dipole subs I canīt comprehend. In my room dipole subs are much better than my conventional BR sub. Could you elaborate on your complaints, your EQ and positioning of the dipole subs, so that we might see what went wrong?

Rudolf
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Old 23rd July 2004, 01:09 PM   #3
Fuling is offline Fuling  Sweden
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Yes, I realized that OB down to 120Hz would be asking too much out of those little things. As i mentioned earlier it wonīt be any problems to change the crossover frequency, so thatīs what Iīll do. If the Fostex drivers only play from 200-250Hz they should be able to do it with only a small baffle, say 35-45 cm wide.

Iīd be happy as long as they take care of the vocal range and anything above that. The Scanspeaks plays good up to some 4kHz or so, so thereīs plenty of room for playing with Xo freqs.

Well, nevermind my dipole subs. Iīve moved them around a bit since yesterday and itīs getting better and better.
The reason for building new speakers is not that Iīm not happy with the current speakers but that Iīm curious about fullrange units.

One idea is to build separate baffles for the Fostexīs so that I can combine them with different bass systems and find out whatīs best
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Old 23rd July 2004, 10:08 PM   #4
Rudolf is offline Rudolf  Germany
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To give you some kind of guideline:
I have used Fostex FF85K in OBs. Qts is 0,47, fs=122 Hz and Xmax=0,55 mm. Those little guys felt most happy, when they were highpassed >200Hz with 24 dB/Oct.
So 250 Hz xover seems to be safe ground. And the baffle should be wide enough with 35 cm, if itīs 80-90 cm tall and standing on the floor.

Regarding dipole position:
Having the dipoles 1/3 room depth from the front wall and (myself) sitting 1/3 room depth from the back wall leaves the last 1/3 room depth between me and the speakers. It is almost nearfield. But the dipoles excite the three lowest room modes in the least efficient way while your ears are excited in the most efficient way. Seems to me the best position you can get for dipole woofers in a room (and a very efficient way to upset your wife/partner too).
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Old 23rd July 2004, 10:37 PM   #5
Fuling is offline Fuling  Sweden
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Hi Rudolf

Quote:
I have used Fostex FF85K in OBs
So, how did they sound?

I was thinking 120 cm tall baffles, but is that important?
I read somewhere that the important measures are the distances from the driver to the side edges and to the top edge.
I want the drivers to be 95-100 cm above the floor if possible (Iīm 204 cm tall )

BTW: Horns, more precisly Buschhorns, are they worth trying?
I ran into several articles about them when searching for info about the Fostex drivers and they seem quite interesting.
Iīll probably build a pair as a side project some day.

Dipole subs:

The problem is that if Iīd follow the 1/3 rule, one of the speakers would be about 50 cm closer to the back wall than the other.
My room is not rectangular and itīs not much I can do about it.

Before I got into dipoles this wasnīt such a big problem, thatīs one reason why Iīm going back to closed boxes for the woofers.
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